WPF 行为和事件 - 附加到适当的事件

Question

我这里有一个处理拖放的行为，我通过视图附加了鼠标事件。项目的视图模型继承自 IDraggable。我使用 Caliburn.Micro 作为 MVVM 框架。

<ItemsControl x:Name="Items">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <Canvas />
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
    <ItemsControl.ItemContainerStyle>
        <Style TargetType="ContentPresenter">
            <Setter Property="Canvas.Left" Value="{Binding Path=X}" />
            <Setter Property="Canvas.Top" Value="{Binding Path=Y}" />
            <Setter Property="Width" Value="{Binding Path=Width}" />
            <Setter Property="Height" Value="{Binding Path=Height}" />
        </Style>
    </ItemsControl.ItemContainerStyle>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Border>
                <!-- item contents -->

                <i:Interaction.Behaviors>
                    <behaviors:DragOnCanvasBehavior DraggableItem="{Binding}">
                        <i:Interaction.Triggers>
                            <i:EventTrigger EventName="PreviewMouseLeftButtonDown">
                                <i:InvokeCommandAction CommandName="StartDrag" />
                            </i:EventTrigger>
                            <i:EventTrigger EventName="PreviewMouseLeftButtonUp">
                                <i:InvokeCommandAction CommandName="StopDrag" />
                            </i:EventTrigger>
                            <i:EventTrigger EventName="PreviewMouseMove">
                                <i:InvokeCommandAction CommandName="Dragging" />
                            </i:EventTrigger>
                        </i:Interaction.Triggers>
                    </behaviors:DragOnCanvasBehavior>
                </i:Interaction.Behaviors>
            </Border>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

然后行为将鼠标事件附加到元素的鼠标处理程序：

public class DragOnCanvasBehavior : Behavior<DependencyObject>
{
    public static readonly DependencyProperty DraggableItemProperty =
        DependencyProperty.RegisterAttached(
            "DraggableItem",
            typeof(IDraggable),
            typeof(DragOnCanvasBehavior),
            new PropertyMetadata(new PropertyChangedCallback((d, e) =>
            {
                ((DragOnCanvasBehavior)d).draggable = (IDraggable)e.NewValue;
            })));

    private IDraggable draggable;

    public DragOnCanvasBehavior()
    {
        this.StartDrag = new RelayCommand((o) =>
        {
            ((UIElement)this.AssociatedObject).MouseLeftButtonDown += this.ElementOnMouseLeftButtonDown;
        });

        this.StopDrag = new RelayCommand((o) =>
        {
            ((UIElement)this.AssociatedObject).MouseLeftButtonUp += this.ElementOnMouseLeftButtonUp;
        });

        this.Dragging = new RelayCommand((o) =>
        {
            ((UIElement)this.AssociatedObject).MouseMove += this.ElementOnMouseMove;
        });
    }

    public IDraggable DraggableItem
    {
        get { return (IDraggable)this.GetValue(DraggableItemProperty); }
        set { this.SetValue(DraggableItemProperty, value); }
    }

    public ICommand Dragging { get; private set; }
    public ICommand StartDrag { get; private set; }
    public ICommand StopDrag { get; private set; }

    // these handle the drag through the IDraggable properties
    // and the mouse event args
    private void ElementOnMouseLeftButtonDown(object sender, MouseButtonEventArgs e) {}
    private void ElementOnMouseLeftButtonUp(object sender, MouseButtonEventArgs e) {}
    private void ElementOnMouseMove(object sender, MouseEventArgs e) {}
}

它有效，但我很确定我在这里做错了什么。鼠标事件附加在行为构造函数中，但它们是 "hard-linked" 事件（这意味着我无法将触发器更改为 mousedown/up/move 以外的其他内容）。

但是，我必须能够访问 ElementOnMousexxx 方法中的鼠标位置，所以我不确定如何正确执行此操作。

Answer 1

好的，事实证明您不需要 MouseEventArgs 来获取鼠标光标位置，您可以只使用 System.Windows.Input.Mouse。您也不需要 "sender" 对象，当使用 Behavior<T> 时，您可以只使用 this.AssociatedObject

public DragOnCanvasBehavior()
{
    this.StartDrag = new RelayCommand((o) =>
    {
        this.OnStartDrag();
    });
}

private void OnStartDrag()
{
    // get mouse position
    this.mouseStartPosition = Mouse.GetPosition(Application.Current.MainWindow);

    // access control properties
    ((UIElement)this.AssociatedObject).CaptureMouse();
}

WPF 行为和事件 - 附加到适当的事件

WPF behaviors and events - attaching to proper events

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events

triggers

mvvm