Android 高版本中无法在后台震动 Ignoring inc

有用户反馈在Android 10上，app到后台之后无法震动，调试后发现有一行红色的提示

VibratorService: Ignoring incoming vibration as process with uid = 10054 is background, usage = USAGE_UNKNOWN

调用震动的代码是这样:

  Vibrator mVibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE);
   long[] patern = {0,1000,1000};
   mVibrator.vibrate(patern, 1);

本来好好的呀，咋就突然不行了？
我们去找找这个类 VibratorService。先去 http://androidxref.com 看看，发现没有10.0的源码，那就先找找9.0的。我们发现了它：/frameworks/base/services/core/java/com/android/server/VibratorService.java
然而仔细搜索并没有"background"字样，说明确实10.0有修改，9.0并不同。androidxref确实年久失修啊，只更新到 2018-08-11 。
也可以去这里看代码：http://aospxref.com/android-10.0.0_r2/xref/frameworks/base/

我们找了一个社区https://www.androidos.net.cn/android/10.0.0_r6/xref/frameworks/base/services/core/java/com/android/server
确实有10.0代码，同样的目录下找到它 VibratorService，搜索"background",只有一个结果：

 public void vibrate(int uid, String opPkg, VibrationEffect effect, int usageHint, String reason,
            IBinder token) {
           。。。省略代码
                Vibration vib = new Vibration(token, effect, usageHint, uid, opPkg, reason);
                if (mProcStatesCache.get(uid, ActivityManager.PROCESS_STATE_IMPORTANT_FOREGROUND)
                        > ActivityManager.PROCESS_STATE_IMPORTANT_FOREGROUND
                        && !vib.isNotification() && !vib.isRingtone() && !vib.isAlarm()) {
                    Slog.e(TAG, "Ignoring incoming vibration as process with"
                            + " uid = " + uid + " is background,"
                            + " usage = " + AudioAttributes.usageToString(vib.usageHint));
                    return;
                }
                   。。。省略代码
    }

分析下：mProcStatesCache存储的是整形的SparseArray，在启动service是会注册监听ActivityManager.UID_OBSERVER_PROCSTATE | ActivityManager.UID_OBSERVER_GONE,
ActivityManager.PROCESS_STATE_UNKNOWN，然后保存和移除状态，应该是保存了app当前的状态，大于ActivityManager.PROCESS_STATE_IMPORTANT_FOREGROUND就是比前台状态优先级低的状态了，且不是isNotification&&不是isRingtone&&不是isAlarm，就报错了。

看看这几个判断的方法：

 private static boolean isNotification(int usageHint) {
        switch (usageHint) {
            case AudioAttributes.USAGE_NOTIFICATION:
            case AudioAttributes.USAGE_NOTIFICATION_COMMUNICATION_REQUEST:
            case AudioAttributes.USAGE_NOTIFICATION_COMMUNICATION_INSTANT:
            case AudioAttributes.USAGE_NOTIFICATION_COMMUNICATION_DELAYED:
                return true;
            default:
                return false;
        }
    }

    private static boolean isRingtone(int usageHint) {
        return usageHint == AudioAttributes.USAGE_NOTIFICATION_RINGTONE;
    }

    private static boolean isAlarm(int usageHint) {
        return usageHint == AudioAttributes.USAGE_ALARM;
    }

就是说要加usage了，而且mVibrator.vibrate(pattern, 1, audioAttributes)方法在低版本不存在，于是我们代码改成这样:

 Vibrator mVibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE);
   long[] patern = {0,1000,1000};
    AudioAttributes audioAttributes = null;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            audioAttributes = new AudioAttributes.Builder()
                    .setContentType(AudioAttributes.CONTENT_TYPE_SONIFICATION)
                    .setUsage(AudioAttributes.USAGE_ALARM) //key
                    .build();
            mVibrator.vibrate(pattern, 1, audioAttributes);
        }else {
            mVibrator.vibrate(pattern, 1);
        }

又可以愉快地震动啦~~~
其实这个setUsage(AudioAttributes.USAGE_ALARM)可以设置成USAGE_NOTIFICATION_RINGTONE或者USAGE_NOTIFICATION应该都可以。