的ListView的NullPointerException问题

Question

我试图创建，需要一个简单的listeView与个人适配器设置好的这样一个XML文件：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:orientation="vertical"> 
    <ListView 
     android:id="@+id/listpromo" 
     android:layout_width="fill_parent" 
     android:layout_height="fill_parent"/> 
</LinearLayout> 

和我的活动：

public class ListSample_category3 extends Activity 
    { 

     public final static String ITEM_TITLE = "title"; 
     public final static String ITEM_COMPANY= "company"; 
     public final static String ITEM_DATE = "availabledate"; 
     private ListView list; 

     public Map<String,?> createItem(String title, String company, String date) 
     { 
      Map<String,String> item = new HashMap<String,String>(); 
      item.put(ITEM_TITLE, title); 
      item.put(ITEM_COMPANY, company); 
      item.put(ITEM_DATE, date); 
      return item; 
     } 

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

      List<Map<String,?>> security = new LinkedList<Map<String,?>>(); 
      security.add(createItem("Remember passwords", "Cisco", "2012-02-10")); 
      security.add(createItem("Clear passwords", "Microsoft", "2012-02-10")); 
      security.add(createItem("Show security warnings", "Apple", "2012-02-10")); 

      // create our list and custom adapter 
      SeparatedListAdapter adapter = new SeparatedListAdapter(this); 

      adapter.addSection("Categorie 1", new ArrayAdapter<String>(this, 
       R.layout.list_item_category3, new String[] { "First item", "Item two" })); 

      adapter.addSection("Categorie 2", new SimpleAdapter(this, security, R.layout.list_complex_category3, 
       new String[] { ITEM_TITLE, ITEM_COMPANY, ITEM_DATE }, new int[] { R.id.list_complex_title, R.id.list_complex_company, R.id.list_complex_date })); 

      // create ListView 
      //ListView list = new ListView(this); 
      list = (ListView) findViewById(R.id.listpromo); 

      // OnItemClickListener on all items 
      OnItemClickListener listener = new OnItemClickListener() 
      { 
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) 
        { 

        } 
      }; 
      list.setOnItemClickListener(listener); 
      list.setItemsCanFocus(true); 

      list.setAdapter(adapter); 
      this.setContentView(list); 

     } 
    } 

但我有一个NullPointerException：

08-05 17:00:26.304: E/AndroidRuntime(3226): FATAL EXCEPTION: main 
08-05 17:00:26.304: E/AndroidRuntime(3226): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dev.prixo/com.dev.prixo.OngletsActivity}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dev.prixo/com.dev.prixo.ListSample_category3}: java.lang.NullPointerException 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.os.Handler.dispatchMessage(Handler.java:99) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.os.Looper.loop(Looper.java:130) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.ActivityThread.main(ActivityThread.java:3687) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at java.lang.reflect.Method.invokeNative(Native Method) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at java.lang.reflect.Method.invoke(Method.java:507) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at dalvik.system.NativeStart.main(Native Method) 
08-05 17:00:26.304: E/AndroidRuntime(3226): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dev.prixo/com.dev.prixo.ListSample_category3}: java.lang.NullPointerException 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.ActivityThread.startActivityNow(ActivityThread.java:1491) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:676) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.widget.TabHost.setCurrentTab(TabHost.java:348) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.widget.TabHost.addTab(TabHost.java:227) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at com.dev.prixo.OngletsActivity.onCreate(OngletsActivity.java:34) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  ... 11 more 
08-05 17:00:26.304: E/AndroidRuntime(3226): Caused by: java.lang.NullPointerException 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at com.dev.prixo.ListSample_category3.onCreate(ListSample_category3.java:77) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615) 
08-05 17:00:26.304: E/AndroidRuntime(3226):  ... 20 more 

告诉我该怎么办，请..

这是我SeperatedListAdapter：

public class SeparatedListAdapter extends BaseAdapter 
{ 
    public final Map<String,Adapter> sections = new LinkedHashMap<String,Adapter>(); 
    public final ArrayAdapter<String> headers; 
    public final static int TYPE_SECTION_HEADER = 0; 

    public SeparatedListAdapter(Context context) 
    { 
     headers = new ArrayAdapter<String>(context, R.layout.list_header_category3); 
    } 

    public void addSection(String section, Adapter adapter) 
    { 
     this.headers.add(section); 
     this.sections.put(section, adapter); 
    } 

    public Object getItem(int position) 
    { 
     for(Object section : this.sections.keySet()) 
     { 
      Adapter adapter = sections.get(section); 
      int size = adapter.getCount() + 1; 

      // check if position inside this section 
      if(position == 0) return section; 
      if(position < size) return adapter.getItem(position - 1); 

      // otherwise jump into next section 
      position -= size; 
     } 
     return null; 
    } 

    public int getCount() 
    { 
     // total together all sections, plus one for each section header 
     int total = 0; 
     for(Adapter adapter : this.sections.values()) 
      total += adapter.getCount() + 1; 
     return total; 
    } 

    public int getViewTypeCount() 
    { 
     // assume that headers count as one, then total all sections 
     int total = 1; 
     for(Adapter adapter : this.sections.values()) 
      total += adapter.getViewTypeCount(); 
     return total; 
    } 

    public int getItemViewType(int position) 
    { 
     int type = 1; 
     for(Object section : this.sections.keySet()) 
     { 
      Adapter adapter = sections.get(section); 
      int size = adapter.getCount() + 1; 

      // check if position inside this section 
      if(position == 0) return TYPE_SECTION_HEADER; 
      if(position < size) return type + adapter.getItemViewType(position - 1); 

      // otherwise jump into next section 
      position -= size; 
      type += adapter.getViewTypeCount(); 
     } 
     return -1; 
    } 

    public boolean areAllItemsSelectable() 
    { 
     return false; 
    } 

    public boolean isEnabled(int position) 
    { 
     return (getItemViewType(position) != TYPE_SECTION_HEADER); 
    } 

    public View getView(int position, View convertView, ViewGroup parent) 
    { 
     int sectionnum = 0; 
     for(Object section : this.sections.keySet()) { 
      Adapter adapter = sections.get(section); 
      int size = adapter.getCount() + 1; 

      // check if position inside this section 
      if(position == 0) return headers.getView(sectionnum, convertView, parent); 
      if(position < size) return adapter.getView(position - 1, convertView, parent); 

      // otherwise jump into next section 
      position -= size; 
      sectionnum++; 
     } 
     return null; 
    } 

    public long getItemId(int position) 
    { 
     return position; 
    } 
} 

Answer 1

你不能说findViewById()没有设置内容查看。您必须设置包含ListView的XML布局。

setContentView(R.layout.yourlayout)。否则，您的ListView list将为空。

所以在你onCreate()：

protected void onCreate(Bundle bundle) { 
    super.onCreate(bundle); 
    setContentView(R.layout.yourlayout); 
} 

，并删除这条线在你onCreate()的底部：

setContentView(listview);