Xamarin 实现android gridview 多选

gridViewStudent = FindViewById<GridView> (Resource.Id.gridViewStudent);
//GridViewAdapter 自定义的Adapter
GridViewAdapter gridAdapter = new GridViewAdapter (this,stu);
            //更新图片  使用默认SimpleAdapter，需重写ViewBinder
            //adapter.ViewBinder = new ViewBinder ();
            gridViewStudent.Adapter = gridAdapter;
            //gridView.ChoiceMode = ChoiceMode.MultipleModal;//长按多选多选模式
            gridViewStudent.ChoiceMode = ChoiceMode.Multiple;//设置多选模式
//GridMultiChoiceListener自定义监听
            gridViewStudent.SetMultiChoiceModeListener (new GridMultiChoiceListener(this));// 设置多选模式监听器

public class GridViewAdapter:BaseAdapter
    {
        Context context;
        List<Student> data;
        //List<int> selected = new  List<int>();
        public GridViewAdapter(Context c,List<Student> data){
            context = c;
            this.data = data;
        }

        /*public void SelectedItem(int selected)
        {
            this.selected.Add (selected);
        }*/

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

        public override Java.Lang.Object GetItem (int position)
        {
            return position;
        }

        public override long GetItemId (int position)
        {
            return position;
        }
                
                //主要方法
        public override View GetView (int position, View convertView, ViewGroup parent)
        {
            GridItem item;

            if (convertView == null) {
                item = new GridItem (context);

                item.LayoutParameters = new GridView.LayoutParams (GridView.LayoutParams.WrapContent,
                    GridView.LayoutParams.WrapContent);                    

            } else {
                item = convertView as GridItem;
            }

            item.ID.Text = data[position].ID;
            item.Name.Text = data [position].Name;
            return item;

        }
    }

public class GridItem:RelativeLayout,ICheckable
    {
        bool _checked;

        public ImageView HeadImg {
            get;
            set;
        }

        public ImageView SelectedImg {
            get;
            set;
        }

        public TextView Name {
            get;
            set;
        }
        public TextView ID {
            get;
            set;
        }

        public GridItem (Context context) : base (context)
        {

//从布局文件加载元素            
　　　　　　　LayoutInflater.From(context).Inflate(Resource.Layout.gridItem,this);
            HeadImg = FindViewById<ImageView>(Resource.Id.imageHead);
            SelectedImg = FindViewById<ImageView>(Resource.Id.imageSelect);
            Name = FindViewById<TextView> (Resource.Id.textStuName);
            ID = FindViewById<TextView> (Resource.Id.textStuID);
        }
                //进行状态切换
        public bool Checked {
            get {return _checked; } 
            set { 
                _checked = value;
                SelectedImg.Visibility=value?ViewStates.Visible:ViewStates.Gone;
                SetBackgroundDrawable (value ? Resources.GetDrawable (Resource.Drawable.gridBackground) : null);
            }
        }

        public void Toggle ()
        {
            Checked = !_checked;
        }
    }

//这里继承一下Java.Lang.Object对象，不然要实现C#IDisposable接口
class GridMultiChoiceListener:Java.Lang.Object, GridView.IMultiChoiceModeListener
    {
        private Context context;

        public GridMultiChoiceListener(Context context)
        {
            this.context = context;
        }

        public void OnItemCheckedStateChanged (ActionMode mode, int position, long id, bool isChecked) 
        {
            //mode.Invalidate ();
        }

        public bool OnActionItemClicked (ActionMode mode, IMenuItem item)
        {
            return true;
        }

        public bool OnCreateActionMode (ActionMode mode, IMenu menu)
        {
            return true;
        }

        public void OnDestroyActionMode (ActionMode mode)
        {

        }

        public bool OnPrepareActionMode (ActionMode mode, IMenu menu)
        {
            return true;
        }
            
    }