我正在为观点实施“拖放”。当拖动开始时,我将视图的可见性设置为INVISIBLE
,然后,如果拖动被中断,则返回VISIBLE
:
public boolean onTouch(View v, MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN) {
// Skipped some code
boolean dragStarted = v.startDrag(data, shadowBuilder, v, 0);
if (dragStarted) {
v.setVisibility(View.INVISIBLE)
}
}
}
和
if (event.getAction() == DragEvent.ACTION_DRAG_ENDED) {
View droppedView = (View) event.getLocalState();
droppedView.setVisibility(View.VISIBLE);
}
当调用“Drag ended”事件时,我会遇到异常:
E/AndroidRuntime(7118): FATAL EXCEPTION: main
E/AndroidRuntime(7118): java.util.ConcurrentModificationException
E/AndroidRuntime(7118): at java.util.HashMap$HashIterator.nextEntry(HashMap.java:792)
E/AndroidRuntime(7118): at java.util.HashMap$KeyIterator.next(HashMap.java:819)
E/AndroidRuntime(7118): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:1046)
E/AndroidRuntime(7118): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:1048)
E/AndroidRuntime(7118): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:1048)
E/AndroidRuntime(7118): at android.view.ViewGroup.dispatchDragEvent(ViewGroup.java:1048)
E/AndroidRuntime(7118): at android.view.ViewRootImpl.handleDragEvent(ViewRootImpl.java:3471)
E/AndroidRuntime(7118): at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2620)
E/AndroidRuntime(7118): at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(7118): at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(7118): at android.app.ActivityThread.main(ActivityThread.java:4575)
E/AndroidRuntime(7118): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(7118): at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(7118): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
E/AndroidRuntime(7118): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
E/AndroidRuntime(7118): at dalvik.system.NativeStart.main(NativeMethod)
为什么以及如何解决它?
答案 0 :(得分:40)
你可以试试这个
if (event.getAction() == DragEvent.ACTION_DRAG_ENDED) {
final View droppedView = (View) event.getLocalState();
droppedView.post(new Runnable(){
@Override
public void run() {
droppedView.setVisibility(View.VISIBLE);
}
});
}
看起来Android本身在您结束拖动的同时尝试访问View状态。
修改强>
更准确的解释。通过设置setVisibility()
,您可以在Android内部视图集合中包含或排除View
,这应该响应拖动事件。在发送拖动事件期间使用此集合,因此尝试setVisibility
(换句话说,尝试修改拖动事件的侦听器)导致ConcurrentModificationException
答案 1 :(得分:0)
最好的方法是:
view.post(new Runnable() {
public void run() {
view.setVisibility(View.VISIBLE);
}
});
如果我们使用:
if (event.getAction() == DragEvent.ACTION_DRAG_ENDED) {
final View droppedView = (View) event.getLocalState();
droppedView.post(new Runnable(){
@Override
public void run() {
droppedView.setVisibility(View.VISIBLE);
}
});
}
您仍将强制关闭Null.pointer。 ...
答案 2 :(得分:-1)
也许this可以提供帮助。这里给定的链接说:而不是DragEvent.ACTION_DRAG_ENDED
使用DragEvent.ACTION_DROP
。