Android监听应用是否处于前台的代码

有时候在开发应用程序时需要监听App当前处于前台还是后台来做一些处理，下面代码可作为参考：

import android.app.Activity;
import android.app.Application;
import android.os.Bundle;

import com.bose.commontools.logger.BoseLogger;

public class UmeLifecycleHandler implements Application.ActivityLifecycleCallbacks {
    private static int resumed;
    private static int paused;
    private static int started;
    private static int stopped;

    private static int appCount;
    private static boolean isRunInBackground;

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

    @Override
    public void onActivityStarted(Activity activity) {
        ++started;
        appCount++;
        if (isRunInBackground) {
            back2App();
        }
    }

    @Override
    public void onActivityResumed(Activity activity) {
        ++resumed;
        if (resumed > paused) {
//            AppBus.getInstance().post(new BusEventData(BusEventConstants.APP_REOPEN));
        }
    }

    @Override
    public void onActivityPaused(Activity activity) {
        ++paused;
        android.util.Log.w("gudd", "application is in foreground: " + (resumed > paused));
        Logger.i("gudd application is in foreground: %s", resumed > paused);
    }

    @Override
    public void onActivityStopped(Activity activity) {
        ++stopped;
        appCount--;
        if (appCount == 0) {
            leaveApp();

        }
        Logger.i("gudd application is visible: %s", started > stopped);

    }

    @Override
    public void onActivityDestroyed(Activity activity) {
    }

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

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

    public static boolean isApplicationInForeground() {
        // 当所有 Activity 的状态中处于 resumed 的大于 paused 状态的，即可认为有Activity处于前台状态中
        return resumed > paused;
    }

    // 从后台回到前台
    private void back2App() {
        BoseLogger.i("gudd application returned to foreground.");
        isRunInBackground = false;
//        AppBus.getInstance().post(new EventCode(BusEventConstants.APP_REOPEN));
    }

    // 离开应用进入后台或退出应用
    private void leaveApp() {
        Logger.i("gudd application in the background.");
        isRunInBackground = true;
    }
}

leaveApp()则表示应用当前的状态为进入后台。