实例说明
在本实例中，我们制作一个应用程序，通过选择不同的按钮来产生不同的随机图形。程序运行结果如图62-1所示。
图62-1 运行结果
技术要点
l DrawEllipse方法
l DrawLine方法
l DrawBezier方法
l DrawArc方法
实现过程
■ 新建项目
打开Visual Studio.NET，选择"新建项目"，在项目类型窗口中选择"Visual Basic项目"，在模板窗口中选择"Windows应用程序"，在名称域中输入"RndPic"，然后选择保存路径。单击"确认"。
■ 添加窗体和控件
选择菜单"项目|添加Windows窗体"，为项目添加一窗体frmRndPic；在主窗体frmmain上添加六个Button按钮。
■ 设置属性
对窗体上的控件设置属性，对frmmain而言，将Button按钮的Text属性改为和界面一致即可。在这里就不再列出。下面在表62-1中列出了窗体frmRndPic的主要属性。
表62-1 窗体frmRndPic的主要属性值
窗体/控件 属性 值
FrmRndPic BorderStyle 0-None
BackColor &H80000007
WindowState 2-Maximized
' 选择按钮，执行不同的画图操作
Private Sub btnLine_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles btnLine.Click
item = 5
frmRndpic.DefInstance.Show()
End Sub
Private Sub btnPoint_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles btnPoint.Click
item = 1
frmRndpic.DefInstance.Show()
End Sub
Private Sub btnCircle_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles btnCircle.Click
item = 2
frmRndpic.DefInstance.Show()
End Sub
Private Sub btnEllipse_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles btnEllipse.Click
item = 3
frmRndpic.DefInstance.Show()
End Sub
Private Sub btnArc_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles btnArc.Click
item = 4
frmRndpic.DefInstance.Show()
End Sub
Private Sub btnRectangle_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles btnRectangle.Click
item = 6
frmRndpic.DefInstance.Show()
End Sub
Private Sub frmRndpic_KeyPress(ByVal eventSender As System.Object,ByVal eventArgs As System.Windows.Forms.KeyPressEventArgs) Handles MyBase.KeyPress
Dim KeyAscii As Short = Asc(eventArgs.KeyChar)
' ESC的键值为27，当按下ESC键时，返回主界面
If KeyAscii = 27 Then
Me.Close()
frmmain.DefInstance.Show()
End If
If KeyAscii = 0 Then
eventArgs.Handled = True
End If
End Sub
' 执行划线操作
Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
Dim loopnum As Int16
Dim gp As Graphics = e.Graphics
Dim newpen As New Pen(Color.FromArgb(255 * Rnd(),255 * Rnd(),255 * Rnd()),2)
Select Case item
Case 1
'画贝塞尔线
For loopnum = 1 To 100
newpen = New Pen(Color.FromArgb(255 * Rnd(),2)
p.DrawBezier(newpen,Rnd() * Me.Height,Rnd() * Me.Width,Rnd() * Me.Width)
Next
'画随机圆
Case 2
Dim cirx,ciry As Short
For loopnum = 1 To 100
newpen = New Pen(Color.FromArgb(255 * Rnd(),2)
cirx = Rnd() * Me.Height : ciry = Rnd() * Me.Width
gp.DrawEllipse(newpen,cirx,ciry,cirx)
Next
'画随机椭圆
Case 3
For loopnum = 1 To 100
newpen = New Pen(Color.FromArgb(255 * Rnd(),2)
gp.DrawEllipse(newpen,Rnd() * Me.Height)
Next
Case 4
For loopnum = 1 To 100
newpen = New Pen(Color.FromArgb(255 * Rnd(),2)
gp.DrawArc(newpen,Rnd() * Me.Height)
Next
Case 5
'画随机直线
for loopnum = 1 To 100
newpen = New Pen(Color.FromArgb(255 * Rnd(),2)
'newpen.Color = Color.Black
gp.DrawLine(newpen,Rnd() * Me.Height)
Next
Case 6
'画随机矩形
For loopnum = 1 To 100
newpen = New Pen(Color.FromArgb(255 * Rnd(),2)
gp.DrawRectangle(newpen,Rnd() * Me.Width)
Next
End Select
End Sub
■ 运行结果
单击菜单"调试|启动"或单击 图标运行程序。
小结
本实例说明了绘图的几种方法，可以看出主要使用了画直线（DrawLine）方法、画椭圆（DrawEllipse）方法。在VB.NET中使用画图跟以前完全不一样。它使用封装的类system.Drawing来画图。