实现 CustomAdapter 以片段化 ListView

Question

我正尝试在 Fragment 和 ListView 上实现 CustomAdapter，但它在 androidListView.setAdapter(androidListAdapter);

中显示错误 NullPointerException

之前试过没有fragment的CustomAdapter，成功了

这是我的片段代码：

public class LaporanFragment extends Fragment {
private ArrayAdapter<String> mLaporanAdapter;
String androidListViewStrings[] = {"Android ListView Example", "Android Custom ListView Example", "Custom ListView Example",
        "Android List Adapter", "Custom Adapter ListView", "ListView Tutorial",
        "ListView with Image and Text", "Custom ListView Text and Image", "ListView Custom Tutorial"};

Integer image_id[] = {R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher,
        R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher,
        R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher};

public LaporanFragment(){
}

@Override
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_laporan, container, false);
    LaporanAdapter androidListAdapter = new LaporanAdapter(getActivity(), image_id, androidListViewStrings);
    ListView androidListView = (ListView) rootView.findViewById(R.id.list_view_laporan);
    androidListView.setAdapter(androidListAdapter); **//Error nullPointerExeption on this line**

    return rootView;
}}

这是我的自定义适配器代码：

public class LaporanAdapter extends ArrayAdapter {
String[] androidListViewStrings;
Integer[] imagesId;
Context context;

public LaporanAdapter(Activity context, Integer[] imagesId, String[] textListView) {
    super(context, R.layout.list_item_laporan, textListView);
    this.androidListViewStrings = textListView;
    this.imagesId = imagesId;
    this.context = context;
}

@Override
public View getView(int i, View view, ViewGroup viewGroup) {
    LayoutInflater layoutInflater = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View viewRow = layoutInflater.inflate(R.layout.list_item_laporan, null,
            true);
    TextView mtextView = (TextView) viewRow.findViewById(R.id.list_item_laporan_textview);
    ImageView mimageView = (ImageView) viewRow.findViewById(R.id.image_view);
    mtextView.setText(androidListViewStrings[i]);
    mimageView.setImageResource(imagesId[i]);
    return viewRow;
}}

更新：

Logcat 输出：

FATAL EXCEPTION: main
          Process: id.co.gloftech.pelaporandishub, PID: 4859
          java.lang.RuntimeException: Unable to start activity ComponentInfo{id.co.gloftech.pelaporandishub/id.co.gloftech.pelaporandishub.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
              at android.app.ActivityThread.access0(ActivityThread.java:151)
              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
              at android.os.Handler.dispatchMessage(Handler.java:102)
              at android.os.Looper.loop(Looper.java:135)
              at android.app.ActivityThread.main(ActivityThread.java:5254)
              at java.lang.reflect.Method.invoke(Native Method)
              at java.lang.reflect.Method.invoke(Method.java:372)
              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
           Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
              at id.co.gloftech.pelaporandishub.LaporanFragment.onCreateView(LaporanFragment.java:85)
              at android.support.v4.app.Fragment.performCreateView(Fragment.java:2087)
              at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1113)
              at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1295)
              at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)
              at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1682)
              at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:388)
              at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:607)
              at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:181)
              at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1236)
              at android.app.Activity.performStart(Activity.java:6006)
              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2288)
              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
              at android.app.ActivityThread.access0(ActivityThread.java:151) 
              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
              at android.os.Handler.dispatchMessage(Handler.java:102) 
              at android.os.Looper.loop(Looper.java:135) 
              at android.app.ActivityThread.main(ActivityThread.java:5254) 
              at java.lang.reflect.Method.invoke(Native Method) 
              at java.lang.reflect.Method.invoke(Method.java:372)

还有 fragment_laporan.xml

<FrameLayout 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" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity$LaporanFragment">

<ListView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/list_view_forecast"></ListView>

Answer 1

您输入的 ListView id 有误。所以 rootView.findViewById(R.id.list_view_laporan) 将 return null 并导致 NPE。

改变，

ListView androidListView = (ListView) rootView.findViewById(R.id.list_view_laporan);

到，

ListView androidListView = (ListView) rootView.findViewById(R.id.list_view_forecast);

实现 CustomAdapter 以片段化 ListView

Implement CustomAdapter to Fragment ListView

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