uwp：数据绑定编程问题

Question

我正在使用 uwp 进行开发，但遇到了数据绑定问题。我有一个 listView，其中填充了一个名为 PlaylistLeftOption class 的自定义面板元素。此 class 继承 Panel class 属性，继承 FrameworkElement class 属性及其方法，因此我有一个可用的 SetBinding 方法。现在我试图绑定高度值（它等于其他元素）所以我在其他外部单例 class 中创建了一个名为 PerformanceItemHeight 的静态属性。因为我需要动态地填充列表视图，所以我试图将值绑定到构造函数中，但它不起作用。这是构造函数中的代码：

    public PlaylistLeftOption()
    {
        mainGrid.Background = new SolidColorBrush(Colors.Red);
        mainGrid.BorderBrush = new SolidColorBrush(Colors.Black);
        mainGrid.BorderThickness = new Thickness(0.5,0.25,0.5,0.25);

        WidthVal = 200;
        HeightVal = 50;

        var myBinding = new Binding();
        myBinding.Source = PerformanceLayout.Instance.PerformanceItemHeight;
        myBinding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
        myBinding.Mode = BindingMode.TwoWay;
        SetBinding(HeightValProperty, myBinding);

        Children.Add(mainGrid);
    }

这是属性:

     public static readonly DependencyProperty HeightValProperty = DependencyProperty.Register(
      "HeightVal",
      typeof(double),
      typeof(PlaylistLeftOption),
      new PropertyMetadata(50)
    );

    public double HeightVal
    {
        get => (double)GetValue(HeightValProperty);
        set
        {
            SetValue(HeightValProperty, value);
            Height = HeightVal;
            mainGrid.Height = HeightVal;
            globalSize.Height = HeightVal;
        }
    }

这是 PerformanceItemHeight 的代码：

    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        // Raise the PropertyChanged event, passing the name of the property whose value has changed.
        this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    private double _performanceItemHeight = 50;
    public double PerformanceItemHeight {
        get => _performanceItemHeight;
        set {
            _performanceItemHeight = value;
            this.OnPropertyChanged();
        }
    }

为什么 via xaml 有效？我尝试通过 xaml 在列表视图中添加 PlaylistLeftOption 项，没问题！谢谢

Answer 1

通过测试，HeightVal 的绑定在 XAML 中有效，而 HeightVal 的绑定在代码隐藏中无效。您可以在文档 Custom dependency properties 的 Implementing the wrapper 部分中看到原因，其中指出您的包装器实现应仅执行 GetValue 和 SetValue 操作。否则，通过 XAML 设置属性与通过代码设置属性时会出现不同的行为。

您可以添加一个property-changed callback method来主动通知HeightVal的变化。

例如：

public static readonly DependencyProperty HeightValProperty = DependencyProperty.Register(
  "HeightVal",
  typeof(double),
  typeof(PlaylistLeftOption),
  new PropertyMetadata(100, new PropertyChangedCallback(OnHeightValChanged))
);
private static void OnHeightValChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    PlaylistLeftOption playlistLeftOption = d as PlaylistLeftOption;
    if(playlistLeftOption != null)
    {
        var height = (Double)e.NewValue;
        playlistLeftOption.HeightVal = height;
    }
}

并像这样更改绑定代码：

var myBinding = new Binding();
myBinding.Source = PerformanceLayout.Instance;
myBinding.Path = new PropertyPath("PerformanceItemHeight");
myBinding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
myBinding.Mode = BindingMode.TwoWay;
SetBinding(HeightValProperty, myBinding);

uwp：数据绑定编程问题

uwp: data binding programmatically issue

xaml

data-binding

uwp

binding

programmatically