vb.net graphic 简单的画图程序

概述Dim g As Graphics = Me.CreateGraphics 需要局部定义  每次实用需要定义--不能定义成全局   Public Class Form1 Dim DrawState As Boolean Dim PreX As Single Dim PreY As Single Dim eP As New Pen(Color.Black, 3

Dim g As Graphics = Me.CreateGraphics

需要局部定义 每次实用需要定义--不能定义成全局

Public Class Form1    Dim DrawState As Boolean    Dim PreX As Single    Dim PreY As Single    Dim eP As New Pen(color.Black,3)          ' 构造黑色画笔，并将它赋给对象变量eP    'Dim g As Graphics = Me.CreateGraphics     ' 在窗体上构造一块画布，并将它赋给对象变量g    Private Sub Form1_Load(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles MyBase.Load        ' 将DrawState初始化为False，表示提笔        DrawState = False    End Sub    Private Sub Form1_MouseDown(ByVal sender As Object,ByVal e As System.windows.Forms.MouseEventArgs) Handles Me.MouseDown        ' 当鼠标左键被按下时，把DrawState设为True，表示落笔开始画线        Dim g As Graphics = Me.CreateGraphics        If e.button = windows.Forms.Mousebuttons.left Then            DrawState = True     ' 设置画图状态            PreX = e.X          ' PreX和PreY保存了线条的起点。            PreY = e.Y        End If        ' 当按住鼠标右键时，画一个直径为50的圆        If e.button = windows.Forms.Mousebuttons.Right Then            g.DrawEllipse(eP,e.X - 25,e.Y - 25,100,100)        End If    End Sub    Private Sub Form1_MouseMove(ByVal sender As Object,ByVal e As System.windows.Forms.MouseEventArgs) Handles Me.MouseMove        ' 当鼠标移动时，如果处于画线状态，则在(PreX，PreY)与(X，Y)之间画一条直线        Dim g As Graphics = Me.CreateGraphics        If DrawState = True Then            g.Drawline(eP,PreX,PreY,e.X,e.Y)            PreX = e.X            PreY = e.Y        End If    End Sub    Private Sub Form1_MouseUp(ByVal sender As Object,ByVal e As System.windows.Forms.MouseEventArgs) Handles Me.MouseUp        ' 当释放鼠标左键时，解除画线状态        If e.button = windows.Forms.Mousebuttons.left Then            DrawState = False        End If    End SubEnd Class

改法1

Public Class Form1    Dim DrawState As Boolean    Dim PreX As Single    Dim PreY As Single    Dim eP As New Pen(color.Black,3)          ' 构造黑色画笔，并将它赋给对象变量eP    Dim g As Graphics     ' 在窗体上构造一块画布，并将它赋给对象变量g    Private Sub Form1_Load(ByVal sender As System.Object,ByVal e As System.windows.Forms.MouseEventArgs) Handles Me.MouseDown        ' 当鼠标左键被按下时，把DrawState设为True，表示落笔开始画线        'Dim g As Graphics = Me.CreateGraphics        If e.button = windows.Forms.Mousebuttons.left Then            DrawState = True     ' 设置画图状态            PreX = e.X          ' PreX和PreY保存了线条的起点。            PreY = e.Y        End If        ' 当按住鼠标右键时，画一个直径为50的圆        If e.button = windows.Forms.Mousebuttons.Right Then            g.DrawEllipse(eP,ByVal e As System.windows.Forms.MouseEventArgs) Handles Me.MouseMove        ' 当鼠标移动时，如果处于画线状态，则在(PreX，PreY)与(X，Y)之间画一条直线        'Dim g As Graphics = Me.CreateGraphics        If DrawState = True Then            g.Drawline(eP,ByVal e As System.windows.Forms.MouseEventArgs) Handles Me.MouseUp        ' 当释放鼠标左键时，解除画线状态        If e.button = windows.Forms.Mousebuttons.left Then            DrawState = False        End If    End SubPrivate Sub Form1_Resize(ByVal sender As Object,ByVal e As System.EventArgs) Handles Me.Resize        g = Me.CreateGraphics    End SubEnd Class

改法2

将声明定义到模块中

总结

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