Android里的观察者模式应用

Android里的观察者模式应用

例子：Browser里有许多Tab，现在比较流行的标签页浏览。每当Browser的BrowserSettings（公用）发生变化时，会对每一个

Browser的Tab马上有效。在这里TAb是观察者，BrowserSettings是被观察者。

class BrowserSettings extends Observable {

/**
* Add a WebSettings object to the list of observers that will be updated
* when update() is called.
*
* @param s A WebSettings object that is strictly tied to the life of a
*            WebView.
*/
public Observer addObserver(WebSettings s) {
Observer old = mWebSettingsToObservers.get(s);
if (old != null) {
super.deleteObserver(old);
}
Observer o = new Observer(s);
mWebSettingsToObservers.put(s, o);
super.addObserver(o);
return o;
}

/**
* Delete the given WebSettings observer from the list of observers.
* @param s The WebSettings object to be deleted.
*/
public void deleteObserver(WebSettings s) {
Observer o = mWebSettingsToObservers.get(s);
if (o != null) {
mWebSettingsToObservers.remove(s);
super.deleteObserver(o);
}
}

/*
* Package level method for obtaining a single app instance of the
* BrowserSettings.
*/
/*package*/ static BrowserSettings getInstance() {
if (sSingleton == null ) {
sSingleton = new BrowserSettings();
}
return sSingleton;
}

void update() {
setChanged();
notifyObservers();
}

/*
* An observer wrapper for updating a WebSettings object with the new
* settings after a call to BrowserSettings.update().
*/
static class Observer implements java.util.Observer {
// Private WebSettings object that will be updated.
private WebSettings mSettings;

Observer(WebSettings w) {
mSettings = w;
}

public void update(Observable o, Object arg) {
}
}
}