嵌套類INotifyPropertyChanged的將無法工作

Question

得到了一些代碼時出現了意外的結果：

如果我與MYCLASS代替嵌套類，那麼就沒有問題。我錯過了什麼？ 如果我將文本（綁定到其他控件）或綁定圖像，則無關緊要。

XAML代碼：

<Window x:Class="WpfApplication1.MainWindow" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Title="MainWindow" Height="350" Width="525"> 
<Window.Resources> 

    <DataTemplate x:Key="DataTemplate_Level"> 
     <Image Source="{Binding Path=MyClass.ImageSource}" Width="48" Height="48"/> 
    </DataTemplate> 

</Window.Resources> 
<Grid> 
    <ItemsControl x:Name="h" ItemTemplate="{DynamicResource DataTemplate_Level}"/> 
</Grid> 
</Window> 

類代碼：

using System; 
using System.Collections.ObjectModel; 
using System.ComponentModel; 
using System.Windows; 
using System.Windows.Media; 
using System.Windows.Media.Imaging; 

namespace WpfApplication1 
{ 
/// <summary> 
/// Interaction logic for MainWindow.xaml 
/// </summary> 
public partial class MainWindow : Window 
{ 
    public MainWindow() 
    { 
     InitializeComponent(); 
     var myClass = new WrappedClass() 
          { 
           MyClass = new MyClass() 
          }; 

     var image = new BitmapImage(new Uri("Tiles.png", UriKind.Relative)); 
     int TileSize = 16; 
     var cropRectangle = new Int32Rect((int)0, 0, TileSize, TileSize); 
     var croppedBitmap = new CroppedBitmap(image, cropRectangle); 


     var observableCollection = new ObservableCollection<WrappedClass>(); 
     observableCollection.Add(myClass); 
     observableCollection.Add(myClass); 
     observableCollection.Add(myClass); 

     h.ItemsSource = observableCollection; 
    } 

    public class WrappedClass : INotifyPropertyChanged 
    { 
     private MyClass _myClass; 
     public MyClass MyClass 
     { 
      get 
      { 
       return _myClass; 
      } 
      set 
      { 
       _myClass = value; 
       PropertyChanged.Invoke(this, new PropertyChangedEventArgs("MyClass")); 
      } 
     } 
     public event PropertyChangedEventHandler PropertyChanged; 
    } 

    public class MyClass : INotifyPropertyChanged 
    { 
     private ImageSource _imageSource; 
     private string _text = "test"; 

     public MyClass() 
     { 
      var image = new BitmapImage(new Uri("Tiles.png", UriKind.Relative)); 
      int TileSize = 16; 
      var cropRectangle = new Int32Rect((int)0, 0, TileSize, TileSize); 
      _imageSource = new CroppedBitmap(image, cropRectangle); 
     } 

     public string Text 
     { 
      get 
      { 
       return _text; 
      } 
      set 
      { 
       _text = value; 
       PropertyChanged.Invoke(this,new PropertyChangedEventArgs("Text")); 
      } 
     } 
     public ImageSource ImageSource 
     { 
      get 
      { 
       return _imageSource; 
      } 
      set 
      { 
       _imageSource = value; 
       PropertyChanged.Invoke(this, new PropertyChangedEventArgs("ImageSource")); 
      } 
     } 
     public event PropertyChangedEventHandler PropertyChanged; 
    } 
    } 
} 

Answer 1

我猜你得到一個空引用錯誤，可能是包裹在一個調用錯誤，因爲它很可能會在你的構造發生。

不要這樣做：

PropertyChanged.Invoke(this, new PropertyChangedEventArgs("MyClass")); 

相反，創建一個空檢查的方法：

public void FirePropertyChange(string propertyName) 
    { 
     var handler = PropertyChanged; 
     if (handler != null) 
     { 
      handler.Invoke(this, new PropertyChangedEventArgs(propertyName)); 
     } 
    } 

，並調用它像這樣：

FirePropertyChange("MyClass"); 

Answer 2

一對夫婦的這裏的東西

1. 確保您的所有類都實現了INotifyPropertyChanged。特別是在處理UserControls時。
2. 我不喜歡硬編碼字符串屬性 - 看看我的帖子在這裏如何使用反射做到這一點。

http://tsells.wordpress.com/2011/02/08/using-reflection-with-wpf-and-the-inotifypropertychanged-interface/