判断APP是否处于前台小工具

原理：

Application在Api14之后添加了新的Callback方法

    @Override
    public void registerActivityLifecycleCallbacks(ActivityLifecycleCallbacks callback) {
        super.registerActivityLifecycleCallbacks(callback);
    }

通过该方法我们可以监听所有Activity的生命周期

代码：

/**
 * 用于判断App是否在后台
 */
public class AppLifecycleHandler implements Application.ActivityLifecycleCallbacks {
    private static int resumed;
    private static int paused;
    private static int started;
    private static int stopped;

    public AppLifecycleHandler() {
        resetVariables();
    }

    private void resetVariables() {
        resumed = 0;
        paused = 0;
        started = 0;
        stopped = 0;
    }

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

    @Override
    public void onActivityDestroyed(Activity activity) {
    }

    @Override
    public void onActivityResumed(Activity activity) {
        ++resumed;
    }

    @Override
    public void onActivityPaused(Activity activity) {
        ++paused;
    }

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

    @Override
    public void onActivityStarted(Activity activity) {
        ++started;
    }

    @Override
    public void onActivityStopped(Activity activity) {
        ++stopped;
        android.util.Log.w("test", "application is visible: " + (started > stopped));
    }

    public static boolean isApplicationVisible() {
        return started > stopped;
    }

    public static boolean isApplicationInForeground() {
        return resumed > paused;
    }

    public static boolean isApplicationInBackground() {
        return started == stopped;
    }
}

使用方法：

在Application的onCreate方法中初始化

//程序的生命周期监听
registerActivityLifecycleCallbacks(new AppLifecycleHandler ());