自定义监听器

定义界面

//In this interface, you can define messages, which will be send to owner.
public interface MyCustomListener {
    //In this case we have two messages, 
    //the first that is sent when the process is successful.
    void onSuccess(List<Bitmap> bitmapList);
    //And The second message, when the process will fail.
    void onFailure(String error);
}

创建监听器

在下一步中，我们需要在对象中定义一个实例变量，该变量将通过 MyCustomListener 发送回调。并为我们的听众添加 setter。

public class SampleClassB {
    private MyCustomListener listener;

    public void setMyCustomListener(MyCustomListener listener) {
        this.listener = listener;
    }
}

实现监听器

现在，在其他类中，我们可以创建 SampleClassB 的实例。

public class SomeActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        SampleClassB sampleClass = new SampleClassB();
    }
}

接下来我们可以通过两种方式将我们的听众设置为 sampleClass：

通过我们类的工具 MyCustomListener：

public class SomeActivity extends Activity implements MyCustomListener {
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        SampleClassB sampleClass = new SampleClassB();
        sampleClass.setMyCustomListener(this);
    }

    @Override
    public void onSuccess(List<Bitmap> bitmapList) {

    }

    @Override
    public void onFailure(String error) {

    }
}

或者只是实例化一个匿名的内部类：

public class SomeActivity extends Activity {
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        SampleClassB sampleClass = new SampleClassB();
        sampleClass.setMyCustomListener(new MyCustomListener() {

            @Override
            public void onSuccess(List<Bitmap> bitmapList) {

            }

            @Override
            public void onFailure(String error) {

            }
        });
    }
}

触发器监听器

public class SampleClassB {
    private MyCustomListener listener;

    public void setMyCustomListener(MyCustomListener listener) {
        this.listener = listener;
    }

    public void doSomething() {
        fetchImages();
    }

    private void fetchImages() {
        AsyncImagefetch imageFetch = new AsyncImageFetch();
        imageFetch.start(new Response<Bitmap>() {
            @Override
            public void onDone(List<Bitmap> bitmapList, Exception e) {
                //do some stuff if needed

                //check if listener is set or not.
                if(listener == null)
                    return;
                //Fire proper event. bitmapList or error message will be sent to
                //class which set listener.
                if(e == null)
                    listener.onSuccess(bitmapList);
                else
                    listener.onFailure(e.getMessage());
            }
        });
    }
}