前言
某天早晨，吃完早餐嘉裤，坐回工位郑临，打開電腦，開啟chrome屑宠，進(jìn)入友盟頁面厢洞，發(fā)現(xiàn)了一個(gè)崩潰信息：
java.lang.RuntimeException: Unable to resume activity {com.youdao.youdaomath/com.youdao.youdaomath.view.PayCourseVideoActivity}: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3824)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3856)
at android.app.servertransaction.ResumeActivityItem.execute(ResumeActivityItem.java:51)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:145)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1831)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:201)
at android.app.ActivityThread.main(ActivityThread.java:6806)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)
Caused by: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:8000)
at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:1292)
at android.view.View.requestLayout(View.java:23147)
at android.view.View.requestLayout(View.java:23147)
at android.widget.TextView.checkForRelayout(TextView.java:8914)
at android.widget.TextView.setText(TextView.java:5736)
at android.widget.TextView.setText(TextView.java:5577)
at android.widget.TextView.setText(TextView.java:5534)
at android.widget.Toast.setText(Toast.java:332)
at com.youdao.youdaomath.view.common.CommonToast.showShortToast(CommonToast.java:40)
at com.youdao.youdaomath.view.PayCourseVideoActivity.checkNetWork(PayCourseVideoActivity.java:137)
at com.youdao.youdaomath.view.PayCourseVideoActivity.onResume(PayCourseVideoActivity.java:218)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1413)
at android.app.Activity.performResume(Activity.java:7400)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3816)
一眼看上去似乎是比較常見的子線程修改UI的問題。并且是在Toast上面報(bào)出的，常識(shí)告訴我Toast在子線程彈出是會(huì)報(bào)錯(cuò)躺翻，但是應(yīng)該是提示Looper沒有生成的錯(cuò)丧叽，而不應(yīng)該是上面所報(bào)出的錯(cuò)誤。那么會(huì)不會(huì)是生成Looper以后報(bào)的錯(cuò)的?
一公你、
所以我先做了一個(gè)demo踊淳，如下：
@Override
protected void onResume() {
super.onResume();
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
Toast.makeText(MainActivity.this,"子線程彈出Toast",Toast.LENGTH_SHORT).show();
}
});
thread.start();
}
運(yùn)行一下，果不其然崩潰掉,錯(cuò)誤信息就是提示我必須準(zhǔn)備好looper才能彈出toast：
java.lang.RuntimeException: Can't toast on a thread that has not called Looper.prepare()
at android.widget.Toast$TN.<init>(Toast.java:393)
at android.widget.Toast.<init>(Toast.java:117)
at android.widget.Toast.makeText(Toast.java:280)
at android.widget.Toast.makeText(Toast.java:270)
at com.netease.photodemo.MainActivity$1.run(MainActivity.java:22)
at java.lang.Thread.run(Thread.java:764)
接下來就在toast里面準(zhǔn)備好looper陕靠，再試試吧：
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
Looper.prepare();
Toast.makeText(MainActivity.this,"子線程彈出Toast",Toast.LENGTH_SHORT).show();
Looper.loop();
}
});
thread.start();
運(yùn)行發(fā)現(xiàn)是能夠正確的彈出Toast的：
那么問題就來了迂尝，為什么會(huì)在友盟中出現(xiàn)這個(gè)崩潰呢？
二剪芥、
然后仔細(xì)看了下報(bào)錯(cuò)信息有兩行重要信息被我之前略過了:
at com.youdao.youdaomath.view.PayCourseVideoActivity.onResume(PayCourseVideoActivity.java:218)
t android.widget.Toast.setText(Toast.java:332)
發(fā)現(xiàn)是在主線程報(bào)了Toast設(shè)置Text的時(shí)候的錯(cuò)誤雹舀。這就讓我很納悶了，子線程修改UI會(huì)報(bào)錯(cuò)粗俱，主線程也會(huì)報(bào)錯(cuò)说榆？
感覺這么多年Android白做了。這不是最基本的知識(shí)么寸认？
于是我只能硬著頭皮往源碼深處看了:
先來看看Toast是怎么setText的：
public static Toast makeText(@NonNull Context context, @Nullable Looper looper,
@NonNull CharSequence text, @Duration int duration) {
Toast result = new Toast(context, looper);
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;
}
很常規(guī)的一個(gè)做法签财，先是inflate出來一個(gè)View對(duì)象，再從View對(duì)象找出對(duì)應(yīng)的TextView偏塞，然后TextView將文本設(shè)置進(jìn)去唱蒸。至于setText在我之前的文章震驚！Android子線程也能修改UI灸叼？有詳細(xì)說過神汹，是在ViewRootImpl里面進(jìn)行checkThread是否在主線程上面。所以感覺似乎一點(diǎn)問題都沒有古今。那么既然出現(xiàn)了這個(gè)錯(cuò)誤屁魏，總得有原因吧，或許是自己源碼看漏了?
那就重新再看一遍ViewRootImpl#checkThread方法吧:
void checkThread() {
if (mThread != Thread.currentThread()) {
throw new CalledFromWrongThreadException(
"Only the original thread that created a view hierarchy can touch its views.");
}
}
這一看捉腥，還真的似乎給我了一點(diǎn)頭緒氓拼，系統(tǒng)在checkThread的時(shí)候并不是將Thread.currentThread和MainThread作比較，而是跟mThread作比較抵碟，那么有沒有一種可能mThread是子線程?一想到這里桃漾，我就興奮了，全類查看mThread到底是怎么初始化的:
public ViewRootImpl(Context context, Display display) {
...代碼省略...
mThread = Thread.currentThread();
...代碼省略...
}
可以發(fā)現(xiàn)全類只有這一處對(duì)mThread進(jìn)行了賦值拟逮。那么會(huì)不會(huì)是子線程初始化了ViewRootimpl呢撬统？似乎我之前好像也沒有研究過Toast為什么會(huì)彈出來，所以順便就先去了解下Toast是怎么show出來的好了:
/**
* Show the view for the specified duration.
*/
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
}
}
調(diào)用Toast的show方法時(shí)敦迄，會(huì)通過Binder獲取Service即NotificationManagerService恋追，然后執(zhí)行enqueueToast方法（NotificationManagerService的源碼就不做分析）粒竖，然后會(huì)執(zhí)行Toast里面如下方法:
@Override
public void show(IBinder windowToken) {
if (localLOGV) Log.v(TAG, "SHOW: " + this);
mHandler.obtainMessage(SHOW, windowToken).sendToTarget();
}
發(fā)送一個(gè)Message，通知進(jìn)行show的操作：
@Override
public void show(IBinder windowToken) {
if (localLOGV) Log.v(TAG, "SHOW: " + this);
mHandler.obtainMessage(SHOW, windowToken).sendToTarget();
}
在Handler的handleMessage方法中找到了SHOW的case几于，接下來就要進(jìn)行真正show的操作了:
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 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);
// 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.
try {
mWM.addView(mView, mParams);
trySendAccessibilityEvent();
} catch (WindowManager.BadTokenException e) {
/* ignore */
}
}
}
代碼有點(diǎn)長蕊苗，我們最需要關(guān)心的就是mWm.addView方法。相信看過ActivityThread的同學(xué)應(yīng)該知道m(xù)Wm.addView方法是在ActivityThread的handleResumeActivity里面也有調(diào)用過沿彭，意思就是進(jìn)行ViewRootImpl的初始化朽砰，然后通過ViewRootImp進(jìn)行View的測(cè)量，布局喉刘，以及繪制瞧柔。
看到這里，我想到了一個(gè)可能的原因：那就是我的Toast是一個(gè)全局靜態(tài)的Toast對(duì)象睦裳，然后第一次是在子線程的時(shí)候show出來造锅，這個(gè)時(shí)候ViewRootImpl在初始化的時(shí)候就會(huì)將子線程的對(duì)象作為mThread，然后下一次在主線程彈出來就出錯(cuò)了吧廉邑？想想應(yīng)該是這樣的哥蔚。
三、
所以繼續(xù)做我的demo來印證我的想法：
@Override
protected void onResume() {
super.onResume();
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
Looper.prepare();
sToast = Toast.makeText(MainActivity.this,"子線程彈出Toast",Toast.LENGTH_SHORT);
sToast.show();
Looper.loop();
}
});
thread.start();
}
public void click(View view) {
sToast.setText("主線程彈出Toast");
sToast.show();
}
做了個(gè)靜態(tài)的toast蛛蒙，然后點(diǎn)擊按鈕的時(shí)候彈出toast糙箍，運(yùn)行一下：
發(fā)現(xiàn)竟然沒問題，這時(shí)候又開始懷疑人生了牵祟，這到底怎么回事深夯。ViewRootImpl此時(shí)的mThread應(yīng)該是子線程啊，沒道理還能正常運(yùn)行诺苹，怎么辦呢咕晋？debug一步一步調(diào)試吧，一步一步調(diào)試下來收奔，發(fā)現(xiàn)在View的requestLayout里面parent竟然為空了：
然后在仔細(xì)看了下當(dāng)前View是一個(gè)LinearLayout掌呜，然后這個(gè)View的子View是TextView，文本內(nèi)容是"主線程彈出toast"筹淫，所以應(yīng)該就是Toast在new的時(shí)候inflate的布局
View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null);
在Android源碼社區(qū)中搜索"transient_notification"找到了對(duì)應(yīng)的toast布局文件站辉，打開一看呢撞，果然如此：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background="?android:attr/toastFrameBackground">
<TextView
android:id="@android:id/message"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_marginHorizontal="24dp"
android:layout_marginVertical="15dp"
android:layout_gravity="center_horizontal"
android:textAppearance="@style/TextAppearance.Toast"
android:textColor="@color/primary_text_default_material_light"
/>
</LinearLayout>
也就是說此時(shí)的View已經(jīng)是頂級(jí)View了损姜，它的parent應(yīng)該就是ViewRootImpl善玫，那么為什么ViewRootImpl是null呢贬媒，明明之前已經(jīng)show過了∥海看來只能往Toast的hide方法找原因了
四绷蹲、
所以重新回到Toast的類中,查看下Toast的hide方法(此處直接看Handler的hide處理棒卷，之前的操作與show類似):
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.removeViewImmediate(mView);
}
// Now that we've removed the view it's safe for the server to release
// the resources.
try {
getService().finishToken(mPackageName, this);
} catch (RemoteException e) {
}
mView = null;
}
}
此處調(diào)用了mWm的removeViewImmediate顾孽，即WindowManagerImpl里面的removeViewImmediate方法：
@Override
public void removeViewImmediate(View view) {
mGlobal.removeView(view, true);
}
會(huì)調(diào)用WindowManagerGlobal的removeView方法：
public void removeView(View view, boolean immediate) {
if (view == null) {
throw new IllegalArgumentException("view must not be null");
}
synchronized (mLock) {
int index = findViewLocked(view, true);
View curView = mRoots.get(index).getView();
removeViewLocked(index, immediate);
if (curView == view) {
return;
}
throw new IllegalStateException("Calling with view " + view
+ " but the ViewAncestor is attached to " + curView);
}
}
然后調(diào)用removeViewLocked方法：
private void removeViewLocked(int index, boolean immediate) {
ViewRootImpl root = mRoots.get(index);
View view = root.getView();
if (view != null) {
InputMethodManager imm = InputMethodManager.getInstance();
if (imm != null) {
imm.windowDismissed(mViews.get(index).getWindowToken());
}
}
boolean deferred = root.die(immediate);
if (view != null) {
//此處調(diào)用View的assignParent方法將viewParent置空
view.assignParent(null);
if (deferred) {
mDyingViews.add(view);
}
}
}
所以也就是說在Toast時(shí)間到了以后，會(huì)調(diào)用hide方法比规，此時(shí)會(huì)將parent置成空若厚，所以我剛才試的時(shí)候才沒有問題。那么按道理說只要在Toast沒有關(guān)閉的時(shí)候點(diǎn)擊再次彈出toast應(yīng)該就會(huì)報(bào)錯(cuò)蜒什。
所以還是原來的代碼测秸，再來一次，這次不等Toast關(guān)閉灾常，再次點(diǎn)擊：
果然如預(yù)期所料霎冯，此時(shí)在主線程彈出Toast就會(huì)崩潰。
五钞瀑、
那么問題原因找到了：是在項(xiàng)目子線程中有彈出過Toast沈撞，然后Toast并沒有關(guān)閉，又在主線程彈出了同一個(gè)對(duì)象的toast雕什，會(huì)造成崩潰缠俺。此時(shí)內(nèi)心有個(gè)困惑：如果是子線程彈出Toast，那我就需要寫Looper.prepare方法和Looper.loop方法贷岸，為什么我自己一點(diǎn)印象都沒有晋修。于是我全局搜索了Looper.prepare，發(fā)現(xiàn)并沒有找到對(duì)應(yīng)的代碼凰盔。所以我就全局搜索了Toast調(diào)用的地方墓卦，發(fā)現(xiàn)在JavaBridge的回調(diào)當(dāng)中找到了：
class JSInterface {
@JavascriptInterface
public void handleMessage(String msg) throws JSONException {
LogHelper.e(TAG, "msg::" + msg);
JSONObject jsonObject = new JSONObject(msg);
String callType = jsonObject.optString(JS_CALL_TYPE);
switch (callType) {
...代碼省略..
case JSCallType.SHOW_TOAST:
showToast(jsonObject);
break;
default:
break;
}
}
}
/**
* 彈出吐司
* @param jsonObject
* @throws JSONException
*/
public void showToast(JSONObject jsonObject) throws JSONException {
JSONObject payDataObj = jsonObject.getJSONObject("data");
String message = payDataObj.optString("data");
CommonToast.showShortToast(message);
}
但是看到這段代碼，又有疑問了户敬，我并沒有在Javabridge的回調(diào)中看到有任何準(zhǔn)備Looper的地方落剪，那么為什么Toast沒有崩潰掉？
所以在此處加了一段代碼：
class JSInterface {
@JavascriptInterface
public void handleMessage(String msg) throws JSONException {
LogHelper.e(TAG, "msg::" + msg);
JSONObject jsonObject = new JSONObject(msg);
String callType = jsonObject.optString(JS_CALL_TYPE);
Thread currentThread = Thread.currentThread();
Looper looper = Looper.myLooper();
switch (callType) {
...代碼省略..
case JSCallType.SHOW_TOAST:
showToast(jsonObject);
break;
default:
break;
}
}
}
并且加了一個(gè)斷點(diǎn)尿庐，來查看下此時(shí)的情況：
確實(shí)當(dāng)前線程是JavaBridge線程,另外JavaBridge線程中已經(jīng)提前給開發(fā)者準(zhǔn)備好了Looper忠怖。所以也難怪一方面奇怪自己怎么沒有寫Looper的印象，一方面又很好奇為什么這個(gè)線程在開發(fā)者沒有準(zhǔn)備Looper的情況下也能正常彈出Toast抄瑟。
總結(jié)
至此凡泣，真相終于找出來了。相比較發(fā)生這個(gè)bug 的原因,解決方案就顯得非常簡(jiǎn)單了皮假。只需要在CommonToast的showShortToast方法內(nèi)部判斷是否為主線程調(diào)用鞋拟，如果不是的話，new一個(gè)主線程的Handler惹资，將Toast扔到主線程彈出來贺纲。這樣就會(huì)避免了子線程彈出。
PS：本人還得吐槽一下Android褪测，Android官方一方面明明宣稱不能在主線程以外的線程進(jìn)行UI的更新猴誊，另一方面在初始化ViewRootImpl的時(shí)候又不把主線程作為成員變量保存起來潦刃，而是直接獲取當(dāng)前所處的線程作為mThread保存起來，這樣做就有可能會(huì)出現(xiàn)子線程更新UI的操作懈叹。從而引起類似我今天的這個(gè)bug乖杠。
