windows.forms命名空間f定義的rectangle類主要用於表示繪圖的矩形區域。該類有乙個方法contains，用於判斷指定的點在不在矩形區域內部。contains方法的主要形式如下所示：
overloads public function contains (point)as boolean
overloads public function conta/ns (rectangle) as boolean
對話方塊form類的方法中，包括creategraphics，即建立與對話方塊關聯的圖形裝置物件。
不需新增任何控制項
public class form1
dim mygraph as graphics
dim mybrush as new solidbrush(color.blue)
dim circlerect as new rectangle
private sub form1_load(byval sender as object, byval e as system.eventargs) handles me.load
mygraph = me.creategraphics
end sub
private sub form1_mousedown(byval sender as object, byval e as system.windows.forms.mouseeventargs) handles me.mousedown
if e.button = mousebuttons.left then
circlerect.x = e.x
circlerect.y = e.y
end if
end sub
private sub form1_mouseup(byval sender as object, byval e as system.windows.forms.mouseeventargs) handles me.mouseup
if e.button = mousebuttons.left then
circlerect.width = e.x - circlerect.x
circlerect.height = e.y - circlerect.y
mygraph.drawellipse(new pen(brushes.red, 5), circlerect)
dim c as integer
c = int(rnd() * 15)
mybrush.color = drawing.colortranslator.fromwin32(qbcolor(c))
mygraph.fillellipse(mybrush, circlerect)
end if
end sub
end class
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