前言
上次看到有人說(shuō)Toast屬于UI操作，只能在主線程中使用。其實(shí)不是這樣的，Toast是特殊的UI操作，由系統(tǒng)管理，我們只需在線程中創(chuàng)建MessageQueue和Looper讓Toast能夠回調(diào)當(dāng)前線程即可在任意線程使用，主線程由于屬于ActivityThread，默認(rèn)創(chuàng)建了消息隊(duì)列，所以可以直接使用Toast，Thread中則需要：
Looper.prepare();
Toast.makeText(context,text,duration).show();
Looper.loop();
注意：
- 文中大量涉及到進(jìn)程間通訊機(jī)制Binder的使用，建議先看些Binder的資料
- 文中源碼過(guò)長(zhǎng)的有省略，想要閱讀源碼的朋友可以在這兩個(gè)網(wǎng)站上查看：1、http://androidxref.com 2、 http://www.grepcode.com/
下面結(jié)合源碼詳細(xì)介紹一下Toast的顯示之路，為了方便理解，先展示UML圖：
總結(jié)
因?yàn)槊總€(gè)Toast顯示時(shí)間可能沖突，因此需要一個(gè)管理者來(lái)統(tǒng)一管理他們，在一個(gè)隊(duì)列中一個(gè)一個(gè)顯示，所以要使用管理者（NMS）的binder引用將Toast入隊(duì)，顯示又要調(diào)用使用線程的binder引用，因此Toast的顯示大量用到了進(jìn)程間通信。
- 在使用線程中調(diào)用Toast.makeText(),創(chuàng)建一個(gè)Toast實(shí)例
- 調(diào)用toast.show();在這個(gè)方法中又調(diào)用getService()獲取NotificationManagerService的binder引用，將toast和mTN（繼承自ITransientNotification.Stub的TN類的實(shí)例，用來(lái)提供給NMS一個(gè)Binder引用，需要顯示Toast時(shí)可以調(diào)用TN的方法）等信息enqueue(),插入NMS中的待顯示序列。
- 輪到某個(gè)Toast顯示時(shí)，在NMS中調(diào)用TN類的show()方法，在show方法中又通過(guò)handler在使用線程中直接獲取WindowManagerImpl然后addView，將Toast添加在Window中。
- 顯示的同時(shí)NMS也發(fā)送了一個(gè)延時(shí)消息，顯示時(shí)間過(guò)后就會(huì)調(diào)用ＴＮ的hide()方法，通過(guò)handler在使用線程中調(diào)用WindowManagerImpl的removeVIew()方法刪除該Toast
序列圖.png
源碼分析
Toast的創(chuàng)建
創(chuàng)建Toast我們都會(huì)，最簡(jiǎn)單的方法就是 makeText();
看一下源碼：
public static Toast makeText(Context context, CharSequence text, @Duration int duration) {
//創(chuàng)建一個(gè)Toast
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);
//Toast中要顯示的TextView
TextView tv = (TextView)v.findViewById(com.android.internal.R.id.message);
tv.setText(text);
result.mNextView = v;
//Toast顯示的時(shí)間
result.mDuration = duration;
return result;
}
重要語(yǔ)句已注釋，現(xiàn)在我們知道在調(diào)用makeText時(shí)返回值就是創(chuàng)建完畢的Toast。下面看show()方法。
加入NMS的Toast隊(duì)列
系統(tǒng)中有可能很多程序都想要顯示Toast，如果同時(shí)出現(xiàn)就失去了原有的作用，因此必須有一個(gè)管理者來(lái)統(tǒng)一管理所有需要顯示的Toast，這個(gè)管理者就是系統(tǒng)服務(wù)之一：NotificationManagerService
public void show() {
if (mNextView == null) {
throw new RuntimeException("setView must have been called");
}
//獲取NotificationManagerService的客戶端
INotificationManager service = getService();
String pkg = mContext.getOpPackageName();
//tn是系統(tǒng)將會(huì)調(diào)用的回調(diào)，來(lái)真正實(shí)現(xiàn)將Toast顯示在當(dāng)前Window
TN tn = mTN;
tn.mNextView = mNextView;
try {
service.enqueueToast(pkg, tn, mDuration);
} catch (RemoteException e) {
// Empty
}
}
看到這里，我們發(fā)現(xiàn)了兩個(gè)重要的類，INotificationManager和TN。
INotificationManager：（AIDL聲明的接口，具體實(shí)現(xiàn)在INotificationManager.Stub里,而系統(tǒng)服務(wù)NotificationManagerService正式繼承了INOtificationManager.Stub）是系統(tǒng)服務(wù)NMS在本地的binder引用，也就是客戶端，我們要跨進(jìn)程調(diào)用NMS的方法就要用到它。獲取方法：
static private INotificationManager getService() {
if (sService != null) {
return sService;
}
sService = INotificationManager.Stub.asInterface(ServiceManager.getService("notification"));
return sService;
}
TN:是真正實(shí)現(xiàn)將Toast顯示到當(dāng)前Window的工具，它繼承自ITransientNotification.Stub，也就是一個(gè)服務(wù)端，NMS可以調(diào)用TN的binder引用來(lái)調(diào)用TN的show()和hide()方法來(lái)顯示隱藏Toast。
通過(guò)調(diào)用NotificationManagerService的enqueue()方法,很明顯是要把包名，回調(diào)、顯示時(shí)間發(fā)送過(guò)去統(tǒng)一排隊(duì)，一個(gè)一個(gè)顯示。下面看看排隊(duì)時(shí)發(fā)生了什么
NMS回調(diào)TN
排隊(duì)時(shí)發(fā)生了什么呢，貼上源碼：重要的就是這個(gè)同步的部分，前面省略
synchronized (mToastQueue) {
//這里獲取請(qǐng)求線程的pid和Uid
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.
//英文注釋很清楚了，這個(gè)index表示這條Toast是不是已經(jīng)存在在隊(duì)列中且尚未顯示，如果是，則刷新。
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;
}
}
}
}
record = new ToastRecord(callingPid, pkg, callback, duration);
mToastQueue.add(record);
index = mToastQueue.size() - 1;
keepProcessAliveLocked(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);
}
}
這其中的內(nèi)容主要就是判斷一下Toast在index中位置是不是0，如果是，就顯示，不是，就刷新自己。下面還要看看showNextToastLocked();
private void showNextToastLocked() {
ToastRecord record = mToastQueue.get(0);
while (record != null) {
if (DBG) Slog.d(TAG, "Show pkg=" + record.pkg + " callback=" + record.callback);
try {
//正主終于來(lái)了，當(dāng)年存入ToastRecord的回調(diào)終于派上用場(chǎng)，這里調(diào)用的，就是TN的show方法。
record.callback.show();
//計(jì)算好時(shí)間，顯示既定時(shí)間之后就刪除，這個(gè)函數(shù)一會(huì)兒再說(shuō)。
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);
}
keepProcessAliveLocked(record.pid);
if (mToastQueue.size() > 0) {
record = mToastQueue.get(0);
} else {
record = null;
}
}
}
}
剛才終于通過(guò)binder引用回調(diào)了TN的show方法，那么我們回過(guò)頭去看：
TN調(diào)用WMS顯示Toast
代碼很長(zhǎng)，但是總結(jié)一下其實(shí)就是在請(qǐng)求線程中執(zhí)行handleShow()方法，利用WindowManager的addView()方法，在Window中添加toast。
@Override
public void show() {
if (localLOGV) Log.v(TAG, "SHOW: " + this);
mHandler.post(mShow);
}
final Runnable mShow = new Runnable() {
@Override
public void run() {
handleShow();
}
};
public void handleShow() {
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;
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();
}
}
NMS回調(diào)TN
在NMS中又是怎么計(jì)時(shí)的呢，還記得剛才在回調(diào)TN的show()方法之后調(diào)用的方法嗎？scheduleTimeoutLocked();
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);
}
很簡(jiǎn)單的一個(gè)函數(shù)，取需要顯示的時(shí)間delay，然后發(fā)送一個(gè)延遲delay時(shí)間的消息，并且將ToastRecorder對(duì)象傳遞過(guò)去，這個(gè)消息是干嘛呢，繼續(xù)往下看：
private final class WorkerHandler extends Handler
{
@Override
public void handleMessage(Message msg)
{
switch (msg.what)
{
case MESSAGE_TIMEOUT:
handleTimeout((ToastRecord)msg.obj);
break;
}
}
}
收到消息后，執(zhí)行handleTimeOut方法，并且將該ToastRecorder對(duì)象傳遞過(guò)去：
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);
}
}
}
直接看最后一句，cancelToastLocked，在一個(gè)Toast顯示的時(shí)候其他Toast不能顯示，現(xiàn)在肯定是先取消這個(gè)鎖，繼續(xù)看：
private void cancelToastLocked(int index) {
ToastRecord record = mToastQueue.get(index);
try {
//在這里調(diào)用了TN的hide()方法
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
}
mToastQueue.remove(index);
keepProcessAliveLocked(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();
}
}
在這個(gè)函數(shù)里面，首先是調(diào)用TN的hide()方法，隱藏顯示完畢的Toast，然后判斷還有沒(méi)有需要顯示的Toast，如果有的話，繼續(xù)顯示下一條。
TN調(diào)用WMS刪除Toast
到這里已經(jīng)差不多了，TN的hide被客戶端調(diào)用，發(fā)生的情況和show()差不多，也是在請(qǐng)求線程中通過(guò)WindowManager，remove掉剛才添加的Toast。
@Override
public void hide() {
if (localLOGV) Log.v(TAG, "HIDE: " + this);
mHandler.post(mHide);
}
final Runnable mHide = new Runnable() {
@Override
public void run() {
handleHide();
// Don't do this in handleHide() because it is also invoked by handleShow()
mNextView = null;
}
};
public void handleHide() {
if (localLOGV) Log.v(TAG, "HANDLE HIDE: " + this + " mView=" + mView);
if (mView != null) {
// note: checking parent() just to make sure the view has
// been added... i have seen cases where we get here when
// the view isn't yet added, so let's try not to crash.
if (mView.getParent() != null) {
if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this);
mWM.removeView(mView);
}
mView = null;
}
}
