RecyclerView 始终为空

Question

我正在尝试在我的应用程序中实现 RecyclerView，但我根本无法让它工作。它抛出 NPE，我找不到原因，因为我已经根据官方 Google 教程完成了所有操作。

Logcat 输出：

04-26 23:04:41.823  22356-22356/com.example.app W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41670d88)
04-26 23:04:41.823  22356-22356/com.example.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.app, PID: 22356
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.app/com.example.app.PastEventActivity}: android.view.InflateException: Binary XML file line #6: Error inflating class fragment
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2237)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286)
            at android.app.ActivityThread.access0(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:212)
            at android.app.ActivityThread.main(ActivityThread.java:5135)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:877)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: android.view.InflateException: Binary XML file line #6: Error inflating class fragment
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:713)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
            at android.support.v7.app.ActionBarActivityDelegateBase.setContentView(ActionBarActivityDelegateBase.java:240)
            at android.support.v7.app.ActionBarActivity.setContentView(ActionBarActivity.java:102)
            at com.example.app.PastEventActivity.onCreate(PastEventActivity.java:22)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2201)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286)
            at android.app.ActivityThread.access0(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:212)
            at android.app.ActivityThread.main(ActivityThread.java:5135)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:877)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.app.fragments.PastEventFragment.onCreateView(PastEventFragment.java:34)
            at android.app.Fragment.performCreateView(Fragment.java:1700)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:870)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1044)
            at android.app.FragmentManagerImpl.addFragment(FragmentManager.java:1146)
            at android.app.Activity.onCreateView(Activity.java:4786)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:689)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
            at android.support.v7.app.ActionBarActivityDelegateBase.setContentView(ActionBarActivityDelegateBase.java:240)
            at android.support.v7.app.ActionBarActivity.setContentView(ActionBarActivity.java:102)
            at com.example.app.PastEventActivity.onCreate(PastEventActivity.java:22)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2201)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286)
            at android.app.ActivityThread.access0(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:212)
            at android.app.ActivityThread.main(ActivityThread.java:5135)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:877)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
            at dalvik.system.NativeStart.main(Native Method)

PastEventFragment.java

public class PastEventFragment extends Fragment {
    private RecyclerView mRecyclerView;

    public PastEventFragment() {

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        super.onCreateView(inflater, container, savedInstanceState);
        View pastEvent = inflater.inflate(R.layout.fragment_past_event, container, false);
        mRecyclerView = (RecyclerView) pastEvent.findViewById(R.id.pe_rv);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
        return pastEvent;
    }
}

fragment_past_event.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/backrepeat">
    <android.support.v7.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:name="@+id/pe_rv"
        />
</LinearLayout>

PastEventActivity.java

public class PastEventActivity extends ActionBarActivity {
    ActionBar actionBar;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_past_event);
    }
}

activity_past_event.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <fragment
        android:name="com.example.app.fragments.PastEventFragment"
        android:id="@+id/fragment_pe"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        />
</LinearLayout>

这段代码有什么问题？我尝试了其他问题的许多解决方案，但 none 对我有用。我正在寻求帮助，因为我将我的代码与官方指南和一些非官方教程进行了比较，它应该可以正常工作。

Answer 1

请定义XML命名空间，将xmlns:tools="http://schemas.android.com/tools"到fragment_past_event.xmlLinearLayout放在主命名空间下面

Answer 2

您正在布局中使用 android:name="@+id/pe_rv"。

你应该使用android:id="@+id/pe_rv"

<android.support.v7.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/pe_rv"
        />

Answer 3

在观察你的 logcat 之后，我认为你在 Inflating RecyclerView 上有第一个异常，然后是 NullPointer 异常。

您是否检查过 libs 文件夹中的 android-support-v7-recyclerview.jar 库？如果是，则检查目标 sdk 版本是否为 21

的清单文件

 <uses-sdk
        android:minSdkVersion="11" //or anything you need
        android:targetSdkVersion="21" />

因为在互联网上尝试了所有方法后，我通过将目标从 17 更改为 21 解决了 recyclerview 膨胀错误。

也许这对将来的某个人有帮助，而不是像我一样浪费时间。

Answer 4

您在 PastEventFragment.java 中缺少 setContentView 指令，我遇到了同样的问题。

RecyclerView 始终为空

RecyclerView is always null

android

android-fragments

android-support-library

android-recyclerview