java - 将适配器应用于 Spinner 会导致 NullPointerException？

Question

我有一个包含 2 个 fragment 的基本 Android 应用程序。

我正在尝试用一些 String 填充 Spinner 中的一个 Fragments。这是我的方法(顺便说一句，如果我在 onCreate 中注释掉整个 Try 语句，这一切都有效。

public class RadarSelectionFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    public static final String ARG_SECTION_NUMBER = "section_number";

    public RadarSelectionFragment() {
    }

    @Override
    public final View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        // Create a new TextView and set its text to the fragment's section
        // number argument value.\
        if (getArguments().getInt(ARG_SECTION_NUMBER) == 1) {
            return inflater.inflate(R.layout.radars, container, false);
        } else {
            return container;
        }

    }

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        try {
            Spinner s = (Spinner) findViewById(R.id.stateselector);
            ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(getActivity(), R.array.states, android.R.layout.simple_spinner_item);
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            s.setAdapter(adapter);
        } catch (Exception e) {
            Toast.makeText(getActivity(), e.toString(), 1).show();
        }
    }
} 

R.array.states 是一个包含澳大利亚各州和领地的数组，R.id.stateselector 定义为:

    <Spinner
        android:id="@+id/stateselector"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"/>

如果我注释掉 Try 语句，则不显示任何项目。

这一切都是按照来自 - http://developer.android.com/guide/topics/ui/controls/spinner.html 的教程完成的

非常感谢任何帮助!!!

编辑 1:堆栈跟踪

01-20 22:25:09.402: E/AndroidRuntime(8442): FATAL EXCEPTION: main
01-20 22:25:09.402: E/AndroidRuntime(8442): java.lang.NullPointerException
01-20 22:25:09.402: E/AndroidRuntime(8442):     at com.example.radarau.MainActivity$RadarSelectionFragment.onCreate(MainActivity.java:176)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.support.v4.app.Fragment.performCreate(Fragment.java:1437)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:877)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.support.v4.app.FragmentManagerImpl.performPendingDeferredStart(FragmentManager.java:807)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.support.v4.app.Fragment.setUserVisibleHint(Fragment.java:801)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.support.v4.app.FragmentPagerAdapter.setPrimaryItem(FragmentPagerAdapter.java:130)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.support.v4.view.ViewPager.populate(ViewPager.java:1010)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.support.v4.view.ViewPager.populate(ViewPager.java:881)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1366)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.View.measure(View.java:15513)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4827)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.View.measure(View.java:15513)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:847)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.View.measure(View.java:15513)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4827)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2176)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.View.measure(View.java:15513)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1874)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1089)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1265)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:989)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4351)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.Choreographer.doCallbacks(Choreographer.java:562)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.Choreographer.doFrame(Choreographer.java:532)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.os.Handler.handleCallback(Handler.java:725)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.os.Handler.dispatchMessage(Handler.java:92)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.os.Looper.loop(Looper.java:137)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at android.app.ActivityThread.main(ActivityThread.java:5039)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at java.lang.reflect.Method.invokeNative(Native Method)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at java.lang.reflect.Method.invoke(Method.java:511)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-20 22:25:09.402: E/AndroidRuntime(8442):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

您不能在 onCreate 方法中使用 findViewById，因为尚未创建 View 层次结构。尝试将您的代码移动到 onActivityCreated:

public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    try {
        Spinner s = (Spinner) findViewById(R.id.stateselector);
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(getActivity(), R.array.states, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        s.setAdapter(adapter);
    } catch (Exception e) {
        Toast.makeText(getActivity(), e.toString(), 1).show();
    }
}