我正在尝试使用ListView来填充ListAdapter，但每次创建片段时，都会在列表应添加项目的最后一行上抛出NullPointerException
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
list = (ListView) getActivity().findViewById(R.id.list);
JSONObject jsonObject1 = null;
JSONObject jsonObject2 = null;
JSONArray jsonArray1 = null;
JSONArray jsonArray2 = null;
try
{
jsonObject1 = new JSONObject(MainActivity.dispensaries);
jsonArray1 = jsonObject1.optJSONArray("dispensaries");
for(int i = 0 ; i<jsonArray1.length() ; i++)
{
try {
JSONObject object = jsonArray1.getJSONObject(i);
if(MainActivity.ID.equals(object.get("dispensary_id")))
{
jsonObject2 = object;
}
} catch (JSONException e) {
e.printStackTrace();
}
}
jsonArray2 = jsonObject2.optJSONArray("dispensary_products");
Log.e(TAG , "jsonArray = " + jsonArray2);
}
catch(JSONException e)
{
e.printStackTrace();
}
for(int i = 0 ; i<jsonArray2.length() ; i++)
{
try {
JSONObject object = jsonArray2.getJSONObject(i);
if(object.has("product_id")) {
names.add(object);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
Log.e(TAG , "list = " + names);
adapter = new DispensaryMenuAdapter(getContext(), names);
list.setAdapter(adapter); //here is where the exception is thrown
}
}
以下是例外文字：
java.lang.NullPointerException: Attempt to invoke a virtual method on a null object reference
at com.example.dragosandrei.greenkinexdorian.DispensaryMenuFragment.onViewCreated(DispensaryMenuFragment.java:95)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1314)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1528)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1595)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:758)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2363)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2149)
at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2103)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1984)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:626)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1268)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1116)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1642)
at android.view.View.measure(View.java:19917)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:714)
at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:90)
at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1391)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:784)
at android.view.View.measure(View.java:19917)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:19917)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:19917)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure(View.java:19917)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1081)
at android.view.View.measure(View.java:19917)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
at android.view.View.measure(View.java:19917)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1485)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:775)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:657)
at android.view.View.measure(View.java:19917)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.view.View.measure(View.java:19917)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1485)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:775)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:657)
at android.view.View.measure(View.java:19917)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
E/AndroidRuntime: at com.android.internal.policy.DecorView.onMeasure(DecorView.java:729)
at android.view.View.measure(View.java:19917)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2436)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1482)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1741)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1366)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6768)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:926)
at android.view.Choreographer.doCallbacks(Choreographer.java:735)
at android.view.Choreographer.doFrame(Choreographer.java:667)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:912)
at android.os.Handler.handleCallback(Handler.java:761)
at android.os.Handler.dispatchMessage(Handler.java:98)
at android.os.Looper.loop(Looper.java:156)
at android.app.ActivityThread.main(ActivityThread.java:6523)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)
这是XML文件：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ListView
android:id="@+id/dispensaryMenuList"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:layout_weight="1"
android:scrollbarSize="3dp"
android:scrollbarStyle="outsideOverlay"
android:scrollbars="vertical"
android:scrollingCache="true"
android:layout_marginBottom="50sp"
android:smoothScrollbar="true" />
</RelativeLayout>
如果您需要ListAdapter's代码
答案 0 :(得分：2)
问题在于这一行：
list = (ListView) getActivity().findViewById(R.id.list);
您不应该从您的片段中调用getActivity().findViewById。要从Fragments布局获取视图，请使用以下命令：
list = (ListView) view.findViewById(R.id.list);