Question

[解决了UI线程的问题]

我想在后台线程中拍照，然后将其发送到服务器，之后我想从服务器接收响应

问题是拍照部分是好的，发送到服务器也很好，但接收响应不起作用。有什么想法吗？

Answer 1

您无法从后台线程更新UI（视图）（在本例中为doInBackground），覆盖onPostExecute并调用此capturedImageHolder.setImageBitmap(scaleDownBitmapImage(bitmap, 400, 400));

        class TakePhotoTask extends AsyncTask<byte[], String, Bitmap> {

                @Override
                protected Void doInBackground(byte[]... data) {
                    Bitmap bitmap = BitmapFactory.decodeByteArray(data[0], 0, data.length);
                    if (bitmap == null) {
                    //Toast.makeText(MainActivity.this, "Captured image is empty", Toast.LENGTH_LONG).show();
                        return null;
                    }

                    //capturedImageHolder.setImageBitmap(scaleDownBitmapImage(bitmap, 400, 400));
                    try {
                        Bitmap bmp = ((BitmapDrawable) capturedImageHolder.getDrawable()).getBitmap();
                        ByteArrayOutputStream bos = new ByteArrayOutputStream();
                        bmp.compress(Bitmap.CompressFormat.PNG, 100, bos);
                        byte[] array = bos.toByteArray();
                        final String tmp = Base64.encodeToString(array, Base64.NO_WRAP);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return bitmap;
                }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                super.onPostExecute(bitmap);
                capturedImageHolder.setImageBitmap(scaleDownBitmapImage(bitmap, 400, 400));
            }
}

Answer 2

您需要在onPostExecute回调方法中放置访问UI元素的代码。但由于您还需要访问Bitmap对象，因此我建议您更改AsyncTask类定义，以包含Bitmap作为第三个参数。

class TakePhotoTask extends AsyncTask<byte[], String, Bitmap> {
     @Override
     protected Bitmap doInBackground(byte[]... data) {
       //since we want to decode the entire byte-array and not just 0th byte
        Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);
         if (bitmap == null) {
             return null;
         }
         //the rest of your code/logic goes here...
         return bitmap;
       }

然后在你的后执行方法中：

protected void onPostExecute(Bitmap  bitmap) {
  if(bitmap == null ){return; }
  capturedImageHolder.setImageBitmap(scaleDownBitmapImage(bitmap, 400, 400));
     try {
          //I am not sure what the purpose of this section of the code is...
          //so I just left it here
          Bitmap bmp = ((BitmapDrawable) capturedImageHolder.getDrawable()).getBitmap();
          ByteArrayOutputStream bos = new ByteArrayOutputStream();
          bmp.compress(Bitmap.CompressFormat.PNG, 100, bos);
          byte[] array = bos.toByteArray();
          final String tmp = Base64.encodeToString(array, Base64.NO_WRAP);
      } catch (Exception e) {
        e.printStackTrace();
     }
  showDialog("Image Taken ?");
}

我希望这会有所帮助。

Android - 方法必须从UI线程调用

2 个答案: