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从另一个更新依赖项属性

xaml data-binding wpf c#

Rob · 技术社区 · 15 年前

我有一个字符串依赖属性(searchText),更新后需要更新集合依赖属性(results)。
我的收藏DP:

public IEnumerable<string> Results{
  get { return (IEnumerable<string>) GetValue(ResultsProperty); }
  set { SetValue(ResultsProperty, value); }
}
public static readonly DependencyProperty ResultsProperty= 
DependencyProperty.Register("Results", typeof(IEnumerable<string>), typeof(MainWindowVM), new UIPropertyMetadata(new List<string>()));

我没有运气就试过这个。我在结果处放置了一个断点。线和它从来没有被击中。

public string SearchText{
  get { return (string) GetValue(SearchTextProperty); }
  set {
    Results =
          from T in Tree.GetPeople(value)
          select T.FullName;
    SetValue(SearchTextProperty, value);
  }
}
public static readonly DependencyProperty SearchTextProperty= 
DependencyProperty.Register("SearchText", typeof(string), typeof(MainWindowVM), new UIPropertyMetadata(""));

XAML:

<TextBox DockPanel.Dock="Top" Text="{Binding SearchValue, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />

<ListBox DockPanel.Dock="Top" ItemsSource="{Binding NameResults}" SelectedItem="{Binding Search}" />

2 回复 | 直到 10 年前

Jesse Squire 15 年前

在XAML中或通过绑定设置依赖属性时,运行时将始终绕过实例属性别名并直接调用 GetValue 和 SetValue . 正是因为这样,才不会调用实例设置器。

您可能希望考虑在依赖属性中注册一个方法,当该属性更改时将调用该方法。在创建 PropertyMetadata 对于依赖属性。

我相信下面的例子可以实现你想要做的。在这个例子中,我的类有两个依赖属性,分别命名为First和Second。当我设置第一个值时,将调用我的更改处理程序,并设置第二个值。

public class DependencyPropertyTest : DependencyObject
{
  public static readonly DependencyProperty FirstProperty;
  public static readonly DependencyProperty SecondProperty;

  static DependencyPropertyTest()
  {
    FirstProperty  = DependencyProperty.Register("FirstProperty", 
                                                  typeof(bool), 
                                                  typeof(DependencyPropertyTest), 
                                                  new PropertyMetadata(false, FirstPropertyChanged));

    SecondProperty = DependencyProperty.Register("SecondProperty", 
                                                 typeof(string), 
                                                 typeof(DependencyPropertyTest), 
                                                 new PropertyMetadata(null));
  } // End constructor

  private bool First
  {
    get { return (bool)this.GetValue(FirstProperty); }
    set { this.SetValue(FirstProperty, value);       }

  } // End property First

  private string Second
  {
    get { return (string)this.GetValue(SecondProperty); }
    set { this.SetValue(SecondProperty, value);         }

  } // End property Second

  private static void FirstPropertyChanged(DependencyObject dependencyObject, 
                                           DependencyPropertyChangedEventArgs ea)
  {
    DependencyPropertyTest instance = dependencyObject as DependencyPropertyTest;

    if (instance == null)
    {
      return;
    }

    instance.Second = String.Format("First is {0}.", ((bool)ea.NewValue).ToString());

  } // End method FirstPropertyChanged
} // End class DependencyPropertyTest

希望有帮助。

Community Egal 7 年前

正如我所评论的,目前接受的答案在原则上是正确的,除非它必须使用 SetCurrentValue 方法而不是执行简单的赋值。见 this answer 更多的解释。

以下是与此修复程序相同的代码:

public class DependencyPropertyTest : DependencyObject
{
  public static readonly DependencyProperty FirstProperty;
  public static readonly DependencyProperty SecondProperty;

  static DependencyPropertyTest()
  {
    FirstProperty  = DependencyProperty.Register("FirstProperty", 
                                                  typeof(bool), 
                                                  typeof(DependencyPropertyTest), 
                                                  new PropertyMetadata(false, FirstPropertyChanged));

    SecondProperty = DependencyProperty.Register("SecondProperty", 
                                                 typeof(string), 
                                                 typeof(DependencyPropertyTest), 
                                                 new PropertyMetadata(null));
  } // End constructor

  private bool First
  {
    get { return (bool)this.GetValue(FirstProperty); }
    set { this.SetValue(FirstProperty, value);       }

  } // End property First

  private string Second
  {
    get { return (string)this.GetValue(SecondProperty); }
    set { this.SetValue(SecondProperty, value);         }

  } // End property Second

  private static void FirstPropertyChanged(DependencyObject dependencyObject, 
                                           DependencyPropertyChangedEventArgs ea)
  {
    DependencyPropertyTest instance = dependencyObject as DependencyPropertyTest;

    if (instance == null)
    {
      return;
    }

    // SetCurrentValue should be used here!
    instance.SetCurrentValue(SecondProperty,
      String.Format("First is {0}.", ((bool)ea.NewValue).ToString());

  } // End method FirstPropertyChanged
} // End class DependencyPropertyTest