安卓：如何等待的AsyncTask在MainThread完成？(Android: how to wa

我知道，你首先要去这是......为什么世界上的挫折感，你再使用的AsyncTask。

因此，这里是我的问题，我的工作在一些Android应用程序（API 7的Android 2.1或更高版本），并且我在模拟器，一切测试是很好，于是我对HTC感觉测试，它说NetworkOnMainThreadExeption！

我下载了一些照片，然后在地图上绘制。

因此，要解决这个问题，在这种情况下，每一个（互联网连接）下载照片，我必须把上的AsyncTask工作。

所以我需要一个方法是如何知道什么时候所有照片都做了，所以我可以开始绘制..

我尝试了这么多，没有结果，我不知道。 我买了一个处理解决方案，但如果净较慢的运行我得到空指针（因为图片不下载）。

所以，请帮助我。

编辑：

这里的理念是：

Bitmap bubbleIcon ;
    onCreate(){
     ...
// i am making call for Async
new ImgDown().execute(url);
//and then i calling functions and classes to draw with that picture bubbleIcon !
DrawOnMap(bubbleIcon);
}




//THIS IS ASYNC AND FOR EX. SUPPOSE I NEED TO DOWNLOAD THE PIC FIRST
     class ImgDown extends AsyncTask<String, Void, Bitmap> {

        private String url;

        public ImgDown() {
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            url = params[0];
            try {
                return getBitmapFromURL(url);
            } catch (Exception err) {
            }

            return null;

        }

        @Override
        protected void onPostExecute(Bitmap result) {
            bubbleIcon = result;
            bubbleIcon = Bitmap
                    .createScaledBitmap(bubbleIcon, 70, 70, true);

        }

        public Bitmap getBitmapFromURL(String src) {
            try {
                Log.e("src", src);
                URL url = new URL(src);
                HttpURLConnection connection = (HttpURLConnection) url
                        .openConnection();
                connection.setDoInput(true);
                connection.connect();
                InputStream input = connection.getInputStream();
                // /tuka decode na slika vo pomalecuk kvalitet!
                BitmapFactory.Options options = new BitmapFactory.Options();
                options.inSampleSize = 3;
                Bitmap myBitmap = BitmapFactory
                        .decodeStream(new FlushedInputStream(input));
                Log.e("Bitmap", "returned");
                return myBitmap;
            } catch (IOException e) {
                e.printStackTrace();
                Log.e("getBitmapFromURL", e.getMessage());
                return null;
            }
        }

        class FlushedInputStream extends FilterInputStream {
            public FlushedInputStream(InputStream inputStream) {
                super(inputStream);
            }

            public long skip(long n) throws IOException {
                long totalBytesSkipped = 0L;
                while (totalBytesSkipped < n) {
                    long bytesSkipped = in.skip(n - totalBytesSkipped);
                    if (bytesSkipped == 0L) {
                        int byteValue = read();
                        if (byteValue < 0) {
                            break; // we reached EOF
                        } else {
                            bytesSkipped = 1; // we read one byte
                        }
                    }
                    totalBytesSkipped += bytesSkipped;
                }
                return totalBytesSkipped;
            }
        }
    }

我希望现在更加清晰。

Answer 1:

class OpenWorkTask extends AsyncTask {

    @Override
    protected Boolean doInBackground(String... params) {
        // do something
        return true;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        // The results of the above method
        // Processing the results here
        myHandler.sendEmptyMessage(0);
    }

}

Handler myHandler = new Handler() {

    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
        case 0:
            // calling to this function from other pleaces
            // The notice call method of doing things
            break;
        default:
            break;
        }
    }
};

Answer 2:

你可以写自己的委托转授权完成任务，使用OOP原理的信息：

task_delegate.java

public interface TaskDelegate {
    void TaskCompletionResult(String result);
}

main_activity.java

public class MainActivity extends Activity implements TaskDelegate {

    //call this method when you need     
    private void startAsynctask() {
      myAsyncTask = new MyAsyncTask(this);
      myAsyncTask.execute();
     }

//your code

    @Override
    public void TaskCompletionResult(String result) {
        GetSomethingByResult(result);
    }
}

my_asynctask.java

public class MyAsyncTask extends AsyncTask<Void, Integer, String> {

    private TaskDelegate delegate;

    protected MyAsyncTask(TaskDelegate delegate) {
        this.delegate = delegate;
    }

    //your code 

    @Override
    protected void onPostExecute(String result) {

        delegate.TaskCompletionResult(result);
    }
}

Answer 3:

class openWorkTask extends AsyncTask<String, String, Boolean> {

    @Override
    protected Boolean doInBackground(String... params) {
        //do something
        return true;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        // The results of the above method
        // Processing the results here
    }
}

Answer 4:

如果我是你，我会用一个进度对话框。 这样，用户就可以看到某些事情正在发生，而下载的AsyncTask的图片。 在PostExecute，请从你的主代码来检查，如果这些照片是空的方法。 记住，你不能更新doInBackground方法的UI所以做任何UI工作，无论是onPreExecute或onPostExecute

private class DownloadPictures extends AsyncTask<String, Void, String> 
{

    ProgressDialog progressDialog;

    @Override
    protected String doInBackground(String... params) 
    {

        //Download your pictures

        return null;

    }

    @Override
    protected void onPostExecute(String result) 
    {

        progressDialog.cancel();

        //Call your method that checks if the pictures were downloaded

    }

    @Override
    protected void onPreExecute() {

        progressDialog = new ProgressDialog(
                YourActivity.this);
        progressDialog.setMessage("Downloading...");
        progressDialog.setCancelable(false);
        progressDialog.show();

    }

    @Override
    protected void onProgressUpdate(Void... values) {
        // Do nothing
    }

}

文章来源: Android: how to wait AsyncTask to finish in MainThread?