模拟时钟 - 在绘制新图像之前无法删除之前的图像

Question

我正在为我正在编写的程序放置一个模拟时钟。我有时钟工作，关于数学是否正确等，但是我无法从生成时钟面的新图像之前删除上一个滴答的图像。我的代码如下，我认为cg.Dispose();行会做到这一点，但它不想。我也尝试在每次打勾结束时处理位图，但是它也引发了错误。在表单中，我有一个pictureBox和一个长度为1000ms的计时器。另外值得注意的是我有表盘的代码，但我只是没有把它包含在这！

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

    namespace ClockStreamlined 
    { 
public partial class Form1 : Form 
{ 
    Bitmap bmp; 
    Graphics cg; 

    public Form1() 
    { 
     InitializeComponent(); 
    } 

    private void Form1_Load(object sender, EventArgs e) 
    { 

     timer1.Enabled = true; 
     bmp = new Bitmap(pictureBox1.Width, pictureBox1.Height); 

    } 

    private void timer1_Tick(object sender, EventArgs e) 
    { 
     pictureBox1.Refresh(); 
     cg = Graphics.FromImage(bmp); 
     // Get components of the DateTime 
     DateTime DateTimenow = DateTime.Now; 
     double hour = DateTimenow.Hour; 
     double minute = DateTimenow.Minute; 
     double second = DateTimenow.Second; 

     // Define increment movements for each clock hand 
     double hourHandangle = (30 * hour) + (minute * 0.5); 
     double minuteHandangle = 6 * minute; 
     double secondHandangle = 6 * second; 

     // Define xy position variables for hour minute & second 
     double x_hour = 0; 

     double x_minute = 0; 

     double x_second = 0; 

     // Calculate hour hand position 

     double y_hour = -(((pictureBox1.Width)/2) - 50) * Math.Cos((hourHandangle * 2 * Math.PI)/360); 
     if (hourHandangle >= 0 && hourHandangle <= 180) 
     { 
      x_hour = (((pictureBox1.Width)/2) - 50) * Math.Sin((hourHandangle * 2 * Math.PI)/360); 
     } 

     else 
     { 
      x_hour = -(((pictureBox1.Width)/2) - 50) * -1 * Math.Sin((hourHandangle * 2 * Math.PI)/360); 
     } 

     // Calculate minute hand position 

     double y_minute = -(((pictureBox1.Width)/2) - 30) * Math.Cos((minuteHandangle * 2 * Math.PI)/360); 

     if (minuteHandangle >= 0 && minuteHandangle <= 100) 
     { 
      x_minute = (((pictureBox1.Width)/2) - 30) * Math.Sin((minuteHandangle * 2 * Math.PI)/360); 
     } 
     else 
     { 
      x_minute = -(((pictureBox1.Width)/2) - 30) * -1 * Math.Sin((minuteHandangle * 2 * Math.PI)/360); 
     } 

     // Calculate second hand position 
     double y_second = -(((pictureBox1.Width)/2) - 10) * Math.Cos((secondHandangle * 2 * Math.PI)/360); 
     if (secondHandangle >= 0 && secondHandangle <= 100) 
     { 
      x_second = (((pictureBox1.Width)/2) - 10) * Math.Sin((secondHandangle * 2 * Math.PI)/360); 
     } 
     else 
     { 
      x_second = -(((pictureBox1.Width)/2) - 10) * -1 * Math.Sin((secondHandangle * 2 * Math.PI)/360); 
     } 

     // Get points that define hour hand 
     int y_hrpoint = Convert.ToInt32(y_hour); 
     int x_hrpoint = Convert.ToInt32(x_hour); 

     // Get points that define minute hand 
     int y_minpoint = Convert.ToInt32(y_minute); 
     int x_minpoint = Convert.ToInt32(x_minute); 

     // Get points that define second hand 
     int x_secpoint = Convert.ToInt32(x_second); 
     int y_secpoint = Convert.ToInt32(y_second); 

     // Create pen 
     Pen blackPen = new Pen(Color.Black, 3); 

     // Create points that define hour hand 
     Point point1hr = new Point(x_hrpoint + ((pictureBox1.Width)/2), y_hrpoint + ((pictureBox1.Width)/2)); 
     Point point2hr = new Point(((pictureBox1.Width)/2), ((pictureBox1.Width)/2)); 

     // Create points that define minute hand 
     Point point1min = new Point(x_minpoint + ((pictureBox1.Width)/2), y_minpoint + ((pictureBox1.Width)/2)); 
     Point point2min = new Point(((pictureBox1.Width)/2), ((pictureBox1.Width)/2)); 

     // Create points that define second hand 
     Point point1sec = new Point(x_secpoint + ((pictureBox1.Width)/2), y_secpoint + ((pictureBox1.Width)/2)); 
     Point point2sec = new Point(((pictureBox1.Width)/2), ((pictureBox1.Width)/2)); 

     // Draw to Bitmap 
     // Draw line to screen. 
     cg.DrawLine(blackPen, point1hr, point2hr); 
     cg.DrawLine(blackPen, point1min, point2min); 
     cg.DrawLine(blackPen, point1sec, point2sec); 
     pictureBox1.Image = bmp; 
     cg.Dispose(); 
     Invalidate(); 

    } 
} 
    } 

Answer 1

让bmp在timer1_Tick函数的局部变量，并在timer1_Tick开始创建bmp位图各一次。

public partial class Form1 : Form 
{ 
    public Form1() 
    { 
     InitializeComponent(); 
    } 

    private void Form1_Load(object sender, EventArgs e) 
    { 
     timer1.Enabled = true; 

    } 

    private void timer1_Tick(object sender, EventArgs e) 
    { 
     Bitmap bmp = new Bitmap(pictureBox1.Width, pictureBox1.Height);; 
     Graphics cg = Graphics.FromImage(bmp); 

     // your other code from timer1_Tick 
     // Get components of the DateTime 
     DateTime DateTimenow = DateTime.Now; 
     double hour = DateTimenow.Hour; 
     double minute = DateTimenow.Minute; 
     double second = DateTimenow.Second; 

     // .... 

     pictureBox1.Image = bmp; 
     cg.Dispose(); 
    } 
} 

Answer 2

要清除以前的图纸您需要调用cg.Clear(Color.White)与任何你想要的背景颜色。

如果您的计时器计时器使面板失效，那么面板的OnPaint事件将执行实际绘图也会更好。你也并不需要使用位图。

public Form1() 
{ 
    InitializeComponent(); 
} 

private void timer1_Tick(object sender, EventArgs e) 
{ 
    pictureBox1.Invalidate(); 
} 

private void pictureBox1_Paint(object sender, PaintEventArgs e) 
{ 
    // Compute hand positions. 
    // ... 


    // Clear the previous drawing. 
    e.Graphics.Clear(Color.White); 

    // Create pen, draw the hands. 
    using (Pen blackPen = new Pen(Color.Black, 3)) 
    { 
     e.Graphics.DrawLine(blackPen, point1hr, point2hr); 
     e.Graphics.DrawLine(blackPen, point1min, point2min); 
     e.Graphics.DrawLine(blackPen, point1sec, point2sec); 
    } 
}