我无法将 ComboBox 停靠在 TableLayoutPanel 单元格中

Question

Please see the image below: I want to dock a ComboxBox control in a cell of my TableLayoutPanel.

The ComboBox Dock property is set to Fill and the Anchor property to top, bottom, left and right .

Answer 1

As suggested already you cannot change the height of combobox and textbox using anchor or dock property. You can change the font size in Font property. the default is 8.25pt.

Like Here

Answer 2

TL; DR

It's expected behavior, for ComboBox setting Dock to Fill doesn't fill the container. it's Height is calculated based on its Font height or for an owner-draw ComboBox based on its ItemHeight .

If it's really necessary for you to change the behavior, you can hack the behavior by overriding its SetBoundsCore method.

---

Long Answer - A ComboBox which supports Dock = Fill

The height of ComboBox is controlled based on the following rules:

• If the control's DrawMode is Normal, then the height will be based on Font.Height
• If the control's DrawMode is OwnerDraw then the height will be based on the ItemHeight

So it doesn't support Docking-Fill.

But you can hack the behavior; You can derive from ComboBox and change the behavior by overriding SetBoundsCore :

using System.Windows.Forms;
public class MyComboBox : ComboBox
{
    public MyComboBox()
    {
        DrawMode = DrawMode.OwnerDrawFixed;
    }
    protected override void SetBoundsCore(
        int x, int y, int width, int height, BoundsSpecified specified)
    {
        base.SetBoundsCore(x, y, width, height, specified);
        if (Dock == DockStyle.Fill ||
            Dock == DockStyle.Left ||
            Dock == DockStyle.Right)
        {
            var d = SystemInformation.FixedFrameBorderSize.Height;
            ItemHeight = height - 2 * d;
        }
        else
        {
            ItemHeight = FontHeight + 2;
        }
    }
    protected override void OnDrawItem(DrawItemEventArgs e)
    {
        e.DrawBackground();
        var text = e.Index >= 0 ? GetItemText(e.Index) : string.Empty;
        TextRenderer.DrawText(e.Graphics, text, e.Font, e.Bounds, e.ForeColor,
            TextFormatFlags.Left | TextFormatFlags.VerticalCenter);
        base.OnDrawItem(e);
    }
}

And as result: