前言
某天早晨,吃完早餐,坐回工位,打开电脑,开启 chrome,进入友盟页面,发现了一个崩溃信息:
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较常见的子线程修改UI的问题。并且是在Toast上面报出的,常识告诉我Toast在子线程弹出是会报错,但是应该是提示Looper没有生成的错,而不应该是上面所报出的错误。那么会不会是生成Looper以后报的错的?
一、
所以我先做了一个demo,如下:
@Override protected void onResume() { super.onResume(); Thread thread = new Thread(new Runnable() { @Override public void run() { Toast.makeText(MainActivity.this,"子线程弹出Toast",Toast.LENGTH_SHORT).show(); } }); thread.start(); }
运行一下,果不其然崩溃掉,错误信息就是提示我必须准备好looper才能弹出toast:
java.lang.RuntimeException: Can't toast on a thread that has not called Looper.prepare() at android.widget.Toast$TN.(Toast.java:393) at android.widget.Toast.(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)
接下来就在toast里面准备好looper,再试试吧:
Thread thread = new Thread(new Runnable() { @Override public void run() { Looper.prepare(); Toast.makeText(MainActivity.this,"子线程弹出Toast",Toast.LENGTH_SHORT).show(); Looper.loop(); } }); thread.start();
运行发现是能够正确的弹出Toast的:
!image](//upload-images.jianshu.io/upload_images/10239771-212081efa66d5c73.jpg?imageMogr2/auto-orient/strip|imageView2/2/w/454/format/webp)
那么问题就来了,为什么会在友盟中出现这个崩溃呢?
二、
然后仔细看了下报错信息有两行重要信息被我之前略过了:
at com.youdao.youdaomath.view.PayCourseVideoActivity.onResume(PayCourseVideoActivity.java:218)
t android.widget.Toast.setText(Toast.java:332)
发现是在主线程报了Toast设置Text的时候的错误。这就让我很纳闷了,子线程修改UI会报错,主线程也会报错?感觉这么多年Android白做了。这不是最基本的知识么?于是我只能硬着头皮往源码深处看了:先来看看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; }
很常规的一个做法,先是inflate出来一个View对象,再从View对象找出对应的TextView,然后TextView将文本设置进去,所以感觉似乎一点问题都没有。那么既然出现了这个错误,总得有原因吧,或许是自己源码看漏了?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."); } }
这一看,还真的似乎给我了一点头绪,系统在checkThread的时候并不是将Thread.currentThread和MainThread作比较,而是跟mThread作比较,那么有没有一种可能mThread是子线程?一想到这里,我就兴奋了,全类查看mThread到底是怎么初始化的:
public ViewRootImpl(Context context, Display display) { ...代码省略... mThread = Thread.currentThread(); ...代码省略... }
可以发现全类只有这一处对mThread进行了赋值。那么会不会是子线程初始化了ViewRootimpl呢?似乎我之前好像也没有研究过Toast为什么会弹出来,所以顺便就先去了解下Toast是怎么show出来的好了:
/** * 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 } }
调用Toast的show方法时,会通过Binder获取Service即NotificationManagerService,然后执行enqueueToast方法(NotificationManagerService的源码就不做分析),然后会执行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(); }
发送一个Message,通知进行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,接下来就要进行真正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 */ } } }
代码有点长,我们最需要关心的就是mWm.addView方法。相信看过ActivityThread的同学应该知道mWm.addView方法是在ActivityThread的handleResumeActivity里面也有调用过,意思就是进行ViewRootImpl的初始化,然后通过ViewRootImp进行View的测量,布局,以及绘制。看到这里,我想到了一个可能的原因:那就是我的Toast是一个全局静态的Toast对象,然后第一次是在子线程的时候show出来,这个时候ViewRootImpl在初始化的时候就会将子线程的对象作为mThread,然后下一次在主线程弹出来就出错了吧?想想应该是这样的。
三、
所以继续做我的demo来印证我的想法:
@Override protected void onResume() { super.onResume(); Thread thread = new Thread(new Runnable() { @Override public void run() { Looper.prepare(); sToast = Toast.makeText(MainActivity.this,"子线程弹出Toast",Toast.LENGTH_SHORT); sToast.show(); Looper.loop(); } }); thread.start(); } public void click(View view) { sToast.setText("主线程弹出Toast"); sToast.show(); }
做了个静态的toast,然后点击按钮的时候弹出toast,运行一下:
image
发现竟然没问题,这时候又开始怀疑人生了,这到底怎么回事。ViewRootImpl此时的mThread应该是子线程啊,没道理还能正常运行,怎么办呢?debug一步一步调试吧,一步一步调试下来,发现在View的requestLayout里面parent竟然为空了:
然后在仔细看了下当前 View是一个LinearLayout,然后这个View的子View是TextView,文本内容是"主线程弹出toast",所以应该就是Toast在new的时候inflate的布局
View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null);
在Android源码社区中搜索"transient_notification"找到了对应的toast布局文件,打开一看,果然如此:
也就是说此时的View已经是顶级View了,它的parent应该就是ViewRootImpl,那么为什么ViewRootImpl是null呢,明明之前已经show过了。看来只能往Toast的hide方法找原因了
四、
所以重新回到Toast的类中,查看下Toast的hide方法(此处直接看Handler的hide处理,之前的操作与show类似):
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; } }
此处调用了mWm的removeViewImmediate,即WindowManagerImpl里面的removeViewImmediate方法:
@Override public void removeViewImmediate(View view) { mGlobal.removeView(view, true); }
会调用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); } }
然后调用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) { //此处调用View的assignParent方法将viewParent置空 view.assignParent(null); if (deferred) { mDyingViews.add(view); } } }
所以也就是说在Toast时间到了以后,会调用hide方法,此时会将parent置成空,所以我刚才试的时候才没有问题。那么按道理说只要在Toast没有关闭的时候点击再次弹出toast应该就会报错。所以还是原来的代码,再来一次,这次不等Toast关闭,再次点击:
果然如预期所料,此时在主线程弹出Toast就崩溃。
五、
那么问题原因找到了:是在项目子线程中有弹出过Toast,然后Toast并没有关闭,又在主线程弹出了同一个对象的toast,会造成崩溃。此时内心有个困惑:如果是子线程弹出Toast,那我就需要写Looper.prepare方法和Looper.loop方法,为什么我自己一点印象都没有。于是我全局搜索了Looper.prepare,发现并没有找到对应的代码。所以我就全局搜索了Toast调用的地方,发现在JavaBridge的回调当中找到了:
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) { ...代码省略.. case JSCallType.SHOW_TOAST: showToast(jsonObject); break; default: break; } } } /** * 弹出吐司 * @param jsonObject * @throws JSONException */ public void showToast(JSONObject jsonObject) throws JSONException { JSONObject payDataObj = jsonObject.getJSONObject("data"); String message = payDataObj.optString("data"); CommonToast.showShortToast(message); }
但是看到这段代码,又有疑问了,我并没有在Javabridge的回调中看到有任何准备Looper的地方,那么为什么Toast没有崩溃掉?所以在此处加了一段代码:
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) { ...代码省略.. case JSCallType.SHOW_TOAST: showToast(jsonObject); break; default: break; } } }
并且加了一个断点,来查看下此时的情况:
确实当前线程是JavaBridge线程,另外JavaBridge线程中已经提前给开发者准备好了Looper。所以也难怪一方面奇怪自己怎么没有写Looper的印象,一方面又很好奇为什么这个线程在开发者没有准备Looper的情况下也能正常弹出Toast。
总结
至此,真相终于找出来了。相比较发生这个bug 的原因,解决方案就显得非常简单了。只需要在CommonToast的showShortToast方法内部判断是否为主线程调用,如果不是的话,new一个主线程的Handler,将Toast扔到主线程弹出来。这样就会避免了子线程弹出。
PS:本人还得吐槽一下 Android,Android官方一方面明明宣称不能在主线程以外的线程进行UI的更新,另一方面在初始化ViewRootImpl的时候又不把主线程作为成员变量保存起来,而是直接获取当前所处的线程作为mThread保存起来,这样做就有可能会出现子线程更新UI的操作。从而引起类似我今天的这个bug。
结尾
其实对于程序员来说,要学习的知识内容、技术有太多太多,要想不被环境淘汰就只有不断提升自己,从来都是我们去适应环境,而不是环境来适应我们!
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