Question

我收到来自Visual Studio的一个非常令人困惑的错误消息，告诉我我不能在标记为“（等待）”的方法上使用“await”。以下是完整的信息：

错误1“await”运算符只能在异步方法中使用。请考虑使用“async”修饰符标记此方法，并将其返回类型更改为'Task<Windows.Phone.Media.Capture.AudioVideoCaptureDevice>'

这是我的代码：

    private AudioVideoCaptureDevice SetupController()
    {
        CameraSensorLocation Location = CameraSensorLocation.Back;
        AudioVideoCaptureDevice CameraController = await AudioVideoCaptureDevice.OpenAsync(Location, AudioVideoCaptureDevice.GetAvailableCaptureResolutions(Location).First());

        CameraController.SetProperty(KnownCameraAudioVideoProperties.VideoTorchMode, VideoTorchMode.On);

        return CameraController;
    }

错误在于这一行：

AudioVideoCaptureDevice CameraController = await AudioVideoCaptureDevice.OpenAsync(Location, AudioVideoCaptureDevice.GetAvailableCaptureResolutions(Location).First());

Answer 1

使用await时 - 必须在支持异步操作的方法中使用它。当你返回一个值时 - 将其设为Task<>

尝试使您的方法异步：

private async Task<AudioVideoCaptureDevice> SetupController()
{
  // your code
}

因为它现在是异步的，所以使用它：

AudioVideoCaptureDevice myDevice = await SetupController(); // which should also be run from async method

尝试等待“（等待）Windows.Foundation.IAsyncOperation”时出现语法错误

1 个答案: