限制后台启动activity

android 10+ 如果未满足相关条件，则后台不允许启动activity，并会打印如下相关的log：

// anything that has fallen through would currently be aborted
Slog.w(TAG, "Background activity start [callingPackage: " + callingPackage+ "; callingUid: " + callingUid+ "; appSwitchState: " + appSwitchState+ "; isCallingUidForeground: " + isCallingUidForeground+ "; callingUidHasAnyVisibleWindow: " + callingUidHasAnyVisibleWindow+ "; callingUidProcState: " + DebugUtils.valueToString(ActivityManager.class,"PROCESS_STATE_", callingUidProcState)+ "; isCallingUidPersistentSystemProcess: " + isCallingUidPersistentSystemProcess+ "; realCallingUid: " + realCallingUid+ "; isRealCallingUidForeground: " + isRealCallingUidForeground+ "; realCallingUidHasAnyVisibleWindow: " + realCallingUidHasAnyVisibleWindow+ "; realCallingUidProcState: " + DebugUtils.valueToString(ActivityManager.class,"PROCESS_STATE_", realCallingUidProcState)+ "; isRealCallingUidPersistentSystemProcess: "+ isRealCallingUidPersistentSystemProcess+ "; originatingPendingIntent: " + originatingPendingIntent+ "; allowBackgroundActivityStart: " + allowBackgroundActivityStart+ "; intent: " + intent+ "; callerApp: " + callerApp+ "; inVisibleTask: " + (callerApp != null && callerApp.hasActivityInVisibleTask())+ "]");

限制的例外情况

在 Android 10 或更高版本上运行的应用只有在满足以下一项或多项条件时，才能启动 Activity：

ROOT_UID/SYSTEM_UID/NFC_UID等重要uid

final boolean useCallingUidState =originatingPendingIntent == null || checkedOptions == null|| !checkedOptions.getIgnorePendingIntentCreatorForegroundState();
.......
if (useCallingUidState) {if (callingUid == Process.ROOT_UID || callingAppId == Process.SYSTEM_UID|| callingAppId == Process.NFC_UID) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG,"Activity start allowed for important callingUid (" + callingUid + ")");}return false;}......

home 进程

        if (useCallingUidState) {......if (isHomeApp(callingUid, callingPackage)) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG,"Activity start allowed for home app callingUid (" + callingUid + ")");}return false;}

Ime窗口所在uid下的进程

        if (useCallingUidState) {......// IME should always be allowed to start activity, like IME settings.final WindowState imeWindow = mRootWindowContainer.getCurrentInputMethodWindow();if (imeWindow != null && callingAppId == imeWindow.mOwnerUid) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "Activity start allowed for active ime (" + callingUid + ")");}return false;}

应用具有可见窗口，例如前台 Activity

应用是persistent系统进程，并正在执行UI操作

// 是persistent系统进程，并正在执行UI操作
final boolean isCallingUidPersistentSystemProcess =callingUidProcState <= ActivityManager.PROCESS_STATE_PERSISTENT_UI;
// 如果允许应用程序切换，则允许具有可见应用程序窗口的普通应用程序启动活动，
// 或者将允许具有非应用程序可见窗口的动态壁纸等应用程序。
final boolean appSwitchAllowedOrFg =appSwitchState == APP_SWITCH_ALLOW || appSwitchState == APP_SWITCH_FG_ONLY;
final boolean allowCallingUidStartActivity =((appSwitchAllowedOrFg || mService.mActiveUids.hasNonAppVisibleWindow(callingUid))&& callingUidHasAnyVisibleWindow)|| isCallingUidPersistentSystemProcess;
if (useCallingUidState && allowCallingUidStartActivity) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "Activity start allowed: callingUidHasAnyVisibleWindow = " + callingUid+ ", isCallingUidPersistentSystemProcess = "+ isCallingUidPersistentSystemProcess);}return false;
}

应用声明了START_ACTIVITIES_FROM_BACKGROUND 权限

特权system/priv-app/目录下的app才可以申请豁免

        if (useCallingUidState) {// don't abort if the callingUid has START_ACTIVITIES_FROM_BACKGROUND permissionif (mService.checkPermission(START_ACTIVITIES_FROM_BACKGROUND, callingPid, callingUid)== PERMISSION_GRANTED) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG,"Background activity start allowed: START_ACTIVITIES_FROM_BACKGROUND "+ "permission granted for uid "+ callingUid);}return false;}

应用是Recent组件所在uid下进程（这里一般为home进程）

        if (useCallingUidState) {.......// don't abort if the caller has the same uid as the recents componentif (mSupervisor.mRecentTasks.isCallerRecents(callingUid)) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "Background activity start allowed: callingUid (" + callingUid+ ") is recents");}return false;}

应用是设备所有者

应用是在设备所有者模式下运行的设备政策控制器。示例用例包括完全托管的企业设备，以及数字标识牌和自助服务终端等专用设备。

        if (useCallingUidState) {......// don't abort if the callingUid is the device ownerif (mService.isDeviceOwner(callingUid)) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "Background activity start allowed: callingUid (" + callingUid+ ") is device owner");}return false;}

应用通过 CompanionDeviceManager API 与配套硬件设备相关联。

此 API 支持应用启动 API，以响应用户在配对设备上执行的操作。

        if (useCallingUidState) {......// don't abort if the callingUid has companion devicefinal int callingUserId = UserHandle.getUserId(callingUid);if (mService.isAssociatedCompanionApp(callingUserId,callingUid)) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "Background activity start allowed: callingUid (" + callingUid+ ") is companion app");}return false;}

用户已向应用授予 SYSTEM_ALERT_WINDOW 权限

**注意：**在 Android 10（Go 版本）上运行的应用无法获得SYSTEM_ALERT_WINDOW权限。
注意：如果应用程序以 API 级别 23 或更高级别为目标，则应用程序用户必须通过权限管理屏幕明确向应用程序授予此权限。

        if (useCallingUidState) {......// don't abort if the callingUid has SYSTEM_ALERT_WINDOW permissionif (mService.hasSystemAlertWindowPermission(callingUid,callingPid, callingPackage)) {Slog.w(TAG, "Background activity start for " + callingPackage+ " allowed because SYSTEM_ALERT_WINDOW permission is granted.");return false;}}

关于areBackgroundActivityStartsAllowed系列

如果此时我们没有 callerApp，则没有向 startActivity() 提供调用者。 基于 PendingIntent 的启动就是这种情况，因为创建者的进程可能未启动且处于活动状态。 如果是这种情况，我们会在调用者允许的情况下为 send() 调用者检索 WindowProcessController，以便我们可以根据其状态做出决定。

// 遗留行为允许使用调用者前台状态绕过 BAL 限制。
final boolean balAllowedByPiSender =PendingIntentRecord.isPendingIntentBalAllowedByCaller(checkedOptions);
int callerAppUid = callingUid;
if (callerApp == null && balAllowedByPiSender) {callerApp = mService.getProcessController(realCallingPid, realCallingUid);callerAppUid = realCallingUid;
}
if (callerApp != null && useCallingUidState) {// first check the original calling processif (callerApp.areBackgroundActivityStartsAllowed(appSwitchState)) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "Background activity start allowed: callerApp process (pid = "+ callerApp.getPid() + ", uid = " + callerAppUid + ") is allowed");}return false;}// only if that one wasn't allowed, check the other onesfinal ArraySet uidProcesses =mService.mProcessMap.getProcesses(callerAppUid);if (uidProcesses != null) {for (int i = uidProcesses.size() - 1; i >= 0; i--) {final WindowProcessController proc = uidProcesses.valueAt(i);if (proc != callerApp&& proc.areBackgroundActivityStartsAllowed(appSwitchState)) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG,"Background activity start allowed: process " + proc.getPid()+ " from uid " + callerAppUid + " is allowed");}return false;}}}
}

应用的某个 Activity 刚在不久前启动/结束

如果不允许应用程序切换，我们将忽略所有启动activity宽限期异常，因此应用程序无法在按下主页按钮后在 onPause() 中自行启动。

在停止应用程序切换的时间之后启动或finish activity的10s内可后台启动Activity

    boolean areBackgroundActivityStartsAllowed(int pid, int uid, String packageName,int appSwitchState, boolean isCheckingForFgsStart,boolean hasActivityInVisibleTask, boolean hasBackgroundActivityStartPrivileges,long lastStopAppSwitchesTime, long lastActivityLaunchTime,long lastActivityFinishTime) {if (appSwitchState == APP_SWITCH_ALLOW) {// 如果调用者中的任何activity最近启动或finish，则允许，final long now = SystemClock.uptimeMillis();// 启动或finish有10s宽限if (now - lastActivityLaunchTime < ACTIVITY_BG_START_GRACE_PERIOD_MS|| now - lastActivityFinishTime < ACTIVITY_BG_START_GRACE_PERIOD_MS) {// 得在停止应用程序切换的时间之后启动或finish才行if (lastActivityLaunchTime > lastStopAppSwitchesTime|| lastActivityFinishTime > lastStopAppSwitchesTime) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "[Process(" + pid+ ")] Activity start allowed: within "+ ACTIVITY_BG_START_GRACE_PERIOD_MS + "ms grace period");}return true;}if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "[Process(" + pid + ")] Activity start within "+ ACTIVITY_BG_START_GRACE_PERIOD_MS+ "ms grace period but also within stop app switch window");}}}

具有后台启动activity特权的Active Instrumentation所在进程

        // Allow if the proc is instrumenting with background activity starts privs.if (hasBackgroundActivityStartPrivileges) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "[Process(" + pid+ ")] Activity start allowed: process instrumenting with background "+ "activity starts privileges");}return true;}

应用在前台任务的返回栈中拥有 Activity

android U或许会取消

    boolean hasActivityInVisibleTask() {return (mActivityStateFlags & ACTIVITY_STATE_FLAG_HAS_ACTIVITY_IN_VISIBLE_TASK) != 0;}

        // Allow if the caller has an activity in any foreground task.if (hasActivityInVisibleTask&& (appSwitchState == APP_SWITCH_ALLOW || appSwitchState == APP_SWITCH_FG_ONLY)) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "[Process(" + pid+ ")] Activity start allowed: process has activity in foreground task");}return true;}

应用中的某个服务被另一个可见应用绑定

请注意，绑定到服务的应用必须保持可见，以便后台应用成功启动 Activity。

        // Allow if the caller is bound by a UID that's currently foreground.if (isBoundByForegroundUid()) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "[Process(" + pid+ ")] Activity start allowed: process bound by foreground uid");}return true;}private boolean isBoundByForegroundUid() {synchronized (this) {if (mBoundClientUids != null) {for (int i = mBoundClientUids.size() - 1; i >= 0; i--) {if (mUidHasActiveVisibleWindowPredicate.test(mBoundClientUids.get(i))) {return true;}}}}return false;}

    /** A uid is considered to be foreground if it has a visible non-toast window. */@HotPath(caller = HotPath.START_SERVICE)boolean hasActiveVisibleWindow(int uid) {if (mVisibleActivityProcessTracker.hasVisibleActivity(uid)) {return true;}return mActiveUids.hasNonAppVisibleWindow(uid);}

应用收到系统的 PendingIntent 通知

对于服务和广播接收器的挂起 Intent，应用可在该挂起 Intent 发送几秒钟后启动 Activity

应用收到另一个可见应用发送的 PendingIntent

应用的 Service有带BIND_ALLOW_BACKGROUND_ACTIVITY_STARTS的connection

需要声明START_ACTIVITIES_FROM_BACKGROUND权限

Android 10 (API 级别 29) 及更高版本对后台应用可启动 Activity 的时间施加限制。这些限制有助于最大限度地减少对用户造成的中断，并且可以让用户更好地控制其屏幕上显示的内容。
**注意：**为启动 Activity，系统仍会将运行前台服务的应用视为“后台”应用。

详情见BackgroundLaunchProcessController 介绍

        // Allow if the flag was explicitly set.if (isBackgroundStartAllowedByToken(uid, packageName, isCheckingForFgsStart)) {if (DEBUG_ACTIVITY_STARTS) {Slog.d(TAG, "[Process(" + pid+ ")] Activity start allowed: process allowed by token");}return true;}

应用在具有相同uid的现有Task中启动活动

        // Do not allow background activity start in new task or in a task that uid is not present.// Also do not allow pinned window to start single instance activity in background,// as it will recreate the window and makes it to foreground.boolean blockBalInTask = (newTask|| !targetTask.isUidPresent(mCallingUid)|| (LAUNCH_SINGLE_INSTANCE == mLaunchMode && targetTask.inPinnedWindowingMode()));if (mRestrictedBgActivity && blockBalInTask && handleBackgroundActivityAbort(r)) {Slog.e(TAG, "Abort background activity starts from " + mCallingUid);return START_ABORTED;}

普通App如何获得允许

• 申请 SYSTEM_ALERT_WINDOW 权限，且用户通过权限管理屏幕明确向应用程序授予此权限
• 应用收到系统的 PendingIntent 通知
• 应用收到另一个可见应用发送的 PendingIntent
• 应用中的某个服务被另一个可见应用绑定