android获取当前栈顶的activity

在Application的onCreate方法中：

 @Override
    public void onCreate() {
        

        registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle savedInstanceState) {

            }

            @Override
            public void onActivityStarted(Activity activity) {

            }

            @Override
            public void onActivityResumed(Activity activity) {
                MyActivityManager.getInstance().setCurrentActivity(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) {

            }
        });
       
    }

创建一个ActivityManager类

public class MyActivityManager {
    private static MyActivityManager sInstance = new MyActivityManager();

    private WeakReference<Activity> sCurrentActivityWeakRef;

    private   activityUpdateLock = new  ();
    private MyActivityManager() {

    }

    public static MyActivityManager getInstance() {
        return sInstance;
    }

    public Activity getCurrentActivity() {
        Activity currentActivity = null;
        synchronized (activityUpdateLock){
            if (sCurrentActivityWeakRef != null) {
                currentActivity = sCurrentActivityWeakRef.get();
            }
        }
        return currentActivity;
    }

    public void setCurrentActivity(Activity activity) {
        synchronized (activityUpdateLock){
            sCurrentActivityWeakRef = new WeakReference<Activity>(activity);
        }

    }
}

在需要获取当前应用栈顶activity时

MyActivityManager.getInstance().getCurrentActivity()；

这样就获取到当前栈顶的activity了