如何处理来自 AsyncTask 的返回值

您可以通过在返回的 AsyncTask 上调用 AsyhncTask 的 get（） 方法来获取结果，但它会在等待获取结果时将其从异步任务转换为同步任务。

String serverResponse = apiObj.execute(nameValuePairs).get();

由于 AsyncTask 位于单独的类中，因此可以创建一个接口类并在 AsyncTask 中声明它，并在要从中访问结果的类中将新的接口类实现为委托。这里有一个很好的指南：如何将 OnPostExecute（） 的结果获取到主活动，因为 AsyncTask 是一个单独的类？

我将尝试将上述链接应用于您的上下文。

（IApiAccessResponse）

public interface IApiAccessResponse {
    void postResult(String asyncresult);
}

（ApiAccess）

public class ApiAccess extends AsyncTask<List<NameValuePair>, Integer, String> {
...
    public IApiAccessResponse delegate=null;
    protected String doInBackground(List<NameValuePair>... nameValuePairs) {
        //do all your background manipulation and return a String response
        return response
    }

    @Override
    protected void onPostExecute(String result) {
        if(delegate!=null)
        {
            delegate.postResult(result);
        }
        else
        {
            Log.e("ApiAccess", "You have not assigned IApiAccessResponse delegate");
        }
    } 
}

（您的主类，它实现 IApiAccessResponse）

ApiAccess apiObj = new ApiAccess (0, "/User");
//Assign the AsyncTask's delegate to your class's context (this links your asynctask and this class together)
apiObj.delegate = this;
apiObj.execute(nameValuePairs); //ERROR

//this method has to be implement so that the results can be called to this class
void postResult(String asyncresult){
     //This method will get call as soon as your AsyncTask is complete. asyncresult will be your result.
}

我建议实现一个处理程序回调。您将片段（或活动的）处理程序传递给 AsyncTask，AsyncTask 将在完成后调用该处理程序。异步任务还可以传回任意对象。

下面是一个示例 AsyncTask，我在它自己的文件中（未子类化）中提供它：

public class MyTask extends AsyncTask<Void, String, String> {

    private static final String TAG = "MyTask";
    private Handler mCallersHandler;
    private Candy    mObject1;
    private Popsicle mObject2;

    // Return codes
    public static final int MSG_FINISHED = 1001;

    public SaveVideoTask(Handler handler, Candy candyCane, Popsicle grapePop ) {
        this.mCallersHandler = handler;
        this.mObject1        = candyCane;
        this.mObject2        = grapePop;
    }

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

        // Do all of the processing that you want to do...
        // You already have the private fields because of the constructor
        // so you can use mObject1 and mObject2
        Dessert objectToReturn = mObject1 + mObject2;

        // Tell the handler (usually from the calling thread) that we are finished, 
        // returning an object with the message
        mCallersHandler.sendMessage( Message.obtain( mCallersHandler, MSG_FINISHED, objectToReturn ) );

        return (null);
    }
}

此示例假定您的 AsyncTask 需要一块糖果和一根冰棍。然后，它会将甜点返回到您的片段中。

您可以使用以下命令从片段中的一行中构造并运行 AsyncTask：

( new MyTask( mFragmentHandler, candyCane, grapePop ) ).execute();

但是，当然，您首先需要设置片段的处理程序（myFragmentHandler）。为此，您的片段（或活动）应如下所示（注意“实现 Handler.Callback”）：

public class MyFragment extends Fragment implements Handler.Callback {

    private Handler mFragmentHandler;
    private Candy candyCane;
    private Popsicle grapePop;

    @Override
    public void onCreate(Bundle savedInstanceState) {

        // Standard creation code
        super.onCreate(savedInstanceState);
        setRetainInstance(true);

        // Create a handler for this fragment 
        mFragmentHandler = new Handler(this);

        // Other stuff...
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup parent,
            Bundle savedInstanceState) {

        // Inflate the layout
        View v = inflater.inflate(R.layout.my_fragment_layout, parent, false );

        // The candyCane and grapePop don't need to be set up here, but 
        // they MUST be set up before the button is pressed. 
        // Here would be a good place to at least initialize them...

        // Perhaps you have a button in "my_fragment_layout" that triggers the AsyncTask...
        Button mButton  = (Button) v.findViewById(R.id.mButton);
        mButton.setOnClickListener( new OnClickListener() {
            @Override
            public void onClick(View v) {
                ( new MyTask( mFragmentHandler, candyCane, grapePop ) ).execute();
            }
        });
        return v;
    }

    @SuppressWarnings("unchecked")
    @Override
    public boolean handleMessage(Message msg) {

        switch (msg.what) {

        case MyTask.MSG_FINISHED:

            // Let's see what we are having for dessert 
            Dessert myDessert = (Dessert) msg.obj;
            break;

        }
        return false;
    }

}

如果使用这些代码段，按下按钮将触发异步任务。在处理异步任务时，调用片段将继续执行。然后，当 AsyncTask 完成时，它将向片段发送一条消息，指出它已完成，并传递一个包含该消息的对象。此时，片段将看到消息，并执行任何操作。

注意：可能有拼写错误。这是从一个非常大而复杂的代码中切割出来的。