为DataGridView 添加复选框，实现全选功能

原文链接：http://www.codeproject.com/Articles/42437/Toggling-the-States-of-all-CheckBoxes-Inside-a-Dat

1、 指定DataGridView的第一列为DataGridViewCheckBoxColumn

2、 为第一列的标题栏添加一个CheckBox,假设为HeaderCheckBox
同时为HeaderCheckBox定义好 MouseClick 和 KeyUp 事件

private void frmSelectAll_Load(object sender, EventArgs e) 
{
   … 
   
   AddHeaderCheckBox();
   HeaderCheckBox.KeyUp += new KeyEventHandler(HeaderCheckBox_KeyUp);
   HeaderCheckBox.MouseClick += new MouseEventHandler(HeaderCheckBox_MouseClick);
   … 
}

private void AddHeaderCheckBox()
{
    HeaderCheckBox = new CheckBox();
    HeaderCheckBox.Size = new Size(15, 15);

    //Add the CheckBox into the DataGridView
    this.dgvSelectAll.Controls.Add(HeaderCheckBox);
}

private void HeaderCheckBox_MouseClick(object sender, MouseEventArgs e) 
{
    HeaderCheckBoxClick((CheckBox)sender); 
}

private void HeaderCheckBox_KeyUp(object sender, KeyEventArgs e)
{
    if(e.KeyCode == Keys.Space)
       HeaderCheckBoxClick((CheckBox)sender);
}

private void HeaderCheckBoxClick(CheckBox HCheckBox)
{
    IsHeaderCheckBoxClicked = true;

    foreach (DataGridViewRow Row in dgvSelectAll.Rows)
        ((DataGridViewCheckBoxCell)Row.Cells[0]).Value = HCheckBox.Checked;

    dgvSelectAll.RefreshEdit();

    TotalCheckedCheckBoxes = HCheckBox.Checked ? TotalCheckBoxes : 0;

    IsHeaderCheckBoxClicked = false;
}

3、 以上代码发现HeaderCheckBox不在正确的位置显示
所以添加绘制代码，调整位置

private void frmSelectAll_Load(object sender, EventArgs e)
{
   ...
   dgvSelectAll.CellPainting += new DataGridViewCellPaintingEventHandler(dgvSelectAll_CellPainting);   
   ...
}

private void dgvSelectAll_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
{
   if (e.RowIndex == -1 && e.ColumnIndex == 0)
      ResetHeaderCheckBoxLocation(e.ColumnIndex, e.RowIndex);
}

private void ResetHeaderCheckBoxLocation(int ColumnIndex, int RowIndex)
{
    //Get the column header cell bounds
    Rectangle oRectangle = this.dgvSelectAll.GetCellDisplayRectangle(ColumnIndex, RowIndex, true);

    Point oPoint = new Point();

    oPoint.X = oRectangle.Location.X + (oRectangle.Width - HeaderCheckBox.Width) / 2 + 1;
    oPoint.Y = oRectangle.Location.Y + (oRectangle.Height - HeaderCheckBox.Height) / 2 + 1;

    //Change the location of the CheckBox to make it stay on the header
    HeaderCheckBox.Location = oPoint;
}

4、 到此为止，第一列的显示，全选/全不选功能已经做好
此时，如果DataGridView的ReadOnly为True，则发现点击CheckBox，无法修改其选中状态
而设置ReadOnly为false，则发现可以修改CheckBox的状态，但是DataGridView处于编辑状态

private void frmSelectAll_Load(object sender, EventArgs e)
{
   ...
   dgvSelectAll.CurrentCellDirtyStateChanged += new EventHandler(dgvSelectAll_CurrentCellDirtyStateChanged);  
   ...
}


private void dgvSelectAll_CurrentCellDirtyStateChanged(object sender, EventArgs e)
{
    if (dgvSelectAll.CurrentCell is DataGridViewCheckBoxCell)
        dgvSelectAll.CommitEdit(DataGridViewDataErrorContexts.Commit);
}

注意：如果仅希望第一列可以修改，其他列不能修改，可以把其他列设置为只读

5、 单击HeaderCheckBox，让DataGridView处于全选状态
然后取消部分记录的选中状态，此时HeaderCheckBox仍然为选中状态，而不是预期中的非选中状态

private void frmSelectAll_Load(object sender, EventArgs e)
{
   ...
   dgvSelectAll.CellValueChanged += new DataGridViewCellEventHandler(dgvSelectAll_CellValueChanged);
   ...
}

private void dgvSelectAll_CellValueChanged(object sender, DataGridViewCellEventArgs e)
{
    if (!IsHeaderCheckBoxClicked)
        RowCheckBoxClick((DataGridViewCheckBoxCell)dgvSelectAll[e.ColumnIndex, e.RowIndex]);
}   

private void RowCheckBoxClick(DataGridViewCheckBoxCell RCheckBox)
{
    if (RCheckBox != null)
    {
        //Modifiy Counter;            
        if ((bool)RCheckBox.Value && TotalCheckedCheckBoxes < TotalCheckBoxes)
            TotalCheckedCheckBoxes++;
        else if (TotalCheckedCheckBoxes > 0)
            TotalCheckedCheckBoxes--;

        //Change state of the header CheckBox.
        if (TotalCheckedCheckBoxes < TotalCheckBoxes)
            HeaderCheckBox.Checked = false;
        else if (TotalCheckedCheckBoxes == TotalCheckBoxes)
            HeaderCheckBox.Checked = true;
    }
} 

6、 IsHeaderCheckBoxClicked的作用
因为HeaderCheckBox状态的改变，会触发DataGridView的CellValueChanged事件
而DataGridView的CellValueChanged事件也会导致HeaderCheckBox状态修改
所以，这里用了一个全局变量，来避免程序进入死循环