使用方式

一般使用

Toast.makeText(this,"Short Toast", Toast.LENGTH_SHORT).show();

自定义Toast，通过如下接口注入自定义视图

##Toast.java##
public void setView(View view) {mNextView = view;
}

接下来步入正题，Toast的显示流程

Toast流程分析

显示show()

从show方法开始，自定义toast会创建Toast.TN binder对象，用于与NMS交互；最终将toast相关信息转入NMS入队

##Toast.java##public void show() {//..//1.获取NMSINotificationManager service = getService();String pkg = mContext.getOpPackageName();//2.创建TN，用于与NMS通信的binder对象，自定义的toast会用到TN tn = mTN;//3.自定义toast视图tn.mNextView = mNextView;final int displayId = mContext.getDisplayId();//4.调用NMS接口toast入队（主要区别为自定义toast会传入TN参数，后续用来与NMS交互）try {if (Compatibility.isChangeEnabled(CHANGE_TEXT_TOASTS_IN_THE_SYSTEM)) {if (mNextView != null) {// It's a custom toastservice.enqueueToast(pkg, mToken, tn, mDuration, displayId);} else {// It's a text toastITransientNotificationCallback callback =new CallbackBinder(mCallbacks, mHandler);service.enqueueTextToast(pkg, mToken, mText, mDuration, displayId, callback);}} else {service.enqueueToast(pkg, mToken, tn, mDuration, displayId);}} catch (RemoteException e) {// Empty}
}

NMS中的入队流程，入队接口最终汇入同一主流；显示会进行一系列前置条件判断；之后会判断当前toast是否存在于队列中，存在则直接刷新；反之，则将消息封装成ToastRecord则进行入队；
若入队为首个，则直接开始调度显示showNextToastLocked()
PS：入队之前还会有一个门槛，NMS会有单应用toast个数阈值，阈值以下，正常入队，阈值以上则直接拦截；直到该应用toast个数消费小于阈值后可正常入队（推测这也是android的一种防攻击降负载的策略）

##NotificationManagerService.java##final IBinder mService = new INotificationManager.Stub() {@Overridepublic void enqueueTextToast(String pkg, IBinder token, CharSequence text, int duration,int displayId, @Nullable ITransientNotificationCallback callback) {enqueueToast(pkg, token, text, null, duration, displayId, callback);}@Overridepublic void enqueueToast(String pkg, IBinder token, ITransientNotification callback,int duration, int displayId) {enqueueToast(pkg, token, null, callback, duration, displayId, null);}private void enqueueToast(String pkg, IBinder token, @Nullable CharSequence text,@Nullable ITransientNotification callback, int duration, int displayId,@Nullable ITransientNotificationCallback textCallback) {//...synchronized (mToastQueue) {int callingPid = Binder.getCallingPid();long callingId = Binder.clearCallingIdentity();try {ToastRecord record;int index = indexOfToastLocked(pkg, token);// 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) {//1.相同toast只更新时长，不改变位置record = mToastQueue.get(index);record.update(duration);} else {// Limit the number of toasts that any given package can enqueue.// Prevents DOS attacks and deals with leaks.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++;//2.队列中同包名toast大于阈值，则直接return，不入队if (count >= MAX_PACKAGE_NOTIFICATIONS) {Slog.e(TAG, "Package has already posted " + count+ " toasts. Not showing more. Package=" + pkg);return;}}}Binder windowToken = new Binder();mWindowManagerInternal.addWindowToken(windowToken, TYPE_TOAST, displayId);//3.将toast信息封装为ToastRecordrecord = getToastRecord(callingUid, callingPid, pkg, token, text, callback,duration, windowToken, displayId, textCallback);//4.入队mToastQueue.add(record);index = mToastQueue.size() - 1;keepProcessAliveForToastIfNeededLocked(callingPid);}// If it's at index 0, it's the current toast.  It doesn't matter if it's// new or just been updated, show it.// If the callback fails, this will remove it from the list, so don't// assume that it's valid after this.if (index == 0) {//5.显示toastshowNextToastLocked();}} finally {Binder.restoreCallingIdentity(callingId);}}}

再来看下Toast信息封装成ToastRecord部分getToastRecord()；ToastRecord为抽象类，实现类分别为:
TextToastRecord ：默认文本类Toast
CustomToastRecord ：自定义Toast
此处的callback实现即为Toast.TN，自定义Toast时会创建传入非空

##NotificationManagerService.java##private ToastRecord getToastRecord(int uid, int pid, String packageName, IBinder token,@Nullable CharSequence text, @Nullable ITransientNotification callback, int duration,Binder windowToken, int displayId,@Nullable ITransientNotificationCallback textCallback) {if (callback == null) {return new TextToastRecord(this, mStatusBar, uid, pid, packageName, token, text,duration, windowToken, displayId, textCallback);} else {return new CustomToastRecord(this, uid, pid, packageName, token, callback, duration,windowToken, displayId);}
}

接着第2点，NMS中调度Toast显示showNextToastLocked()，while循环，取出列表首个record进行显示

##NotificationManagerService.java##void showNextToastLocked() {ToastRecord record = mToastQueue.get(0);while (record != null) {//Toast显示if (record.show()) {//成功则启动退出的延迟计时scheduleDurationReachedLocked(record);return;}//失败则取出下一个int index = mToastQueue.indexOf(record);if (index >= 0) {mToastQueue.remove(index);}record = (mToastQueue.size() > 0) ? mToastQueue.get(0) : null;}
}

ToastRecord中的show()，如第3点可知，此处存在两种业务
(1) 先看默认文本类Toast：TextToastRecord ；此处的mStatusBar为StatusBarManagerService的binder代理

##TextToastRecord.java##
//...
private final StatusBarManagerInternal mStatusBar;
//...
@Override
public boolean show() {if (DBG) {Slog.d(TAG, "Show pkg=" + pkg + " text=" + text);}if (mStatusBar == null) {Slog.w(TAG, "StatusBar not available to show text toast for package " + pkg);return false;}mStatusBar.showToast(uid, pkg, token, text, windowToken, getDuration(), mCallback);return true;
}

再来看StatusBarManagerService，又会通过IStatusBar的binder将信息传入下一级，IStatusBar又是哪位的代理?！SystemUI

##StatusBarManagerService.java##private volatile IStatusBar mBar;
@Override
public void showToast(int uid, String packageName, IBinder token, CharSequence text,IBinder windowToken, int duration,@Nullable ITransientNotificationCallback callback) {if (mBar != null) {try {mBar.showToast(uid, packageName, token, text, windowToken, duration, callback);} catch (RemoteException ex) { }}
}

SystemUI中存在一个叫CommandQueue的类，实现了该binder接口；之后Handler消息调度，将消息传递至CommandQueue.Callbacks转出

##CommandQueue##public class CommandQueue extends IStatusBar.Stub implements CallbackController<Callbacks>,DisplayManager.DisplayListener {@Overridepublic void showToast(int uid, String packageName, IBinder token, CharSequence text,IBinder windowToken, int duration, @Nullable ITransientNotificationCallback callback) {synchronized (mLock) {//参数赋值mHandler.obtainMessage(MSG_SHOW_TOAST, args).sendToTarget();}
}//Handler实现：
case MSG_SHOW_TOAST: {args = (SomeArgs) msg.obj;String packageName = (String) args.arg1;IBinder token = (IBinder) args.arg2;CharSequence text = (CharSequence) args.arg3;IBinder windowToken = (IBinder) args.arg4;ITransientNotificationCallback callback =(ITransientNotificationCallback) args.arg5;int uid = args.argi1;int duration = args.argi2;for (Callbacks callbacks : mCallbacks) {callbacks.showToast(uid, packageName, token, text, windowToken, duration,callback);}break;
}

这里虽然通过遍历Callbacks集合回调，但所有的Callbacks中只有一处真正实现了showToast()接口，就是SystemUI中的ToastUI
ToastUI在启动时即会将自身注册至CommandQueue中，至此便到了Toast显示的最后一步
ToastPresenter

##ToastUI.java##@Override
public void start() {mCommandQueue.addCallback(this);
}@Override
@MainThread
public void showToast(int uid, String packageName, IBinder token, CharSequence text,IBinder windowToken, int duration, @Nullable ITransientNotificationCallback callback) {if (mPresenter != null) {hideCurrentToast();}Context context = mContext.createContextAsUser(UserHandle.getUserHandleForUid(uid), 0);View view = ToastPresenter.getTextToastView(context, text);mCallback = callback;mPresenter = new ToastPresenter(context, mAccessibilityManager, mNotificationManager,packageName);mPresenter.show(view, token, windowToken, duration, mGravity, 0, mY, 0, 0, mCallback);
}

ToastPresenter为android系统提供的API，show方法中会进行layoutParams调整，同时移除之前；最终调用WMS的addView添加窗口，完成Toast的显示
从createLayoutParams()方法中，可以看出Toast视图的统一层级为：WindowManager.LayoutParams.TYPE_TOAST；
PS：推测google通过ToastPresenter来统一Toast的显示，规范层级使用

##ToastPresenter.java##/*** Shows the toast in {@code view} with the parameters passed and callback {@code callback}.*/
public void show(View view, IBinder token, IBinder windowToken, int duration, int gravity,int xOffset, int yOffset, float horizontalMargin, float verticalMargin,@Nullable ITransientNotificationCallback callback) {checkState(mView == null, "Only one toast at a time is allowed, call hide() first.");mView = view;mToken = token;//根据Toast参数重新调整默认layoutParamsadjustLayoutParams(mParams, windowToken, duration, gravity, xOffset, yOffset,horizontalMargin, verticalMargin);if (mView.getParent() != null) {mWindowManager.removeView(mView);}try {//WMS添加窗口mWindowManager.addView(mView, mParams);} catch (WindowManager.BadTokenException e) {// Since the notification manager service cancels the token right after it notifies us// to cancel the toast there is an inherent race and we may attempt to add a window// after the token has been invalidated. Let us hedge against that.Log.w(TAG, "Error while attempting to show toast from " + mPackageName, e);return;}trySendAccessibilityEvent(mView, mPackageName);if (callback != null) {try {callback.onToastShown();} catch (RemoteException e) {Log.w(TAG, "Error calling back " + mPackageName + " to notify onToastShow()", e);}}
}/*** Creates {@link WindowManager.LayoutParams} with default values for toasts.*/
private WindowManager.LayoutParams createLayoutParams() {WindowManager.LayoutParams params = new WindowManager.LayoutParams();params.height = WindowManager.LayoutParams.WRAP_CONTENT;params.width = WindowManager.LayoutParams.WRAP_CONTENT;params.format = PixelFormat.TRANSLUCENT;params.windowAnimations = R.style.Animation_Toast;//指定视图层级params.type = WindowManager.LayoutParams.TYPE_TOAST;params.setFitInsetsIgnoringVisibility(true);params.setTitle(WINDOW_TITLE);params.flags = WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON| WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;setShowForAllUsersIfApplicable(params, mPackageName);return params;
}

至此，默认文本类的TextToastRecord流程结束

(2)自定义Toast：CustomToastRecord；此处的callback是否有点熟悉？对，没错，就是之前提到的自定义Toast会创建一个用于与NMS交互的binder - Toast.TN

##CustomToastRecord.java##public final ITransientNotification callback;
@Override
public boolean show() {if (DBG) {Slog.d(TAG, "Show pkg=" + pkg + " callback=" + callback);}try {callback.show(windowToken);return true;} catch (RemoteException e) {Slog.w(TAG, "Object died trying to show custom toast " + token + " in package "+ pkg);mNotificationManager.keepProcessAliveForToastIfNeeded(pid);return false;}
}

Toast.TN，show()方法也是通过Handler调度；一路看下去可发现；最终也是通过ToastPresenter进行最终的显示

##Toast.java##private static class TN extends ITransientNotification.Stub {@Override@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023)public void show(IBinder windowToken) {if (localLOGV) Log.v(TAG, "SHOW: " + this);mHandler.obtainMessage(SHOW, windowToken).sendToTarget();}
}
//Handler调度
case SHOW: {IBinder token = (IBinder) msg.obj;handleShow(token);break;
}
//show业务实现
public void handleShow(IBinder windowToken) {if (localLOGV) Log.v(TAG, "HANDLE SHOW: " + this + " mView=" + mView+ " mNextView=" + mNextView);// If a cancel/hide is pending - no need to show - at this point// the window token is already invalid and no need to do any work.if (mHandler.hasMessages(CANCEL) || mHandler.hasMessages(HIDE)) {return;}if (mView != mNextView) {// remove the old view if necessaryhandleHide();mView = mNextView;mPresenter.show(mView, mToken, windowToken, mDuration, mGravity, mX, mY,mHorizontalMargin, mVerticalMargin,new CallbackBinder(getCallbacks(), mHandler));}
}

显示流程小总结：

默认文本类Toast：（分别跨越了app，system_server，systemui三个进程）
Toast -> NMS -> TextToastRecord -> StatusBarManagerService -> CommandQueue -> ToastUI -> ToastPresenter

自定义类Toast：（跨越了app，system_server两个进程）
Toast -> NMS -> CustomToastRecord -> Toast.TN -> ToastPresenter
至此，Toast已经走完了显示的所有流程，正常显示在了屏幕上；如何退出的呢？

延迟退出计时

回到第4点中所讲的；record.show()流程无异常都会返回true，进行后续流程显示；延迟退出则通过scheduleDurationReachedLocked(record)

##NotificationManagerService.java##@GuardedBy("mToastQueue")
void showNextToastLocked() {ToastRecord record = mToastQueue.get(0);while (record != null) {if (record.show()) {scheduleDurationReachedLocked(record);return;}int index = mToastQueue.indexOf(record);if (index >= 0) {mToastQueue.remove(index);}record = (mToastQueue.size() > 0) ? mToastQueue.get(0) : null;}
}

延迟的业务即通过Handler发送延迟消息，此处我们在Toast中设置的时长就会排上用场；
默认情况下：Toast.LENGTH_LONG - 3.5s，Toast.LENGTH_SHORT - 2s；
当然，此时长也会受其他因素的影响，即：无障碍辅助功能；注释也很清楚，如下；
辅助功能用户可能需要更长的超时时间。该api将原始延迟与用户的偏好进行比较，并返回较长的延迟。如果没有偏好，则返回原始延迟。
对应会在Settings中存在设置项：本地模拟器Pixel（API_30），设置-无障碍-等待操作的时长可进行时长或默认设置

##NotificationManagerService.java##//PhoneWindowManager中此处定义为3.5s
static final int LONG_DELAY = PhoneWindowManager.TOAST_WINDOW_TIMEOUT;
static final int SHORT_DELAY = 2000; // 2 secondsprivate void scheduleDurationReachedLocked(ToastRecord r)
{mHandler.removeCallbacksAndMessages(r);Message m = Message.obtain(mHandler, MESSAGE_DURATION_REACHED, r);//默认时长计算int delay = r.getDuration() == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;//无障碍功能对delay的影响// Accessibility users may need longer timeout duration. This api compares original delay// with user's preference and return longer one. It returns original delay if there's no// preference.delay = mAccessibilityManager.getRecommendedTimeoutMillis(delay,AccessibilityManager.FLAG_CONTENT_TEXT);mHandler.sendMessageDelayed(m, delay);
}

退出cancel()

延迟计时结束后；最后就来到的Toast的退出；延迟消息到达走如下方法

##NotificationManagerService.java##private void handleDurationReached(ToastRecord record)
{if (DBG) Slog.d(TAG, "Timeout pkg=" + record.pkg + " token=" + record.token);synchronized (mToastQueue) {int index = indexOfToastLocked(record.pkg, record.token);if (index >= 0) {cancelToastLocked(index);}}
}

cancelToastLocked()具体业务如下；获取对应的ToastRecord对象，调用hide()方法；最后判断，Toast队列非空则重新开始调度显示下一个Toast

##NotificationManagerService.java##void cancelToastLocked(int index) {ToastRecord record = mToastQueue.get(index);record.hide();ToastRecord lastToast = mToastQueue.remove(index);mWindowManagerInternal.removeWindowToken(lastToast.windowToken, false /* removeWindows */,lastToast.displayId);// We passed 'false' for 'removeWindows' so that the client has time to stop// rendering (as hide above is a one-way message), otherwise we could crash// a client which was actively using a surface made from the token. However// we need to schedule a timeout to make sure the token is eventually killed// one way or another.scheduleKillTokenTimeout(lastToast);keepProcessAliveForToastIfNeededLocked(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();}
}

ToastRecord的hide()方法与show()方法流程大致相同，此处不再过多赘述，最终都是到ToastPresenter中，通过WMS接口立即移除视图

##ToastPresenter.java##public void hide(@Nullable ITransientNotificationCallback callback) {checkState(mView != null, "No toast to hide.");if (mView.getParent() != null) {mWindowManager.removeViewImmediate(mView);}try {mNotificationManager.finishToken(mPackageName, mToken);} catch (RemoteException e) {Log.w(TAG, "Error finishing toast window token from package " + mPackageName, e);}if (callback != null) {try {callback.onToastHidden();} catch (RemoteException e) {Log.w(TAG, "Error calling back " + mPackageName + " to notify onToastHide()", e);}}mView = null;mToken = null;
}

Toast的显示/隐藏回调；接口如下，CallbackBinder为binder对象，把收到的toast显示状态传递到Callback给到外部使用者；那CallbackBinder的状态又是哪里传递的呢？在ToastPresenter中

##Toast.java##public abstract static class Callback {/*** Called when the toast is displayed on the screen.*/public void onToastShown() {}/*** Called when the toast is hidden.*/public void onToastHidden() {}
}private static class CallbackBinder extends ITransientNotificationCallback.Stub {@Overridepublic void onToastShown() {mHandler.post(() -> {for (Callback callback : getCallbacks()) {callback.onToastShown();}});}@Overridepublic void onToastHidden() {mHandler.post(() -> {for (Callback callback : getCallbacks()) {callback.onToastHidden();}});}
}

分别在show与hide时进行状态回调；不同在于：
默认类Toast的最终显示是在SystemUI进程的ToastPresenter，因此回调需要跨进程
自定义类Toast的最终显示是在App进程（准确来讲是调用Toast.show()方法的进程）Toast.TN的ToastPresenter中，因此回调不会涉及跨进程
感兴趣的话可以自行看下这两种CallbackBinder的创建与注入即可。

##ToastPresenter.java##public void show(View view, IBinder token, IBinder windowToken, int duration, int gravity,int xOffset, int yOffset, float horizontalMargin, float verticalMargin,@Nullable ITransientNotificationCallback callback) {//..if (callback != null) {try {callback.onToastShown();} catch (RemoteException e) {Log.w(TAG, "Error calling back " + mPackageName + " to notify onToastShow()", e);}}
}public void hide(@Nullable ITransientNotificationCallback callback) {//..if (callback != null) {try {callback.onToastHidden();} catch (RemoteException e) {Log.w(TAG, "Error calling back " + mPackageName + " to notify onToastHide()", e);}}//..
}

时序图

附上时序图

到这里Toast流程分析便告一段落，over

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