“等待”运算符只能在 Xamarin Android 的异步方法中使用 [重复]

Question

我是 Xamarin Android 的新手，我正在开发一个简单的应用程序，用于从服务器获取和显示图像。 这是我的代码-

 public void testWCF2()
        {
            var imgView = FindViewById<ImageView>(Resource.Id.imageView123);
            using(var bm = await GetImageFromUrl(@"http://xamarin.com/content/images/pages/forms/example-app.png"))    //At this line an error is showing The 'await' operator can only be used within an async method. Consider marking this method with the 'async' modifier and changing its return type to 'Task'. 
                imgView.SetImageBitmap(bm);

        }

    private async Task<Bitmap> GetImageFromUrl(string url)
    {
        using(var client = new HttpClient())
        {
            var msg = await client.GetAsync(url);
            if (msg.IsSuccessStatusCode)
            {
                using(var stream = await msg.Content.ReadAsStreamAsync())
                {
                    var bitmap = await BitmapFactory.DecodeStreamAsync(stream);
                    return bitmap;
                }
            }
        }
        return null;
    }

请有人帮帮我。

谢谢

Answer 1

您需要将async 修饰符添加到您的方法中，例如：

        public async void testWCF2()
        {
            var imgView = FindViewById<ImageView>(Resource.Id.imageView123);
            using(var bm = await GetImageFromUrl(@"http://xamarin.com/content/images/pages/forms/example-app.png"))    
                imgView.SetImageBitmap(bm);
        }

MSDN 说：

使用 async 修饰符指定方法 lambda 表达式或匿名方法是异步的。如果在方法或表达式上使用此修饰符，则称为异步方法。