依赖属性依赖于另一个 [英] Dependency Property dependent on another

问题描述

如何注册一个依赖关系属性，该依赖关系属性的值是使用另一个依赖关系属性的值计算的？

How can one register a dependency property whose value is calculated using the value of another dependency property?

由于WPF在运行时绕过.NET属性包装器，一次，不应在getter和setter中包含逻辑。解决方案通常是使用 PropertyChangedCallback s。但是，这些被声明为静态的。

Because the .NET property wrappers are bypassed by WPF at run-time, one should not include logic in the getters and setters. The solution to that is typically to use PropertyChangedCallbacks. But those are declared static.

例如，完成此人为任务的正确方法是什么：

For example, what is the proper way to accomplish this contrived task:

public bool TestBool
{
  get { return (bool)GetValue(TestBoolProperty); }
  set 
  { 
    SetValue(TestBoolProperty, value);
    TestDouble = ((value)?(100.0):(200.0)); // HERE IS THE DEPENDENCY
  }
}
public static readonly DependencyProperty TestBoolProperty =
  DependencyProperty.Register("TestBool", typeof(bool), typeof(ViewModel));

public double TestDouble
{
  get { return ((double)GetValue(TestDoubleProperty)); }
  set { SetValue(TestDoubleProperty, value); }
}
public static readonly DependencyProperty TestDoubleProperty =
  DependencyProperty.Register("TestDouble", typeof(double), typeof(ViewModel));

只要依赖项不是循环的，是否有适当的方法来实现？

As long as the dependency is not circular, is there a proper means to accomplish this?

推荐答案

嗯...我想您最好看看依赖属性值强制。这是一个带有强制性的示例：

Hmmm... I think you'd better look at dependency properties value coercion. Here is an example with coercion:

public class ViewModel : DependencyObject
{
  public bool TestBool
  {
    get { return (bool)GetValue(TestBoolProperty); }
    set { SetValue(TestBoolProperty, value); }
  }
  public static readonly DependencyProperty TestBoolProperty =
    DependencyProperty.Register("TestBool", typeof(bool), typeof(ViewModel), new PropertyMetadata(false, OnTestBoolPropertyChanged));

  private static void OnTestBoolPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
  {
    var vm = (ViewModel)d;
    vm.CoerceValue(TestDoubleProperty);
  }

  public double TestDouble
  {
    get { return ((double)GetValue(TestDoubleProperty)); }
    set { SetValue(TestDoubleProperty, value); }
  }
  public static readonly DependencyProperty TestDoubleProperty =
    DependencyProperty.Register("TestDouble", typeof(double), typeof(ViewModel), new PropertyMetadata(0.0, null, OnCoerceTestDouble));

  private static object OnCoerceTestDouble(DependencyObject d, object baseValue)
  {
    var vm = (ViewModel) d;
    var testBool = vm.TestBool;
    return ((testBool) ? (100.0) : (200.0));
  }
}

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