Question

VB.NET画线的问题

picArea.Image = Image.FromFile(Application.StartupPath & "\Images\default.png")
Dim mybitmap As Bitmap
mybitmap = New Bitmap(picArea.Width, picArea.Height)
picArea.Image = mybitmap

Dim Graph As Graphics = picArea.CreateGraphics

Graph = Graphics.FromImage(picArea.Image)
Graph.DrawLine(Pens.Blue, 0, 0, 111, 111)
Graph.DrawLine(Pens.Red, 111, 111, 200, 0)

怎么加载的图片不见了，如果不画后面的线图就能正常显示！

Answer 1

picArea.Image = Image.FromFile(Application.StartupPath & "\Images\default.png")
Dim mybitmap As Bitmap
'mybitmap = New Bitmap(picArea.Width, picArea.Height)//你这样是创建了一个空白的底片
mybitmap = New Bitmap(picArea.Image) '这才是利用了图片的背景
picArea.Image = mybitmap
Dim Graph As Graphics = picArea.CreateGraphics
Graph = Graphics.FromImage(picArea.Image)
Graph.DrawLine(Pens.Blue, 0, 0, 111, 111)
Graph.DrawLine(Pens.Red, 111, 111, 200, 0)