自定義監聽器

定義介面

//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);
}

建立監聽器

在下一步中，我們需要在物件中定義一個例項變數，該變數將通過 MyCustomListener 傳送回撥。併為我們的聽眾新增 setter。

public class SampleClassB {
    private MyCustomListener listener;

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

實現監聽器

現在，在其他類中，我們可以建立 SampleClassB 的例項。

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

接下來我們可以通過兩種方式將我們的聽眾設定為 sampleClass：

通過我們類的工具 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) {

    }
}

或者只是例項化一個匿名的內部類：

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) {

            }
        });
    }
}

觸發器監聽器

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());
            }
        });
    }
}