C#中事件执行的先后循序问题...

C# code

private void Form1_Load(object sender, EventArgs e)        {            Squer squer1 = new Squer();            squer1.startpoint.X = 50;            squer1.startpoint.Y = 50;            squer1.DrawSquer(this.pictureBox1.Handle);        }        private void pictureBox1_Paint(object sender, PaintEventArgs e)        {            Squer squer1 = new Squer();            squer1.startpoint.X = 50;            squer1.startpoint.Y = 50;            squer1.DrawSquer(this.pictureBox1.Handle);        }

C# code

class Squer    {        private Color bc_color = Color.Red;        private int size = 50;        public Point startpoint;        public Squer()        {        }                 public void DrawSquer(System.IntPtr windowhandle)        {            Graphics g = Graphics.FromHwnd(windowhandle);            SolidBrush b=new SolidBrush(Color.Red);            g.FillRectangle(b, startpoint.X, startpoint.Y, size, size);        }    }

建一个winform窗体，里面放一个pictureBox执行上面的代码，为什么pictureBox中什么也没有...

[解决办法]
这个要用windows重绘事件啊

改动下代码
public void DrawSquer(System.IntPtr windowhandle, PaintEventArgs e)
{
Graphics g = Graphics.FromHwnd(windowhandle);
SolidBrush b=new SolidBrush(Color.Red);

g.FillRectangle(b, startpoint.X, startpoint.Y, size, size);
}

调用把事件对象 e 传进去，注意如果Picture控件在容器里，
squer1.DrawSquer(this.pictureBox1.Handle, e);

比如panel，父容器也要重绘，否则显示不出来
父

[解决办法]
注意，picture控件如果在容器里面。
比如panel，父容器也要重绘，否则显示不出来

[解决办法]
Graphics.FromHwnd事实上创建一个新的graphics，而不是传到paint 事件中的 Graphics 对象，因此在你在squer中画的 还没显示出来就被 默认的的盖住了。

解决该问题，两个办法。

1. 也就是最佳方法 用E.Graphics去画图。这是推荐的方法。
2. 用异步的方式去画，即是调用begininvoke。请看以下代码：

C# code

    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        private void pictureBox1_Paint(object sender, PaintEventArgs e)        {            Squer squer1 = new Squer();            squer1.startpoint.X = this.pictureBox1.Left;            squer1.startpoint.Y = this.pictureBox1.Top;            this.BeginInvoke((Action)(() => squer1.DrawSquer(this.pictureBox1.Handle)));        }    }    class Squer    {        private Color bc_color = Color.Red;        private int size = 50;        public Point startpoint;        public Squer()        {        }        public void DrawSquer(System.IntPtr windowhandle)        {            Graphics g = Graphics.FromHwnd(windowhandle);            SolidBrush b = new SolidBrush(Color.Red);            g.FillRectangle(b, startpoint.X, startpoint.Y, size, size);        }    }