本文以一个用户控件【User Control】实现温度计的小例子，简述用户控件的相关知识，以供学习分享使用，如有不足之处，还请指正。
概述
一般而言，用户控件【User Control】，是在Visual Studio提供的默认控件不能满足实际的工作需要，才需要在现有控件的基础之上进行新的扩展，来实现自己的功能。用户控件有自己特有的属性，事件，方法来支撑特定的功能。用户控件封装实现的细节，可以进行方便的复用。
用户控件分类
用户控件主要有以下三种分类，本例采用的是第三种。
涉及知识点
本例中主要涉及以下知识点：
示例效果图
本例中示例效果图如下所示：
关键代码
本例中的关键代码如下：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace DemoThermometer
{
public partial class Thermometer : UserControl
{
#region 属性与构造函数
private int interval = 10;
/// <summary>
/// 刻度间隔
/// </summary>
public int Interval
{
get { return interval; }
set { interval = value; }
}
private int minValue = -50;
/// <summary>
/// 最低温度
/// </summary>
public int MinValue
{
get { return minValue; }
set { minValue = value; }
}
private int maxValue = 50;
/// <summary>
/// 最高温度
/// </summary>
public int MaxValue
{
get { return maxValue; }
set { maxValue = value; }
}
private float curValue = 0;
/// <summary>
/// 当前温度
/// </summary>
public float CurValue
{
get { return curValue; }
set { curValue = value; }
}
private Color thermoColor = Color.Red;
/// <summary>
/// 温度条颜色
/// </summary>
public Color ThermoColor
{
get { return thermoColor; }
set { thermoColor = value; }
}
private Color backGroundColor = Color.SkyBlue;
/// <summary>
/// 温度计背景色
/// </summary>
public Color BackGroundColor
{
get { return backGroundColor; }
set { backGroundColor = value; }
}
private Font thermoFont=new Font("宋体",10,FontStyle.Regular);
/// <summary>
/// 温度计上字体
/// </summary>
public Font ThermoFont
{
get { return thermoFont; }
set { thermoFont = value; }
}
private string thermoTitle = "温度计";
/// <summary>
/// 标题
/// </summary>
public string ThermoTitle
{
get { return this.thermoTitle; }
set { this.thermoTitle = value; }
}
private bool showTip = false;
/// <summary>
/// 是否显示提示
/// </summary>
public bool ShowTip
{
get { return showTip; }
set { showTip = value; }
}
private ToolTip tip=new ToolTip();
public Thermometer()
{
InitializeComponent();
}
#endregion
protected override void OnPaint(PaintEventArgs e)
{
//base.OnPaint(e);
//this.BackColor = this.backGroundColor;
int width = this.Width;
int height = this.Height - 50 ;
Graphics g = e.Graphics;
int c_x = width / 2;
int c_y = height / 2;
int padding = this.Padding.All;//空白
int r = (width - 2 * padding)/2;//半径
int d = 2 * r;//直径
int dis = 2;//两个半圆之间的间隔
int dis2 = 2 * dis;//填充与边框之间的距离
int startAngle1 = -180;
int startAngle2 = 0;
int sweepAngle1 = 180;
//首先画顶端一个半圆
g.DrawPie(Pens.Black, new Rectangle(padding, padding, d, d),startAngle1, sweepAngle1);
g.DrawPie(Pens.Black, new Rectangle(padding+ dis, padding+ dis, d-2* dis, d-2* dis), startAngle1, sweepAngle1);
//填充背景色
g.FillPie(new SolidBrush(this.backGroundColor), new Rectangle(padding + dis2, padding + dis2, d - 2*dis2, d - 2*dis2), startAngle1, sweepAngle1);
//画底端一个半圆
g.DrawPie(Pens.Black, new Rectangle(padding, height-d-padding, d, d), startAngle2, sweepAngle1);
g.DrawPie(Pens.Black, new Rectangle(padding + dis, height-d-padding + dis, d - 2*dis, d - 2*dis), startAngle2, sweepAngle1);
g.FillPie(new SolidBrush(this.backGroundColor), new Rectangle(padding + dis2, height - d - padding+dis2, d - 2*dis2, d - 2*dis2), startAngle2, sweepAngle1);
//画一个矩形
g.DrawRectangle(Pens.Black, new Rectangle(padding, padding + r, d, height - d - 2 * padding));
g.DrawRectangle(Pens.Black, new Rectangle(padding+dis, padding + r+dis, d-2*dis, height - d - 2 * padding-2*dis));
//背景色填充，去掉边界线
g.FillRectangle(new SolidBrush(this.backGroundColor), new Rectangle(padding+3, padding + r-2, 2 * r-6, 6));
g.FillRectangle(new SolidBrush(this.backGroundColor), new Rectangle(padding + 3, height-r-padding-4, 2 * r - 6, 8));
//背景色填充中间部分
g.FillRectangle(new SolidBrush(this.backGroundColor), new Rectangle(padding + dis2, padding + r + dis2, d - 2*dis2, height -d - 2 * padding - 2*dis2));
//画刻度
int s_s_x_1 = padding + r - 20;
int s_s_x_2 = width-padding - r + 20;
int s_s_y = padding + r+4;
int total = this.maxValue - this.minValue;
int scale_width = 5;//刻度宽度
int scale = total / this.interval;
int pscale = (height - 2 * r - 2 * padding) / this.interval;//像素间隔
//竖线
g.DrawLine(Pens.Black, new Point(s_s_x_1, s_s_y ), new Point(s_s_x_1, s_s_y + this.interval* pscale));
g.DrawLine(Pens.Black, new Point(s_s_x_2, s_s_y), new Point(s_s_x_2, s_s_y + this.interval * pscale));
for (int i = 0; i <= this.interval; i++) {
//横线刻度
g.DrawLine(Pens.Black, new Point(s_s_x_1- scale_width, s_s_y + i * pscale), new Point(s_s_x_1, s_s_y + i * pscale));
g.DrawLine(Pens.Black, new Point(s_s_x_2, s_s_y + i * pscale), new Point(s_s_x_2 + scale_width, s_s_y + i * pscale));
//画刻度数字
g.DrawString((this.maxValue - (scale * i)).ToString(), this.thermoFont, new SolidBrush( this.ForeColor), new Point(s_s_x_1-35, s_s_y + i * pscale-10));
g.DrawString((this.maxValue - (scale * i)).ToString(), this.thermoFont, new SolidBrush(this.ForeColor), new Point(s_s_x_2 + 10, s_s_y + i * pscale-10));
}
int white_width = 3;//中间白色线宽度
//画条白色细线
g.FillRectangle(Brushes.White, new Rectangle(c_x- white_width, r/2, white_width*2, height-r));
//在底部画一个圆球
g.FillPie(new SolidBrush(this.thermoColor), new Rectangle(c_x-r/2+5, height - r - padding, r-10, r-10), 0, 360);
//根据当前温度画红色线
int red_width = 5;//红色温度线宽度
float ii = ( this.curValue-this.minValue) / this.interval;
g.FillRectangle(new SolidBrush(this.thermoColor), new RectangleF(c_x - red_width, height - r - padding- (ii * pscale)-4, 2* red_width, ii * pscale+5));//此处有一像素的误差
//画标志字符单℃位
g.DrawString("℃", this.thermoFont, new SolidBrush(this.ForeColor), new Point(c_x - 30, r / 2 - 10));
Font titleFont = new Font("宋体", 13, FontStyle.Bold);
//绘制标题
SizeF tsize = g.MeasureString(this.thermoTitle, titleFont);
g.DrawString(this.thermoTitle, titleFont, new SolidBrush(this.ForeColor), new PointF(c_x- (tsize.Width/2), height + 5));
string cur = string.Format("当前温度：{0}℃", this.curValue);
SizeF tsize2 = g.MeasureString(cur, this.thermoFont);
g.DrawString(cur, this.thermoFont, new SolidBrush(this.thermoColor), new PointF(c_x - (tsize2.Width / 2), height + 10+tsize.Height));
}
/// <summary>
/// 当鼠标覆盖进去时
/// </summary>
/// <param name="e"></param>
protected override void OnMouseHover(EventArgs e)
{
this.showTip = true;
//需要显示的内容
int x = this.Width / 2;
int y = (this.Height-50) / 2;
StringBuilder sbTips = new StringBuilder();
//sbTips.AppendLine(this.ThermoTitle);
sbTips.AppendLine(string.Format("当前温度：{0}", this.curValue));
sbTips.AppendLine("单位：℃");
tip.ToolTipTitle = this.ThermoTitle;
tip.IsBalloon = true;
tip.UseFading = true;
//t.SetToolTip(this, sbTips.ToString());
tip.Show(sbTips.ToString(), this, x, y);
}
protected override void OnMouseLeave(EventArgs e)
{
this.showTip = false;
tip.Hide(this);
}
}
}
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