ActivityLifecycleCallbacks管理Activity栈（监听home键）

Android在API14之后添加了用于监听应用Activity生命周期的回调接口ActivityLifecycleCallbacks，使用时需要在Application中进行注册。

image

可以看到ActivityLifecycleCallbacks中的方法跟Activity生命周期方法基本是一致的。

注册与取消注册

public class MyApplication extends Application {
    public static final String TAG = MyApplication.class.getSimpleName();

    /** Activity监听回调 */
    private ActivityLifecycleCallbacks activityLifecycleCallbacks = new ActivityLifecycleCallbacks() {
        ....
    };

    @Override
    public void onCreate() {
        super.onCreate();

        //可注册多次，注册多个生命周期回调
        registerActivityLifecycleCallbacks(activityLifecycleCallbacks);
        //Activity管理
        registerActivityLifecycleCallbacks(ActivityManager.getInstance());
    }

    @Override
    public void onTerminate() {
        super.onTerminate();
        //Android API中没有对此方法的过多解释，不过通常此方法会在app退出是被调用（并不是100%）

        unregisterActivityLifecycleCallbacks(activityLifecycleCallbacks);
    }
}

需要注意的是Android允许注册多个ActivityLifecycleCallbacks，并且同时生效。

优雅的管理Activity

实现ActivityLifecycleCallbacks接口，并创建Activity的任务栈，通过监听回调实现Activity的进栈和出栈。需要在Application中进行注册。

/**
 * Activity管理类

 * 需要在Application中调用registerActivityLifecycleCallbacks注册
 */
public class ActivityManager implements Application.ActivityLifecycleCallbacks {
    //Activity栈
    private Stack activities = new Stack<>();
    private static ActivityManager activityManager;

    private ActivityManager(){
    }

    /**
     * 单例
     * @return activityManager instance
     */
    public static ActivityManager getInstance(){
        if(activityManager == null){
            synchronized (ActivityManager.class){
                if(activityManager == null){
                    activityManager = new ActivityManager();
                }
            }
        }

        return activityManager;
    }

    /**
     * 获取Activity任务栈
     * @return activity stack
     */
    public Stack getActivityStack(){
        return activities;
    }

    /**
     * Activity 入栈
     * @param activity Activity
     */
    public void addActivity(Activity activity){
        activities.add(activity);
    }

    /**
     * Activity出栈
     * @param activity Activity
     */
    public void removeActivity(Activity activity){
        if(activity != null){
            activities.remove(activity);
        }
    }

    /**
     * 结束某Activity
     * @param activity Activity
     */
    public void finishActivity(Activity activity){
        if(activity != null){
            removeActivity(activity);
            activity.finish();
        }
    }

    /**
     * 获取当前Activity
     * @return current activity
     */
    public Activity getCurrentActivity(){
        return activities.lastElement();
    }

    /**
     * 结束当前Activity
     */
    public void finishActivity(){
        finishActivity(activities.lastElement());
    }

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
        addActivity(activity);
    }

    @Override
    public void onActivityStarted(Activity activity) {

    }

    @Override
    public void onActivityResumed(Activity activity) {

    }

    @Override
    public void onActivityPaused(Activity activity) {

    }

    @Override
    public void onActivityStopped(Activity activity) {

    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {

    }

    @Override
    public void onActivityDestroyed(Activity activity) {
        removeActivity(activity);
    }
}

通过上面的Activity管理栈可以扩展实现如下需求：

• 监听应用中集成的第三方SDK中的Activity的启动。
• 可以控制应用中某个Activity被初始化的数量，如商城应用中的商品详情页，避免无限制的创建Activity。
• 判断应用是否处于前台可见状态，通过onActivityResumed和onActivityPaused回调方法实现。

监听Home键

我们在开发过程中有时候会碰到一些特殊需求需要监听home键，释放一些资源或者销毁activity等。但Home键事件不同于其他普通按键可以通过OnKeyDown、dispatchKeyEvent等按键监听方法捕获处理，Android系统并没有提供直接监听Home键的方法。但是，当按下Home键是系统会发送Intent.ACTION_CLOSE_SYSTEM_DIALOGS广播（多任务键也会发送此广播）。我们可以通过监听此广播，来间接的监听Home键事件。

public class HomeKeyListenerBroadcast extends BroadcastReceiver {
    private Context context;
    private OnHomeKeyPressListener onHomeKeyPressListener;

    private boolean isRegiested = false;

    public HomeKeyListenerBroadcast(Context context){
        this.context = context;
    }

    public HomeKeyListenerBroadcast(Context context, OnHomeKeyPressListener onHomeKeyPressListener){
        this.context = context;
        this.onHomeKeyPressListener = onHomeKeyPressListener;
    }

    public void setOnHomeKeyPressListener(OnHomeKeyPressListener onHomeKeyPressListener){
        this.onHomeKeyPressListener = onHomeKeyPressListener;
    }

    /**
     * 广播注册
     */
    public void registerSelf(){
        if(context != null){
            IntentFilter filter = new IntentFilter();
            filter.addAction(Intent.ACTION_CLOSE_SYSTEM_DIALOGS);
            context.registerReceiver(this, filter);
            isRegiested = true;
        }
    }

    /**
     * 广播UnRegister
     */
    public void unRegisterSelf(){
        if(isRegiested){
            context.unregisterReceiver(this);
            isRegiested = false;
        }
    }


    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (Intent.ACTION_CLOSE_SYSTEM_DIALOGS.equals(action)) {
            String reason = intent.getStringExtra("reason");
            if ("homekey".equals(reason)) {
                // 按下HOME健
                if (onHomeKeyPressListener != null) {
                    onHomeKeyPressListener.onHomeKeyPress();
                }
            } else if ("recentapps".equals(reason)) {
                // 长按HOME键
                if (onHomeKeyPressListener != null) {
                    onHomeKeyPressListener.onRecentAppsKeyLongPress();
                }
            }
        }
    }

    /**
     * 事件回调接口
     */
    public interface OnHomeKeyPressListener{
        void onHomeKeyPress();
        void onRecentAppsKeyLongPress();
    }
}

代码很简单，不做过多解释了。需要注意的是此广播肯定是动态注册的，在需要的Activity中进行注册并监听按键事件，记得要在onDestroy中取消注册。