我试图在Visual Studio 2015中创建一个小的绘图应用程序.我的项目属于
Windows窗体应用程序的类别.我有以下问题：
private void Form1_MouseMove(object sender,MouseEventArgs e)
{
if (a == 1)
{
if (r == 1 || el == 1)
{
int x = Math.Min(inX,e.X);
int y = Math.Min(inY,e.Y);
int width = Math.Max(inX,e.X) - Math.Min(inX,e.X);
int height = Math.Max(inY,e.Y) - Math.Min(inY,e.Y);
rect = new Rectangle(x,y,width,height);
Refresh();
}
else if (l == 1)
{
ep = e.Location;
Refresh();
}
else
{
ep = e.Location;
g = this.CreateGraphics();
g.DrawLine(p,sp,ep);
sp = ep;
}
}
}
我的代码的这一部分创建了一个Rectangular(第2个if),一个线段(第3个if)和一条线.它的工作原理与MS Paint几乎相同;在用户释放鼠标左键(鼠标向上)之前,矩形或线段不会完成.但是当我再次尝试创建另一个矩形时最终制作了一个矩形,表单刷新(Refresh();)并且我丢失了之前绘制的所有矩形或线条.我试过替换Refresh(); with Invalidate(rect);和Update();,但我没有得到我想要的结果.
相反,我明白了：
解决方法
您应该将所有绘图都放到一个单独的位图“缓冲区”中.将形状绘制到该位图,然后在实际需要更新屏幕时,将缓冲区绘制到屏幕上.
此外,无论何时调用Graphics.FromImage,您都需要记住Dispose,否则它会像疯了一样泄漏资源.
令人难以置信的简单例子
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;
namespace DrawExample
{
public partial class Form1 : Form
{
private Bitmap _canvas; //This is the offscreen drawing buffer
private Point _anchor; //The start point for click-drag operations
private Rectangle? _ghost;
private Brush _ghostBrush;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender,EventArgs e)
{
_ghostBrush = new SolidBrush(Color.FromArgb(200,200,255)); //This creates a slightly blue,transparent brush for the ghost preview
ResizeCanvas();
}
private void Form1_Resize(object sender,EventArgs e)
{
ResizeCanvas();
}
/// <summary>
/// Resizes the offscreen bitmap to match the current size of the window,it preserves what is currently in the bitmap.
/// </summary>
private void ResizeCanvas()
{
Bitmap tmp = new Bitmap(this.Width,this.Height,PixelFormat.Format32bppRgb);
using (Graphics g = Graphics.FromImage(tmp))
{
g.Clear(Color.White);
if (_canvas != null)
{
g.DrawImage(_canvas,0);
_canvas.Dispose();
}
}
_canvas = tmp;
}
private void Form1_MouseDown(object sender,MouseEventArgs e)
{
if (e.Button == MouseButtons.Left)
{
_anchor = new Point(e.X,e.Y);
}
}
private void Form1_MouseMove(object sender,MouseEventArgs e)
{
if (e.Button == MouseButtons.Left)
{
_ghost = new Rectangle(_anchor.X,_anchor.Y,e.X - _anchor.X,e.Y - _anchor.Y);
this.Invalidate();
}
}
private void Form1_MouseUp(object sender,MouseEventArgs e)
{
if (e.Button == MouseButtons.Left)
{
//Create a Graphics for the offscreen bitmap
using (Graphics g = Graphics.FromImage(_canvas))
{
Rectangle rect = new Rectangle(_anchor.X,e.Y - _anchor.Y);
g.FillRectangle(Brushes.White,rect);
g.DrawRectangle(Pens.Black,rect);
}
_ghost = null;
//This queues up a redraw call for the form
this.Invalidate();
}
}
private void Form1_Paint(object sender,PaintEventArgs e)
{
if (_ghost.HasValue)
{
using (Bitmap tmp = new Bitmap(_canvas))
{
using (Graphics g = Graphics.FromImage(tmp))
{
g.FillRectangle(_ghostBrush,_ghost.Value);
g.DrawRectangle(Pens.Black,_ghost.Value);
e.Graphics.DrawImage(tmp,0);
}
}
}
else
{
e.Graphics.DrawImage(_canvas,0);
}
}
//This stops the flickering
protected override void OnPaintBackground(PaintEventArgs e)
{
//Do nothing
}
}
}
