NullPointerException與ArrayAdapter

Question

我使用Eclipse，我有一個使用默認「RelativeLayout」佈局的活動。我包括一個微調到佈局，這裏是當前xml：

<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context="mahana.timestat.InputMenu" > 

    <Spinner 
     android:id="@+id/activitiesSpinner" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_alignParentLeft="true" 
     android:layout_alignParentTop="true" /> 

</RelativeLayout> 

在我的.java，我找到了微調，創建一個ArrayList，手動填充它，創建一個適配器，並將其設置爲適配器的微調。下面是代碼：

//find the spinner: 
Spinner activitiesSpinner = (Spinner) findViewById(R.id.activitiesSpinner); 
//create an arrayList: 
ArrayList<String> activities = new ArrayList<String>(); 
//clear it and insert two strings: 
activities.clear(); 
activities.add("First"); 
activities.add("Second"); 
//create an adapter (I expect the error to be somewhere in here) 
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, R.id.activitiesSpinner, activities); 
//and finally set the adapter for the spinner 
activitiesSpinner.setAdapter(adapter); 

當我使用adapter.getCount()方法，它示出了右邊的數字（2）。 當我評論最後一行時，我在那裏設置適配器，它運行良好，並在我的設備上顯示一個空的微調框。 當我離開最後一行並運行它時，它在nullPointerException中崩潰。下面是跟蹤：

10-02 19:50:05.645: E/AndroidRuntime(21432): FATAL EXCEPTION: main 
10-02 19:50:05.645: E/AndroidRuntime(21432): Process: mahana.timestat, PID: 21432 
10-02 19:50:05.645: E/AndroidRuntime(21432): java.lang.NullPointerException 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:392) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.widget.AbsSpinner.onMeasure(AbsSpinner.java:193) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.widget.Spinner.onMeasure(Spinner.java:504) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.View.measure(View.java:16538) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.View.measure(View.java:16538) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.View.measure(View.java:16538) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.View.measure(View.java:16538) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2373) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.View.measure(View.java:16538) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1964) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1160) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1342) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1047) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5896) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.Choreographer.doCallbacks(Choreographer.java:574) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.Choreographer.doFrame(Choreographer.java:544) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.os.Handler.handleCallback(Handler.java:733) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.os.Handler.dispatchMessage(Handler.java:95) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.os.Looper.loop(Looper.java:136) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at android.app.ActivityThread.main(ActivityThread.java:5103) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at java.lang.reflect.Method.invokeNative(Native Method) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at java.lang.reflect.Method.invoke(Method.java:515) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:606) 
10-02 19:50:05.645: E/AndroidRuntime(21432): at dalvik.system.NativeStart.main(Native Method) 

當我試圖尋找這個問題的時候，我主要是發現，人們意外地在他們的ArrayList的地方留下了一個空值，但這裏絕對不是我的問題，因爲我手動填充它。 任何想法的問題可能會被讚賞。

Answer 1

因爲您使用的是默認simple_spinner_item佈局，因此其中包含TextView和text1 id而不是Spinner。所以強似R.id.activitiesSpinner在ArrayAdapter構造第三個參數傳遞android.R.id.text1：

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, 
           android.R.layout.simple_spinner_item, 
           android.R.id.text1, activities); 

OR

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, 
           android.R.layout.simple_spinner_item,activities);