AsyncTask没有足够快地向主线程返回结果

问题描述：

我有一个asynctask，它从oracle数据库中获取了userPin.在我的主线程中，然后在按钮上运行asynctask.数据库中的值分配给名为userPinRetrieved的变量.

I have an asynctask that is getting a userPin from my oracle database. In my Main thread then on a button I am running the asynctask. The value from the database is assigned to a variable called userPinRetrieved.

当我调试此变量时，它接收到正确的值.但是，当我正常运行该应用程序时，它会收到null.经过一些研究并使用Thread.Sleep(x)之后，我可以看到这是由于asynctask没有及时将结果返回给主线程和变量.

When I debug this variable it is receiving the correct value. However, when I am running the app normally it is receiving null. After doing some research and using Thread.Sleep(x) I can see that is due to the fact that the asynctask is not returning the result to the main thread and the variable in time.

已建议我不要使用Thread.Sleep(x)，我有什么选择?

I have been advised not to use Thread.Sleep(x), what alternatives do I have?

这是我的代码:

AsyncTask:

            String line;
                BufferedReader br=new BufferedReader(new InputStreamReader(con.getInputStream()));
                while ((line=br.readLine()) != null) {
                    JSONObject json = new JSONObject(line);
                    Log.d("Line",line);
                    if (json.getString("userPin") == null){
                        userPinRetrieved = "PIN NOT RECEIVED";
                        Log.d("userpin", userPinRetrieved);
                    } else {
                        userPinRetrieved = json.getString("userPin");
                        Log.d("userpin", userPinRetrieved);
                    }
                }
            }

        } catch (Exception e) {
            Log.v("ErrorAPP", e.toString());
        }
        return "";
    }

    @Override
    protected void onPostExecute(String userPinRetrieved) {
    }

    @Override
    protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
    }
}

登录按钮:

 signIn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            AsyncTaskRunner postReq = new AsyncTaskRunner();
            postReq.execute("start");
            try {
                Thread.sleep(30000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }


            Toast.makeText(UserLogin.this, userPinRetrieved + " " + userPin, Toast.LENGTH_LONG).show();        

            if (userPin.equals(userPinRetrieved)) {
                Toast.makeText(UserLogin.this, "Access Granted!", Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(getApplicationContext(), MainActivity.class);
                startActivity(intent);
                Toast.makeText(UserLogin.this, "Hello " + employee, Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(UserLogin.this, "Access Denied! Incorrect Pin", Toast.LENGTH_SHORT).show();
            }
        }
    });

有人可以提供建议吗?

谢谢

答

AsyncTask的重点是将处理移到另一个线程，因为您不知道运行某个任务将花费多少时间.您可以在onPostExecute方法中处理异步任务的结果.

The point of AsyncTask is to move the processing to another thread because you don't know how much time it will take to run a certain task. You can process the result of the async task inside the onPostExecute method.

因此将结果的用法移到那里:

So move the usage of the result to there:

 @Override
    protected void onPostExecute(String userPinRetrieved) {
       if (userPin.equals(userPinRetrieved)) {
                Toast.makeText(UserLogin.this, "Access Granted!", Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(getApplicationContext(), MainActivity.class);
                startActivity(intent);
                Toast.makeText(UserLogin.this, "Hello " + employee, Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(UserLogin.this, "Access Denied! Incorrect Pin", Toast.LENGTH_SHORT).show();
            }
    }

您还可以定义在处理完成时将被调用的方法:

You can also define a method that will be called when the processing is finished:

protected void onPostExecute(String userPinRetrieved) {
       processValue(userPinRetrieved);
    }

在AsyncTask中从活动中引用变量时，请务必小心，如果活动在处理AsyncTask时被破坏，则可能导致内存泄漏.

You need to be careful when referencing variables from your activity in the AsyncTask, if the activity gets destroyed during the processing of your AsyncTask it can cause a memory leak.

AsyncTask没有足够快地向主线程返回结果

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