Question

所以我正在制作Xamarin.Forms应用程序。我有一个StackLayout，我要为其快照（仅元素，而不是整个屏幕）。

这是界面：

public interface IViewSnapShot
{
    Task<byte[]> CaptureAsync(Xamarin.Forms.View view);
}

这是事件：

private async Task SavePic_ClickedAsync(object sender, EventArgs e)
    {
        var imageByte = await DependencyService.Get<IViewSnapShot>().CaptureAsync(BlueprintSnapshot);
    }

这是特定于Android平台的：

public class MakeViewSnapshot : IViewSnapShot
{
    Task<byte[]> IViewSnapShot.CaptureAsync(Xamarin.Forms.View view)
    {
        var nativeView = view.GetRenderer().View;
        var wasDrawingCacheEnabled = nativeView.DrawingCacheEnabled;
        nativeView.DrawingCacheEnabled = true;
        nativeView.BuildDrawingCache(false);
        Bitmap bitmap = nativeView.GetDrawingCache(false);
        // TODO: Save bitmap and return filepath
        nativeView.DrawingCacheEnabled = wasDrawingCacheEnabled;

        byte[] bitmapData;
        using (var stream = new MemoryStream())
        {
            bitmap.Compress(Bitmap.CompressFormat.Png, 0, stream);
            bitmapData = stream.ToArray();
        }

        return bitmapData;
    }
}

问题是bitmapData给出了错误

无法将类型'byte []'隐式转换为'System.Threading.Tasks.Task'

我有搜索互联网，每篇文章都说这是将位图转换为byte []数组的方法。知道如何解决此错误吗？

稍后，我想将byte []数组上传到Web api。

Answer 1

您可以使用Task.FromResult()将结果包装到byte[]中，而不是返回Task：

return Task.FromResult(bitmapData);

您的代码可能如下所示：

public class MakeViewSnapshot : IViewSnapShot
{
    Task<byte[]> IViewSnapShot.CaptureAsync(Xamarin.Forms.View view)
    {
        var nativeView = view.GetRenderer().View;
        var wasDrawingCacheEnabled = nativeView.DrawingCacheEnabled;
        nativeView.DrawingCacheEnabled = true;
        nativeView.BuildDrawingCache(false);
        Bitmap bitmap = nativeView.GetDrawingCache(false);
        // TODO: Save bitmap and return filepath
        nativeView.DrawingCacheEnabled = wasDrawingCacheEnabled;

        byte[] bitmapData;
        using (var stream = new MemoryStream())
        {
            bitmap.Compress(Bitmap.CompressFormat.Png, 0, stream);
            bitmapData = stream.ToArray();
        }

        return Task.FromResult(bitmapData);
    }
}

然后稍后要获取byte[]返回的CaptureAsync()时，只需致电：

byte[] result = CaptureAsync(<Your_parameters>).Result;

无法将位图转换为字节[]

1 个答案: