关于VB.NET画饼图的问题
我用VB.NET编了一个画饼图的程序，为什么运行以后，结果只显示了一下就消失了？

程序如下：
Private Sub FormGraphics1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Dim MyGraphics As Graphics = Me.PictureBox1.CreateGraphics
Dim MyBrush As New SolidBrush(Color.Red)
Dim MyProportion As Single
Dim MyRect As New Rectangle
Dim MyPoint As New PointF
Dim R As Single
Const PI = 3.1415926
MyGraphics.Clear(PictureBox1.BackColor)
Dim MyStartAngel As Double
Dim MySweepAngel As Double

R = Math.Min(Me.PictureBox1.Width, Me.PictureBox1.Height) / 2 - 15
MyPoint.X = Me.PictureBox1.Width / 2
MyPoint.Y = Me.PictureBox1.Height / 2
MyRect.X = MyPoint.X - R
MyRect.Y = MyPoint.Y - R
MyRect.Width = R * 2
MyRect.Height = R * 2

MyStartAngel = 0
MyProportion = 0.25
MySweepAngel = 360 * MyProportion
MyBrush.Color = Color.Red
MyGraphics.FillPie(MyBrush, MyRect, MyStartAngel, MySweepAngel)

MyStartAngel = MyStartAngel + MySweepAngel
MyProportion = 0.75
MySweepAngel = 360 * MyProportion
MyBrush.Color = Color.Blue
MyGraphics.FillPie(MyBrush, MyRect, MyStartAngel, MySweepAngel)

End Sub


[解决办法]
放在Pic的Paint事件中，否则每次切换重新绘制的时候，会造成图形的丢失；

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