java 监听器实现原理

监听器实现者：

public class MyActivity extends Activity implements InternetManager.Listener {

    private TextView mText;
    private InternetManager mInetMgr;

    /* called just like onCreate at some point in time */ 
    public void onStateChange(boolean state) {
        if (state) {
            mText.setText("on");
        } else {
            mText.setText("off");
        }
    }

    public void onCreate() {
        mInetMgr = new InternetManager();
        mInetMgr.registerListener(this);
        mInetMgr.doYourWork();
    }
}

自定义类，监听器作为内部属性(包含方法)，

类中存在调用监听器内部方法的地方，

set不同的监听器实现者，处理的方式便不一样，

监听器相当于一个钩子，做回调使用。

public class InternetManager {
    // all the listener stuff below
    public interface Listener {
        public void onStateChange(boolean state);
    }

    private Listener mListener = null;
    public void registerListener (Listener listener) {
        mListener = listener;
    }

    // -----------------------------
    // the part that this class does

    private boolean isInternetOn = false;
    public void doYourWork() {
        // do things here
        // at some point
        isInternetOn = true;
        // now notify if someone is interested.
        if (mListener != null)
            mListener.onStateChange(isInternetOn);
    }
}