.Net MAUI - 如何更改从源拖动到目标时显示的图像？

Question

我正在 .Net MAUI 中开发一个使用拖放功能的 UI。拖放不是问题；工作正常。问题是我想在拖动图像时更改图像显示。不是拖动源也不是放置目标，而是光标后面的图像。

下面的示例显示了该行为。我想改变它，以便随着光标移动的图像是不同的。

如果我对圣诞节有两个愿望，那就是隐藏 MAUI 在拖动图像时放在图像顶部的“复制”工具提示图形。

XAML

<Frame Margin="20" HorizontalOptions="Center" BorderColor="LightBlue" ZIndex="1" MaximumWidthRequest="400" MaximumHeightRequest="400" BackgroundColor="LightBlue">
    <Image x:Name="reds"  Source="reds_trans_bg.png" MaximumHeightRequest="100" MinimumHeightRequest="100" MaximumWidthRequest="100" MinimumWidthRequest="100">
        <Image.GestureRecognizers>
            <DragGestureRecognizer  CanDrag="True" DragStarting="DragGestureRecognizer_DragStarting_2"  />
        </Image.GestureRecognizers>
    </Image>
</Frame>

<Frame Margin="20" HorizontalOptions="Center" BorderColor="LightBlue" ZIndex="1" MaximumWidthRequest="400" MaximumHeightRequest="400" BackgroundColor="LightBlue">
    <Frame.GestureRecognizers>
        <DropGestureRecognizer AllowDrop="True" Drop="DropGestureRecognizer_Drop_2" />
    </Frame.GestureRecognizers>
    <VerticalStackLayout VerticalOptions="Center" BackgroundColor="LightBlue">
        <Image Source="washer_trans_bg.png" BackgroundColor="LightBlue" ZIndex="100" MaximumWidthRequest="100" MaximumHeightRequest="100" >
        </Image>
        <HorizontalStackLayout HorizontalOptions="Center" BackgroundColor="LightBlue">
            <Label x:Name="contents" Text="test" BackgroundColor="LightBlue" TextColor="White" FontAttributes="Bold">
            </Label>
        </HorizontalStackLayout>
    </VerticalStackLayout>
</Frame>

代码

private void DragGestureRecognizer_DragStarting_2(object sender, DragStartingEventArgs e)
{
    var image = (sender as Element)?.Parent as Image;
    e.Data.Properties.Add("Text", "Red");
}

private void DropGestureRecognizer_Drop_2(object sender, DropEventArgs e)
{
    var data = e.Data.Properties["Text"].ToString();
    
    contents.Text = $"Red: {++count}";
}

Answer 1

据我所知，唯一可以开箱即用地执行此操作的平台是 iOS 和 Mac Catalyst。

来自文档。

void OnDragStarting(object sender, DragStartingEventArgs e)
{
#if IOS || MACCATALYST
    Func<UIKit.UIDragPreview> action = () =>
    {
        var image = UIKit.UIImage.FromFile("dotnet_bot.png");
        UIKit.UIImageView imageView = new UIKit.UIImageView(image);
        imageView.ContentMode = UIKit.UIViewContentMode.Center;
        imageView.Frame = new CoreGraphics.CGRect(0, 0, 250, 250);
        return new UIKit.UIDragPreview(imageView);
    };

    e.PlatformArgs.SetPreviewProvider(action);
#endif
}