wpf - 依赖 属性依赖于另一个

Question

如何注册一个依赖属性，其值是使用另一个依赖属性的值计算的？

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

例如，完成这个人为任务的正确方法是什么:

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));

只要依赖不是循环的，是否有适当的方法来实现这一点？

Answer 1

嗯...我觉得你最好看看依赖属性 value coercion .这是强制转换的示例:

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));
  }
}