android - 当我尝试设置适配器时应用程序崩溃

Question

我有一个带有 JSON 适配器的工作 ListView，但是当我尝试在另一个 listView 上设置另一个适配器时，我的应用程序因未知原因崩溃。

我正在使用 TabLayout 和 PageAdapter。

当我评论以下行时(MainActivity.java，下面的方法 1):

insListView.setAdapter(mJSONAdapterIns);

应用程序可以运行。

MainActivity getUpdates(方法 1)- 有效 - 在 TabFragment1.java 中调用:

// 4. Access the ListView
                mainListView = (ListView) findViewById(R.id.main_listview);
                // 10. Create a JSONAdapter for the ListView
                mJSONAdapter = new JSONAdapter(MainActivity.this, getLayoutInflater());
                // Set the ListView to use the ArrayAdapter
                mainListView.setAdapter(mJSONAdapter);

MainActivity getInstagram() -方法 2 - 崩溃 - 在 TabFragment2.java 中调用:

insListView = (ListView) findViewById(R.id.instagram_listview);
        // 5. Set this activity to react to list items being pressed
        //mainListView.setOnItemClickListener(MainActivity.this);
        // 10. Create a JSONAdapter for the ListView
        mJSONAdapterIns = new JSONAdapterIns(MainActivity.this, getLayoutInflater());
        // Set the ListView to use the ArrayAdapter
        insListView.setAdapter(mJSONAdapterIns); //Crashes if this line is NOT commented

我使用 MainActivity 从选项卡 fragment 中调用这两个方法。

TabFragment1.java - 效果很好:

公共(public) View onCreateView(最终LayoutInflater inflater，ViewGroup容器，Bundle savingInstanceState){

final View v = inflater.inflate(R.layout.fb_list, container, false);
MainActivity king = (MainActivity)getActivity();
king.getUpdates(); // Setting the first list adapter (Method 1)
return v;

}

getUpdates() 正在更新我的第一个 ListView ，一切都很好。

TabFragment2.java - 调用“崩溃”方法:

public class TabFragment2 extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        final View v = inflater.inflate(R.layout.instagram_list, container, false);

        MainActivity king = (MainActivity)getActivity();
        king.getInstagram(); //Causes crash in the setAdapter line

        return v;
    }
}

Logcat 错误:

    1647-1647/il.co.test.test W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xb2cfab20)
08-26 10:59:45.050    1647-1647/il.co.test.test E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: il.co.test.test, PID: 1647
    java.lang.NullPointerException
            at il.co.test.test.MainActivity.getInstagram(MainActivity.java:175)
            at il.co.test.test.TabFragment2.onCreateView(TabFragment2.java:20)
            at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1016)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1197)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1562)
            at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:535)
            at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:1106)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:952)
            at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1474)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1916)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1295)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
            at android.view.Choreographer.doCallbacks(Choreographer.java:574)
            at android.view.Choreographer.doFrame(Choreographer.java:544)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            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:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)
08-26 10:59:59.010    1647-1647/? I/Process﹕ Sending signal. PID: 1647 SIG: 9

如何修复此崩溃？

编辑1: 尝试在方法 2 中添加以下行并注释 setAdapter。

TextView test = (TextView) findViewById(R.id.x1);
        test.setText("TEST");

应用程序也崩溃了。

看起来 findViewById 返回 NULL。为什么？

instagram_list.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity"
    android:layoutDirection="rtl"
    android:textDirection="rtl"
    android:background="#ffffff">

    <TextView
        android:id="@+id/x1"
        android:text="TEST"

        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />


    <!-- List whose dataset is defined in code with an adapter -->
    <ListView
        android:id="@+id/instagram_listview"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:layout_marginTop="15dp"
        android:paddingStart="5dp"
        android:paddingEnd="5dp"
        android:layoutDirection="rtl"
        android:textDirection="rtl"
        android:divider="@android:color/transparent"
        android:dividerHeight="20.0sp"

        />


</LinearLayout>

Prera​​k 回答后的新 logcat:

08-26 11:59:12.720    1599-1599/il.co.test.test E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: il.co.test.test, PID: 1599
    java.lang.IllegalStateException: System services not available to Activities before onCreate()
            at android.app.Activity.getSystemService(Activity.java:4532)
            at il.co.test.test.MainActivity.getInstagram(MainActivity.java:172)
            at il.co.test.test.TabFragment2.onCreateView(TabFragment2.java:25)
            at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1016)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1197)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1562)
            at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:535)
            at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:1106)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:952)
            at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1474)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
            at android.view.View.measure(View.java:16497)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1916)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1295)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
            at android.view.Choreographer.doCallbacks(Choreographer.java:574)
            at android.view.Choreographer.doFrame(Choreographer.java:544)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            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:779)
            at com.android.internal.os.ZygoteInit

Answer 1

在 MainActivity.java 中膨胀 instagram_list.xml，如下所示:

LayoutInflater inflater = (LayoutInflater) getSystemService( Context.LAYOUT_INFLATER_SERVICE );
View view = inflater.inflate(R.layout.instagram_list, null);

之后，实例化您的 ListView 就像

insListView = (ListView) view.findViewById(R.id.instagram_listview);

因此 getInstagram() 方法的完整代码为:

LayoutInflater inflater = (LayoutInflater) getSystemService( Context.LAYOUT_INFLATER_SERVICE );
View view = inflater.inflate(R.layout.instagram_list, null);
insListView = (ListView) view.findViewById(R.id.instagram_listview);

mJSONAdapterIns = new JSONAdapterIns(MainActivity.this, getLayoutInflater());
insListView.setAdapter(mJSONAdapterIns);

或者 @juanhl 在评论中建议的其他方法可以将 view 从 TabFragment2 传递到 getInstagram() 方法，如下所示:

final View v = inflater.inflate(R.layout.instagram_list, container, false);
MainActivity king = (MainActivity)getActivity();
king.getInstagram(v); //Pass the view as an agruement

在您的 getInstagram() 方法中，您可以这样做:

public void getInstagram(View v)
{
   insListView = (ListView) v.findViewById(R.id.instagram_listview);

   mJSONAdapterIns = new JSONAdapterIns(MainActivity.this, getLayoutInflater());
   insListView.setAdapter(mJSONAdapterIns);    
}