winform 下拉框（自定义下拉框控件）

项目中遇到需要下拉框列表内容为线类型或点类型图形的需求，想到可以使用手绘线条和图形的方式来实现下拉列表内容自定义，记录下来供大家参考学习之用。

在项目中添加一个组件

添加完之后会显示如下设计界面

这里直接点击切换到代码视图即可

注意：新建的组件默认继承Component，我们这里是要自定义一个ComboBox下拉框，所以要继承自ComboBox，此类位于using System.Windows.Forms命名空间下

线的类型列表

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace CustomComponents
{
    /// <summary>
    /// 填充线型
    /// </summary>
    public partial class FillLineTypeCbo : ComboBox
    {
        public FillLineTypeCbo()
        {
      		//初始化组件
            InitializeComponent();
        }

        public FillLineTypeCbo(IContainer container)
        {
            container.Add(this);

            InitializeComponent();
            InitItems();
        }

        private void InitItems()
        {
            this.DrawMode = DrawMode.OwnerDrawFixed;//手动绘制所有元素
            this.DropDownStyle = ComboBoxStyle.DropDownList;//下拉框样式设置为不能编辑
            this.Items.Clear();//清空原有项 
        }

        public enum LineType
        {
            DoubleHorizontalLine = 0,//双横线
            VerticalLine,//垂直线
            LeftSlash,//左斜线
            RightSlash,//右斜线
            VerticalGridlines,//垂直网格线
            CrossGridlines,//交叉网格线
            SolidBrush,//实心刷
            HollowBrush,//空心刷
        }
        //protected
        protected override void OnDrawItem(DrawItemEventArgs e)
        {
            if (e.Index >= 0)//判断是否需要重绘
            {
                int typeId = int.Parse(this.Items[e.Index].ToString());//获取选项id

                Font font = new Font("宋体", 9);//定义字体
                Rectangle rect = e.Bounds;
                //rect.Inflate(-2, -2);//缩放一定大小
                rect.Inflate(5, -2);//缩放一定大小
                Pen pen = null;
                SolidBrush solidBrush = new SolidBrush(Color.Black);

                float offSet = rect.Height / 2;
                float x = rect.Width / 10;
                float y = rect.Top + offSet;//如果设置成e.ItemHeigh*e.Index +offSet,则在选中节点后，由于Item位置固定，因此Item不能显示出来。
                switch (typeId)
                {
                    case (int)LineType.DoubleHorizontalLine:
                        pen = new Pen(Color.Black, 1);
                        e.Graphics.DrawLine(pen, new PointF(x, y), new PointF(8 * x, y));//绘制水平线
                        e.Graphics.DrawLine(pen, new PointF(x, y + 5), new PointF(8 * x, y + 5));
                        //e.Graphics.DrawLine(pen, new PointF(x, y+2), new PointF(x, y+2));
                        break;
                    case (int)LineType.VerticalLine:
                        pen = new Pen(Color.Black, 1);
                        //绘制垂直线
                        int xNum = 0;
                        for (int i = 0; i < 10; i++)
                        {
                            e.Graphics.DrawLine(pen, new PointF(x + xNum, y - 4), new PointF(1 * x + xNum, y + 6));
                            xNum += 7;

                        }
                        break;
                    case (int)LineType.LeftSlash:
                        pen = new Pen(Color.Black, 1);
                        //绘制左斜线
                        int xNumLeftSlash = 0;
                        for (int i = 0; i < 10; i++)
                        {
                            e.Graphics.DrawLine(pen, new PointF(x + xNumLeftSlash, y - 4), new PointF(x + 5 + xNumLeftSlash, y + 7));
                            xNumLeftSlash += 7;
                        }
                        break;
                    case (int)LineType.RightSlash:
                        pen = new Pen(Color.Black, 1);
                        //绘制右斜线
                        int xNumRightSlash = 0;
                        for (int i = 0; i < 10; i++)
                        {
                            e.Graphics.DrawLine(pen, new PointF(x + xNumRightSlash + 7, y - 4), new PointF(x + xNumRightSlash, y + 7));
                            xNumRightSlash += 7;
                        }
                        break;
                    case (int)LineType.VerticalGridlines:
                        pen = new Pen(Color.Black, 1);
                        //绘制垂直网格线
                        xNum = 0;
                        for (int i = 0; i < 10; i++)//绘制竖线
                        {
                            e.Graphics.DrawLine(pen, new PointF(x + xNum, y - 4), new PointF(1 * x + xNum, y + 6));
                            xNum += 7;