注意：我知道这个问题是重复的，您可能会被鼓励低估，但是，
我最近在Playstore上部署了我的APK，并为少数用户（4）收到了NullPointerException：
Exception java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Object.equals(java.lang.Object)' on a null object reference
android.widget.AdapterView.getPositionForView (AdapterView.java:607)
com.snap.testsnapboard.AlbumSelectActivity$1.onItemClick (AlbumSelectActivity.java:114)
android.widget.AdapterView.performItemClick (AdapterView.java:305)
android.widget.AbsListView.performItemClick (AbsListView.java:1146)
android.widget.AbsListView$PerformClick.run (AbsListView.java:3057)
android.widget.AbsListView.onTouchUp (AbsListView.java:3876)
android.widget.AbsListView.onTouchEvent (AbsListView.java:3641)
android.view.View.dispatchTouchEvent (View.java:8481)
android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:2400)
android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:2093)
android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:2406)
android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:2107)
android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:2406)
android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:2107)
android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:2406)
android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:2107)
android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:2406)
android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:2107)
com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent (PhoneWindow.java:2369)
com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent (PhoneWindow.java:1719)
android.app.Activity.dispatchTouchEvent (Activity.java:2785)
com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent (PhoneWindow.java:2330)
android.view.View.dispatchPointerEvent (View.java:8676)
android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent (ViewRootImpl.java:4141)
android.view.ViewRootImpl$ViewPostImeInputStage.onProcess (ViewRootImpl.java:4007)
android.view.ViewRootImpl$InputStage.deliver (ViewRootImpl.java:3562)
android.view.ViewRootImpl$InputStage.onDeliverToNext (ViewRootImpl.java:3615)
android.view.ViewRootImpl$InputStage.forward (ViewRootImpl.java:3581)
android.view.ViewRootImpl$AsyncInputStage.forward (ViewRootImpl.java:3698)
android.view.ViewRootImpl$InputStage.apply (ViewRootImpl.java:3589)
android.view.ViewRootImpl$AsyncInputStage.apply (ViewRootImpl.java:3755)
android.view.ViewRootImpl$InputStage.deliver (ViewRootImpl.java:3562)
android.view.ViewRootImpl$InputStage.onDeliverToNext (ViewRootImpl.java:3615)
android.view.ViewRootImpl$InputStage.forward (ViewRootImpl.java:3581)
android.view.ViewRootImpl$InputStage.apply (ViewRootImpl.java:3589)
android.view.ViewRootImpl$InputStage.deliver (ViewRootImpl.java:3562)
android.view.ViewRootImpl.deliverInputEvent (ViewRootImpl.java:5825)
android.view.ViewRootImpl.doProcessInputEvents (ViewRootImpl.java:5799)
android.view.ViewRootImpl.enqueueInputEvent (ViewRootImpl.java:5770)
android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent (ViewRootImpl.java:5915)
android.view.InputEventReceiver.dispatchInputEvent (InputEventReceiver.java:185)
android.os.MessageQueue.nativePollOnce (MessageQueue.java)
android.os.MessageQueue.next (MessageQueue.java:143)
android.os.Looper.loop (Looper.java:122)
android.app.ActivityThread.main (ActivityThread.java:5254)
java.lang.reflect.Method.invoke (Method.java)
java.lang.reflect.Method.invoke (Method.java:372)
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:902)
com.android.internal.os.ZygoteInit.main (ZygoteInit.java:697)
此异常源自行while ((v = (View) listItem.getParent()) != null && !v.equals(this)) {
AdapterView.java中的：
/**
* Returns the position within the adapter's data set for the view, where
* view is a an adapter item or a descendant of an adapter item.
* <p>
* <strong>Note:</strong> The result of this method only reflects the
* position of the data bound to <var>view</var> during the most recent
* layout pass. If the adapter's data set has changed without a subsequent
* layout pass, the position returned by this method may not match the
* current position of the data within the adapter.
*
* @param view an adapter item, or a descendant of an adapter item. This
* must be visible in this AdapterView at the time of the call.
* @return the position within the adapter's data set of the view, or
* {@link #INVALID_POSITION} if the view does not correspond to a
* list item (or it is not currently visible)
*/
public int getPositionForView(View view) {
View listItem = view;
try {
View v;
while ((v = (View) listItem.getParent()) != null && !v.equals(this)) {
listItem = v;
}
} catch (ClassCastException e) {
// We made it up to the window without find this list view
return INVALID_POSITION;
}
if (listItem != null) {
// Search the children for the list item
final int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
if (getChildAt(i).equals(listItem)) {
return mFirstPosition + i;
}
}
}
// Child not found!
return INVALID_POSITION;
}
其他值得一提的事情：
addFooterView() 为此，我写了以下代码：
// Since we have a Footer view attached to the ListView, the position selected
// might not always map 1-to-1 with the ArrayList we are using to represent the
// Album model objects list. Lets check if the Footer view has been selected and
// in this case, do nothing.
if(myListView.getPositionForView(loadMoreView) == arg2){
// Blank return
return;
}
这是最终在AdapterView.java内调用方法的代码。现在，为什么在while循环中存在空检查并且所有UI处理仅在主线程中发生时会有NullPointerException？
答案 0 :(得分：1)
我想告诉你一些关于空指针异常的提示。
如果listItem为null，它将创建异常...如果listItem不为null但listItem.getParent（）为null，它也将创建异常...或者当您将任何对象转换为另一个对象时为null ..引发异常。
(v = (View) listItem.getParent()) != null && !v.equals(this)
在你的情况下，listItem.getParent（）为null，这就是它抛出异常的原因。
你应该这样做：
if(v != null && listItem != null && listItem.getParent() != null && (v = (View) listItem.getParent()) != null && !v.equals(this) {
}
我希望它不会抛出异常。
答案 1 :(得分：1)
我不得不覆盖这个方法，我今天才发现这个问题，但我有665行并没有看到答案
我最好的猜测是修复不在某些API中，而是从API 27导入方法并稍微修改它以传递适配器
public int getPositionForView(View view, AdapterView av)
{
View listItem = view;
try
{
View v;
while ((v = (View) listItem.getParent()) != null && !v.equals(av))
{
listItem = v;
}
}
catch (ClassCastException e)
{
// We made it up to the window without find this list view
return -1;
}
if (listItem != null)
{
// Search the children for the list item
final int childCount = av.getChildCount();
for (int i = 0; i < childCount; i++)
{
if (av.getChildAt(i).equals(listItem))
{
return av.getFirstVisiblePosition() + i;
}
}
}
// Child not found!
return -1;
}
它始终有效