在C# WinForms 应用程序中，经常需要在DataGridView控件中使用组合框列（ComboBoxColumn）来显示下拉列表。但是，标准的DataGridViewComboBoxColumn不支持动态过滤其数据源。本文将介绍如何创建一个自定义的DataGridViewComboBoxColumn，使其能够根据当前选中的行动态过滤下拉列表中的项。
在标准的DataGridViewComboBoxColumn中，DataSource属性的数据源是静态的，无法根据用户的选择动态过滤。为了解决这个问题，需要创建一个自定义的DataGridViewComboBoxColumn类，它能够根据当前选中的行来过滤下拉列表中的项。
创建自定义的DataGridViewComboBoxColumn
首先，需要创建一个自定义的DataGridViewComboBoxColumn类，命名为ContextualDataGridViewComboBoxColumn。这个类将继承自DataGridViewComboBoxColumn，并添加一个FilteredRequest属性，用于存储过滤后的项列表。
public class ContextualDataGridViewComboBoxColumn : DataGridViewComboBoxColumn
{
public ContextualDataGridViewComboBoxColumn()
{
CellTemplate = new ContextualDataGridViewComboBoxCell();
}
public IEnumerable FilteredRequest { get; set; }
}
接下来，需要创建一个自定义的DataGridViewComboBoxCell类，命名为ContextualDataGridViewComboBoxCell。这个类将继承自DataGridViewComboBoxCell，并重写EditType属性，使其返回自定义的DataGridViewComboBoxEditingControl。
public class ContextualDataGridViewComboBoxCell : DataGridViewComboBoxCell
{
public override Type EditType
{
get { return typeof(ContextualDataGridViewComboBoxEditingControl); }
}
public IEnumerable FilteredRequest
{
get { return (OwningColumn as ContextualDataGridViewComboBoxColumn).FilteredRequest; }
}
}
然后，需要创建一个自定义的DataGridView ComboBoxEditingControl类，命名为ContextualDataGridViewComboBoxEditingControl。这个类将继承自DataGridViewComboBoxEditingControl，并重写OnMeasureItem和OnDrawItem方法，以实现对下拉列表项的动态过滤 。
public class ContextualDataGridViewComboBoxEditingControl : DataGridViewComboBoxEditingControl
{
public ContextualDataGridViewComboBoxEditingControl()
{
DrawMode = DrawMode.OwnerDrawVariable;
MouseWheel += ContextualDataGridViewComboBoxEditingControl_MouseWheel;
KeyDown += ContextualDataGridViewComboBoxEditingControl_KeyDown;
}
public IEnumerable FilteredRequest
{
get
{
try
{
var currentCell = (EditingControlDataGridView.CurrentCell as ContextualDataGridViewComboBoxCell);
if (currentCell != null)
return currentCell.FilteredRequest;
return null;
}
catch (Exception)
{
return null;
}
}
}
protected override void OnMeasureItem(MeasureItemEventArgs e)
{
if (e.Index < 0)
return;
if (FilteredRequest != null && !FilteredRequest.Contains(Items[e.Index]))
e.ItemHeight = 0;
else
base.OnMeasureItem(e);
}
protected override void OnDrawItem(DrawItemEventArgs e)
{
if (e.Index < 0)
return;
if (FilteredRequest != null && !FilteredRequest.Contains(Items[e.Index]))
return;
e.DrawBackground();
e.Graphics.DrawString(GetItemText(Items[e.Index]), this.Font, Brushes.Black, new RectangleF(e.Bounds.X, e.Bounds.Y, e.Bounds.Width, e.Bounds.Height));
}
private void ContextualDataGridViewComboBoxEditingControl_KeyDown(object sender, KeyEventArgs e)
{
if (!DroppedDown && FilteredRequest != null)
{
if (e.KeyCode == Keys.Up)
changeSelectedItem(-1);
else if (e.KeyCode == Keys.Down)
changeSelectedItem(1);
e.Handled = true;
}
}
private void ContextualDataGridViewComboBoxEditingControl_MouseWheel(object sender, MouseEventArgs e)
{
if (!DroppedDown && FilteredRequest != null)
{
if (e.Delta < 0)
changeSelectedItem(1);
else if (e.Delta > 0)
changeSelectedItem(-1);
((HandledMouseEventArgs)e).Handled = true;
}
}
private void changeSelectedItem(int delta)
{
int tmpIndex = SelectedIndex;
tmpIndex += delta;
while (tmpIndex > -1 && tmpIndex < Items.Count)
{
if (FilteredRequest.Contains(Items[tmpIndex]))
{
SelectedIndex = tmpIndex;
break;
}
tmpIndex += delta;
}
}
}