组合框文本垂直居中对齐

Question

我在 .net framework 1.1 上创建了自定义组合框，我可以自定义绘制下拉项，但我不能在左中设置或绘制组合框文本，组合框文本总是呈现左上角，但我需要文本应该呈现在左中.

[ToolboxBitmap(typeof(ComboBox))]
public class MenComboBox :ComboBox
{
    private Image _image = Image.FromFile("Expand.png");
    public MenComboBox()
    {
        this.DrawMode = DrawMode.OwnerDrawFixed;
        this.BackColor = Color.White;
        this.ItemHeight = 18;
        this.Font = new Font("Arial",12f,FontStyle.Regular);
    }       
    protected override void OnDrawItem(DrawItemEventArgs e)
    {

            if (!DesignMode)
            {
                if (e.Index > -1)
                {
                    int textHeight = (int)e.Graphics.MeasureString(this.Items[e.Index].ToString(), e.Font).Height;
                    Point textPos = new Point(e.Bounds.X + 4, e.Bounds.Y + ((this.ItemHeight - textHeight) / 2));
                    if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
                    {
                        e.Graphics.FillRectangle(Brushes.Blue, e.Bounds);
                        e.Graphics.DrawString(this.Items[e.Index].ToString(),e.Font,Brushes.White,textPos);
                    }
                    else
                    {
                        e.Graphics.FillRectangle(Brushes.White, e.Bounds);
                        e.Graphics.DrawString(this.Items[e.Index].ToString(),e.Font,Brushes.Black,textPos);
                    }
                }
            }

    }
    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        if (m.Msg == 0x000F)
        {
            using (Graphics g = this.CreateGraphics())
            {
                g.FillRectangle(new SolidBrush(BackColor), this.ClientRectangle);
                g.DrawRectangle(Pens.Blue, new Rectangle(this.ClientRectangle.X, this.ClientRectangle.Y, this.ClientRectangle.Width - 1, this.ClientRectangle.Height - 1));
                Rectangle rect = new Rectangle(this.Width - 15, 3, 12, this.Height - 6);
                g.FillRectangle(new SolidBrush(BackColor), rect);
                g.DrawImage(this._image, this.Width - 16, (this.Height - 8) / 2);
                g.Dispose();
            }
        }
    }   
}

Answer 1

在所有者绘制ComboBox ，无论ItemHeight的高度如何，控件的Edit部分的文本将始终显示在ItemHeight 。

要将Edit部件垂直放置在中间，您可以使用GetComboBoxInfo找到Edit元素，然后使用SetWindowPos GetComboBoxInfo设置一个新位置，使其垂直放置在ComboBox中间。

当控件大小发生变化时，您需要重新定位它。 您还需要用颜色填充ComboBox的背景。

这是我使用的代码：

using System;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Windows.Forms;
public class MyComboBox : ComboBox
{
    public MyComboBox()
    {
        SetStyle(ControlStyles.ResizeRedraw, true);
        DrawMode = DrawMode.OwnerDrawFixed;
        ItemHeight = 40;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct RECT
    {
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;
        public int Width { get { return Right - Left; } }
        public int Height { get { return Bottom - Top; } }
    }

    private const int SWP_NOSIZE = 0x0001;
    private const int SWP_NOZORDER = 0x0004;
    private const int SWP_SHOWWINDOW = 0x0040;
    [DllImport("user32.dll", SetLastError = true)]
    static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, 
        int X, int Y, int cx, int cy, int uFlags);

    [DllImport("user32.dll")]
    public static extern bool GetComboBoxInfo(IntPtr hWnd, ref COMBOBOXINFO pcbi);

    [StructLayout(LayoutKind.Sequential)]
    public struct COMBOBOXINFO
    {
        public int cbSize;
        public RECT rcItem;
        public RECT rcButton;
        public int stateButton;
        public IntPtr hwndCombo;
        public IntPtr hwndEdit;
        public IntPtr hwndList;
    }
    protected override void OnResize(EventArgs e)
    {
        base.OnResize(e);
        SetupEdit();
        Invalidate();
    }
    private int buttonWidth = SystemInformation.HorizontalScrollBarArrowWidth;
    protected override void WndProc(ref Message m)
    {
        if (m.Msg == 0xF)
        {
            using (var g = this.CreateGraphics())
            {
                var r = new Rectangle(2, 2,
                    ClientRectangle.Width - buttonWidth - 2,
                    ClientRectangle.Height - 4);
                g.FillRectangle(Brushes.White, r);
            }
        }
        base.WndProc(ref m);
    }
    protected override void OnVisibleChanged(EventArgs e)
    {
        base.OnVisibleChanged(e);
        SetupEdit();
    }
    private void SetupEdit()
    {
        var info = new COMBOBOXINFO();
        info.cbSize = Marshal.SizeOf(info);
        GetComboBoxInfo(this.Handle, ref info);
        SetWindowPos(info.hwndEdit, IntPtr.Zero, 3,
            (this.Height - Font.Height) / 2,
            ClientRectangle.Width - buttonWidth - 3,
            ClientRectangle.Height - Font.Height - 4,
            SWP_NOZORDER);
    }
    protected override void OnDrawItem(DrawItemEventArgs e)
    {
        base.OnDrawItem(e);
        e.DrawBackground();
        var txt = "";
        if (e.Index >= 0)
            txt = GetItemText(Items[e.Index]);
        TextRenderer.DrawText(e.Graphics, txt, Font, e.Bounds, 
            ForeColor, TextFormatFlags.Left | TextFormatFlags.VerticalCenter);
    }
}

Answer 2

好的，下面的代码没有回答关于文本部分的实际问题； 像往常一样，汉斯做对了。

我保留答案是因为我认为它比 OP 代码做得更好。

    if (!DesignMode)
    {
        if (e.Index > -1)
        {
           using (StringFormat fmt = new StringFormat() 
             { Alignment = StringAlignment.Center, LineAlignment = StringAlignment.Center })
           {

            if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
            {
                e.Graphics.FillRectangle(SystemBrushes.MenuHighlight, e.Bounds);
                e.Graphics.DrawString(comboBox1.Items[e.Index].ToString(), 
                                        e.Font,SystemBrushes.HighlightText, e.Bounds, fmt);
            }
            else
            {
                e.Graphics.FillRectangle(SystemBrushes.Window, e.Bounds);
                e.Graphics.DrawString(comboBox1.Items[e.Index].ToString(), 
                                        e.Font, SystemBrushes.MenuText,e.Bounds, fmt);
            }
         }
      }
    }

我没有计算居中位置，而是使用DrawString重载，该重载接受一个目标矩形并添加一个StringFormat以在两个方向上居中。 StringFormat从 .Net 1.1 开始可用，并且确实是IDisposable ，所以我们应该处理我们创建的每个，最好在using子句中..

请注意，对于绘图控件，鼓励使用TextRenderer ，但仅随 .Net 2.0 一起提供。

另请注意，我将Brushes替换为SystemBrushes ..

另外：我的 ComboBox 不会将文本放在左上角而是左中角的文本部分。 也许旧的 .Net1.1 控件是罪魁祸首？