c# - 具有自定义 TextColor、BorderColor 和透明背景颜色的自定义 GroupBox

Question

我正在使用 WinForms。在我的表单中，我有一个 GroupBox。这是一个自定义 组框。我想要 groupbox 的透明背景。我在为 groupbox 创建透明背景时遇到问题 此代码的问题是，当我将组框 backcolor 设置为透明时，我不断收到错误消息。

Error: Control does not support transparent background colors.

g.Clear(BackColor = Color.Transparent);(这是给我问题的那一行)

    private void DrawGroupBox(GroupBox box, Graphics g, Color textColor, Color borderColor)
    {
        if (box != null)
        {
            Brush textBrush = new SolidBrush(textColor);
            Brush borderBrush = new SolidBrush(borderColor);
            Pen borderPen = new Pen(borderBrush);
            SizeF strSize = g.MeasureString(box.Text, box.Font);
            Rectangle rect = new Rectangle(box.ClientRectangle.X,
                                           box.ClientRectangle.Y + (int)(strSize.Height / 2),
                                           box.ClientRectangle.Width - 1,
                                           box.ClientRectangle.Height - (int)(strSize.Height / 2) - 1);

            // Clear text and border
            g.Clear(BackColor = Color.Transparent);

            // Draw text
            g.DrawString(box.Text, box.Font, textBrush, box.Padding.Left, 0);

            // Drawing Border
            //Left
            g.DrawLine(borderPen, rect.Location, new Point(rect.X, rect.Y + rect.Height));
            //Right
            g.DrawLine(borderPen, new Point(rect.X + rect.Width, rect.Y), new Point(rect.X + rect.Width, rect.Y + rect.Height));
            //Bottom
            g.DrawLine(borderPen, new Point(rect.X, rect.Y + rect.Height), new Point(rect.X + rect.Width, rect.Y + rect.Height));
            //Top1
            g.DrawLine(borderPen, new Point(rect.X, rect.Y), new Point(rect.X + box.Padding.Left, rect.Y));
            //Top2
            g.DrawLine(borderPen, new Point(rect.X + box.Padding.Left + (int)(strSize.Width), rect.Y), new Point(rect.X + rect.Width, rect.Y));
        }
    }

    private void groupBox1_Paint(object sender, PaintEventArgs e)
    {
        GroupBox box = sender as GroupBox;
        DrawGroupBox(box, e.Graphics, Color.Red, Color.Blue);
    }

g.Clear(groupBox1.BackColor = Color.Transparent);

如果我这样做，我会得到:

This example consists of a Panel with a dice image inside the panel, and the custom Groupbox.

Answer 1

GroupBox控件支持透明背景，除非你使用System作为FlatStyle，但是对于边框颜色，你需要自己绘制组框。

你可以继承自GroupBox 然后因为GroupBox 支持Transparent 背景，所以你可以简单地覆盖OnPaint并在不对背景做任何事情的情况下呈现您的组框。

代码

using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;
using System.Windows.Forms.VisualStyles;
public class GroupBoxEx : GroupBox
{
    private Color borderColor = Color.Black;
    [DefaultValue(typeof(Color), "Black")]
    public Color BorderColor
    {
        get { return borderColor; }
        set { borderColor = value; this.Invalidate(); }
    }
    private Color textColor = Color.Black;
    [DefaultValue(typeof(Color), "Black")]
    public Color TextColor
    {
        get { return textColor; }
        set { textColor = value; this.Invalidate(); }
    }
    protected override void OnPaint(PaintEventArgs e)
    {
        GroupBoxState state = base.Enabled ? GroupBoxState.Normal : 
            GroupBoxState.Disabled;
        TextFormatFlags flags = TextFormatFlags.PreserveGraphicsTranslateTransform | 
            TextFormatFlags.PreserveGraphicsClipping | TextFormatFlags.TextBoxControl | 
            TextFormatFlags.WordBreak;
        Color titleColor = this.TextColor;
        if (!this.ShowKeyboardCues) 
            flags |= TextFormatFlags.HidePrefix;
        if (this.RightToLeft == RightToLeft.Yes) 
            flags |= TextFormatFlags.RightToLeft | TextFormatFlags.Right;
        if (!this.Enabled) 
            titleColor = SystemColors.GrayText;
        DrawUnthemedGroupBoxWithText(e.Graphics, new Rectangle(0, 0, base.Width,
            base.Height), this.Text, this.Font, titleColor, flags, state);
        RaisePaintEvent(this, e);
    }
    private void DrawUnthemedGroupBoxWithText(Graphics g, Rectangle bounds, 
        string groupBoxText, Font font, Color titleColor, 
        TextFormatFlags flags, GroupBoxState state)
    {
        Rectangle rectangle = bounds;
        rectangle.Width -= 8;
        Size size = TextRenderer.MeasureText(g, groupBoxText, font, 
            new Size(rectangle.Width, rectangle.Height), flags);
        rectangle.Width = size.Width;
        rectangle.Height = size.Height;
        if ((flags & TextFormatFlags.Right) == TextFormatFlags.Right)
            rectangle.X = (bounds.Right - rectangle.Width) - 8;
        else
            rectangle.X += 8;
        TextRenderer.DrawText(g, groupBoxText, font, rectangle, titleColor, flags);
        if (rectangle.Width > 0)
            rectangle.Inflate(2, 0);
        using (var pen = new Pen(this.BorderColor))
        {
            int num = bounds.Top + (font.Height / 2);
            g.DrawLine(pen, bounds.Left, num - 1, bounds.Left, bounds.Height - 2);
            g.DrawLine(pen, bounds.Left, bounds.Height - 2, bounds.Width - 1,
                bounds.Height - 2);
            g.DrawLine(pen, bounds.Left, num - 1, rectangle.X - 3, num - 1);
            g.DrawLine(pen, rectangle.X + rectangle.Width + 2, num - 1, 
                bounds.Width - 2, num - 1);
            g.DrawLine(pen, bounds.Width - 2, num - 1, bounds.Width - 2,
               bounds.Height - 2);
        }
    }
}

截图

关于控件的一些注意事项

• GroupBox 控件支持透明背景，除非您将 System 用作 FlatStyle。
• 也可以继承Panel，因为它是一个容器控件，还支持透明背景色。
• 如果您需要制作一个继承自 Control 的自定义控件以支持透明背景，您应该在构造函数中添加 SetStyle(ControlStyles.SupportsTransparentBackColor, true);。
• 以上代码是在原GroupBox的绘制代码的基础上，我做了一些修改以满足您的要求，并且仍然保持原样GroupBox。
添加了
• BorderColor 属性以支持自定义边框颜色。
• 使用 GroupBox 的 ForeColor 属性来呈现控件的标题可能会很烦人，因为 ForeColor 是一个环境属性，将由子项继承控制。为此，我创建了另一个属性，如 TextColor。 (默认情况下，组框的子项将使用组框的前景色，除非您更改其前景色属性。)