在擴展BaseAdapter的CustomAdapter上的錯誤

Question

你好我正在試圖構建一個自定義的適配器來擴展基本適配器或者陣列適配器。但是，我都收到了同樣的錯誤。這是我日誌的一部分。

Error (29111)/AndroidRuntime: Caused by: 
android.runtime.JavaProxyThrowable: System.NullReferenceException: Object 
reference not set to an instance of an object 
Error (29111)/AndroidRuntime: at app2.NoteAdapter.GetView (System.Int32 
position, Android.Views.View convertView, Android.Views.ViewGroup parent) 
[0x0002e] in <1fa21d766827459f835e8535977f72f9>:0 
Error (29111)/AndroidRuntime: at 
Android.Widget.BaseAdapter.n_GetView_ILandroid_view_View 
_Landroid_view_ViewGroup_ (System.IntPtr jnienv, System.IntPtr native__this, 
System.Int32 position, System.IntPtr native_convertView, System.IntPtr 
native_parent) [0x00018] in <d855bac285f44dda8a0d8510b679b1e2>:0 
Error (29111)/AndroidRuntime: at (wrapper dynamic-method) 
System.Object:f5ec6c83-541f-4cff-a749-2883ba3ae9b3 
(intptr,intptr,int,intptr,intptr) 
Error (29111)/AndroidRuntime:  at 
md56e50694a3408ec27ef32796f24258eb7.NoteAdapter.n_getView(Native Method) 
Error (29111)/AndroidRuntime:  at 
md56e50694a3408ec27ef32796f24258eb7.NoteAdapter.getView(NoteAdapter.java:56) 
Error (29111)/AndroidRuntime:  at 
android.widget.AbsListView.obtainView(AbsListView.java:2370) 
Error (29111)/AndroidRuntime:  at 
android.widget.ListView.measureHeightOfChildren(ListView.java:1284) 
Error (29111)/AndroidRuntime:  at 
android.widget.ListView.onMeasure(ListView.java:1192) 

定製適配器的代碼是下面的一個：

public class NoteAdapter:BaseAdapter<DataModelNotes> 
{ 
// Context _context; 
    List<DataModelNotes> _notes; 
    private readonly Activity _activity; 
    public NoteAdapter(Activity activity, List<DataModelNotes> notes):base() 
    { 
     _activity = activity; 

     _notes = notes; 
    } 

    public override int Count 
    { 
     get { return _notes.Count; } 
    } 

    public override long GetItemId(int position) 
    { 
     return position; 
    } 

    public override DataModelNotes this[int position] 
    { 
     get { return _notes[position]; } 
    } 


    public override View GetView(int position, View convertView, ViewGroup parent) 
    { 
     DataModelNotes note = this[position]; 
     var view = convertView; 
      if (view == null) 
     { 
      view = _activity.LayoutInflater.Inflate(Resource.Layout.custom_notes_row, null); 
      } 
     var title = convertView.FindViewById<TextView>(Resource.Id.noteTitle); 
     var summary = convertView.FindViewById<TextView>(Resource.Id.noteSummary); 

     title.Text = note.Title; 
     summary.Text = note.Summary; 
     return view; 
    } 
} 

}

，我在我的listfragment做的唯一事情就是下面這樣：

public class NoteListFragment : ListFragment 
{ 

    List<DataModelNotes> notes; 
    public NoteListFragment() 
    { 
    } 

    public override void OnCreate(Bundle savedInstanceState) 
    { 
     base.OnCreate(savedInstanceState); 

    } 

    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) 
    { 

     notes = new List<DataModelNotes>(); 
     DataModelNotes note = new DataModelNotes(); 
     note.Id = 0; 
     note.Title = "adaadassaddsa"; 
     note.Summary = "sdfsfdsfdsdfsds"; 
     notes.Add(note); 
     NoteAdapter ad = new NoteAdapter(this.Activity as NotesMainActivity, notes); 
     this.ListAdapter = ad; 
     return base.OnCreateView(inflater, container, savedInstanceState); 
    } 

自定義佈局只是包含2個textview的線性佈局。我無法理解我做錯了什麼。我嘗試了很多東西，但錯誤依然存在。有人能給我一些幫助嗎？

Answer 1

您在第一次調用時意外地引用了「convertView」，它可能是null，在膨脹佈局並將其設置爲「view」變量之後。所以只需將其更改爲：

var view = convertView; 
if (view == null) 
{ 
    view = _activity.LayoutInflater.Inflate(Resource.Layout.custom_notes_row, null); 
} 
var title = view.FindViewById<TextView>(Resource.Id.noteTitle); 
var summary = view.FindViewById<TextView>(Resource.Id.noteSummary);