Android app添加后台拉起机制

本demo源码下载地址 App拉起机制源码下载

简介：

做智能售卖设备需要app一直在前台显示，但是有时由于一些不当操作或者系统原因会使app退出，导致设备不能使用。这时就需要拉起机制了。

拉起机制目前实现方式主要有2种。

1、利用Activity生命周期

创建一个类MyApp继承自Application类，在该类通过监听所有activity生命周期来判断activity是否全部销毁，以此来判断app是否退出。
代码如下：

/**
*  监听各个Activity生命周期情况
*/
private void startActivityLifeListener(){registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {@Overridepublic void onActivityCreated(Activity activity, Bundle savedInstanceState) {showLog("add activity "+activity.toString());}@Overridepublic void onActivityStarted(Activity activity) {mActivityCount++;showLog(activity.getComponentName()+" onActivityStarted activityCounts= "+mActivityCount);}@Overridepublic void onActivityResumed(Activity activity) {}@Overridepublic void onActivityPaused(Activity activity) {showLog(activity.getComponentName().toString()+" onActivityPaused");}@Overridepublic void onActivityStopped(Activity activity) {mActivityCount--;showLog(activity.getComponentName()+" onActivityStopped activityCounts= "+mActivityCount);if (mActivityCount <= 0){// 5秒后拉起new Handler().postDelayed(new Runnable() {@Overridepublic void run() {showLog("try to restart");Intent intent = new Intent(getApplicationContext(), MainActivity.class);intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);startActivity(intent);}}, 5000);}}@Overridepublic void onActivitySaveInstanceState(Activity activity, Bundle outState) {}@Overridepublic void onActivityDestroyed(Activity activity) {showLog("remove activity "+activity.toString());}});
}

然后在onCreate方法里面调用startActivityLifeListener()方法。

2、利用RunningAppProcessInfo类判断

通过ActivityManager类获取所有正在运行的进程，然后利用app包名找到应用的运行进程，再判断是否处于后台，不过该方法在有些系统版本可能不能用。
创建一个远程服务类PullUpService在后台一直运行轮询检查app是否后台运行。代码如下：

package com.mhwang.apppullup;import android.app.ActivityManager;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.os.IBinder;
import android.os.SystemClock;
import android.util.Log;import java.util.List;/** 后台拉起服务
* Author : mhwang
* Date : 2018/11/6
* Version : V1.0
*/
public class PullUpService extends Service implements Runnable{private boolean running = false;private Intent intent;private Thread thread;private static void showLog(String s){Log.d("PullUpService=>", s);}public IBinder onBind(Intent intent) {return null;}public void onCreate(){super.onCreate();intent = getPackageManager().getLaunchIntentForPackage(getPackageName());if (intent != null) {intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);}showLog("onCreate");}@Overridepublic int onStartCommand(Intent intent, int flags, int startId) {showLog("onStartCommand");if(thread == null){thread = new Thread(this);thread.start();}return START_STICKY;}@Overridepublic void onDestroy() {showLog("onDestroy");running = false;if(thread != null && !thread.isInterrupted()){try {thread.interrupt();thread.join(100);} catch (InterruptedException e) {e.printStackTrace();}}thread = null;super.onDestroy();}@Overridepublic void run() {running = true;showLog("background service start");while(running){showLog("check background");if(isBackground(PullUpService.this)){showLog("restart activity");startActivity(intent);}SystemClock.sleep(10 * 1000);         // 由于模拟器较卡，这里提高10秒检查一次}}/** 判断是否处于后台* @param context* @return true：处于后台, false：不处于后台*/public static boolean isBackground(Context context) {ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);List<ActivityManager.RunningAppProcessInfo> appProcesses = activityManager.getRunningAppProcesses();if(appProcesses == null){return false;}for (ActivityManager.RunningAppProcessInfo appProcess : appProcesses) {if (appProcess.processName.equals(context.getPackageName())) {if (appProcess.importance != ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {return true;} else {return false;}}}return false;}}

记得在AndroidMainifest.xml注册该服务。

<service android:name=".PullUpService" android:process=":remote"/>

然后在MyApp类开启服务：

如下图所示，使用back键和home键退出app，每隔5秒后都能有效拉起（图示效果运行在模拟器系统版本4.4.2）。但是有个缺点就是使用多任务键杀死时，由于此时整个app都被干掉了，因此MyApp里面的拉起机制不能生效。