AsyncTask -如何在onPostExecute之后将值传回activity类？

在AsyncTask中，可以通过以下几种方式将值传回activity类：

使用接口回调：定义一个接口，在AsyncTask中实现该接口，并在onPostExecute方法中调用接口的方法将值传回activity类。activity类需要实现该接口，并在实现的方法中处理传回的值。

public interface AsyncTaskListener {
    void onTaskComplete(String result);
}

public class MyAsyncTask extends AsyncTask<Void, Void, String> {
    private AsyncTaskListener listener;

    public MyAsyncTask(AsyncTaskListener listener) {
        this.listener = listener;
    }

    @Override
    protected String doInBackground(Void... voids) {
        // 后台任务逻辑
        return "结果";
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        listener.onTaskComplete(result);
    }
}

public class MainActivity extends AppCompatActivity implements AsyncTaskListener {
    private TextView resultTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        resultTextView = findViewById(R.id.resultTextView);

        MyAsyncTask myAsyncTask = new MyAsyncTask(this);
        myAsyncTask.execute();
    }

    @Override
    public void onTaskComplete(String result) {
        resultTextView.setText(result);
    }
}

使用广播：在AsyncTask中发送一个自定义广播，在activity类中注册该广播，并在广播接收器中处理传回的值。

public class MyAsyncTask extends AsyncTask<Void, Void, String> {
    private Context context;

    public MyAsyncTask(Context context) {
        this.context = context;
    }

    @Override
    protected String doInBackground(Void... voids) {
        // 后台任务逻辑
        return "结果";
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        Intent intent = new Intent("com.example.RESULT_ACTION");
        intent.putExtra("result", result);
        context.sendBroadcast(intent);
    }
}

public class MainActivity extends AppCompatActivity {
    private TextView resultTextView;
    private BroadcastReceiver receiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String result = intent.getStringExtra("result");
            resultTextView.setText(result);
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        resultTextView = findViewById(R.id.resultTextView);

        IntentFilter filter = new IntentFilter("com.example.RESULT_ACTION");
        registerReceiver(receiver, filter);

        MyAsyncTask myAsyncTask = new MyAsyncTask(this);
        myAsyncTask.execute();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(receiver);
    }
}

使用EventBus：EventBus是一个开源的事件总线库，可以用于组件间的通信。在AsyncTask中发布一个事件，在activity类中订阅该事件，并在订阅方法中处理传回的值。

public class MyAsyncTask extends AsyncTask<Void, Void, String> {
    @Override
    protected String doInBackground(Void... voids) {
        // 后台任务逻辑
        return "结果";
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        EventBus.getDefault().post(new TaskCompleteEvent(result));
    }
}

public class TaskCompleteEvent {
    private String result;

    public TaskCompleteEvent(String result) {
        this.result = result;
    }

    public String getResult() {
        return result;
    }
}

public class MainActivity extends AppCompatActivity {
    private TextView resultTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        resultTextView = findViewById(R.id.resultTextView);

        EventBus.getDefault().register(this);

        MyAsyncTask myAsyncTask = new MyAsyncTask();
        myAsyncTask.execute();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        EventBus.getDefault().unregister(this);
    }

    @Subscribe(threadMode = ThreadMode.MAIN)
    public void onTaskComplete(TaskCompleteEvent event) {
        resultTextView.setText(event.getResult());
    }
}

以上是三种常用的方式，可以根据具体需求选择适合的方式将值传回activity类。