Question

我的项目类型是xamarin形式的PCL。我想截屏，正在使用以下代码。但是，当我调试代码时，Activity始终为null。我试图找出问题，但没有成功。你能告诉我我在做什么错吗。

public interface IScreenshotManager
{
   Task<byte[]> CaptureAsync();
}

对于Android：

[assembly: Xamarin.Forms.Dependency(typeof(ScreenshotService))]
namespace MyProject.Droid
{
    public class ScreenshotService : IScreenshotService
    {
        public static Activity Activity { get; set; }               

        public async System.Threading.Tasks.Task<byte[]> Capture()
        {
            if (Activity == null)  // Activity is always null Error here
            {
                throw new Exception("You have to set ScreenshotManager.Activity in your Android project");
            }

            var view = Activity.Window.DecorView;
            view.DrawingCacheEnabled = true;

            Bitmap bitmap = view.GetDrawingCache(true);

            byte[] bitmapData;

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

            return bitmapData;
        }
    }

}

调用函数

 byte[] screenshotData = await DependencyService.Get<IScreenshotService>().Capture();

Answer 1

如果您未分配，显然Activity是null。您可以使用CurrentActivity nuget包来获取当前活动（或者您可以在Activity OnCreate方法中分配它，因为Xamarin从一开始就始终使用相同的Activity）。

Answer 2

The old deprecated way would be var view = ((Activity)Xamarin.Forms.Forms.Context).Window.DecorView; Xamarin automatically assigns the Activity to Forms.Context.Since the release of Xamarin 2.5, Xamarin.Forms.Forms.Context is obsolete.

Now you could use this :

var currentContext = Android.App.Application.Context;

尝试进行屏幕截图时，活动为null

2 个答案: