判断Android前后台切换的方法

自定义在Application，在Application中注册registerActivityLifecycleCallbacks监听所有的Activity，在onActivityStarted和onActivityStopped事件中进行处理。registerActivityLifecycleCallbacks只有在API 14才增加的。代码如下：

public class AppNameApplication extends Application {

    private int activityCount;

    @Override
    public void onCreate() {
        super.onCreate();
        registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
            @Override
            public void onActivityStarted(Activity activity) {
                activityCount++;
                if (activityCount== 1){
                    //从后台切换到前台
                }
            }

            @Override
            public void onActivityStopped(Activity activity) {
                activityCount--;
                if (activityCount== 0){
                    //从前台切换到后台
                }
            }

        });
    }
}