一 问题引出
前两天做一个需求，需求中有界面有加载网络，加载网络的时候要弹个dialog显示正在加载，等到服务器返回数据后，dialog消失。
开发前，搜索了一下，发现google推荐DialogFragment，但是有很多评论说坑比较多，所以我就没有用它而是直接用了Dialog，然后就出问题了。（其实想想也知道，google推出DialogFragment取代Dialog肯定是Dialog不够好的，就像用DataStore取代SharedPreferences一样。）
出现的具体问题就是，activity 生命周期内去show一个dialog，然后activity 在destroy之后再去dismiss这个dialog，虽然在dismiss之前有判断dialog.isShowing()，但还是会闪退。因为activity destroy之后，WindowManagerGlobal中的mView中已经清空了。再次去移除时，找不到，直接throw new IllegalArgumentException("View=" + view + " not attached to window manager");
val dialog:Dialog = Dialog(activity, themeId)
if (!activity.isDestroyed) {
dialog.show()
}
...
if (dialog != null && dialog.isShowing) {
dialog.dismiss() //闪退
}
二 报错日志：
11-30 17:26:08.599 E/AndroidRuntime(12701): FATAL EXCEPTION: main
11-30 17:26:08.599 E/AndroidRuntime(12701): Process: com.mobile.myapp, PID: 12701
11-30 17:26:08.599 E/AndroidRuntime(12701): java.lang.IllegalArgumentException: View=com.android.internal.policy.PhoneWindow$DecorView{2fb63f2 V.E...... R......D 0,0-720,1440} not attached to window manager
11-30 17:26:08.599 E/AndroidRuntime(12701): at android.view.WindowManagerGlobal.findViewLocked(WindowManagerGlobal.java:448)
11-30 17:26:08.599 E/AndroidRuntime(12701): at android.view.WindowManagerGlobal.removeView(WindowManagerGlobal.java:372)
11-30 17:26:08.599 E/AndroidRuntime(12701): at android.view.WindowManagerImpl.removeViewImmediate(WindowManagerImpl.java:116)
11-30 17:26:08.599 E/AndroidRuntime(12701): at android.app.Dialog.dismissDialog(Dialog.java:372)
11-30 17:26:08.599 E/AndroidRuntime(12701): at android.app.Dialog.dismiss(Dialog.java:351)
11-30 17:26:08.599 E/AndroidRuntime(12701): at com.luck.game.adv.ReaperAdvRequestUtilsKt$createInteractionExpressAdListener$1.run(SourceFile:141)
11-30 17:26:08.599 E/AndroidRuntime(12701): at android.os.Handler.handleCallback(Handler.java:815)
11-30 17:26:08.599 E/AndroidRuntime(12701): at android.os.Handler.dispatchMessage(Handler.java:104)
11-30 17:26:08.599 E/AndroidRuntime(12701): at android.os.Looper.loop(Looper.java:207)
11-30 17:26:08.599 E/AndroidRuntime(12701): at android.app.ActivityThread.main(ActivityThread.java:5821)
11-30 17:26:08.599 E/AndroidRuntime(12701): at java.lang.reflect.Method.invoke(Native Method)
11-30 17:26:08.599 E/AndroidRuntime(12701): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:805)
11-30 17:26:08.599 E/AndroidRuntime(12701): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:695)
三 解决方法
解决方法也很简答，dismiss之前多加一个判断，activity是否已经销毁了。
if (dialog != null && dialog.isShowing && !activity.isDestroyed) {
dialog.dismiss()
}
google推出DialogFragment，解决了生命周期的问题，而这个报错就是由生命周期引起的。所以后续的需求，还是尽量用google推荐的把，毕竟咱整个android都是它们造的，它自己肯定很了解这些缺陷，推荐的这些东西肯定是解决了一些问题的。
四 原因分析：
- 先看Dialog的源码，发现在dismiss之前有判断标志位，所以直观的认为即使activity销毁了，也是不会报错的：
/**
* Dismiss this dialog, removing it from the screen. This method can be
* invoked safely from any thread. Note that you should not override this
* method to do cleanup when the dialog is dismissed, instead implement
* that in {@link #onStop}.
*/
@Override
public void dismiss() {
if (Looper.myLooper() == mHandler.getLooper()) {
dismissDialog();
} else {
mHandler.post(mDismissAction);
}
}
void dismissDialog() {
if (mDecor == null || !mShowing) { //有判断标志位mShowing，所以认为不太容易出现异常，即使activity销毁了。
return;
}
if (mWindow.isDestroyed()) {
Log.e(TAG, "Tried to dismissDialog() but the Dialog's window was already destroyed!");
return;
}
try {
mWindowManager.removeViewImmediate(mDecor); // 但是在这里，它实实在在的抛了异常。
} finally {
if (mActionMode != null) {
mActionMode.finish();
}
mDecor = null;
mWindow.closeAllPanels();
onStop();
mShowing = false;
sendDismissMessage();
}
}
其实在activity销毁之后，这个标志位并没有改变，所以通过判断这个标志位，是不足以避免抛出异常的。
从报错日志堆栈中可以看出，抛出异常的真正原因在
E/AndroidRuntime(12701): at android.view.WindowManagerGlobal.findViewLocked(WindowManagerGlobal.java:448)
看这里的源代码：
//WindowManagerGlobal.java
private int findViewLocked(View view, boolean required) {
final int index = mViews.indexOf(view);
if (required && index < 0) {
throw new IllegalArgumentException("View=" + view + " not attached to window manager");
}
return index;
}
可见，是mViews里面已经没有Dialog的view了，所以抛出了异常。
- mViews里面什么时候移除的Dialog的view呢？在源码中搜索，发现有如下代码：
//WindowManagerGlobal.java
void doRemoveView(ViewRootImpl root) {
synchronized (mLock) {
final int index = mRoots.indexOf(root);
if (index >= 0) {
mRoots.remove(index);
mParams.remove(index);
final View view = mViews.remove(index); //移除对应的view
mDyingViews.remove(view);
}
}
if (ThreadedRenderer.sTrimForeground && ThreadedRenderer.isAvailable()) {
doTrimForeground();
}
}
而在ViewRootImpl.java中，又有如下代码：
void doDie() {
checkThread();
if (LOCAL_LOGV) Log.v(mTag, "DIE in " + this + " of " + mSurface);
synchronized (this) {
if (mRemoved) {
return;
}
mRemoved = true;
if (mAdded) {
dispatchDetachedFromWindow();
}
if (mAdded && !mFirst) {
destroyHardwareRenderer();
if (mView != null) {
int viewVisibility = mView.getVisibility();
boolean viewVisibilityChanged = mViewVisibility != viewVisibility;
if (mWindowAttributesChanged || viewVisibilityChanged) {
// If layout params have been changed, first give them
// to the window manager to make sure it has the correct
// animation info.
try {
if ((relayoutWindow(mWindowAttributes, viewVisibility, false)
& WindowManagerGlobal.RELAYOUT_RES_FIRST_TIME) != 0) {
mWindowSession.finishDrawing(mWindow);
}
} catch (RemoteException e) {
}
}
mSurface.release();
}
}
mAdded = false;
}
WindowManagerGlobal.getInstance().doRemoveView(this); //调用移除
}
- 确认ViewRootImpl.java的doDie()方法有在activity销毁时调用： 在activity销毁的时候，在一个自定义view里面的onDetachedFromWindow中，主动抛出一个空指针异常，并捕获和打印其堆栈：
12-24 10:22:48.160 W/System.err(30566): java.lang.NullPointerException: WeatherViewPager onDetachedFromWindow YQ
12-24 10:22:48.160 W/System.err(30566): at net.test.myapp.WeatherViewPager.onDetachedFromWindow(WeatherViewPager.java:207)
12-24 10:22:48.160 W/System.err(30566): at android.view.View.dispatchDetachedFromWindow(View.java:19690)
12-24 10:22:48.160 W/System.err(30566): at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3819)
12-24 10:22:48.160 W/System.err(30566): at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3811)
12-24 10:22:48.160 W/System.err(30566): at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3811)
12-24 10:22:48.160 W/System.err(30566): at android.view.ViewRootImpl.dispatchDetachedFromWindow(ViewRootImpl.java:4204)
12-24 10:22:48.161 W/System.err(30566): at android.view.ViewRootImpl.doDie(ViewRootImpl.java:7223) //确认有调用
12-24 10:22:48.161 W/System.err(30566): at android.view.ViewRootImpl.die(ViewRootImpl.java:7200)
12-24 10:22:48.161 W/System.err(30566): at android.view.WindowManagerGlobal.removeViewLocked(WindowManagerGlobal.java:527)
12-24 10:22:48.161 W/System.err(30566): at android.view.WindowManagerGlobal.removeView(WindowManagerGlobal.java:465)
12-24 10:22:48.161 W/System.err(30566): at android.view.WindowManagerImpl.removeViewImmediate(WindowManagerImpl.java:126)
12-24 10:22:48.161 W/System.err(30566): at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:5122)
12-24 10:22:48.161 W/System.err(30566): at android.app.servertransaction.DestroyActivityItem.execute(DestroyActivityItem.java:44)
12-24 10:22:48.161 W/System.err(30566): at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:176)
12-24 10:22:48.161 W/System.err(30566): at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
12-24 10:22:48.161 W/System.err(30566): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2065)
12-24 10:22:48.161 W/System.err(30566): at android.os.Handler.dispatchMessage(Handler.java:107)
12-24 10:22:48.161 W/System.err(30566): at android.os.Looper.loop(Looper.java:214)
12-24 10:22:48.161 W/System.err(30566): at android.app.ActivityThread.main(ActivityThread.java:7656)
12-24 10:22:48.161 W/System.err(30566): at java.lang.reflect.Method.invoke(Native Method)
12-24 10:22:48.161 W/System.err(30566): at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:503)
12-24 10:22:48.161 W/System.err(30566): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:948)
- 完工，今日事今日毕。一直想着准备好了再记录，而总有不满意和不完美的地方，拖着事情不闭环，不如先记录下来，后续再慢慢完善和润色语言
