android listen

2022-04-04 14:07:08

android监听机制，应该是一种观察者模式。

摘抄网上教程，观察者模式的结构如下：

其中涉及的角色有：

　　●　　抽象主题(Subject)角色：抽象主题角色把所有对观察者对象的引用保存在一个聚集（比如ArrayList对象）里，每个主题都可以有任何数量的观察者。抽象主题提供一个接口，可以增加和删除观察者对象，抽象主题角色又叫做抽象被观察者(Observable)角色。

　　●　　具体主题(ConcreteSubject)角色：将有关状态存入具体观察者对象；在具体主题的内部状态改变时，给所有登记过的观察者发出通知。具体主题角色又叫做具体被观察者(Concrete Observable)角色。

　　●　　抽象观察者(Observer)角色：为所有的具体观察者定义一个接口，在得到主题的通知时更新自己，这个接口叫做更新接口。

　　●　　具体观察者(ConcreteObserver)角色：存储与主题的状态自恰的状态。具体观察者角色实现抽象观察者角色所要求的更新接口，以便使本身的状态与主题的状态像协调。如果需要，具体观察者角色可以保持一个指向具体主题对象的引用。

android4.4 InCallUI中，用一个类CallList来维护当前所有的Call信息，当某个call状态发生改变之后，要通知到UI进行界面更新；这个类似于一个被观察者：

 public void addListener(Listener listener) {
        Preconditions.checkNotNull(listener);
        mListeners.add(listener);
    }

 

    public void removeListener(Listener listener) {
        Preconditions.checkNotNull(listener);
        mListeners.remove(listener);
    }

    private void notifyListenersOfChange() {
        for (Listener listener : mListeners) {
            listener.onCallListChange(this);
        }
    }

可以添加一些列观察者，并负责notify到他们。

在被观察者类中定义了一些接口。

/**
     * Listener interface for any class that wants to be notified of changes
     * to the call list.
     */
    public interface Listener {
        /**
         * Called when a new incoming call comes in.
         * This is the only method that gets called for incoming calls. Listeners
         * that want to perform an action on incoming call should respond in this method
         * because {@link #onCallListChange} does not automatically get called for
         * incoming calls.
         */
        public void onIncomingCall(Call call);

        /**
         * Called anytime there are changes to the call list.  The change can be switching call
         * states, updating information, etc. This method will NOT be called for new incoming
         * calls and for calls that switch to disconnected state. Listeners must add actions
         * to those method implementations if they want to deal with those actions.
         */
        public void onCallListChange(CallList callList);

        /**
         * Called when a call switches to the disconnected state.  This is the only method
         * that will get called upon disconnection.
         */
        public void onDisconnect(Call call);
    }

观察者要实现这些接口，以便得到通知后，要做相应的处理工作。

class InCallPresenter implements CallList.Listener {

    /**
     * Called when a call becomes disconnected. Called everytime an existing call
     * changes from being connected (incoming/outgoing/active) to disconnected.
     */
    @Override
    public void onDisconnect(Call call) {
        hideDialpadForDisconnect();
        maybeShowErrorDialogOnDisconnect(call);

        // We need to do the run the same code as onCallListChange.
        onCallListChange(CallList.getInstance());

        if (isActivityStarted()) {
            mInCallActivity.dismissKeyguard(false);
        }
    }

}

转自https://www.cnblogs.com/caidi/p/4091423.html

android listen

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