我的回调方法从不使用接口调用

Question

我正在尝试实现一个 callback 方法，以便在 Thread 完成时调用它的工作。我使用的是 interface 方法而不是 Handler 方法。

我有一个主要的 UI Thread，它是 onCreate(Bundle) 方法，还有一个 Thread 我从 onCreate(Bundle) 方法中调用。

（仅发布相关代码）。

MainActivity.java:

public class MainActivity extends AppCompatActivity implements GetDataFromTheWebThreadCallback
{
    public static GetDataFromTheWebThread getDataFromTheWebThread;
    private GetDataFromTheWebEventNotifier eventNotifier;
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        this.eventNotifier = new GetDataFromTheWebEventNotifier(MainActivity.this);

        // The thread that will search the web for data
        this.getDataFromTheWebThread = new GetDataFromTheWebThread();
        getDataFromTheWebThread.start();
     }

        @Override
        public void finishParsing() // The callback method that never called
        {
            Toast.makeText(MainActivity.this,"Callback Method Called",Toast.LENGTH_LONG).show();
            Log.d("Callback:", "Callback Method Called");
        }
}

GetDataFromTheWebEventNotifier.java:

public class GetDataFromTheWebEventNotifier
{
    private GetDataFromTheWebThreadCallback callbackInterface;

    public GetDataFromTheWebEventNotifier(GetDataFromTheWebThreadCallback callbackInterface)
    {
        this.callbackInterface = callbackInterface;
    }

    public void onEvent()
    {
            this.callbackInterface.finishParsing();
    }
}

GetDataFromTheWebThreadCallback.java:

public interface GetDataFromTheWebThreadCallback
{
    void finishParsing(); // The method i wish to invoke when certain event will happen
}

GetDataFromTheWebThread.java:

public class GetDataFromTheWebThread extends Thread
{
    public static boolean isFinished = false; // False - the thread is still running. True - the thread is dead

    @Override
    public void run()
    {
        GetDataFromTheWebThread.isFinished = false;
        try
        {
            // Some internet computations...
            Thread.sleep(100);
        }
        catch (InterruptedException e)
        {
            e.printStackTrace();
        }
        GetDataFromTheWebThread.isFinished = true;
    }
}

那我的callback怎么了？

Answer 1

你从不打电话给 onEvent()。您的通知程序是否应该监视 isFinished 变量或其他内容？

Answer 2

至于你的 ThreadClass，有一个带回调的构造函数：

public class GetDataFromTheWebThread extends Thread {
    public static boolean isFinished = false; // False - the thread is still running. True - the thread is dead
    private GetDataFromTheWebThreadCallback mCallback;

    public GetDataFromTheWebThread(GetDataFromTheWebThreadCallback c) {
      mCallback = c;
    }

    @Override
    public void run() {
      GetDataFromTheWebThread.isFinished = false;
      try {
        // Some internet computations...
        Thread.sleep(100);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      GetDataFromTheWebThread.isFinished = true;
      if (mCallback !- null) {
        mCallback.finishParsing();
      }
    }
}

至于您的 Activity，只需在创建线程时传递回调即可：

this.getDataFromTheWebThread = new GetDataFromTheWebThread(this);

以及 :

    @Override
    public void finishParsing()  {
      // You know that this function is called from a background Thread.
      // Therefore from here, run what you have to do on the UI Thread
      runOnUiThread(new Runnable() {
        @Override
        public void run() {
          Toast.makeText(MainActivity.this,"Callback Method Called",Toast.LENGTH_LONG).show();
          Log.d("Callback:", "Callback Method Called");
        }});

    }

Answer 3

实际上你并没有调用onEvent()。并检查 AsyncTask.

我的回调方法从不使用接口调用

My callback method is never called using an interface

multithreading

android

interface

callback

ui-thread