C#中WinForm下datagrid中实现下拉列表---类源码

class  DataGridComboBoxColumn: DataGridColumnStyle 
    {
        private ComboBox myComboBox = new ComboBox ();
        private DataView ChoiceDataViewSource;
        private string ChoiceDisplayField;
        private string ChoiceValueField;
        private bool isEditing;

        public DataGridComboBoxColumn(DataView ChoiceDataViewSource,string ChoiceDisplayField,string ChoiceValueField) : base() 
        {
            this.ChoiceDataViewSource =ChoiceDataViewSource;
            this.ChoiceDisplayField =ChoiceDisplayField;
            this.ChoiceValueField =ChoiceValueField;
            myComboBox.DropDownStyle =System.Windows .Forms .ComboBoxStyle .DropDownList  ;
            myComboBox.Visible = false;
            myComboBox.DataSource =this.ChoiceDataViewSource;
            myComboBox.DisplayMember= this.ChoiceDisplayField;
            myComboBox.ValueMember =this.ChoiceValueField;
        }
        protected override void Abort(int rowNum)
        {
            isEditing = false;
            myComboBox.SelectedIndexChanged -= 
                new EventHandler(ComboBoxSelectedIndexChanged );
            Invalidate();
        }

        protected override bool Commit
            (CurrencyManager dataSource, int rowNum) 
        {
            myComboBox.Bounds = Rectangle.Empty;
         
            myComboBox.SelectedIndexChanged -= 
                new EventHandler(ComboBoxSelectedIndexChanged );

            if (!isEditing)
                return true;

            isEditing = false;

            try 
            {
                System.Object  value = myComboBox.SelectedValue;
                SetColumnValueAtRow(dataSource, rowNum, value);
            } 
            catch (Exception) 
            {
                Abort(rowNum);
                return false;
            }

            Invalidate();
            return true;
        }

        protected override void Edit(
            CurrencyManager source, 
            int rowNum,
            Rectangle bounds, 
            bool readOnly,
            string instantText, 
            bool cellIsVisible) 
        {
            object value =GetColumnValueAtRow(source, rowNum);
            if (cellIsVisible) 
            {
                myComboBox.Bounds = new Rectangle
                    (bounds.X + 2, bounds.Y + 2, 
                    bounds.Width - 4, bounds.Height - 4);
                int i=    Find (value);
                if (myComboBox.Items .Count >i) 
                {
                    myComboBox.SelectedIndex =i;
                }
                myComboBox.Visible = true;
                myComboBox.SelectedIndexChanged += 
                    new EventHandler(ComboBoxSelectedIndexChanged );
            } 
            else 
            {
                myComboBox.SelectedIndex =this.Find (value);
                myComboBox.Visible = false;
            }
            if (myComboBox.Visible)
                DataGridTableStyle.DataGrid.Invalidate(bounds);
        }
        protected int Find(System.Object value)
        {
            int int1;
            int int2;
            
            int2=ChoiceDataViewSource.Count ;
            if (int2<=0)
            {
                return -1;
            }
            for (int1=0;int1<int2;int1++)
            {
                if (ChoiceDataViewSource[int1][this.myComboBox .ValueMember ].ToString ().Trim ()==value.ToString ().Trim ())
                {
                    return int1;
                }
            }
            return -1;
        }

        protected override Size GetPreferredSize(
            Graphics g, 
            object value) 
        {
            return new Size(100, myComboBox.PreferredHeight+ 4);
        }

        protected override int GetMinimumHeight() 
        {
            return myComboBox.PreferredHeight + 4;
        }

        protected override int GetPreferredHeight(Graphics g, 
            object value) 
        {
            return myComboBox.PreferredHeight + 4;
        }

        protected override void Paint(Graphics g, 
            Rectangle bounds, 
            CurrencyManager source, 
            int rowNum) 
        {
            Paint(g, bounds, source, rowNum, false);
        }
        protected override void Paint(
            Graphics g, 
            Rectangle bounds,
            CurrencyManager source, 
            int rowNum,
            bool alignToRight) 
        {
            Paint(
                g,bounds, 
                source, 
                rowNum, 
                Brushes.Red, 
                Brushes.Blue, 
                alignToRight);
        }
        protected override void Paint(
            Graphics g, 
            Rectangle bounds,
            CurrencyManager source, 
            int rowNum,
            Brush backBrush, 
            Brush foreBrush,
            bool alignToRight) 
        {
            object value=GetColumnValueAtRow(source, rowNum);
            int int1=Find (value);
            string display="";
            if (int1>=0)
            {
                display=this.ChoiceDataViewSource [int1][this.myComboBox .DisplayMember ].ToString ();
            }
            Rectangle rect = bounds;
            g.FillRectangle(backBrush,rect);
            rect.Offset(0, 2);
            rect.Height -= 2;
            g.DrawString(display, 
                this.DataGridTableStyle.DataGrid.Font, 
                foreBrush, rect);
        }

        protected override void SetDataGridInColumn(DataGrid value) 
        {
            base.SetDataGridInColumn(value);
            if (myComboBox.Parent != null) 
            {
                myComboBox.Parent.Controls.Remove 
                    (myComboBox);
            }
            if (value != null) 
            {
                value.Controls.Add(myComboBox);
            }
        }

        private void ComboBoxSelectedIndexChanged(object sender, EventArgs e) 
        {
            this.isEditing = true;
            base.ColumnStartedEditing(myComboBox);
        }
    }