从鼠标移动事件调用绘画事件 [英] Call paint event from mouse move event

问题描述

当鼠标移到panel2上时，我需要画线.到目前为止，我已经完成了

When mouse move over a panel2, I need to draw lines. So far I have done following

public Form1()
{           
    InitializeComponent();            

}

private void panel2_Paint(object sender, PaintEventArgs e)
{
    if (isDragging)
    {
        letsPaint(sender, e);
    }
}

private void panel2_MouseMove(object sender, MouseEventArgs e)
{
    if (isDragging) 
    {
        mouseMoveX = e.X;
        mouseMoveY = e.Y;                               
        this.Paint += new PaintEventHandler(panel2_Paint);
    }
}

private void letsPaint(object sender, PaintEventArgs e) 
{             
    Pen blackpen = new Pen(Color.Black, 3);
    Graphics g = e.Graphics;
    g.DrawLine(blackpen, mouseClickedX, mouseClickedY, mouseMoveX, mouseMoveY);
    g.Dispose(); 
}

但是当我移动鼠标时什么也没有发生.我想我在这里做错了PaintEventHandler().请告诉我该怎么做以及是否还有更好的方法.

But nothing happens when I move mouse. I think I did something wrong PaintEventHandler() here. Please tell me how to do this and also if there is any better way for this.

我还认为我的方法将在表单上绘制线条，但我需要在panel2上绘制线条.怎么做?提前致谢.

Also I think my method will drawline on the form but I need to draw line on the panel2. How to do? Thanks in advance.

推荐答案

您使无效:

public Form1()
{           
  InitializeComponent();            
  panel2.Paint += new letsPaint;
}

private void panel2_MouseMove(object sender, MouseEventArgs e)
{
  if (isDragging) {
    mouseMoveX = e.X;
    mouseMoveY = e.Y;                               
    panel2.Invalidate();
  }
}

并且您不处置图形对象(您没有创建它)，但是您使用钢笔:

and you don't dispose the graphic object (you didn't create it), but you do the pen:

private void letsPaint(object sender, PaintEventArgs e) {             
  using (Pen blackpen = new Pen(Color.Black, 3)) {
    e.Graphics.DrawLine(blackpen, 
                        mouseClickedX, mouseClickedY, mouseMoveX, mouseMoveY);
  }
}

---

这是一种适用于位图的快捷方法:

---

Here is a quick little method that works with a bitmap:

Bitmap bmp;
Point lastPoint;

public Form1() {
  InitializeComponent();
  bmp = new Bitmap(panel1.ClientSize.Width, panel1.ClientSize.Height, 
                   System.Drawing.Imaging.PixelFormat.Format32bppPArgb);

  panel1.MouseDown += panel1_MouseDown;
  panel1.MouseMove += panel1_MouseMove;
  panel1.Paint += panel1_Paint;
}

void panel1_Paint(object sender, PaintEventArgs e) {
  e.Graphics.DrawImage(bmp, Point.Empty);
}

void panel1_MouseMove(object sender, MouseEventArgs e) {
  if (e.Button == MouseButtons.Left) {
    using (Graphics g = Graphics.FromImage(bmp)) {
      g.DrawLine(Pens.Black, lastPoint, e.Location);
    }
    lastPoint = e.Location;
    panel1.Invalidate();
  }
}

void panel1_MouseDown(object sender, MouseEventArgs e) {
  lastPoint = e.Location;
}

这将闪烁，因此您希望将面板替换为双缓冲面板.像这样:

This will flicker, so you would want to replace your panel with a double-buffered panel. Something like this:

public class PanelEx : Panel {
  public PanelEx() {
    this.DoubleBuffered = true;
  }
}

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