如何綁定文本框的SelectionStart屬性？

Question

我用這個：

<TextBox x:Name="Test"/> 
<TextBlock Text="{Binding SelectionStart, ElementName=Test}"/> 

，但它始終顯示爲0。
我該如何治療呢？
謝謝。

Answer 1

據我所知，該功能尚未包含在Silverlight 2.0中。

閱讀this文章爲變通解決方案。

Answer 2

您無法綁定到SelectionStart，因爲它不是DependencyProperty。

Answer 3

我就遇到了這個問題（SelectionStart和SelectionLength不依賴屬性），並決定將與可綁定選擇開始和結束一個TextBox：

public class SelectionBindingTextBox : TextBox 
{ 
    public static readonly DependencyProperty BindableSelectionStartProperty = 
     DependencyProperty.Register(
     "BindableSelectionStart", 
     typeof(int), 
     typeof(SelectionBindingTextBox), 
     new PropertyMetadata(OnBindableSelectionStartChanged)); 

    public static readonly DependencyProperty BindableSelectionLengthProperty = 
     DependencyProperty.Register(
     "BindableSelectionLength", 
     typeof(int), 
     typeof(SelectionBindingTextBox), 
     new PropertyMetadata(OnBindableSelectionLengthChanged)); 

    private bool changeFromUI; 

    public SelectionBindingTextBox() : base() 
    { 
     this.SelectionChanged += this.OnSelectionChanged; 
    } 

    public int BindableSelectionStart 
    { 
     get 
     { 
      return (int)this.GetValue(BindableSelectionStartProperty); 
     } 

     set 
     { 
      this.SetValue(BindableSelectionStartProperty, value); 
     } 
    } 

    public int BindableSelectionLength 
    { 
     get 
     { 
      return (int)this.GetValue(BindableSelectionLengthProperty); 
     } 

     set 
     { 
      this.SetValue(BindableSelectionLengthProperty, value); 
     } 
    } 

    private static void OnBindableSelectionStartChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs args) 
    { 
     var textBox = dependencyObject as SelectionBindingTextBox; 

     if (!textBox.changeFromUI) 
     { 
      int newValue = (int)args.NewValue; 
      textBox.SelectionStart = newValue; 
     } 
     else 
     { 
      textBox.changeFromUI = false; 
     } 
    } 

    private static void OnBindableSelectionLengthChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs args) 
    { 
     var textBox = dependencyObject as SelectionBindingTextBox; 

     if (!textBox.changeFromUI) 
     { 
      int newValue = (int)args.NewValue; 
      textBox.SelectionLength = newValue; 
     } 
     else 
     { 
      textBox.changeFromUI = false; 
     } 
    } 

    private void OnSelectionChanged(object sender, RoutedEventArgs e) 
    { 
     if (this.BindableSelectionStart != this.SelectionStart) 
     { 
      this.changeFromUI = true; 
      this.BindableSelectionStart = this.SelectionStart; 
     } 

     if (this.BindableSelectionLength != this.SelectionLength) 
     { 
      this.changeFromUI = true; 
      this.BindableSelectionLength = this.SelectionLength; 
     } 
    } 
} 

Answer 4

這可能是一個替代的解決方案：

查看：

<TextBox Text="{Binding Text}"> 
    <i:Interaction.Triggers> 
     <i:EventTrigger EventName="SelectionChanged"> 
      <mvvml:EventToCommand Command="{Binding TextBoxSelectionChangedCommand}" 
           PassEventArgsToCommand="True" /> 
     </i:EventTrigger> 
    </i:Interaction.Triggers> 
</TextBox> 

視圖模型：

#region TextBoxSelectionChangedCommand 
    RelayCommand<RoutedEventArgs> _TextBoxSelectionChangedCommand = null; 
    public ICommand TextBoxSelectionChangedCommand { 
     get { 
      if (_TextBoxSelectionChangedCommand == null) { 
       _TextBoxSelectionChangedCommand = new RelayCommand<RoutedEventArgs>((r) => TextBoxSelectionChanged(r), (r) => true); 
      } 

      return _TextBoxSelectionChangedCommand; 
     } 
    } 

    protected virtual void TextBoxSelectionChanged(RoutedEventArgs _args) { 
     YourCursorPositionVariable = (_args.OriginalSource as System.Windows.Controls.TextBox).SelectionStart; 
    } 
    #endregion 

我同意你必須在ViewModel中投射TextBox組件類型，它是一種耦合，但是創建一個自定義組件也會綁定到一個特定的屬性。