将Action绑定到XAML中UserControl的属性

Question

我有一个用户控件,它有一个按钮和一个依赖属性,用于执行按钮的操作.包含该控件的页面在XAML中设置操作.

MyUserControl.cs

一个按钮,依赖属性ButtonAction类型,Action.单击该按钮时,它将执行ButtonAction.

MainPage.xaml.cs中

行动1

行动2

MainPage.xaml中

MyUserControl使用ButtonAction = Action1呈现一个实例

问题:未从XAML分配ButtonAction属性

MyUserControl.cs

    public sealed partial class MyUserControl : UserControl
{

    public Action ButtonAction {
        get { return (Action)GetValue(ButtonActionProperty); }
        set { SetValue(ButtonActionProperty, value); }
    }

    public static readonly DependencyProperty ButtonActionProperty =
        DependencyProperty.Register("ButtonAction", typeof(Action), typeof(MyUserControl), new PropertyMetadata(null,ButtonAction_PropertyChanged));

    private static void ButtonAction_PropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
        Debug.WriteLine("ButtonAction_PropertyChanged");
        // Is not called!
    }


    public MyUserControl() {
        this.InitializeComponent();
    }

    private void Button_Click(object sender, RoutedEventArgs e) {
        if (ButtonAction != null) {
            // Never reaches here!
            ButtonAction();
        }
    }
}

MyUserControl.xaml

    <Grid>
    <Button Click="Button_Click">Do The Attached Action!</Button>

</Grid>

MainPage.xaml.cs中

    Action Action1 = (
        () => { Debug.WriteLine("Action1 called"); });

    Action Action2 = (() => { Debug.WriteLine("Action2 called"); });

MainPage.xaml中

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <local:MyUserControl x:Name="myUserControl" ButtonAction="{Binding Action1}"/>
</Grid>

如果在MainPage()的代码隐藏中我在事件中分配动作,它确实有效.MainPage.xaml.csLoaded

        private void Page_Loaded(object sender, RoutedEventArgs e) {
        this.myUserControl.ButtonAction = Action1;
    }

在这种情况下,还会调用用户控件中的PropertyChanged回调.(此处理程序仅用于诊断目的.我无法在实践中看到它如何用于支持该属性).

Answer 1

问题出在您的数据绑定中。in应该是公共属性Action1，而您将其定义为私有变量。ButtonAction="{Binding Action1}"

另外，您不能像这样直接在后面的代码中声明普通属性。您将需要一个依赖属性，或者更常见的是，在实现INotifyPropertyChanged.

如果我们采用第二种方法，我们将需要创建一个带有属性的视图模型类，如下所示Action1。请注意，这些OnPropertyChanged内容只是实现的标准方法INotifyPropertyChanged。

public class ViewModel : INotifyPropertyChanged
{
    private Action _action1;
    public Action Action1
    {
        get { return _action1; }
        set
        {
            _action1 = value;
            OnPropertyChanged("Action1");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string name)
    {
        var handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(name));
        }
    }
}

然后您只需将其分配给DataContext您的主页即可。

    public MainPage()
    {
        this.InitializeComponent();

        var vm = new ViewModel();
        vm.Action1 = (() =>
        {
            Debug.WriteLine("Action1 called");
        });

        this.DataContext = vm;
    }

通过这两项更改，您的ButtonAction回调现在应该会被触发。:)