android：从strings.xml填充微调器

Question

我遇到一个问题，用一周中的几天来填充微调器。

布局的xml：

<Spinner 
    android:id="@+id/week_spinner" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:drawSelectorOnTop="true"/> 

的strings.xml

<resources> 
    <string-array name="days_of_week"> 
    <item>Monday</item> 
    <item>Tuesday</item> 
    <item>Wednesday</item> 
    <item>Thursday</item> 
    <item>Friday</item> 
    </string-array> 
</resources> 

的java：

public class AddModule extends Activity { 
    Spinner day; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     day = (Spinner)findViewById(R.id.week_spinner); 

     ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.days_of_week, android.R.layout.simple_spinner_item); 
     adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 
     day.setAdapter(adapter); 
     setContentView(R.layout.activity_add_module); 
    } 
} 

这是造成应用程序崩溃setAdapter线。我收到以下错误

11-05 21:24:31.235: W/dalvikvm(867): threadid=1: thread exiting with uncaught exception (group=0x40a9a228) 
11-05 21:24:31.245: E/AndroidRuntime(867): FATAL EXCEPTION: main 
11-05 21:24:31.245: E/AndroidRuntime(867): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cathal.timetable/com.cathal.timetable.AddModule}: java.lang.NullPointerException 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2202) 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2237) 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.app.ActivityThread.access$600(ActivityThread.java:139) 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1262) 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.os.Handler.dispatchMessage(Handler.java:99) 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.os.Looper.loop(Looper.java:154) 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.app.ActivityThread.main(ActivityThread.java:4974) 
11-05 21:24:31.245: E/AndroidRuntime(867): at java.lang.reflect.Method.invokeNative(Native Method) 
11-05 21:24:31.245: E/AndroidRuntime(867): at java.lang.reflect.Method.invoke(Method.java:511) 
11-05 21:24:31.245: E/AndroidRuntime(867): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
11-05 21:24:31.245: E/AndroidRuntime(867): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
11-05 21:24:31.245: E/AndroidRuntime(867): at dalvik.system.NativeStart.main(Native Method) 11-05 21:24:31.245: E/AndroidRuntime(867): Caused by: java.lang.NullPointerException 11-05 21:24:31.245: E/AndroidRuntime(867): at com.cathal.timetable.AddModule.onCreate(AddModule.java:18) 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.app.Activity.performCreate(Activity.java:4538) 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071) 
11-05 21:24:31.245: E/AndroidRuntime(867): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2158) 
11-05 21:24:31.245: E/AndroidRuntime(867): ... 11 more 

昨天工作正常。我无法弄清楚我是否可能改变了某些东西，或者如果我有日食问题。

Answer 1

super.onCreate(savedInstanceState); 
setContentView(yourView); 
day = (Spinner)findViewById(R.id.week_spinner); 

您忘记在从xml获取微调器之前设置视图。如果你没有设置视图，findViewById返回null。

对null的任何操作参考结果NullPointerException。

Answer 2

Nambari解释了为什么您收到NullPointerException以及如何正确使用findViewById()。

我想更简单的方式指出来设置使用默认设置的微调，只需添加到您的XML：

android:entries="@array/days_of_week" 

而且你可以删除onCreate()您适配器的所有引用。