Android判斷App是否在前台運行

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    //當前應用是否處於前台
    private boolean isForeground(Context context) {
        if (context != null) {
            ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
            List<ActivityManager.RunningAppProcessInfo> processes = activityManager.getRunningAppProcesses();
            for (ActivityManager.RunningAppProcessInfo processInfo: processes) {
                if (processInfo.processName.equals(context.getPackageName())) {
                    if (processInfo.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {
                        return true;
                    }
                }
            }
        }
        return false;
    }

可以根據importance的不同來判斷前台或后台
RunningAppProcessInfo 里面的常量IMOPORTANCE就是上面所說的前台后台，其實IMOPORTANCE是表示這個app進程的重要性，因為系統回收時候，會根據IMOPORTANCE來回收進程的。具體可以去看文檔。。

    public static final int IMPORTANCE_BACKGROUND = 400//后台
    public static final int IMPORTANCE_EMPTY = 500//空進程
    public static final int IMPORTANCE_FOREGROUND = 100//在屏幕最前端、可獲取到焦點 可理解為Activity生命周期的OnResume();
    public static final int IMPORTANCE_SERVICE = 300//在服務中
    public static final int IMPORTANCE_VISIBLE = 200//在屏幕前端、獲取不到焦點可理解為Activity生命周期的OnStart();

但上面的方法有的機型不支持，下面這個方法還是比較靠譜的，但需要一個權限
< uses-permission Android:name =“android.permission.GET_TASKS” />

    //當前應用是否處於前台
    private boolean isForeground(Context context) {
        if (context != null) {
            ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
            ComponentName cn = am.getRunningTasks(1).get(0).topActivity;
            String currentPackageName = cn.getPackageName();
            if (!TextUtils.isEmpty(currentPackageName) && currentPackageName.equals(context.getPackageName())) {
                return true;
            }
            return false;
        }
        return false;
    }

版本4.0以上，可以使用ActivityLifecycle

if (Build.VERSION.SDK_INT >= 14) {
            lifecycle = new SimpleActivityLifecycle();
            registerActivityLifecycleCallbacks(lifecycle);

public class SimpleActivityLifecycle implements Application.ActivityLifecycleCallbacks {

    private boolean isForeground = false;//應用是否處於前端

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

    }

    @Override
    public void onActivityStarted(Activity activity) {

    }

    @Override
    public void onActivityResumed(Activity activity) {
        isForeground = true;
    }

    @Override
    public void onActivityPaused(Activity activity) {
        isForeground = false;
    }

    @Override
    public void onActivityStopped(Activity activity) {

    }

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

    }

    @Override
    public void onActivityDestroyed(Activity activity) {

    }

    public boolean isForeground() {
        return isForeground;
    }
}