Android6.0 屏幕固定功能詳解

可能大家看到這個標題不知道是什麼東西，我先說明下，android6.0在設置->安全->屏幕固定開啟後，然後再長按home鍵出現最近的幾個Activity可以選擇一個圖釘按鈕就開啟了屏幕固定功能。

屏幕固定開啟後，屏幕只能固定在設定的Task上的Activity切換。

一、設置固定屏幕

我們先來看SystemUI/src/com/android/systemui/recents/ScreenPinningRequest.java的代碼，這段代碼就是長按home鍵出現幾個Activity，然後按了圖釘的那個按鈕。在這裡直接調用了AMS的startLockTaskModeOnCurrent函數。

@Override 
public void onClick(View v) { 
if (v.getId() == R.id.screen_pinning_ok_button || mRequestWindow == v) { 
try { 
ActivityManagerNative.getDefault().startLockTaskModeOnCurrent(); 
} catch (RemoteException e) {} 
} 
clearPrompt(); 
}

我們來看AMS的startLockTaskModeOnCurrent函數，先調用ActivityStackSupervisor的topRunningActivityLocked獲取最前面的Activity，然後調用startLockTaskModeLocked函數，參數是TaskRecord。

public void startLockTaskModeOnCurrent() throws RemoteException { 
enforceCallingPermission(android.Manifest.permission.MANAGE_ACTIVITY_STACKS, 
"startLockTaskModeOnCurrent"); 
long ident = Binder.clearCallingIdentity(); 
try { 
synchronized (this) { 
ActivityRecord r = mStackSupervisor.topRunningActivityLocked(); 
if (r != null) { 
startLockTaskModeLocked(r.task); 
} 
} 
} finally { 
Binder.restoreCallingIdentity(ident); 
} 
}

我們再來看topRunningActivityLocked函數，先從mFocusedStack中獲取最前面的Activity。如果沒有再遍歷所有的mStacks獲取。

ActivityRecord topRunningActivityLocked() { 
final ActivityStack focusedStack = mFocusedStack; 
ActivityRecord r = focusedStack.topRunningActivityLocked(null); 
if (r != null) { 
return r; 
} 
// Return to the home stack. 
final ArrayList<ActivityStack> stacks = mHomeStack.mStacks; 
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) { 
final ActivityStack stack = stacks.get(stackNdx); 
if (stack != focusedStack && isFrontStack(stack)) { 
r = stack.topRunningActivityLocked(null); 
if (r != null) { 
return r; 
} 
} 
} 
return null; 
}

在startLockTaskModeLocked函數中主要是調用了ActivityStackSupervisor的setLockTaskModeLocked函數，下面我們來看這個函數，我們的task不為null，第一次mLockTaskModeTasks為空，會發送一個LOCK_TASK_START_MSG消息

void setLockTaskModeLocked(TaskRecord task, int lockTaskModeState, String reason, 
boolean andResume) { 
if (task == null) { 
// Take out of lock task mode if necessary 
final TaskRecord lockedTask = getLockedTaskLocked(); 
if (lockedTask != null) { 
removeLockedTaskLocked(lockedTask); 
if (!mLockTaskModeTasks.isEmpty()) { 
// There are locked tasks remaining, can only finish this task, not unlock it. 
if (DEBUG_LOCKTASK) Slog.w(TAG_LOCKTASK, 
"setLockTaskModeLocked: Tasks remaining, can't unlock"); 
lockedTask.performClearTaskLocked(); 
resumeTopActivitiesLocked(); 
return; 
} 
} 
if (DEBUG_LOCKTASK) Slog.w(TAG_LOCKTASK, 
"setLockTaskModeLocked: No tasks to unlock. Callers=" + Debug.getCallers(4)); 
return; 
} 
// Should have already been checked, but do it again. 
if (task.mLockTaskAuth == LOCK_TASK_AUTH_DONT_LOCK) { 
if (DEBUG_LOCKTASK) Slog.w(TAG_LOCKTASK, 
"setLockTaskModeLocked: Can't lock due to auth"); 
return; 
} 
if (isLockTaskModeViolation(task)) { 
Slog.e(TAG_LOCKTASK, "setLockTaskMode: Attempt to start an unauthorized lock task."); 
return; 
} 
if (mLockTaskModeTasks.isEmpty()) { 
// First locktask. 
final Message lockTaskMsg = Message.obtain(); 
lockTaskMsg.obj = task.intent.getComponent().getPackageName(); 
lockTaskMsg.arg1 = task.userId; 
lockTaskMsg.what = LOCK_TASK_START_MSG;//發送消息 
lockTaskMsg.arg2 = lockTaskModeState; 
mHandler.sendMessage(lockTaskMsg); 
} 
// Add it or move it to the top. 
if (DEBUG_LOCKTASK) Slog.w(TAG_LOCKTASK, "setLockTaskModeLocked: Locking to " + task + 
" Callers=" + Debug.getCallers(4)); 
mLockTaskModeTasks.remove(task); 
mLockTaskModeTasks.add(task);//加入到mLockModeTasks中 
if (task.mLockTaskUid == -1) { 
task.mLockTaskUid = task.effectiveUid; 
} 
if (andResume) { 
findTaskToMoveToFrontLocked(task, 0, null, reason);//把task放最前面 
resumeTopActivitiesLocked();//顯示新的Activity 
} 
}

我們再來看消息處理，在消息處理中主要調用了WMS的disableKeyguard函數。

case LOCK_TASK_START_MSG: { 
// When lock task starts, we disable the status bars. 
try { 
if (mLockTaskNotify == null) { 
mLockTaskNotify = new LockTaskNotify(mService.mContext); 
} 
mLockTaskNotify.show(true); 
mLockTaskModeState = msg.arg2; 
if (getStatusBarService() != null) { 
int flags = 0; 
if (mLockTaskModeState == LOCK_TASK_MODE_LOCKED) { 
flags = StatusBarManager.DISABLE_MASK 
& (~StatusBarManager.DISABLE_BACK); 
} else if (mLockTaskModeState == LOCK_TASK_MODE_PINNED) { 
flags = StatusBarManager.DISABLE_MASK 
& (~StatusBarManager.DISABLE_BACK) 
& (~StatusBarManager.DISABLE_HOME) 
& (~StatusBarManager.DISABLE_RECENT); 
} 
getStatusBarService().disable(flags, mToken, 
mService.mContext.getPackageName()); 
} 
mWindowManager.disableKeyguard(mToken, LOCK_TASK_TAG); 
if (getDevicePolicyManager() != null) { 
getDevicePolicyManager().notifyLockTaskModeChanged(true, 
(String)msg.obj, msg.arg1); 
} 
} catch (RemoteException ex) { 
throw new RuntimeException(ex); 
} 
} break;

二、固定屏幕後Activity啟動流程

在固定屏幕後，如果我們啟動其他TaskRecord的Activity是不能啟動的，我們來看下這個原理。在startActivityUncheckedLocked函數中會調用isLockTaskModeViolation函數來判斷是否進一步的Activity的啟動流程，我們來看下這個函數，調用getLockedTaskLocked來看mLockTaskModeTasks（就是鎖定屏幕的那些Task），如果當前的task就是當前正在固定屏幕的task，直接return false就是可以繼續啟動Activity的流程，而如果不是，我們需要看task的mLockTaskAuth變量。

boolean isLockTaskModeViolation(TaskRecord task, boolean isNewClearTask) { 
if (getLockedTaskLocked() == task && !isNewClearTask) { 
return false; 
} 
final int lockTaskAuth = task.mLockTaskAuth; 
switch (lockTaskAuth) { 
case LOCK_TASK_AUTH_DONT_LOCK: 
return !mLockTaskModeTasks.isEmpty(); 
case LOCK_TASK_AUTH_LAUNCHABLE_PRIV: 
case LOCK_TASK_AUTH_LAUNCHABLE: 
case LOCK_TASK_AUTH_WHITELISTED: 
return false; 
case LOCK_TASK_AUTH_PINNABLE: 
// Pinnable tasks can't be launched on top of locktask tasks. 
return !mLockTaskModeTasks.isEmpty(); 
default: 
Slog.w(TAG, "isLockTaskModeViolation: invalid lockTaskAuth value=" + lockTaskAuth); 
return true; 
} 
}

我們再來看TaskRecord的setLockedTaskAuth函數，在新建一個TaskRecord的時候會調用setIntent函數，而setIntent函數又是在TaskRecord的構造函數中調用的。我們來看這個函數mLockTaskAuth的值是根據mLockTaskMode來定的，而mLockTaskMode又是ActivityInfo傳入的，這個值是在PKMS解析AndroidManifest.xml的時候構造的，默認就是LOCK_TASK_LAUNCH_MODE_DEFAULT，而當沒有白名單mLockTaskAuth最後就是LOCK_TASK_AUTH_PINNABLE。

void setLockTaskAuth() { 
if (!mPrivileged && 
(mLockTaskMode == LOCK_TASK_LAUNCH_MODE_ALWAYS || 
mLockTaskMode == LOCK_TASK_LAUNCH_MODE_NEVER)) { 
// Non-priv apps are not allowed to use always or never, fall back to default 
mLockTaskMode = LOCK_TASK_LAUNCH_MODE_DEFAULT; 
} 
switch (mLockTaskMode) { 
case LOCK_TASK_LAUNCH_MODE_DEFAULT: 
mLockTaskAuth = isLockTaskWhitelistedLocked() ? 
LOCK_TASK_AUTH_WHITELISTED : LOCK_TASK_AUTH_PINNABLE; 
break; 
case LOCK_TASK_LAUNCH_MODE_NEVER: 
mLockTaskAuth = LOCK_TASK_AUTH_DONT_LOCK; 
break; 
case LOCK_TASK_LAUNCH_MODE_ALWAYS: 
mLockTaskAuth = LOCK_TASK_AUTH_LAUNCHABLE_PRIV; 
break; 
case LOCK_TASK_LAUNCH_MODE_IF_WHITELISTED: 
mLockTaskAuth = isLockTaskWhitelistedLocked() ? 
LOCK_TASK_AUTH_LAUNCHABLE : LOCK_TASK_AUTH_PINNABLE; 
break; 
} 
if (DEBUG_LOCKTASK) Slog.d(TAG_LOCKTASK, "setLockTaskAuth: task=" + this + 
" mLockTaskAuth=" + lockTaskAuthToString()); 
}

我們再來看isLockTaskModeViolation函數如下代碼，現在是task的mLockTaskAuth 是LOCK_TASK_AUTH_PINNABLE，而當前處於固定屏幕，所以mLockTaskModeTasks不為null，最後返回true。那Activity啟動流程就不能走下去了，那就是代表啟動普通的Activity會被阻止。

case LOCK_TASK_AUTH_PINNABLE: 
// Pinnable tasks can't be launched on top of locktask tasks. 
return !mLockTaskModeTasks.isEmpty();

三、取消固定屏幕

最後我們再來看看取消固定屏幕，取消屏幕會在PhoneStatusBar中取消，但是一定是要有虛擬鍵，原生就是這麼設定的。最後調用了AMS的stopLockTaskModeOnCurrent函數。這個函數主要是調用了stopLockTaskMode函數，這個函數中主要是調用了ActivityStackSupervisor的setLockTaskModeLocked函數，之前在固定屏幕時也是調用了這個函數，但是這裡我們仔細看，其第一個參數為null。

public void stopLockTaskMode() { 
final TaskRecord lockTask = mStackSupervisor.getLockedTaskLocked(); 
if (lockTask == null) { 
// Our work here is done. 
return; 
} 
final int callingUid = Binder.getCallingUid(); 
final int lockTaskUid = lockTask.mLockTaskUid; 
// Ensure the same caller for startLockTaskMode and stopLockTaskMode. 
// It is possible lockTaskMode was started by the system process because 
// android:lockTaskMode is set to a locking value in the application manifest instead of 
// the app calling startLockTaskMode. In this case {@link TaskRecord.mLockTaskUid} will 
// be 0, so we compare the callingUid to the {@link TaskRecord.effectiveUid} instead. 
if (getLockTaskModeState() == ActivityManager.LOCK_TASK_MODE_LOCKED && 
callingUid != lockTaskUid 
&& (lockTaskUid != 0 
|| (lockTaskUid == 0 && callingUid != lockTask.effectiveUid))) { 
throw new SecurityException("Invalid uid, expected " + lockTaskUid 
+ " callingUid=" + callingUid + " effectiveUid=" + lockTask.effectiveUid); 
} 
long ident = Binder.clearCallingIdentity(); 
try { 
Log.d(TAG, "stopLockTaskMode"); 
// Stop lock task 
synchronized (this) { 
mStackSupervisor.setLockTaskModeLocked(null, ActivityManager.LOCK_TASK_MODE_NONE, 
"stopLockTask", true); 
} 
} finally { 
Binder.restoreCallingIdentity(ident); 
} 
}

我們來看下這個函數，如果為空，現在調用getLockedTaskLocked獲取當前固定屏幕的TaskRecord，然後調用removeLockedTaskLocked去除這個TaskRecord，如果還不為null，調用resumeTopActivitiesLocked啟動下個Activity（一般也就是下個屏幕鎖定的TaskRecord的Activity）。

如果為空了，直接返回。但是在我們下次啟動普通的Activity的時候就恢復正常了，因為mLockTaskModeTasks已經為空了。

void setLockTaskModeLocked(TaskRecord task, int lockTaskModeState, String reason, 
boolean andResume) { 
if (task == null) { 
// Take out of lock task mode if necessary 
final TaskRecord lockedTask = getLockedTaskLocked(); 
if (lockedTask != null) { 
removeLockedTaskLocked(lockedTask); 
if (!mLockTaskModeTasks.isEmpty()) { 
// There are locked tasks remaining, can only finish this task, not unlock it. 
if (DEBUG_LOCKTASK) Slog.w(TAG_LOCKTASK, 
"setLockTaskModeLocked: Tasks remaining, can't unlock"); 
lockedTask.performClearTaskLocked(); 
resumeTopActivitiesLocked(); 
return; 
} 
} 
if (DEBUG_LOCKTASK) Slog.w(TAG_LOCKTASK, 
"setLockTaskModeLocked: No tasks to unlock. Callers=" + Debug.getCallers(4)); 
return; 
}

四、沒有虛擬鍵如何取消屏幕固定

前面說過如果沒有虛擬鍵就不能取消屏幕固定了，我們說下幾種方式

1.使用am命令 am task lock stop可以調用am的stopLockTaskMode函數

2.另一種我們可以在Activity.java中修改代碼，比較長按返回鍵調用AMS的stopLockTaskMode方法，下面就是實現，Activity本身提供了stopLockTask就是調用了AMS的stopLockTaskMode方法

public boolean onKeyLongPress(int keyCode, KeyEvent event) { 
if (keyCode == KeyEvent.KEYCODE_BACK) { 
stopLockTask(); 
} 
return false; 
}

以上所述是小編給大家介紹的Android6.0 屏幕固定功能詳解，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對本站網站的支持！