如何在datagridview 的head上绘制一个全选按钮

　　winform的项目中，经常要用到datagridview控件，但是为控件添加DataGridViewCheckBoxColumn来实现数据行选择这个功能的时候，经常需要提供全选反选功能，如果不重绘控件的话，我们只能再加一个checkbox控件跟datagridview组合来实现全选反选功能，实现了功能，却不是我们想要的效果。

　　当我们添加一个DataGridViewCheckBoxColumn时，发现他的基类里面有个HeaderCell的属性，而且是可写的，也就是DataGridViewColumnHeaderCell这个类，然后再看下继承关系，它最终也是继承自DataGridViewCell类，也就是一个单元格。知道这个以后，问题就很容易解决了，只需要重写下DataGridViewColumnHeaderCell类的paint方法，用CheckBoxRenderer画一个Checkbox到单元格上不就解决了。以下是实现代码：

    public delegate void DataGridViewCheckBoxHeaderEventHander(object sender, datagridviewCheckboxHeaderEventArgs e);


    public class datagridviewCheckboxHeaderEventArgs : EventArgs
    {
        private bool checkedState = false;

        public bool CheckedState
        {
            get { return checkedState; }
            set { checkedState = value; }
        }
    }

    public class DataGridViewCheckBoxHeaderCell : DataGridViewColumnHeaderCell
    {
        Point checkBoxLocation;
        Size checkBoxSize;
        bool _checked = false;
        Point _cellLocation = new Point();
        System.Windows.Forms.VisualStyles.CheckBoxState _cbState =
            System.Windows.Forms.VisualStyles.CheckBoxState.UncheckedNormal;
        public event DataGridViewCheckBoxHeaderEventHander OnCheckBoxClicked;

        protected override void Paint(
            Graphics graphics,
            Rectangle clipBounds,
            Rectangle cellBounds,
            int rowIndex,
            DataGridViewElementStates dataGridViewElementState,
            object value,
            object formattedValue,
            string errorText,
            DataGridViewCellStyle cellStyle,
            DataGridViewAdvancedBorderStyle advancedBorderStyle,
            DataGridViewPaintParts paintParts)
        {
            base.Paint(graphics, clipBounds, cellBounds, rowIndex,
                dataGridViewElementState, value,
                formattedValue, errorText, cellStyle,
                advancedBorderStyle, paintParts);

            Point p = new Point();
            Size s = CheckBoxRenderer.GetGlyphSize(graphics,CheckBoxState.UncheckedNormal);

            p.X = cellBounds.Location.X +
                (cellBounds.Width / 2) - (s.Width / 2) - 1;
            p.Y = cellBounds.Location.Y +
                (cellBounds.Height / 2) - (s.Height / 2);

            _cellLocation = cellBounds.Location;
            checkBoxLocation = p;
            checkBoxSize = s;
            if (_checked)
                _cbState = System.Windows.Forms.VisualStyles.
                    CheckBoxState.CheckedNormal;
            else
                _cbState = System.Windows.Forms.VisualStyles.
                    CheckBoxState.UncheckedNormal;
            
            CheckBoxRenderer.DrawCheckBox
            (graphics, checkBoxLocation, _cbState);
        }

        protected override void OnMouseClick(DataGridViewCellMouseEventArgs e)
        {
            Point p = new Point(e.X + _cellLocation.X, e.Y + _cellLocation.Y);
            if (p.X >= checkBoxLocation.X && p.X <=
                checkBoxLocation.X + checkBoxSize.Width
            && p.Y >= checkBoxLocation.Y && p.Y <=
                checkBoxLocation.Y + checkBoxSize.Height)
            {
                _checked = !_checked;

                datagridviewCheckboxHeaderEventArgs ex = new datagridviewCheckboxHeaderEventArgs();
                ex.CheckedState = _checked;

                object sender = new object();

                if (OnCheckBoxClicked != null)
                {
                    OnCheckBoxClicked(sender, ex);
                    this.DataGridView.InvalidateCell(this);
                }
            }
            base.OnMouseClick(e);
        }
    }

　　使用的时候，只需要将自己定义的DataGridViewCheckBoxHeaderCell赋给HeadCell属性，然后将HeaderCell.Value的值置为空，最后注册OnMouseClick事件，就可以在参数中接收checkbox的checked属性变化了。

　　效果图：