请教各位高手一个Onpaint（）问题，小弟不胜感激

Question

我想每次进度条都随着文本框中的数字而动态的现实，我自己写的代码不能实现，感觉不到动态效果，每次产生一个随机数，进度条都重新画一次，我不知道每次重画怎么实现？各位高手帮帮忙吧，这个问题弄了好久了，还是不行？
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;namespace wenduji
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }     
        private void timer1_Tick(object sender, EventArgs e)
        {
            Random ro = new Random();
            textBox1.Text = ro.Next(10, 50).ToString();
            Graphics dc = this.CreateGraphics();
            this.Show();
            Pen p1 = new Pen(Color.Black);
            Rectangle rec = new Rectangle(20, 100, 200, 30);
            dc.DrawRectangle(p1, rec);
            dc.DrawEllipse(p1, 0, 100, 30, 30);
            dc.DrawString("o", this.Font, Brushes.Black, 225, 70);
            dc.DrawString("C", this.Font, Brushes.Black, 230, 75);
            ////绘制最短的刻度线
            for (int i = 20; i <= 220; i += 4)
            {
                dc.DrawLine(p1, i, 90, i, 100);
            }
            for (int i = 20; i <= 220; i += 40)
            {
                dc.DrawLine(p1, i, 80, i, 100);
                //绘制刻度旁边的数字
                switch (i)
                {
                    case 20:
                        dc.DrawString("0", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 60:
                        dc.DrawString("10", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 100:
                        dc.DrawString("20", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 140:
                        dc.DrawString("30", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 180:
                        dc.DrawString("40", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 220:
                        dc.DrawString("50", this.Font, Brushes.Red, i - 5, 65);
                        break;                }            }
            //绘制稍长的刻度线
            for (int i = 40; i <= 200; i += 40)
            {
                dc.DrawLine(p1, i, 85, i, 100);
            }
            SolidBrush b1 = new SolidBrush(Color.Red);            //dc.FillRectangle(b1,rec);
            float d = float.Parse(textBox1.Text.ToString());
            float a = d * 4 ; //温度对应的矩形宽度
            dc.FillRectangle(b1, 20, 100, a, 30);
            //画一个圆
            dc.FillEllipse(b1, 0, 100, 30, 30);
        }
    }
}

Answer 1

你要把画图的代码放在OnPaint（）方法里
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            textBox1.Text = "10";
        }        private void timer1_Tick(object sender, EventArgs e)
        {
            Random ro = new Random();
            textBox1.Text = ro.Next(10, 50).ToString();
            this.Refresh(); 
        }
        protected override void OnPaint(PaintEventArgs e)
        {
            Graphics dc = e.Graphics;          
            Pen p1 = new Pen(Color.Black);
            Rectangle rec = new Rectangle(20, 100, 200, 30);
            dc.DrawRectangle(p1, rec);
            dc.DrawEllipse(p1, 0, 100, 30, 30);
            dc.DrawString("o", this.Font, Brushes.Black, 225, 70);
            dc.DrawString("C", this.Font, Brushes.Black, 230, 75);
            ////绘制最短的刻度线
            for (int i = 20; i <= 220; i += 4)
            {
                dc.DrawLine(p1, i, 90, i, 100);
            }
            for (int i = 20; i <= 220; i += 40)
            {
                dc.DrawLine(p1, i, 80, i, 100);
                //绘制刻度旁边的数字
                switch (i)
                {
                    case 20:
                        dc.DrawString("0", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 60:
                        dc.DrawString("10", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 100:
                        dc.DrawString("20", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 140:
                        dc.DrawString("30", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 180:
                        dc.DrawString("40", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 220:
                        dc.DrawString("50", this.Font, Brushes.Red, i - 5, 65);
                        break;
                }
            }
            //绘制稍长的刻度线
            for (int i = 40; i <= 200; i += 40)
            {
                dc.DrawLine(p1, i, 85, i, 100);
            }
            SolidBrush b1 = new SolidBrush(Color.Red);            //dc.FillRectangle(b1,rec);
            float d = float.Parse(textBox1.Text);
            float a = d * 4; //温度对应的矩形宽度
            dc.FillRectangle(b1, 20, 100, a, 30);
            //画一个圆
            dc.FillEllipse(b1, 0, 100, 30, 30);
            base.OnPaint(e);
        }
    }
}

Answer 2

虽然这样的实现你要的动态效果，但是你有没有发现这样，如果这样写的话整个界面闪烁的很厉害，特别是值变化得很快的时候。还有直接在窗体上画图不够灵活，当你想把图移动位置就变得很麻烦，需要该很多代码。所以我建议你编写一个自定义的用户控件，利用双缓冲可以减少闪烁，步骤如下：
1.添加一个“用户控件”，编写如下代码：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Text;
using System.Windows.Forms;namespace WindowsApplication1
{
    public partial class UserControl1 : UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
            /*双缓冲以减少闪烁*/
            SetStyle(ControlStyles.OptimizedDoubleBuffer|ControlStyles.AllPaintingInWmPaint|ControlStyles.UserPaint, true);
        }
        private float m_Dvalue = 0f;
        /// <summary>
        /// 温度对应的矩形宽度
        /// </summary>
        public float Dvalue
        {
            get { return m_Dvalue; }
            set { m_Dvalue = value; }
        }
        protected override void OnPaint(PaintEventArgs e)
        {
            Graphics dc = e.Graphics;
            Pen p1 = new Pen(Color.Black);
            Rectangle rec = new Rectangle(20, 100, 200, 30);
            dc.DrawRectangle(p1, rec);
            dc.DrawEllipse(p1, 0, 100, 30, 30);
            dc.DrawString("o", this.Font, Brushes.Black, 225, 70);
            dc.DrawString("C", this.Font, Brushes.Black, 230, 75);
            ////绘制最短的刻度线
            for (int i = 20; i <= 220; i += 4)
            {
                dc.DrawLine(p1, i, 90, i, 100);
            }
            for (int i = 20; i <= 220; i += 40)
            {
                dc.DrawLine(p1, i, 80, i, 100);
                //绘制刻度旁边的数字
                switch (i)
                {
                    case 20:
                        dc.DrawString("0", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 60:
                        dc.DrawString("10", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 100:
                        dc.DrawString("20", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 140:
                        dc.DrawString("30", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 180:
                        dc.DrawString("40", this.Font, Brushes.Red, i - 5, 65);
                        break;
                    case 220:
                        dc.DrawString("50", this.Font, Brushes.Red, i - 5, 65);
                        break;
                }
            }
            //绘制稍长的刻度线
            for (int i = 40; i <= 200; i += 40)
            {
                dc.DrawLine(p1, i, 85, i, 100);
            }
            SolidBrush b1 = new SolidBrush(Color.Red);            //dc.FillRectangle(b1,rec);
            float d = m_Dvalue;
            float a = d * 4; //温度对应的矩形宽度
            dc.FillRectangle(b1, 20, 100, a, 30);
            //画一个圆
            dc.FillEllipse(b1, 0, 100, 30, 30);
            base.OnPaint(e);
        }
    }
}
2.生成解决方案，这时你会在工具栏的最上方多了一个“UserControl1”的控件，把他拉到窗体上，它的属性栏里有个
  “Dvalue”的属性，那个就是上面的温度对应的矩形宽度，你可以在这里直接赋值，也可以编写代码赋值，如下：
        private void timer1_Tick(object sender, EventArgs e)
        {
            Random ro = new Random();
            float d = ro.Next(10, 50);
            textBox1.Text =d .ToString();
            userControl11.Dvalue = d;
            userControl11.Refresh();//刷新控件
            
        }
3，运行程序，^_^