Android App 在片段中创建 ListView 引用时关闭
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【中文标题】Android App 在片段中创建 ListView 引用时关闭【英文标题】：Android App closes while creating a ListView Reference in a Fragment 【发布时间】：2020-07-26 08:33:56 【问题描述】：我正在片段内创建一个自定义列表视图。 在我的主要活动中有两个选项卡。我创建了两个片段类“订阅”和“一次性”。虽然 listView 在订阅片段中被引用，但应用程序停在那里。代码构建完美，但应用程序停在那里。
片段的 XML 类似，除了 ListView ID。
fragment_subscibe.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_
android:layout_
android:orientation="vertical"
tools:context=".OneTime">
<!-- TODO: Update blank fragment layout -->
<ListView
android:layout_
android:layout_
android:id="@+id/listViewSubscription">
</ListView>
</LinearLayout>
现在在我的订阅片段 Java 类中，我有以下方法。
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
// Inflate the layout for this fragment
listView = (ListView)getView().findViewById(R.id.listViewSubscription);
Log.d("SOMETAG", "This doesn't print");
MyAdapter adapter = new MyAdapter(getActivity().getApplicationContext(), customername, phoneNo, amountleft);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener()
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id)
if(position == 0)
Toast.makeText(getContext(), "Position 1 Desc", Toast.LENGTH_SHORT).show();
if(position == 1)
Toast.makeText(getContext(), "Position 2 Desc", Toast.LENGTH_SHORT).show();
if(position == 2)
Toast.makeText(getContext(), "Position 3 Desc", Toast.LENGTH_SHORT).show();
if(position == 3)
Toast.makeText(getContext(), "Position 4 Desc", Toast.LENGTH_SHORT).show();
);
return inflater.inflate(R.layout.fragment_subscribe, container, false);
从日志标签开始注释部分，创建空选项卡。 我正在使用这个 XML 填充 listView，row_order
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_
android:layout_
android:padding="10dp"
android:orientation="vertical">
<LinearLayout
android:layout_
android:layout_
android:orientation="horizontal">
<TextView
android:id="@+id/customer_name"
android:layout_
android:layout_
android:layout_weight="5"
android:text="Customer Name"
android:textStyle="bold">
</TextView>
<TextView
android:id="@+id/address_phoneno"
android:layout_
android:layout_
android:layout_weight="5"
android:text="Phone Number"
android:textStyle="bold">
</TextView>
<TextView
android:id="@+id/amount_left"
android:layout_
android:layout_
android:layout_weight="5"
android:text="Amount Left"
android:textStyle="bold">
</TextView>
</LinearLayout>
<LinearLayout
android:layout_
android:layout_
android:orientation="horizontal"
android:paddingLeft="20sp"
android:paddingRight="10sp">
<TextView
android:id="@+id/product_name"
android:layout_
android:layout_
android:layout_weight="5"
android:gravity="center_vertical"
android:text="Product Name">
</TextView>
<TextView
android:id="@+id/quantity_order"
android:layout_
android:layout_
android:layout_weight="5"
android:gravity="center_vertical"
android:text="Qty">
</TextView>
<TextView
android:id="@+id/amount_order"
android:layout_
android:layout_
android:layout_weight="5"
android:gravity="center_vertical"
android:text="Amount">
</TextView>
<CheckBox
android:id="@+id/delivered_checkbox"
android:layout_
android:layout_
android:gravity="center_vertical">
</CheckBox>
</LinearLayout>
</LinearLayout>
我在关注这个视频：https://www.youtube.com/watch?v=5Tm--PHhbJo
我的错误日志按要求如下：
2020-04-13 23:32:04.407 6602-6602/com.example.myapplication I/art: at void android.app.Activity.performCreate(android.os.Bundle) (Activity.java:6692)
2020-04-13 23:32:04.407 6602-6602/com.example.myapplication I/art: at void android.app.Instrumentation.callActivityOnCreate(android.app.Activity, android.os.Bundle) (Instrumentation.java:1140)
2020-04-13 23:32:04.407 6602-6602/com.example.myapplication I/art: at android.app.Activity android.app.ActivityThread.performLaunchActivity(android.app.ActivityThread$ActivityClientRecord, android.content.Intent) (ActivityThread.java:2709)
2020-04-13 23:32:04.407 6602-6602/com.example.myapplication I/art: at void android.app.ActivityThread.handleLaunchActivity(android.app.ActivityThread$ActivityClientRecord, android.content.Intent, java.lang.String) (ActivityThread.java:2825)
2020-04-13 23:32:04.407 6602-6602/com.example.myapplication I/art: at void android.app.ActivityThread.-wrap12(android.app.ActivityThread, android.app.ActivityThread$ActivityClientRecord, android.content.Intent, java.lang.String) (ActivityThread.java:-1)
2020-04-13 23:32:04.407 6602-6602/com.example.myapplication I/art: at void android.app.ActivityThread$H.handleMessage(android.os.Message) (ActivityThread.java:1557)
2020-04-13 23:32:04.407 6602-6602/com.example.myapplication I/art: at void android.os.Handler.dispatchMessage(android.os.Message) (Handler.java:110)
2020-04-13 23:32:04.407 6602-6602/com.example.myapplication I/art: at void android.os.Looper.loop() (Looper.java:203)
2020-04-13 23:32:04.407 6602-6602/com.example.myapplication I/art: at void android.app.ActivityThread.main(java.lang.String[]) (ActivityThread.java:6339)
2020-04-13 23:32:04.408 6602-6602/com.example.myapplication I/art: at java.lang.Object java.lang.reflect.Method.invoke!(java.lang.Object, java.lang.Object[]) (Method.java:-2)
2020-04-13 23:32:04.408 6602-6602/com.example.myapplication I/art: at void com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run() (ZygoteInit.java:1084)
2020-04-13 23:32:04.408 6602-6602/com.example.myapplication I/art: at void com.android.internal.os.ZygoteInit.main(java.lang.String[]) (ZygoteInit.java:945)
2020-04-13 23:32:04.542 6602-6602/com.example.myapplication V/PhoneWindow: DecorView setVisiblity: visibility = 4, Parent = null, this = DecorView@91465fa[]
2020-04-13 23:32:04.558 6602-6602/com.example.myapplication D/WindowClient: Add to mViews: DecorView@91465fa[MainActivity], this = android.view.WindowManagerGlobal@1880975
2020-04-13 23:32:04.560 6602-6602/com.example.myapplication D/OpenGLRenderer: Dumper init 2 threads <0x9ceecd60>
2020-04-13 23:32:04.560 6602-6602/com.example.myapplication D/OpenGLRenderer: <com.example.myapplication> is running.
2020-04-13 23:32:04.563 6602-6618/com.example.myapplication D/OpenGLRenderer: CanvasContext() 0x9e747d40
2020-04-13 23:32:04.581 6602-6602/com.example.myapplication D/GraphicBuffer: register, handle(0xa54b5400) (w:576 h:960 s:576 f:0x1 u:0x000100)
2020-04-13 23:32:04.582 6602-6602/com.example.myapplication D/ViewRootImpl[MainActivity]: hardware acceleration is enabled, this = ViewRootf4bdd0a com.example.myapplication/com.example.myapplication.MainActivity,ident = 0
2020-04-13 23:32:04.589 6602-6602/com.example.myapplication V/PhoneWindow: DecorView setVisiblity: visibility = 0, Parent = ViewRootf4bdd0a com.example.myapplication/com.example.myapplication.MainActivity,ident = 0, this = DecorView@91465fa[MainActivity]
2020-04-13 23:32:04.616 6602-6602/com.example.myapplication D/AndroidRuntime: Shutting down VM
--------- beginning of crash
2020-04-13 23:32:04.619 6602-6602/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 6602
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at com.example.myapplication.Subscribe.onCreateView(Subscribe.java:80)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2600)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:881)
at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)
at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869)
at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
at androidx.fragment.app.FragmentManagerImpl.execSingleAction(FragmentManagerImpl.java:1696)
at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:299)
at androidx.fragment.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:259)
at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1244)
at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1092)
at androidx.viewpager.widget.ViewPager.onMeasure(ViewPager.java:1622)
at android.view.View.measure(View.java:20234)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6249)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1705)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:797)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:657)
at android.view.View.measure(View.java:20234)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6249)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:214)
at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
at android.view.View.measure(View.java:20234)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6249)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1705)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:797)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:657)
at android.view.View.measure(View.java:20234)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6249)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:214)
at android.view.View.measure(View.java:20234)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6249)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1705)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:797)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:657)
at android.view.View.measure(View.java:20234)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6249)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:214)
at com.android.internal.policy.DecorView.onMeasure(DecorView.java:716)
at android.view.View.measure(View.java:20234)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2655)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1596)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1869)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1481)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7047)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:910)
at android.view.Choreographer.doCallbacks(Choreographer.java:712)
at android.view.Choreographer.doFrame(Choreographer.java:646)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:896)
at android.os.Handler.handleCallback(Handler.java:836)
2020-04-13 23:32:04.619 6602-6602/com.example.myapplication E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:203)
at android.app.ActivityThread.main(ActivityThread.java:6339)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1084)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:945)
【问题讨论】：
非常感谢您的评论。我更新了问题并按照下面的答案修复了错误。 :D 【参考方案1】：您不能在createView 中调用getView，因为您正在创建视图（尚未创建它来获取它）替换createView 中的这一行：
listView = (ListView)getView().findViewById(R.id.listViewSubscription);
这些行：
View rootView = inflater.inflate(R.layout.fragment_subscribe, container, false);
listView = (ListView) rootView.findViewById(R.id.listViewSubscription);
// other codes...
return rootView// return from `createView`
【讨论】：
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