Toast源碼分析
1、概述
Toast是android中經常使用的提示框，系統通過WindowManager.addView()方法在頂層window視窗添加的視圖，是以Toast顯示時可以不依賴Activity界面和應用程式當我們把Toast添加到WindowManager程序時，使用者應用程式退出時toast依然可以顯示并列印，WindowManager和應用程式是不同程序級别的應用是以不會出現子線程更新UI問題（子線程更新UI實質是建立視圖線程和更新視圖線程不一緻導緻系統抛出的異常）。
2、原理分析
Toast通過Toast.makeText()方法建立，調用makeText方法時，系統建立Toast執行個體，并且填充Toast視圖布局
public static Toast makeText(Context context, CharSequence text, @Duration int duration) {
Toast result = new Toast(context);
LayoutInflater inflate = (LayoutInflater)
context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null);
TextView tv = (TextView)v.findViewById(com.android.internal.R.id.message);
tv.setText(text);
result.mNextView = v;
result.mDuration = duration;
return result;
}
Toast建立後通過Toast.show()方法顯示,在show方法中通過getSerice()方法擷取到INotificationManager的代理對象,擷取目前Toast建立應用的包名，組裝TN對象，通過遠端代理調用INotificationManager中的enqueueToast方法，把Toast加入到Toast隊列中，并傳遞包名，TN對象，和顯示時長。
public void show() {
if (mNextView == null) {
throw new RuntimeException("setView must have been called");
}
INotificationManager service = getService();
String pkg = mContext.getOpPackageName();
TN tn = mTN;
tn.mNextView = mNextView;
try {
service.enqueueToast(pkg, tn, mDuration);
} catch (RemoteException e) {
// Empty
}
}
static private INotificationManager getService() {
if (sService != null) {
return sService;
}
sService = INotificationManager.Stub.asInterface(ServiceManager.getService("notification"));
return sService;
}
在INotificationManager的實作類中NotificationManagerService.enqueueToast方法中，判斷NotificationManager中Toast隊列中是否存在目前Toast對象，存在目前對象時更新toast顯示時長，第一次添加toast時不存在，,擷取Toast顯示應用程式是否是系統程式，不是系統程式時限制toast顯示數量最多不超過50，不超過50時建立ToastRecord對象，添加到mToastQueue隊列中，第一次建立Toast時在ToastRecord中不存在傳回-1，建立Toast加入到ToastRecord後指派為0，通過調用showNextToastLocked方法顯示toast視圖。
private final IBinder mService = new INotificationManager.Stub() {
// Toasts
// ============================================================================
@Override
public void enqueueToast(String pkg, ITransientNotification callback, int duration)
{
if (DBG) {
Slog.i(TAG, "enqueueToast pkg=" + pkg + " callback=" + callback
+ " duration=" + duration);
}
if (pkg == null || callback == null) {
Slog.e(TAG, "Not doing toast. pkg=" + pkg + " callback=" + callback);
return ;
}
final boolean isSystemToast = isCallerSystem() || ("android".equals(pkg));
final boolean isPackageSuspended =
isPackageSuspendedForUser(pkg, Binder.getCallingUid());
if (ENABLE_BLOCKED_TOASTS && (!noteNotificationOp(pkg, Binder.getCallingUid())
|| isPackageSuspended)) {
if (!isSystemToast) {
Slog.e(TAG, "Suppressing toast from package " + pkg
+ (isPackageSuspended
? " due to package suspended by administrator."
: " by user request."));
return;
}
}
synchronized (mToastQueue) {
int callingPid = Binder.getCallingPid();
long callingId = Binder.clearCallingIdentity();
try {
ToastRecord record;
int index = indexOfToastLocked(pkg, callback);
// If it's already in the queue, we update it in place, we don't
// move it to the end of the queue.
if (index >= 0) {
record = mToastQueue.get(index);
record.update(duration);
} else {
// Limit the number of toasts that any given package except the android
// package can enqueue. Prevents DOS attacks and deals with leaks.
if (!isSystemToast) {
int count = 0;
final int N = mToastQueue.size();
for (int i=0; i<N; i++) {
final ToastRecord r = mToastQueue.get(i);
if (r.pkg.equals(pkg)) {
count++;
if (count >= MAX_PACKAGE_NOTIFICATIONS) {
Slog.e(TAG, "Package has already posted " + count
+ " toasts. Not showing more. Package=" + pkg);
return;
}
}
}
}
Binder token = new Binder();
mWindowManagerInternal.addWindowToken(token,
WindowManager.LayoutParams.TYPE_TOAST);
record = new ToastRecord(callingPid, pkg, callback, duration, token);
mToastQueue.add(record);
index = mToastQueue.size() - 1;
keepProcessAliveIfNeededLocked(callingPid);
}
// If it's at index 0, it's the current toast. It doesn't matter if it's
// new or just been updated. Call back and tell it to show itself.
// If the callback fails, this will remove it from the list, so don't
// assume that it's valid after this.
if (index == 0) {
showNextToastLocked();
}
} finally {
Binder.restoreCallingIdentity(callingId);
}
}
}
在showNextToastLocked中，調用record.callback.show方法顯示toast視圖，record.callback是調用enqueueToast中傳遞的TN對象，調用tn.show方法發現是通過Handler發送資料給Handler對象處理，在Handler.handleMessage方法中調用handleShow方法，handleShow方法中調用handleHide()方法隐藏以前Toast的視圖，通過WindowManager.addView()添加toast視圖到頂層的window視窗。
void showNextToastLocked() {
ToastRecord record = mToastQueue.get(0);
while (record != null) {
if (DBG) Slog.d(TAG, "Show pkg=" + record.pkg + " callback=" + record.callback);
try {
record.callback.show(record.token);
scheduleTimeoutLocked(record);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Object died trying to show notification " + record.callback
+ " in package " + record.pkg);
// remove it from the list and let the process die
int index = mToastQueue.indexOf(record);
if (index >= 0) {
mToastQueue.remove(index);
}
keepProcessAliveIfNeededLocked(record.pid);
if (mToastQueue.size() > 0) {
record = mToastQueue.get(0);
} else {
record = null;
}
}
}
}
public void show(IBinder windowToken) {
if (localLOGV) Log.v(TAG, "SHOW: " + this);
mHandler.obtainMessage(0, windowToken).sendToTarget();
}
final Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
IBinder token = (IBinder) msg.obj;
handleShow(token);
}
};
public void (IBinder windowToken) {
if (localLOGV) Log.v(TAG, "HANDLE SHOW: " + this + " mView=" + mView
+ " mNextView=" + mNextView);
if (mView != mNextView) {
// remove the old view if necessary
handleHide();
mView = mNextView;
Context context = mView.getContext().getApplicationContext();
String packageName = mView.getContext().getOpPackageName();
if (context == null) {
context = mView.getContext();
}
mWM = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
// We can resolve the Gravity here by using the Locale for getting
// the layout direction
final Configuration config = mView.getContext().getResources().getConfiguration();
final int gravity = Gravity.getAbsoluteGravity(mGravity, config.getLayoutDirection());
mParams.gravity = gravity;
if ((gravity & Gravity.HORIZONTAL_GRAVITY_MASK) == Gravity.FILL_HORIZONTAL) {
mParams.horizontalWeight = 1.0f;
}
if ((gravity & Gravity.VERTICAL_GRAVITY_MASK) == Gravity.FILL_VERTICAL) {
mParams.verticalWeight = 1.0f;
}
mParams.x = mX;
mParams.y = mY;
mParams.verticalMargin = mVerticalMargin;
mParams.horizontalMargin = mHorizontalMargin;
mParams.packageName = packageName;
mParams.hideTimeoutMilliseconds = mDuration ==
Toast.LENGTH_LONG ? LONG_DURATION_TIMEOUT : SHORT_DURATION_TIMEOUT;
mParams.token = windowToken;
if (mView.getParent() != null) {
if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this);
mWM.removeView(mView);
}
if (localLOGV) Log.v(TAG, "ADD! " + mView + " in " + this);
mWM.addView(mView, mParams);
trySendAccessibilityEvent();
}
}
在NotificationManagerService中調用record.callback.show()方法後，通過scheduleTimeoutLocked(）方法通過Handler延時發送隐藏toast視圖後，重新周遊toastRecord隊列顯示下個toast。
private void scheduleTimeoutLocked(ToastRecord r)
{
mHandler.removeCallbacksAndMessages(r);
Message m = Message.obtain(mHandler, MESSAGE_TIMEOUT, r);
long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;
mHandler.sendMessageDelayed(m, delay);
}
mHandler = new WorkerHandler();
private final class WorkerHandler extends Handler
{
@Override
public void handleMessage(Message msg)
{
switch (msg.what)
{
case MESSAGE_TIMEOUT:
handleTimeout((ToastRecord)msg.obj);
break;
case MESSAGE_SAVE_POLICY_FILE:
handleSavePolicyFile();
break;
case MESSAGE_SEND_RANKING_UPDATE:
handleSendRankingUpdate();
break;
case MESSAGE_LISTENER_HINTS_CHANGED:
handleListenerHintsChanged(msg.arg1);
break;
case MESSAGE_LISTENER_NOTIFICATION_FILTER_CHANGED:
handleListenerInterruptionFilterChanged(msg.arg1);
break;
}
}
}
private void handleTimeout(ToastRecord record)
{
if (DBG) Slog.d(TAG, "Timeout pkg=" + record.pkg + " callback=" + record.callback);
synchronized (mToastQueue) {
int index = indexOfToastLocked(record.pkg, record.callback);
if (index >= 0) {
cancelToastLocked(index);
}
}
}
void cancelToastLocked(int index) {
ToastRecord record = mToastQueue.get(index);
try {
record.callback.hide();
} catch (RemoteException e) {
Slog.w(TAG, "Object died trying to hide notification " + record.callback
+ " in package " + record.pkg);
// don't worry about this, we're about to remove it from
// the list anyway
}
ToastRecord lastToast = mToastQueue.remove(index);
mWindowManagerInternal.removeWindowToken(lastToast.token, true);
keepProcessAliveIfNeededLocked(record.pid);
if (mToastQueue.size() > 0) {
// Show the next one. If the callback fails, this will remove
// it from the list, so don't assume that the list hasn't changed
// after this point.
showNextToastLocked();
}
}
3、總結
Toast是通過WindowManager.addView()添加到window視窗的，當把toast添加到NotificationManager中的ToastRecord隊列時，應用程式退出後依然顯示toast視圖，Toast視圖是WindowManager程序中顯示的，是以調用Toast.show時，可以不考慮線程問題（子線程更新UI實質是建立視圖線程和更新視圖線程不一緻導緻系統抛出的異常），但是Toast依賴于Handler消息機制，在子線程中Looper.perpase()沒有調用，在子線程中直接使用Toast.show時會抛Can’t create handler inside thread that has not called Looper.prepare()異常，在子線程中列印toast時 可以使用一下方法，在子線程Looper.loop()時子線程會堵塞。
new Thread(new Runnable() {
@Override
public void run() {
Looper.prepare();
Toast.makeText(MainActivity.this,"dfadf",Toast.LENGTH_SHORT).show();
Looper.loop();
Log.e(TAG, "run: " );
}
}).start();
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