android - fragment 中的微调器 setOnItemSelectedListener

Question

我想在 Fragment 中使用 Spinner，但它在监听器上给我一个错误。我知道这里有一些类似的问题，但我无法弄清楚我的问题是什么。问题是什么？这是我的 onCreateView:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.maps, container, false);

    // Gets the MapView from the XML layout and creates it
    mapView = (MapView) v.findViewById(R.id.mapview);
    mapView.onCreate(savedInstanceState);
    mapView.onResume();

    // Gets to GoogleMap from the MapView and does initialization stuff
    mapView.getMapAsync(this)   

    // get Spinner reference
    Spinner spinner = (Spinner) v.findViewById(R.id.spinner);

    // Spinner click listener
    spinner.setOnItemSelectedListener(this);                  **<======ERROR======**

    // Spinner Drop down elements
    List<String> buses = new ArrayList<>();
    buses.add("Összes megálló - válassz egy járatot");
    buses.add("26");
    buses.add("35");
    buses.add("37");
    buses.add("42");

    // Creating array adapter for spinner
    ArrayAdapter<String> dataAdapter = new ArrayAdapter<>(getActivity(), android.R.layout.simple_spinner_item, buses);

    // Drop down style will be listview with radio button
    dataAdapter.setDropDownViewResource(android.R.layout.select_dialog_singlechoice);

    // attaching data adapter to spinner
    spinner.setAdapter(dataAdapter);

    return v;
}
@Override
public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
    caseno = parent.getSelectedItemPosition();
    switch(caseno) {
        case 0: {

            //some code

            break;
        }
        case 1: {
                //some code

            break;
        }

    }
}

public void onNothingSelected(AdapterView<?> arg0) {
    Toast.makeText(getActivity(), "Nincs kiválasztott járat", Toast.LENGTH_LONG).show();
}

我的布局:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<com.google.android.gms.maps.MapView android:id="@+id/mapview"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_below="@id/line"/>

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:layout_margin="10dp"
    android:background="@drawable/shadow">

    <Spinner
        android:id="@+id/spinner"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingStart="8dp"/>

</RelativeLayout>

错误:

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.koostamas.justtry, PID: 32434
              java.lang.NullPointerException
                  at com.koostamas.justtry.Map.onCreateView(Map.java:151)
                  at android.support.v4.app.Fragment.performCreateView(Fragment.java:2189)
                  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1299)
                  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:757)
                  at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2355)
                  at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2146)
                  at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2098)
                  at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2008)
                  at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:710)
                  at android.os.Handler.handleCallback(Handler.java:733)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:136)
                  at android.app.ActivityThread.main(ActivityThread.java:5146)
                  at java.lang.reflect.Method.invokeNative(Native Method)
                  at java.lang.reflect.Method.invoke(Method.java:515)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)
                  at dalvik.system.NativeStart.main(Native Method)

Answer 1

在Fragment中你需要实现这个接口(interface)AdapterView.OnItemClickListener 或者你可以试试这个

spinner.setOnItemSelectedListener(new OnItemSelectedListener() {

            @Override
            public void onItemSelected(AdapterView<?> adapterView, View view,
                    int position, long id) {
                Object item = adapterView.getItemAtPosition(position);
                if (item != null) {
                    Toast.makeText(getContext(), item.toString(),
                            Toast.LENGTH_SHORT).show();
                }
                Toast.makeText(getContext(), "Selected",
                        Toast.LENGTH_SHORT).show();

            }

            @Override
            public void onNothingSelected(AdapterView<?> adapterView) {
                // TODO Auto-generated method stub

            }
        });