如何从 onPostExecute 传递值

Question

我知道以前有人问过这个问题，我已经看过了：

How to get the result of OnPostExecute() to main activity because AsyncTask is a separate class?

how do i send data back from onPostExecute in an AsyncTask?

how to pass the result of asynctask onpostexecute method into the parent activity android

我尝试创建一个接口来传递值，我还尝试创建一个方法来通过我的 onPostExecute 分配值，最后我尝试像下面这样直接设置变量，但似乎没有任何效果。

public class ClassName extends AppCompatActivity {
    private Bitmap bit;

    public void methodName() {
        new RetrieveFavIcon().execute("https://www.google.com");
        // work with 'bit' value, but bit value is null, why?
    }

    class RetrieveFavIcon extends AsyncTask<String, Void, Bitmap> {
    public TaskListener delegate = null;

    protected Bitmap doInBackground(String... urls) {
        try {
            URL url = new URL(new URL(urls[0].trim()), "/favicon.ico");
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setDoInput(true);
            connection.connect();
            InputStream input = connection.getInputStream();
            Bitmap myBitmap = BitmapFactory.decodeStream(input);
            return myBitmap;
        } catch (IOException e) {
            Log.d("URL return", "failed");
            e.printStackTrace();
            return null;
        }
    }

    protected void onPostExecute(Bitmap bm) {
        if(bm != null) {
            bit = bm;
            Log.d("bitmap", "bitmap not null");
        }
    }
}

Answer 1

您可以使用界面。当异步任务到达 postExecute 时，接口将回调实现接口的类。接口可以将结果传递给类。

创建如下界面：

public interface AsyncResponse {
void processFinish(String output);
}

processFinish() 的参数应该根据您要发送到 MainActivity 的数据。

在 MainActivity 中实现它：

public class Home extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener, AsyncResponse

您需要将接口传递给AsyncTask：

 new AsyncTask(this, MainActivity.this, news).execute();

在 AsyncTask 类中声明一个接口对象。将从 MainActivity 传递的接口分配给这个对象：

public Cover(AsyncResponse delegate, Context context, ArrayList<NewsWrapper>      list) {
    this.delegate = delegate;
}

现在在 postExecute 中：

delegate.processFinish(/*Your Data which you want to send in MainActivity*/);

在MainActivity中重写接口方法processFinish()：

@Override
public void processFinish(/*sent data from AsyncTask*/) {
    /*Use result here*/
}