为什么Drop事件不会在我的UWP测试应用程序中触发？

问题描述

大家好，



我正在使用UWP中的应用程序。我意识到拖放没有按预期工作，所以我最终创建了一个新的UWP应用程序并尝试拖放那里的东西。



我可以让DragEnter开火，但我无法让Drop事件发挥作用。无论我拖动什么，我总是得到一个停止标志符号，如果我在Drop事件上设置一个断点，它就不会触发。



这是我的代码：

Hi all,

I'm working on an app in UWP. I realized that drag and drop didn't work as expected so I eventually created a new UWP app and try to drag and drop things there.

I can get DragEnter to fire, but I can't get the Drop event to work. Whatever I drag, I always get a "stop sign" symbol, and if I set a breakpoint on the Drop event it doesn't fire.

Here's my code:

<Page

    x:Class="DragDropExample.MainPage"

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

    xmlns:local="using:DragDropExample"

    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

    mc:Ignorable="d">

    <Grid x:Name="tb" removed="#FFFD3535">
        <TextBlock x:Name="txtDrag" HorizontalAlignment="Left" Margin="10,136,0,0" TextWrapping="Wrap" Text="This is just a test" VerticalAlignment="Top" CanDrag="True" Foreground="#FF487EF1"/>

        <TextBox x:Name="tbDrop" removed="#FF36DA12" Width="100" Height="100" AllowDrop="True" Drop="tbDrop_Drop" DragEnter="tbDrop_DragEnter" />
        <Grid x:Name="gridDrop" HorizontalAlignment="Left" Margin="100, 100, 0, 0" removed="#FFE81DF1" AllowDrop="True" Height="100" Width="100" VerticalAlignment="Bottom"  />
        <Canvas x:Name="canvasDrag" HorizontalAlignment="Left" Height="50" Margin="230,10,0,0" VerticalAlignment="Top" Width="50" Background="#FFF7F71A" CanDrag="True" Drop="canvasDrag_Drop"/>

    </Grid>
</Page>

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409

namespace DragDropExample
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
        }

        private void tbDrop_Drop(object sender, DragEventArgs e)
        {
            tbDrop.Text = "Dropped";
        }

        private void tbDrop_DragEnter(object sender, DragEventArgs e)
        {
            tbDrop.Text = "Entered";
        }

        private void canvasDrag_Drop(object sender, DragEventArgs e)
        {
            tbDrop.Text = "Dropped on canvas";
        }
    }
}

我缺少什么？



我也想知道如何实际拖动对象而不是仅仅复制它们。 （文本块被拖动，但拖动的是副本，原始文本块仍然存在。）



请注意示例代码很傻 - 我只需要有效的东西，不涉及列表视图中的项目或类似的东西。我希望能够拖动带有图像的图像或画布（用于国际象棋游戏）。



谢谢！



Petter

What am I missing?

I also wonder how I can actually drag the objects rather than just making copies of them. (The textblock gets dragged, but what is dragged is a copy, and the original textblock is still there.)

Note that the example code is silly - I just need something that works and that doesn't involve items in a listview or similiar. Preferably, I'd like to be able to drag images or canvases with images in them (for a chess game).

Thanks!

Petter

推荐答案

private void tbDrop_DragEnter(object sender, DragEventArgs e)
{
    // Check here if data can be generally dropped:
    // - Control is active and not read only
    // - Drag source provides data of a matching type (e.g. a canvas and not text)
    // The result may be stored in a class member variable so the check
    //  must not be executed again with each DragOver event.
    // When using such a variable, it must be cleared inside the 
    //  Drop and DragLeave handlers.
    this.canDrop = CanDrop(sender, e);
    // Call DragOver to check at the actual position and set the effect.
    DragOver(sender, e);
}

private void tbDrop_DragOver(object sender, DragEventArgs e)
{
    e.Effect = DragDropEffects.None;
    // Check here if dropping is possible in general and at the actual position.
    if (this.canDrop && CanDropHere(sender, e))
    {
        // See also MSDN example code for the Effect Property
        if ((e.KeyState & 8) == 8 &&
        (e.AllowedEffect & DragDropEffects.Copy) == DragDropEffects.Copy)
        {
            // CTL KeyState for copy.
            e.Effect = DragDropEffects.Copy;
        }
        else
        {
            // Move by default.
            e.Effect = DragDropEffects.Move;
        }
    }
}

private void tbDrop_Drop(object sender, DragEventArgs e)
{
    // DragOver() has been called by the system just before this and
    //  the effect has been set.
    if (e.Effect != DragDropEffects.None)
    {
        // Drop data here.
        // ...
    }
    // Cleanup (similar code as in DragLeave()).
    this.canDrop = false;
}

private void tbDrop_DragLeave(object sender, DragEventArgs e)
{
    // Cleanup when leaving.
    this.canDrop = false;
}

在拖动源端使用 DropCompleted 处理程序检测是否已发生丢弃以及是否应移动或复制数据。

On the drag source side use the DropCompleted handler to detect if dropping has been occured and if data should be moved or copied.

private void tbDragSource_DropCompleted(UIElement elem, DropCompletedEventArgs e)
{
    if (e.DropResult == DataPackageOperation.Move)
    {
        // Delete item here
    }
}

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