ItemsControl拖放

Question

我有一个带有DataTemplate的ItemsControl,它绑定到整数的ObservableCollection.

<ItemsControl Name="DimsContainer" ItemTemplate="{StaticResource DimensionsTemplate}">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <StackPanel Orientation="Horizontal"/>
        </ItemsPanelTemplate>
   </ItemsControl.ItemsPanel>
</ItemsControl>

并在Windows资源中:

<Window.Resources>
    <DataTemplate x:Key="DimensionsTemplate" >
        <TextBlock Text="{Binding}"
                       Padding="5"
                       VerticalAlignment="Center"
                       FontSize="32"/>
    </DataTemplate>
</Window.Resources>

我正在尝试实现在ItemsControl中拖放项目的能力(即能够重新排序整数).有没有人有一个如何做到这一点的简单例子？我连接了PreviewMouseMove,DragEnter和Drop事件.问题是我无法弄清楚如何确定拖动哪个项目以及拖动它的位置.似乎整个ItemsControl都被传递到事件中.

Answer 1

这是我如何做到的一个例子.

XAML:

<Window.DataContext>
    <local:MyViewModel />
</Window.DataContext>

<Grid>
    <ScrollViewer>
        <ListView ItemsSource="{Binding MyData}" HorizontalAlignment="Stretch" Name="listview" ScrollViewer.PanningMode="VerticalOnly">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <Button Content="{Binding}"
                        Command="{Binding DataContext.MyCommand, RelativeSource={RelativeSource AncestorType=ItemsControl}}" 
                        CommandParameter="{Binding}"
                        Margin="5 2" Width="150" Height="50"
                        FontSize="30" />
                </DataTemplate>
            </ListView.ItemTemplate>
            <ListView.Resources>
                <Style TargetType="Button">
                    <EventSetter Event="PreviewMouseMove" Handler="PreviewMouseMove" />                        
                    <EventSetter Event="Drop" Handler="Drop" />                       
                    <Setter Property="AllowDrop" Value="True" />                        
                </Style>
            </ListView.Resources>
        </ListView>
    </ScrollViewer>
</Grid>

视图模型:

 class MyViewModel
{
    public MyViewModel()
    {
        MyCommand = new ICommandImplementation();
    }

    public ObservableCollection<string> MyData
    {
        get
        {
            return new ObservableCollection<string>(new string[]{
            "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", 
            "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen", "twenty"
            });
        }
    }

    public ICommand MyCommand { get; private set; }

    private class ICommandImplementation : ICommand
    {
        public bool CanExecute(object parameter) { return true; }
        public event EventHandler CanExecuteChanged;
        public void Execute(object parameter) { System.Windows.MessageBox.Show("Button clicked! " + (parameter ?? "").ToString()); }
    }
}

事件:

 private void Drop(object sender, DragEventArgs e)
    {
        var source = e.Data.GetData("Source") as string;
        if (source != null)
        {
            int newIndex = listview.Items.IndexOf((sender as Button).Content);
            var list = listview.ItemsSource as ObservableCollection<string>;
            list.RemoveAt(list.IndexOf(source));
            list.Insert(newIndex, source);
        }
    }

    private void PreviewMouseMove(object sender, MouseEventArgs e)
    {
        if (e.LeftButton == MouseButtonState.Pressed)
        {
            Task.Factory.StartNew(new Action(() =>
                {
                    Thread.Sleep(500);
                    App.Current.Dispatcher.BeginInvoke(new Action(() =>
                        {
                            if (e.LeftButton == MouseButtonState.Pressed)
                            {                                    
                                var data = new DataObject();
                                data.SetData("Source", (sender as Button).Content);
                                DragDrop.DoDragDrop(sender as DependencyObject, data, DragDropEffects.Move);
                                e.Handled = true;
                            }
                        }), null);
                }), CancellationToken.None);
        }           
    }

上面的例子有点复杂,因为每个项目list都是a Button和on Button click我也必须做一些动作.你的情况比较容易.

对许多开发人员而言,拖放可能会让人困惑.但下面是一些关键点如何做到:

1. 使用PreviewMouseMove事件实际开始拖动并在处理程序使用DragDrop.DoDragDrop事件中引发DragDrop相关事件和Cursors.sender参数是在此情况下捕获鼠标的元素UIElement正在被拖动.

2. 如果要更改当前拖动的元素的视觉效果,请使用DragEnter&DragOverevent Mouse.sender 参数是当前拖过的元素/刚刚结束拖延的情况.

3. 使用Dropevent来处理被删除的元素.sender参数是Drop发生的元素.

4. 使用DataObjectobject在这些事件之间传递信息.SetData该类的方法用于在此中添加数据.这个方法有两个参数,它们像key-valuepair 一样工作.一旦设置,您可以通过传递as参数DragDrop使用 GetData方法在下一个被调用的事件中获取此数据key.(即 e.Data.GetData("Source"))

这是一个相对的帖子.