我通过setVisibility(View.INVISIBLE)隐藏视图.稍后,当我尝试通过setVisibility(View.VISIBLE)以不同的方法再次显示视图时,我得到以下异常
03-28 01:32:05.450: E/AndroidRuntime(20895): FATAL EXCEPTION: main 03-28 01:32:05.450: E/AndroidRuntime(20895): java.util.ConcurrentModificationException 03-28 01:32:05.450: E/AndroidRuntime(20895): at java.util.HashMap$HashIterator.nextEntry(HashMap.java:796) 03-28 01:32:05.450: E/AndroidRuntime(20895): at java.util.HashMap$KeyIterator.next(HashMap.java:823) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:946) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:948) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:948) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:948) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:948) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:948) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.view.ViewRoot.handleDragEvent(ViewRoot.java:3027) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.view.ViewRoot.handleMessage(ViewRoot.java:2185) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.os.Handler.dispatchMessage(Handler.java:99) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.os.Looper.loop(Looper.java:132) 03-28 01:32:05.450: E/AndroidRuntime(20895): at android.app.ActivityThread.main(ActivityThread.java:4028) 03-28 01:32:05.450: E/AndroidRuntime(20895): at java.lang.reflect.Method.invokeNative(Native Method) 03-28 01:32:05.450: E/AndroidRuntime(20895): at java.lang.reflect.Method.invoke(Method.java:491) 03-28 01:32:05.450: E/AndroidRuntime(20895): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:844) 03-28 01:32:05.450: E/AndroidRuntime(20895): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602) 03-28 01:32:05.450: E/AndroidRuntime(20895): at dalvik.system.NativeStart.main(Native Method)
当我注释掉将可见性更改为可见的行时,我没有得到异常.
我首先想到异常是由一些其他代码迭代通过一个hashmap引起的,但是,我在迭代我使用的hashmaps时没有做任何修改,也没有多线程,这似乎是最常见的原因.这个例外.当我不改变能见度时,我也没有得到例外.
编辑：
自定义片段中发生异常.下面是我遍历hashmap(mWidgetConfig)的代码,其中包含有关我尝试恢复的自定义窗口小部件配置的信息. hashmap是片段中的公共变量.
在由片段创建的OnDragListener中,我根据某个拖动操作更新了hashmap,如下所示：
// Update the widget configuration of the fragment that created this listener
mFragment.mWidgetConfig.put(startCircleTag,"0");
我还迭代了hashmap来检查某个条件,但是在迭代期间我没有做任何修改：
Iterator<String> keySetItr = mFragment.mWidgetConfig.keySet().iterator();
while(keySetItr.hasNext()) {
String tag = keySetItr.next();
if(mFragment.mWidgetConfig.get(tag).equals((String) destSocket.getTag())) {
// do something,though no modification of the hashmap
break;
}
}
另外,在尝试恢复小部件配置时,我在片段本身中进行了一次迭代.下面是我根据hashmap配置窗口小部件的代码：
public void configureWidgets() {
resetWidgets();
Iterator<String> keySetItr = mWidgetConfig.keySet().iterator();
while(keySetItr.hasNext()) {
String tag = keySetItr.next();
Integer value = Integer.parseInt(mWidgetConfig.get(tag));
ImageView destSocket = null;
switch(value) {
case 0:
// The circle will not be connected to any socket
continue;
case 1:
destSocket = mSocket1;
break;
case 2:
destSocket = mSocket2;
break;
case 3:
destSocket = mSocket3;
break;
}
ImageView startCircle = (ImageView) mLayout.findViewWithTag(tag);
ImageView startPlug = (ImageView) mLayout.findViewWithTag(tag + "_plug");
// Replace the drawable of destSocket
destSocket.setBackgroundDrawable(getActivity().getResources().getDrawable(R.drawable.socket_plugged));
// Hide plug view
startPlug.setVisibility(View.INVISIBLE);
// Draw a line between the start circle view and the destination socket view
mConnectionLinesView.addLine(startCircle,destSocket);
}
}
public void resetWidgets() {
// Remove all lines
mConnectionLinesView.removeLines();
// Show all eventually prevIoUsly hidden plugs
//mPlug1.setVisibility(View.VISIBLE);
//mPlug2.setVisibility(View.VISIBLE);
//mPlug3.setVisibility(View.VISIBLE);
// Set to backround drawable of the socket to the initial one
mSocket1.setBackgroundDrawable(getActivity().getResources().getDrawable(R.drawable.socket).mutate());
mSocket2.setBackgroundDrawable(getActivity().getResources().getDrawable(R.drawable.socket).mutate());
mSocket3.setBackgroundDrawable(getActivity().getResources().getDrawable(R.drawable.socket).mutate());
}
一旦在代码中使用了设置上面“插件”可见性的行,我就会得到异常.
解
抛出异常的原因是我在OnDragListener的DragEvent.ACTION_DRAG_ENDED case语句中调用了配置方法.当我将相同的代码放入DragEvent.ACTION_DROP case语句时,不会抛出异常.不知道为什么.谢谢你的帮助
解决方法
据我所知,这是由ViewGroup实现细节引起的.而且它与多线程无关.
拖动开始时,ViewGroup会创建一个子视图的HashSet,必须通知ACTION_DRAG_ENDED事件.这是一组可见的孩子.当子可见性发生变化时,相应的ViewGroup会修改该集合(如果子集的可见性是可见的,则添加子集).在您的情况下,它会在迭代过程中发生.
想想,最简单的解决方案是推迟可见性变化.
view.post(new Runnable() {
public void run() {
view.setVisibility(View.VISIBLE);
}
});
将代码放入ACTION_DROP case语句时不会发生异常,因为在更改视图可见性时不会迭代该集合.
有关详细信息,请参阅ViewGroup.dispatchDragEvent(DragEvent)源代码.
