MVVM-我如何綁定到屬性，這不是DependancyProperty？

Question

我找到這個問題MVVM and the TextBox's SelectedText property。但是，我無法獲得解決方案。這是我的非工作代碼，我試圖在第二個文本框中顯示第一個文本框的選定文本。

查看：

SelectedText和文本都是從我的ViewModel只是字符串屬性。

<TextBox Text="{Binding Path=Text, UpdateSourceTrigger=PropertyChanged}" Height="155" HorizontalAlignment="Left" Margin="68,31,0,0" Name="textBox1" VerticalAlignment="Top" Width="264" AcceptsReturn="True" AcceptsTab="True" local:TextBoxHelper.SelectedText="{Binding SelectedText, UpdateSourceTrigger=PropertyChanged, Mode=OneWayToSource}" /> 
     <TextBox Text="{Binding SelectedText, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}" Height="154" HorizontalAlignment="Left" Margin="82,287,0,0" Name="textBox2" VerticalAlignment="Top" Width="239" /> 

TextBoxHelper

public static class TextBoxHelper 
{ 
    #region "Selected Text" 
    public static string GetSelectedText(DependencyObject obj) 
    { 
     return (string)obj.GetValue(SelectedTextProperty); 
    } 

    public static void SetSelectedText(DependencyObject obj, string value) 
    { 
     obj.SetValue(SelectedTextProperty, value); 
    } 

    // Using a DependencyProperty as the backing store for SelectedText. This enables animation, styling, binding, etc... 
    public static readonly DependencyProperty SelectedTextProperty = 
     DependencyProperty.RegisterAttached(
      "SelectedText", 
      typeof(string), 
      typeof(TextBoxHelper), 
      new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, SelectedTextChanged)); 

    private static void SelectedTextChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e) 
    { 
     TextBox tb = obj as TextBox; 
     if (tb != null) 
     { 
      if (e.OldValue == null && e.NewValue != null) 
      { 
       tb.SelectionChanged += tb_SelectionChanged; 
      } 
      else if (e.OldValue != null && e.NewValue == null) 
      { 
       tb.SelectionChanged -= tb_SelectionChanged; 
      } 

      string newValue = e.NewValue as string; 

      if (newValue != null && newValue != tb.SelectedText) 
      { 
       tb.SelectedText = newValue as string; 
      } 
     } 
    } 

    static void tb_SelectionChanged(object sender, RoutedEventArgs e) 
    { 
     TextBox tb = sender as TextBox; 
     if (tb != null) 
     { 
      SetSelectedText(tb, tb.SelectedText); 
     } 
    } 
    #endregion 

} 

我在做什麼錯？

Answer 1

這不起作用的原因是屬性更改回調沒有引發（因爲您的虛擬機的綁定值與該屬性的元數據中指定的默認值相同）。但更基礎的是，當所選文本設置爲空時，您的行爲將會分離。在這種情況下，我傾向於使用另一個附加屬性來簡單地監視選定的文本，然後可以綁定SelectedText屬性。所以，像這樣：

#region IsSelectionMonitored 
public static readonly DependencyProperty IsSelectionMonitoredProperty = DependencyProperty.RegisterAttached(
    "IsSelectionMonitored", 
    typeof(bool), 
    typeof(PinnedInstrumentsViewModel), 
    new FrameworkPropertyMetadata(OnIsSelectionMonitoredChanged)); 

[AttachedPropertyBrowsableForType(typeof(TextBox))] 
public static bool GetIsSelectionMonitored(TextBox d) 
{ 
    return (bool)d.GetValue(IsSelectionMonitoredProperty); 
} 

public static void SetIsSelectionMonitored(TextBox d, bool value) 
{ 
    d.SetValue(IsSelectionMonitoredProperty, value); 
} 

private static void OnIsSelectionMonitoredChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e) 
{ 
    TextBox tb = obj as TextBox; 
    if (tb != null) 
    { 
     if ((bool)e.NewValue) 
     { 
      tb.SelectionChanged += tb_SelectionChanged; 
     } 
     else 
     { 
      tb.SelectionChanged -= tb_SelectionChanged; 
     } 

     SetSelectedText(tb, tb.SelectedText); 
    } 
} 
#endregion 

#region "Selected Text" 
public static string GetSelectedText(DependencyObject obj) 
{ 
    return (string)obj.GetValue(SelectedTextProperty); 
} 

public static void SetSelectedText(DependencyObject obj, string value) 
{ 
    obj.SetValue(SelectedTextProperty, value); 
} 

// Using a DependencyProperty as the backing store for SelectedText. This enables animation, styling, binding, etc... 
public static readonly DependencyProperty SelectedTextProperty = 
    DependencyProperty.RegisterAttached(
     "SelectedText", 
     typeof(string), 
     typeof(TextBoxHelper), 
     new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, SelectedTextChanged)); 

private static void SelectedTextChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e) 
{ 
    TextBox tb = obj as TextBox; 
    if (tb != null) 
    { 
     tb.SelectedText = e.NewValue as string;    
    } 
} 

static void tb_SelectionChanged(object sender, RoutedEventArgs e) 
{ 
    TextBox tb = sender as TextBox; 
    if (tb != null) 
    { 
     SetSelectedText(tb, tb.SelectedText); 
    } 
} 
#endregion 

，然後在XAML，你必須將該屬性添加到您的第一個TextBox：

<TextBox ... local:TextBoxHelper.IsSelectionMonitored="True" local:TextBoxHelper.SelectedText="{Binding SelectedText, Mode=OneWayToSource}" /> 

Answer 2

你需要一個普通的.NET屬性包裝了的DependencyProperty，有的像：

public string SelectedText 
{ 
    set {SetSelectedText(this, value);} 
... 

它不是由運行時所需（運行時使用的set/get），但它是由設計師和編譯器需要。

Answer 3

爲了使SelectedTextChanged處理程序觸發SelectedText屬性，必須具有初始值。如果你不初始化這個值（string.Empty作爲最低限度），那麼這個處理程序永遠不會觸發，反過來你永遠不會註冊tb_SelectionChanged處理程序。

Answer 4

你結合的嘗試你TextBox的Text屬性綁定到TextBox的當前數據上下文的SelectedText財產。既然你有附加屬性的工作，不與物業掛您的數據上下文的，你需要在你的結合提供更多的信息：

<TextBox Text="{Binding local:TextBoxHelper.SelectedText, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}" ... /> 

凡local已經與包含的CLR命名空間相關聯TextBoxHelper類。

Answer 5

這個使用類TextBoxHelper爲我工作。正如其他提到的，您需要用非空值初始化TextBoxHelper的SelectedText屬性。不應將數據綁定到視圖上的字符串屬性（SelText），而應將其綁定到應實現INotifyPropertyChanged的虛擬機的字符串屬性。

XAML：

<Window x:Class="TextSelectDemo.Window1" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:local="clr-namespace:TextSelectDemo" 
    Height="300" Width="300"> 
    <StackPanel> 
     <TextBox local:TextBoxHelper.SelectedText="{Binding Path=SelText, Mode=TwoWay}" /> 
     <TextBox Text="{Binding Path=SelText}" /> 
    </StackPanel> 
</Window> 

後面的代碼：

using System.ComponentModel; 
using System.Windows; 

namespace TextSelectDemo 
{ 
    public partial class Window1 : Window, INotifyPropertyChanged 
    { 
     public Window1() 
     { 
      InitializeComponent(); 

      SelText = string.Empty; 

      DataContext = this; 
     } 

     private string _selText; 
     public string SelText 
     { 
      get { return _selText; } 
      set 
      { 
       _selText = value; 
       if (PropertyChanged != null) 
       { 
        PropertyChanged(this, new PropertyChangedEventArgs("SelText")); 
       } 
      } 
     } 

     public event PropertyChangedEventHandler PropertyChanged; 
    } 
}