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);
}
}

实例二：

@Override
public void onStart(Intent intent, int startid) {
super.onStart(intent, startid);

 locationService = ((LocationApplication) getApplication()).locationService;
//获取locationservice实例，建议应用中只初始化1个location实例，然后使用，可以参考其他示例的activity，都是通过此种方式获取locationservice实例的
locationService.registerListener(mListener);//注册监听

if (type == 0) {
locationService.setLocationOption(locationService.getDefaultLocationClientOption());
} else if (type == 1) {
locationService.setLocationOption(locationService.getOption());
}

}

@Override
public void onDestroy() {
Log.i("warn", "ondestroy");
locationService.stop(); //停止定位服务
locationService.unregisterListener(mListener); //注销掉监听
}