Siderite's Blog Part Deux

Some of you may have heard of C# 6, the new version of the Microsoft .NET programming language, but what I am not certain about is that you know you can use it right now. I had expected that a new version of the language will be usable from the brand new upcoming fifth version of the .NET runtime, but actually no, you can use it right now in your projects, because the new features have been implemented in the compiler, in Visual Studio and, you have no idea how cool it is until you try, in ReSharper.

One might say: "Hell, I've seen these syntactic sugar thingies before, they are nothing but a layer over existing functionality. New version, my ass, I stick with what I know!", but you run the risk of doing as one of my junior developer colleagues did once, all red faced and angry, accusing me that I have replaced their code with question marks. I had used the null-coalescing operator to replace five line blocks like if (something == null) { ....

Let me give you some examples of these cool features, features that I have discovered not by assiduously learning them from Microsoft release documents, by but installing ReSharper - only the coolest software ever - who recommends me the changes in existing code. Let's see what it does.

Example 1: properties with getters and no setters

Classic example:

public int Count {
  get {
    return _innerList.Count;
  }
}

Same thing using C# 6 features?

public int Count => _innerList.Count;

Cool or what?

Example 2: null checking in a property chain

Classic example:

if (Granddaddy!=null) {
  if (Daddy!=null) {
    if (Child!=null) {
      return Grandaddy.Daddy.Child.SomeStupidProperty;
    }
  }
}

Same thing using C# 6 features?

return Grandaddy?.Daddy?.Child?.SomeStupidProperty;

Convinced yet?

Example 3: using the name of members as strings

Classic example:

public int Number {
  get { return _number; }
  set {
    if (_number!=value) {
      _number=value;
      OnPropertyChanged("Number");
      //with some custom code you could have used a better, but slower version:
      //OnPropertyChanged(()=>Number);
    }
  }
}

C# 6 version?

public int Number {
  get { return _number; }
  set {
    if (_number!=value) {
      _number=value;
      OnPropertyChanged(nameof(Number));
      // this assumes that we have a base class with a method called OnPropertyChaged, but we can already to things inline:
      PropertyChanged?.Invoke(this,new new PropertyChangedEventArgs(nameof(Number))
    }
  }
}

Example 4: overriding or implementing simple methods

Classic example:

public override string ToString() { 
  return string.Format("{0}, {1}", First, Second);
}

Now:

public override string ToString() => $"{First}, {Second}";

Example 5: exception filters

Classic example:

try {
  SomethingUnpredictable();
}
catch (Exception e) {
  if (e.InnerException!=null) {
    UnpackAndLogException(e);
  } else {
    throw;
  }
}

C# 6 version:

try {
  SomethingUnpredictable();
}
catch (Exception e) when (e.InnerException!=null) {
    UnpackAndLogException(e);
}

Example 6: using static

I don't particularly like this, but it can simplify some code when used right. Classic example:

return degrees*Math.PI/180;

C# 6 way:

//somewhere above:
using static System.Math;

return degrees*PI/180;

There are other more complex features as well, like special index initializers for Dictionary objects, await in catch and finally blocks, Auto-property initializers and Primary Constructors for structs. You can use all these features in any .NET version 4 and above. All you need is the new Roslyn compiler.

Enjoy the new features. I know I will!

There are a lot of people asking around what is the difference between BindingList<T> and ObservableCollection<T> and therefore, there are a lot of answers. I am writing this entry so that next time I look it up, I save StackOverflow some bandwidth. Also, because my blog is cooler :)

So, the first difference between BindingList and ObservableCollection is that BindingList implements cascading notifications of change. If any of the items in the list implements INotifyPropertyChanged, it will accept any change from those items and expose it as a list changed event, including the index of the item that initiated the change. ObservableCollection does not do that. So BindingList is better, right?

Wrong. BindingList is not "properly supported" by WPF, say some. Why is that? Well, because BindingList, as its MSDN page says, is just "an alternative to implementing the complete IBindingList interface". Yes, you've got it. BindingList is a lazy, thin, ineffective implementation of the interface. The Missing Docs blog has a very good explanation of this. Do keep in mind that BindingList was created during the time of Windows Forms and is being used by WPF only as an afterthought.

So let's use ObservableCollection then! No. The functionalities implemented by BindingList are far superior to that of ObservableCollection. Just thinking that you must somehow handle changes of every object in the list is killing the idea.

A subtle recommendation on the same MSDN page goes like this: "the typical solutions programmer will use a class that provides data binding functionality, such as BindingSource, instead of directly using BindingList". Well, what does that mean? It means using System.Windows.Forms.BindingSource, which does about everything, since it implements IBindingListView, IBindingList, IList, ICollection, IEnumerable, ITypedList, ICancelAddNew, ISupportInitializeNotification, ISupportInitialize, ICurrencyManagerProvider and is also a subclass of Component. A bit heavy, though, isn't it?

An interesting idea comes from a StackOverflow user: implement IBindingList on a subclass of ObservableCollection<T>. Should be enough to implement a scalable version of IBindingList.

There is more. The BindingListCollectionView page says "Specifically, IBindingList is required for BindingListCollectionView, and IBindingListView is an optional interface that gives additional sorting and filtering support.", which indicates that IBindingListView is also useful when getting a collection view for your object.

To recap: the best solution seems to be an ObservableCollection<T> that also implements IBindingListView (which itself implements IBindingList). The implementation must be scalable (getting the index of an object that causes a change in an efficient manner), though and I wonder, if I am implementing IBindingList, why should I even bother with inheriting from ObservableCollection? The same StackOverflow user seems interested only in the INotifyCollectionChanged interface for the ObservableCollection which is also implemented by IBindingListView!

Therefore, let's implement a class that explicitly implements IBindingListView and IList<T>, then publish the members we actually use! What could possibly go wrong? My idea is to store the index of an item next to the item, therefore removing the need to search for it. It seems that I must first implement an advanced List<T>, with a fast and efficient IndexOf method, then I can basically just copy paste the BindingList code and use this class of mine as the base. Unfortunately, BindingList uses Collection<T> as the base class, which itself implements IList<T>, IList, IReadOnlyList<T>. It seems I will have to implement all.

Immediately I have hit a snag. IBindingView is very difficult to implement, since it tries to filter using a string that is interpreted as a sort of DSL, so I would use a lot of reflection and weird conditions. Sorting is not much better. This is an interface invented when .NET did not support Predicates and lambda expressions, which would make sorting and filtering trivial and the subject of another post. So I go back to implementing a scalable BindingList, and just implement INotifyCollectionChanged over it.

For an implementation of IBindingView, check this out: BindingListView

Code time.

I've decided to implement the IndexOf caching as a dictionary with the objects as keys. The values are lists of integers representing all indexes of that value or object. Frankly I never realized that IndexOf for lists was not taking a start parameter, so it only returns the first occurrence of an item in the list.

There are three classes: AdvancedCollection is a fast IndexOf implementation of Collection. AdvancedBindingList is the copy pasted code of BindingList, with the base class changed from Collection to AdvancedCollection and with INotifyCollectionChanged implemented over it. SecurityUtils is only needed for the AddNew method of IBindingList and is again copy pasted from the Microsoft code. Enjoy!

Click to collapse/expand

internal static class SecurityUtils
{
    private static volatile ReflectionPermission _memberAccessPermission;
    private static volatile ReflectionPermission _restrictedMemberAccessPermission;

    private static ReflectionPermission memberAccessPermission =>
        _memberAccessPermission ??
        (_memberAccessPermission = new ReflectionPermission(ReflectionPermissionFlag.MemberAccess));

    private static ReflectionPermission restrictedMemberAccessPermission =>
        _restrictedMemberAccessPermission ??
        (_restrictedMemberAccessPermission =
            new ReflectionPermission(ReflectionPermissionFlag.RestrictedMemberAccess));

    private static void demandReflectionAccess(Type type)
    {
        try
        {
            memberAccessPermission.Demand();
        }
        catch (SecurityException)
        {
            demandGrantSet(type.Assembly);
        }
    }

    [SecuritySafeCritical]
    private static void demandGrantSet(Assembly assembly)
    {
        var permissionSet = assembly.PermissionSet;
        var accessPermission = restrictedMemberAccessPermission;
        permissionSet.AddPermission(accessPermission);
        permissionSet.Demand();
    }

    private static bool hasReflectionPermission(Type type)
    {
        try
        {
            demandReflectionAccess(type);
            return true;
        }
        catch (SecurityException)
        {
        }
        return false;
    }

    internal static object SecureCreateInstance(Type type)
    {
        return SecureCreateInstance(type, null, false);
    }

    internal static object SecureCreateInstance(Type type, object[] args, bool allowNonPublic)
    {
        if (type == null)
            throw new ArgumentNullException(nameof(type));
        var bindingAttr = BindingFlags.Instance | BindingFlags.Public | BindingFlags.CreateInstance;
        if (!type.IsVisible)
            demandReflectionAccess(type);
        else if (allowNonPublic && !hasReflectionPermission(type))
            allowNonPublic = false;
        if (allowNonPublic)
            bindingAttr |= BindingFlags.NonPublic;
        return Activator.CreateInstance(type, bindingAttr, null, args, null);
    }

    internal static object SecureCreateInstance(Type type, object[] args)
    {
        return SecureCreateInstance(type, args, false);
    }

    internal static object SecureConstructorInvoke(Type type, Type[] argTypes, object[] args, bool allowNonPublic)
    {
        return SecureConstructorInvoke(type, argTypes, args, allowNonPublic, BindingFlags.Default);
    }

    internal static object SecureConstructorInvoke(Type type, Type[] argTypes, object[] args, bool allowNonPublic,
        BindingFlags extraFlags)
    {
        if (type == null)
            throw new ArgumentNullException(nameof(type));
        if (!type.IsVisible)
            demandReflectionAccess(type);
        else if (allowNonPublic && !hasReflectionPermission(type))
            allowNonPublic = false;
        var bindingAttr = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | extraFlags;
        if (!allowNonPublic)
            bindingAttr &= ~BindingFlags.NonPublic;
        var constructor = type.GetConstructor(bindingAttr, null, argTypes, null);
        return constructor?.Invoke(args);
    }

    private static bool genericArgumentsAreVisible(MethodInfo method)
    {
        return !method.IsGenericMethod || method.GetGenericArguments().All(type => type.IsVisible);
    }

    internal static object FieldInfoGetValue(FieldInfo field, object target)
    {
        var declaringType = field.DeclaringType;
        if (declaringType == null)
        {
            if (!field.IsPublic)
                demandGrantSet(field.Module.Assembly);
        }
        else if (!declaringType.IsVisible || !field.IsPublic)
            demandReflectionAccess(declaringType);
        return field.GetValue(target);
    }

    internal static object MethodInfoInvoke(MethodInfo method, object target, object[] args)
    {
        var declaringType = method.DeclaringType;
        if (declaringType == null)
        {
            if (!method.IsPublic || !genericArgumentsAreVisible(method))
                demandGrantSet(method.Module.Assembly);
        }
        else if (!declaringType.IsVisible || !method.IsPublic || !genericArgumentsAreVisible(method))
            demandReflectionAccess(declaringType);
        return method.Invoke(target, args);
    }

    internal static object ConstructorInfoInvoke(ConstructorInfo ctor, object[] args)
    {
        var declaringType = ctor.DeclaringType;
        if (declaringType != null && (!declaringType.IsVisible || !ctor.IsPublic))
            demandReflectionAccess(declaringType);
        return ctor.Invoke(args);
    }

    internal static object ArrayCreateInstance(Type type, int length)
    {
        if (!type.IsVisible)
            demandReflectionAccess(type);
        return Array.CreateInstance(type, length);
    }
}

public class AdvancedCollection<T> : IList<T>,IList, IReadOnlyList<T>
{
    private readonly List<T> _innerList;
    private readonly Dictionary<T, List<int>> _reverseIndex;
    private readonly object _syncRoot=new object();

    public AdvancedCollection()
    {
        _innerList = new List<T>();
        _reverseIndex = new Dictionary<T, List<int>>();
    }

    public AdvancedCollection(IList<T> list):this()
    {
        _innerList.Clear();
        _innerList.AddRange(list);
        refreshIndexes();
    }

    private void refreshIndexes()
    {
        lock (_syncRoot)
        {
            _reverseIndex.Clear();
            for (var i = 0; i < _innerList.Count; i++)
            {
                var item = _innerList[i];
                List<int> indexes;
                if (!_reverseIndex.TryGetValue(item, out indexes))
                {
                    indexes = new List<int>();
                    _reverseIndex[item] = indexes;
                }
                indexes.Add(i);
            }
        }
    }

    public int IndexOf(T item)
    {
        List<int> indexes;
        if (!_reverseIndex.TryGetValue(item, out indexes)) return -1;
        return indexes.Count == 0 ? -1 : indexes[0];
    }

    public void Insert(int index, T item)
    {
        lock (_syncRoot)
        {
            var indexesList = Enumerable.Range(index, _innerList.Count - index)
                .Select(i => _reverseIndex[_innerList[i]])
                .Distinct();
            foreach (var indexes in indexesList)
            {
                for (var j = 0; j < indexes.Count; j++)
                {
                    if (indexes[j] >= index)
                    {
                        indexes[j]++;
                    }
                }
            }
            _innerList.Insert(index, item);
        }
    }

    public void RemoveAt(int index)
    {
        lock (_syncRoot)
        {
            var indexesList = Enumerable.Range(index, _innerList.Count - index)
                .Select(i => _reverseIndex[_innerList[i]])
                .Distinct();
            foreach (var indexes in indexesList)
            {
                for (var j = 0; j < indexes.Count; j++)
                {
                    var i = indexes[j];
                    if (i == index)
                    {
                        indexes.RemoveAt(j);
                        j--;
                        continue;
                    }
                    if (indexes[j] > index)
                    {
                        indexes[j]--;
                    }
                }
            }
            _innerList.RemoveAt(index);
        }
    }

    public T this[int index]
    {
        get { return _innerList[index]; }
        set
        {
            lock (_syncRoot)
            {
                var indexes = _reverseIndex[_innerList[index]];
                indexes.Remove(index);
                if (!_reverseIndex.TryGetValue(value, out indexes))
                {
                    indexes = new List<int>();
                    _reverseIndex[value] = indexes;
                }
                indexes.Add(index);
                indexes.Sort();
            }
        }
    }


    int IList.Add(object value)
    {
        return add((T) value);
    }

    bool IList.Contains(object value)
    {
        return ((IList<T>) this).Contains((T) value);
    }

    void IList.Clear()
    {
        lock (_syncRoot)
        {
            _innerList.Clear();
            _reverseIndex.Clear();
        }
    }

    int IList.IndexOf(object value)
    {
        return ((IList<T>) this).IndexOf((T) value);
    }

    void IList.Insert(int index, object value)
    {
        ((IList<T>)this).Insert(index, (T)value);
    }

    void IList.Remove(object value)
    {
        var index = ((IList) this).IndexOf(value);
        if (index < 0) return;
        ((IList) this).RemoveAt(index);
    }

    void IList.RemoveAt(int index)
    {
        ((IList<T>) this).RemoveAt(index);
    }

    object IList.this[int index]
    {
        get { return ((IList<T>)this)[index]; }
        set
        {
            var item = (T) value;
            ((IList<T>)this)[index] = item;
        }
    }

    bool IList.IsReadOnly => false;

    bool IList.IsFixedSize => false;

    void ICollection.CopyTo(Array array, int index)
    {
        ((IList)_innerList).CopyTo(array,index);
    }

    public int Count => _innerList.Count;

    object ICollection.SyncRoot => _syncRoot;

    bool ICollection.IsSynchronized => false;

    IEnumerator<T> IEnumerable<T>.GetEnumerator()
    {
        return _innerList.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return ((IEnumerable<T>) this).GetEnumerator();
    }

    public void Add(T item)
    {
        add(item);
    }

    public void Clear()
    {
        ((IList) this).Clear();
    }

    bool ICollection<T>.Contains(T item)
    {
        lock (_syncRoot)
        {
            return _reverseIndex.ContainsKey(item);
        }
    }

    void ICollection<T>.CopyTo(T[] array, int arrayIndex)
    {
        lock (_syncRoot)
        {
            _innerList.CopyTo(array, arrayIndex);
        }
    }

    bool ICollection<T>.Remove(T item)
    {
        var index = ((IList<T>)this).IndexOf(item);
        if (index < 0) return false;
        ((IList<T>)this).RemoveAt(index);
        return true;
    }

    int ICollection<T>.Count => _innerList.Count;

    bool ICollection<T>.IsReadOnly => false;

    int IReadOnlyCollection<T>.Count => _innerList.Count;

    T IReadOnlyList<T>.this[int index] => ((IList<T>) this)[index];

    private int add(T item)
    {
        lock (_syncRoot)
        {
            var index = _innerList.Count;
            _innerList.Add(item);
            List<int> indexes;
            if (!_reverseIndex.TryGetValue(item, out indexes))
            {
                indexes = new List<int>();
                _reverseIndex[item] = indexes;
            }
            indexes.Add(index);
            return index;
        }
    }

    protected virtual void ClearItems()
    {
        ((IList<T>)this).Clear();
    }

    protected virtual void InsertItem(int index, T item)
    {
        ((IList<T>)this).Insert(index,item);
    }

    protected virtual void RemoveItem(int index)
    {
        ((IList<T>)this).RemoveAt(index);
    }

    protected virtual void SetItem(int index, T item)
    {
        this[index] = item;
    }
}

/// <summary>
///     Provides a generic collection that supports data binding.
/// </summary>
/// <typeparam name="T">The type of elements in the list.</typeparam>
[Serializable]
[HostProtection(SecurityAction.LinkDemand, SharedState = true)]
public class AdvancedBindingList<T> : AdvancedCollection<T>, IBindingList, ICancelAddNew, IRaiseItemChangedEvents,
    INotifyCollectionChanged
{
    private int _addNewPos = -1;
    private bool _allowEdit = true;
    private bool _allowNew = true;
    private bool _allowRemove = true;

    [NonSerialized] private PropertyDescriptorCollection _itemTypeProperties;

    [NonSerialized] private int _lastChangeIndex = -1;

    [NonSerialized] private AddingNewEventHandler _onAddingNew;

    [NonSerialized] private PropertyChangedEventHandler _propertyChangedEventHandler;

    private bool _raiseItemChangedEvents;
    private bool _raiseListChangedEvents = true;
    private bool _userSetAllowNew;

    /// <summary>
    ///     Initializes a new instance of the <see cref="T:System.ComponentModel.BindingList`1" /> class using default values.
    /// </summary>
    public AdvancedBindingList()
    {
        initialize();
    }

    /// <summary>
    ///     Initializes a new instance of the <see cref="T:System.ComponentModel.BindingList`1" /> class with the specified
    ///     list.
    /// </summary>
    /// <param name="list">
    ///     An <see cref="T:System.Collections.Generic.IList`1" /> of items to be contained in the
    ///     <see cref="T:System.ComponentModel.BindingList`1" />.
    /// </param>
    public AdvancedBindingList(IList<T> list)
        : base(list)
    {
        initialize();
    }

    private bool itemTypeHasDefaultConstructor
    {
        get
        {
            var type = typeof (T);
            return type.IsPrimitive ||
                    type.GetConstructor(BindingFlags.Instance | BindingFlags.Public | BindingFlags.CreateInstance,
                        null, new Type[0], null) != null;
        }
    }

    /// <summary>
    ///     Gets or sets a value indicating whether adding or removing items within the list raises
    ///     <see cref="E:System.ComponentModel.BindingList`1.ListChanged" /> events.
    /// </summary>
    /// <returns>
    ///     true if adding or removing items raises <see cref="E:System.ComponentModel.BindingList`1.ListChanged" /> events;
    ///     otherwise, false. The default is true.
    /// </returns>
    public bool RaiseListChangedEvents
    {
        get { return _raiseListChangedEvents; }
        set { _raiseListChangedEvents = value; }
    }

    private bool addingNewHandled
    {
        get
        {
            if (_onAddingNew != null)
                return (uint) _onAddingNew.GetInvocationList().Length > 0U;
            return false;
        }
    }

    /// <summary>
    ///     Gets or sets a value indicating whether you can add items to the list using the
    ///     <see cref="M:System.ComponentModel.BindingList`1.AddNew" /> method.
    /// </summary>
    /// <returns>
    ///     true if you can add items to the list with the <see cref="M:System.ComponentModel.BindingList`1.AddNew" /> method;
    ///     otherwise, false. The default depends on the underlying type contained in the list.
    /// </returns>
    public bool AllowNew
    {
        get
        {
            if (_userSetAllowNew || _allowNew)
                return _allowNew;
            return addingNewHandled;
        }
        set
        {
            var num1 = AllowNew ? 1 : 0;
            _userSetAllowNew = true;
            _allowNew = value;
            var num2 = value ? 1 : 0;
            if (num1 == num2)
                return;
            fireListReset();
        }
    }

    /// <summary>
    ///     Gets or sets a value indicating whether items in the list can be edited.
    /// </summary>
    /// <returns>
    ///     true if list items can be edited; otherwise, false. The default is true.
    /// </returns>
    public bool AllowEdit
    {
        get { return _allowEdit; }
        set
        {
            if (_allowEdit == value)
                return;
            _allowEdit = value;
            fireListReset();
        }
    }

    /// <summary>
    ///     Gets or sets a value indicating whether you can remove items from the collection.
    /// </summary>
    /// <returns>
    ///     true if you can remove items from the list with the
    ///     <see cref="M:System.ComponentModel.BindingList`1.RemoveItem(System.Int32)" /> method otherwise, false. The default
    ///     is true.
    /// </returns>
    public bool AllowRemove
    {
        get { return _allowRemove; }
        set
        {
            if (_allowRemove == value)
                return;
            _allowRemove = value;
            fireListReset();
        }
    }

    /// <summary>
    ///     Gets a value indicating whether <see cref="E:System.ComponentModel.BindingList`1.ListChanged" /> events are
    ///     enabled.
    /// </summary>
    /// <returns>
    ///     true if <see cref="E:System.ComponentModel.BindingList`1.ListChanged" /> events are supported; otherwise, false.
    ///     The default is true.
    /// </returns>
    protected virtual bool SupportsChangeNotificationCore => true;

    /// <summary>
    ///     Gets a value indicating whether the list supports searching.
    /// </summary>
    /// <returns>
    ///     true if the list supports searching; otherwise, false. The default is false.
    /// </returns>
    protected virtual bool SupportsSearchingCore => false;

    /// <summary>
    ///     Gets a value indicating whether the list supports sorting.
    /// </summary>
    /// <returns>
    ///     true if the list supports sorting; otherwise, false. The default is false.
    /// </returns>
    protected virtual bool SupportsSortingCore => false;

    /// <summary>
    ///     Gets a value indicating whether the list is sorted.
    /// </summary>
    /// <returns>
    ///     true if the list is sorted; otherwise, false. The default is false.
    /// </returns>
    protected virtual bool IsSortedCore => false;

    /// <summary>
    ///     Gets the property descriptor that is used for sorting the list if sorting is implemented in a derived class;
    ///     otherwise, returns null.
    /// </summary>
    /// <returns>
    ///     The <see cref="T:System.ComponentModel.PropertyDescriptor" /> used for sorting the list.
    /// </returns>
    protected virtual PropertyDescriptor SortPropertyCore => null;

    /// <summary>
    ///     Gets the direction the list is sorted.
    /// </summary>
    /// <returns>
    ///     One of the <see cref="T:System.ComponentModel.ListSortDirection" /> values. The default is
    ///     <see cref="F:System.ComponentModel.ListSortDirection.Ascending" />.
    /// </returns>
    protected virtual ListSortDirection SortDirectionCore => ListSortDirection.Ascending;

    bool IBindingList.AllowNew => AllowNew;

    bool IBindingList.AllowEdit => AllowEdit;

    bool IBindingList.AllowRemove => AllowRemove;

    bool IBindingList.SupportsChangeNotification => SupportsChangeNotificationCore;

    bool IBindingList.SupportsSearching => SupportsSearchingCore;

    bool IBindingList.SupportsSorting => SupportsSortingCore;

    bool IBindingList.IsSorted => IsSortedCore;

    PropertyDescriptor IBindingList.SortProperty => SortPropertyCore;

    ListSortDirection IBindingList.SortDirection => SortDirectionCore;

    /// <summary>
    ///     Occurs when the list or an item in the list changes.
    /// </summary>
    public event ListChangedEventHandler ListChanged;

    object IBindingList.AddNew()
    {
        var obj = AddNewCore();
        _addNewPos = obj != null ? ((IList<T>) this).IndexOf((T) obj) : -1;
        return obj;
    }

    void IBindingList.ApplySort(PropertyDescriptor prop, ListSortDirection direction)
    {
        ApplySortCore(prop, direction);
    }

    void IBindingList.RemoveSort()
    {
        RemoveSortCore();
    }

    int IBindingList.Find(PropertyDescriptor prop, object key)
    {
        return FindCore(prop, key);
    }

    void IBindingList.AddIndex(PropertyDescriptor prop)
    {
    }

    void IBindingList.RemoveIndex(PropertyDescriptor prop)
    {
    }

    /// <summary>
    ///     Discards a pending new item.
    /// </summary>
    /// <param name="itemIndex">The index of the of the new item to be added </param>
    public virtual void CancelNew(int itemIndex)
    {
        if (_addNewPos < 0 || _addNewPos != itemIndex)
            return;
        RemoveItem(_addNewPos);
        _addNewPos = -1;
    }

    /// <summary>
    ///     Commits a pending new item to the collection.
    /// </summary>
    /// <param name="itemIndex">The index of the new item to be added.</param>
    public virtual void EndNew(int itemIndex)
    {
        if (_addNewPos < 0 || _addNewPos != itemIndex)
            return;
        _addNewPos = -1;
    }

    public event NotifyCollectionChangedEventHandler CollectionChanged;

    bool IRaiseItemChangedEvents.RaisesItemChangedEvents => _raiseItemChangedEvents;

    private void fireListReset()
    {
        fireListChanged(ListChangedType.Reset, -1);
        CollectionChanged?.Invoke(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
    }

    /// <summary>
    ///     Occurs before an item is added to the list.
    /// </summary>
    public event AddingNewEventHandler AddingNew
    {
        add
        {
            var num1 = AllowNew ? 1 : 0;
            _onAddingNew = _onAddingNew + value;
            var num2 = AllowNew ? 1 : 0;
            if (num1 == num2)
                return;
            fireListReset();
        }
        remove
        {
            var num1 = AllowNew ? 1 : 0;
            // ReSharper disable once DelegateSubtraction
            _onAddingNew = _onAddingNew - value;
            var num2 = AllowNew ? 1 : 0;
            if (num1 == num2)
                return;
            fireListReset();
        }
    }

    private void initialize()
    {
        _allowNew = itemTypeHasDefaultConstructor;
        if (!typeof (INotifyPropertyChanged).IsAssignableFrom(typeof (T)))
            return;
        _raiseItemChangedEvents = true;
        foreach (var obj in this)
            hookPropertyChanged(obj);
    }

    /// <summary>
    ///     Raises the <see cref="E:System.ComponentModel.BindingList`1.AddingNew" /> event.
    /// </summary>
    /// <param name="e">An <see cref="T:System.ComponentModel.AddingNewEventArgs" /> that contains the event data. </param>
    protected virtual void OnAddingNew(AddingNewEventArgs e)
    {
        _onAddingNew?.Invoke(this, e);
    }

    private object fireAddingNew()
    {
        var e = new AddingNewEventArgs(null);
        OnAddingNew(e);
        return e.NewObject;
    }

    /// <summary>
    ///     Raises the <see cref="E:System.ComponentModel.BindingList`1.ListChanged" /> event.
    /// </summary>
    /// <param name="e">A <see cref="T:System.ComponentModel.ListChangedEventArgs" /> that contains the event data. </param>
    protected virtual void OnListChanged(ListChangedEventArgs e)
    {
        ListChanged?.Invoke(this, e);
    }

    /// <summary>
    ///     Raises a <see cref="E:System.ComponentModel.BindingList`1.ListChanged" /> event of type
    ///     <see cref="F:System.ComponentModel.ListChangedType.Reset" />.
    /// </summary>
    public void ResetBindings()
    {
        fireListReset();
    }

    /// <summary>
    ///     Raises a <see cref="E:System.ComponentModel.BindingList`1.ListChanged" /> event of type
    ///     <see cref="F:System.ComponentModel.ListChangedType.ItemChanged" /> for the item at the specified position.
    /// </summary>
    /// <param name="position">A zero-based index of the item to be reset.</param>
    public void ResetItem(int position)
    {
        fireListChanged(ListChangedType.ItemChanged, position);
        CollectionChanged?.Invoke(this,
            new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Replace, this[position],position));
    }

    private void fireListChanged(ListChangedType type, int index)
    {
        if (!_raiseListChangedEvents)
            return;
        OnListChanged(new ListChangedEventArgs(type, index));
    }

    /// <summary>
    ///     Removes all elements from the collection.
    /// </summary>
    protected override void ClearItems()
    {
        EndNew(_addNewPos);
        if (_raiseItemChangedEvents)
        {
            foreach (var obj in this)
                unhookPropertyChanged(obj);
        }
        base.ClearItems();
        fireListReset();
    }

    /// <summary>
    ///     Inserts the specified item in the list at the specified index.
    /// </summary>
    /// <param name="index">The zero-based index where the item is to be inserted.</param>
    /// <param name="item">The item to insert in the list.</param>
    protected override void InsertItem(int index, T item)
    {
        EndNew(_addNewPos);
        base.InsertItem(index, item);
        if (_raiseItemChangedEvents)
            hookPropertyChanged(item);
        fireListChanged(ListChangedType.ItemAdded, index);
        CollectionChanged?.Invoke(this,
            new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, item,index));
    }

    /// <summary>
    ///     Removes the item at the specified index.
    /// </summary>
    /// <param name="index">The zero-based index of the item to remove. </param>
    /// <exception cref="T:System.NotSupportedException">
    ///     You are removing a newly added item and
    ///     <see cref="P:System.ComponentModel.IBindingList.AllowRemove" /> is set to false.
    /// </exception>
    protected override void RemoveItem(int index)
    {
        if (!_allowRemove && (_addNewPos < 0 || _addNewPos != index))
            throw new NotSupportedException();
        EndNew(_addNewPos);
        if (_raiseItemChangedEvents)
            unhookPropertyChanged(this[index]);
        var item = this[index];
        base.RemoveItem(index);
        fireListChanged(ListChangedType.ItemDeleted, index);
        CollectionChanged?.Invoke(this,
            new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, item,index));
    }

    /// <summary>
    ///     Replaces the item at the specified index with the specified item.
    /// </summary>
    /// <param name="index">The zero-based index of the item to replace.</param>
    /// <param name="item">The new value for the item at the specified index. The value can be null for reference types.</param>
    /// <exception cref="T:System.ArgumentOutOfRangeException">
    ///     <paramref name="index" /> is less than zero.-or-
    ///     <paramref name="index" /> is greater than <see cref="P:System.Collections.ObjectModel.Collection`1.Count" />.
    /// </exception>
    protected override void SetItem(int index, T item)
    {
        if (_raiseItemChangedEvents)
            unhookPropertyChanged(this[index]);
        base.SetItem(index, item);
        if (_raiseItemChangedEvents)
            hookPropertyChanged(item);
        fireListChanged(ListChangedType.ItemChanged, index);
        CollectionChanged?.Invoke(this,
            new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Replace, item,index));
    }

    /// <summary>
    ///     Adds a new item to the collection.
    /// </summary>
    /// <returns>
    ///     The item added to the list.
    /// </returns>
    /// <exception cref="T:System.InvalidOperationException">
    ///     The <see cref="P:System.Windows.Forms.BindingSource.AllowNew" />
    ///     property is set to false. -or-A public default constructor could not be found for the current item type.
    /// </exception>
    public T AddNew()
    {
        return (T) ((IBindingList) this).AddNew();
    }

    /// <summary>
    ///     Adds a new item to the end of the collection.
    /// </summary>
    /// <returns>
    ///     The item that was added to the collection.
    /// </returns>
    /// <exception cref="T:System.InvalidCastException">
    ///     The new item is not the same type as the objects contained in the
    ///     <see cref="T:System.ComponentModel.BindingList`1" />.
    /// </exception>
    protected virtual object AddNewCore()
    {
        var obj = fireAddingNew() ?? getNewInstance();
        Add((T) obj);
        return obj;
    }

    private static object getNewInstance()
    {
        return SecurityUtils.SecureCreateInstance(typeof (T));
    }

    /// <summary>
    ///     Sorts the items if overridden in a derived class; otherwise, throws a <see cref="T:System.NotSupportedException" />
    ///     .
    /// </summary>
    /// <param name="prop">A <see cref="T:System.ComponentModel.PropertyDescriptor" /> that specifies the property to sort on.</param>
    /// <param name="direction">One of the <see cref="T:System.ComponentModel.ListSortDirection" />  values.</param>
    /// <exception cref="T:System.NotSupportedException">Method is not overridden in a derived class. </exception>
    protected virtual void ApplySortCore(PropertyDescriptor prop, ListSortDirection direction)
    {
        throw new NotSupportedException();
    }

    /// <summary>
    ///     Removes any sort applied with
    ///     <see
    ///         cref="M:System.ComponentModel.BindingList`1.ApplySortCore(System.ComponentModel.PropertyDescriptor,System.ComponentModel.ListSortDirection)" />
    ///     if sorting is implemented in a derived class; otherwise, raises <see cref="T:System.NotSupportedException" />.
    /// </summary>
    /// <exception cref="T:System.NotSupportedException">Method is not overridden in a derived class. </exception>
    protected virtual void RemoveSortCore()
    {
        throw new NotSupportedException();
    }

    /// <summary>
    ///     Searches for the index of the item that has the specified property descriptor with the specified value, if
    ///     searching is implemented in a derived class; otherwise, a <see cref="T:System.NotSupportedException" />.
    /// </summary>
    /// <returns>
    ///     The zero-based index of the item that matches the property descriptor and contains the specified value.
    /// </returns>
    /// <param name="prop">The <see cref="T:System.ComponentModel.PropertyDescriptor" /> to search for.</param>
    /// <param name="key">
    ///     The value of
    ///     <paramref>
    ///         <name>property</name>
    ///     </paramref>
    ///     to match.
    /// </param>
    /// <exception cref="T:System.NotSupportedException">
    ///     <see cref="M:System.ComponentModel.BindingList`1.FindCore(System.ComponentModel.PropertyDescriptor,System.Object)" />
    ///     is not overridden in a derived class.
    /// </exception>
    protected virtual int FindCore(PropertyDescriptor prop, object key)
    {
        throw new NotSupportedException();
    }

    private void hookPropertyChanged(T item)
    {
        var notifyPropertyChanged = (object) item as INotifyPropertyChanged;
        if (notifyPropertyChanged == null)
            return;
        if (_propertyChangedEventHandler == null)
            _propertyChangedEventHandler = Child_PropertyChanged;
        notifyPropertyChanged.PropertyChanged += _propertyChangedEventHandler;
    }

    private void unhookPropertyChanged(T item)
    {
        var notifyPropertyChanged = (object) item as INotifyPropertyChanged;
        if (notifyPropertyChanged == null || _propertyChangedEventHandler == null)
            return;
        notifyPropertyChanged.PropertyChanged -= _propertyChangedEventHandler;
    }

    private void Child_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (!RaiseListChangedEvents)
            return;
        if (sender != null && e != null)
        {
            if (!string.IsNullOrEmpty(e.PropertyName))
            {
                T obj;
                try
                {
                    obj = (T) sender;
                }
                catch (InvalidCastException)
                {
                    ResetBindings();
                    return;
                }
                var newIndex = _lastChangeIndex;
                if (newIndex < 0 || newIndex >= Count || !this[newIndex].Equals(obj))
                {
                    newIndex = IndexOf(obj);
                    _lastChangeIndex = newIndex;
                }
                if (newIndex == -1)
                {
                    unhookPropertyChanged(obj);
                    ResetBindings();
                    return;
                }
                if (_itemTypeProperties == null)
                    _itemTypeProperties = TypeDescriptor.GetProperties(typeof (T));
                var propDesc = _itemTypeProperties.Find(e.PropertyName, true);
                OnListChanged(new ListChangedEventArgs(ListChangedType.ItemChanged, newIndex, propDesc));
                return;
            }
        }
        ResetBindings();
    }
}

Siderite's Blog Part Deux

Tuesday, 19 January 2016

SpaceX first stage landings on a sea barge: Three failures should be a strong indicator of a design flaw

Monday, 18 January 2016

3 and 9 Feb, Bucharest: ReactiveX in .NET

Facebook won! I created an account...

Wednesday, 13 January 2016

Apologies for people from domains like co.uk or co.in, etc.

Saturday, 9 January 2016

You can use C# version 6 features right now, and how glorious they are!

We come from the future!

Friday, 8 January 2016

BindingList vs ObservableCollection

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