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) {    }    }}

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