ListView的自定义适配器

Question

我试图做一个自定义的ListView，它应该显示一个笔记标题和创建笔记的时间和日期，每个在单独的TextView中，而每个笔记标题也由存储在颜色值中的颜色值DB。所以，我创建了一个自定义适配器吧：

public class NoteAdapter extends ArrayAdapter<Note> { 

public NoteAdapter(Context context, int resource, int textViewResourceId, List<Note> objects) { 
    super(context, resource, textViewResourceId, objects); 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    // Creating the row 
    View row = super.getView(position, convertView, parent); 

    // Changing the text of time and date 
    ((TextView)row.findViewById(R.id.noteTitle)).setText(getItem(position).getTitle()); 
    ((TextView)row.findViewById(R.id.noteTime)).setText(getItem(position).getTime()); 
    ((TextView)row.findViewById(R.id.noteDate)).setText(getItem(position).getDate()); 

    ((TextView)row.findViewById(R.id.noteTitle)).setTextColor(Color.parseColor(getItem(position).getColor())); 

    // Returning the row 
    return row; 
    } 
} 

，并在主活动我这是怎么实现它：

... 
NoteAdapter adapter; 
NotesManager manager; 
private Note nNoteToDelete; 
ArrayList<Note> lstAllNotes; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 

    // Setting onClickListener for the "Add note" button when the activity starts 
    findViewById(R.id.btnAddNewNote).setOnClickListener(addNewNote); 

    // INSTANTIATING 

    // Manager - to manage all the DB manipulations 
    manager = new NotesManager(this); 

    // Retrieving all the notes in the DB 
    lstAllNotes = manager.getAllNotes(); 

    // Setting the ArrayAdapter, to display retrieved data in the ListView 
    //adapter = new ArrayAdapter<Note>(this, R.layout.note, lstAllNotes); 
    adapter = new NoteAdapter(this, R.layout.main, R.id.noteTitle, lstAllNotes); 

    // Setting the ListAdapter 
    setListAdapter(adapter); 

    // Registering for a single click action for each item in the ListView 
    getListView().setOnItemClickListener(editNote); 

    // Registering for a long click, which will pop up a context menu 
    registerForContextMenu(getListView()); 

} 
... 

但是当我测试的应用程序，它会立即崩溃。我在LogCat中遇到这些错误：

08-08 08:59:52.291: E/AndroidRuntime(21268): FATAL EXCEPTION: main 
08-08 08:59:52.291: E/AndroidRuntime(21268): java.lang.NullPointerException 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at com.notepad.NoteAdapter.getView(NoteAdapter.java:24) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.AbsListView.obtainView(AbsListView.java:2267) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.ListView.measureHeightOfChildren(ListView.java:1244) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.ListView.onMeasure(ListView.java:1156) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.View.measure(View.java:15172) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1390) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.LinearLayout.measureVertical(LinearLayout.java:681) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.LinearLayout.onMeasure(LinearLayout.java:574) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.View.measure(View.java:15172) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.View.measure(View.java:15172) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.LinearLayout.measureVertical(LinearLayout.java:833) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.LinearLayout.onMeasure(LinearLayout.java:574) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.View.measure(View.java:15172) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2148) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.View.measure(View.java:15172) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1848) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1100) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1273) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.Choreographer.doCallbacks(Choreographer.java:555) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.Choreographer.doFrame(Choreographer.java:525) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.os.Handler.handleCallback(Handler.java:615) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.os.Handler.dispatchMessage(Handler.java:92) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.os.Looper.loop(Looper.java:137) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at android.app.ActivityThread.main(ActivityThread.java:4745) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at java.lang.reflect.Method.invokeNative(Native Method) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at java.lang.reflect.Method.invoke(Method.java:511) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
08-08 08:59:52.291: E/AndroidRuntime(21268): at dalvik.system.NativeStart.main(Native Method) 

我在这里错过了什么？为什么它会一直崩溃，我该如何解决它？

Answer 1

试试这个：

public class NoteAdapter extends ArrayAdapter<Note> { 

    LayoutInflater mInflater; 
    List<Note> list; 
    public NoteAdapter(Context context, int resource, int textViewResourceId, List<Note> objects) { 
     super(context, resource, textViewResourceId, objects); 
     mInflater=LayoutInflater.from(context); 
     list=objects; 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 

     final ViewHolder holder; 

     if(convertView==null){ 
      convertView=mInflater.inflate(R.layout.listitem_layout,null);// R.layout.listitem_layout is your custom layout file 
      holder=new ViewHolder(); 

      holder.title=(TextView)convertView.findViewById(R.id.noteTitle); 
      holder.time=(TextView)convertView.findViewById(R.id.noteTime); 
      holder.date=(TextView)convertView.findViewById(R.id.noteDate); 
      convertView.setTag(holder); 
     } 
     else{ 
      holder=(ViewHolder)convertView.getTag(); 
     } 

     Note note=list.get(position); 

     holder.title.setText(note.getTitle()); 
     holder.title.setTextColor(Color.parseColor(note.getColor())); 
     holder.time.setText(note.getTime()); 
     holder.date.setText(note.getDate());  

     return convertView; 
    } 
    class ViewHolder{ 
     TextView title; 
     TextView time; 
     TextView date; 
    } 
} 

Answer 2

你是不是夸大的观点在你的自定义适配器的getView()

你正在做的事情是不对的

// Creating the row 
View row = super.getView(position, convertView, parent); 

尝试做这样的事情哪里row.xml将是布局文件在布局文件夹中

LayoutInflater inflater=LayoutInflater.from(context); 
View row=inflater.inflate(R.layout.row, parent, false); 

其中上下文将是类型的局部变量在构造函数中初始化的上下文。