VB.NET绘制方法？

Question

这是在表单上绘制图像的最佳方法吗？我有大部分的Java经验和VB.net的经验。在Java中有可以调用的repaint（）吗？有一个Me.refresh（）。当你有什么要添加到表单或绘制到表单时，这是你打算调用的。

类别：

    Public Class Form1

    Private Sub Form1_Paint(sender As System.Object, e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
        ' Create image. 
        Dim newImage As Image = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")

        ' Create Point for upper-left corner of image. 
        Dim ulCorner As New Point(50, 50)

        ' Draw image to screen.
        e.Graphics.DrawImage(newImage, ulCorner)

        Dim newImage2 As Image = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")

        ' Create Point for upper-left corner of image. 
        Dim ulCorner2 As New Point(150, 150)

        ' Draw image to screen.
        e.Graphics.DrawImage(newImage2, ulCorner2)

    End Sub

End Class

我在这里尝试了这段代码，只需一个按钮就可以点击事件

Public Class Form1
    Dim i As Integer

    Private Sub Form1_Paint(sender As System.Object, e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint

        i = 0

        ' Create image. 
        Dim newImage As Image = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")

        ' Create Point for upper-left corner of image. 
        Dim ulCorner As New Point(50, 50)

        ' Draw image to screen.
        e.Graphics.DrawImage(newImage, ulCorner)

        Dim newImage2 As Image = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")

        ' Create Point for upper-left corner of image. 
        Dim ulCorner2 As New Point(150, 150)

        ' Draw image to screen.
        e.Graphics.DrawImage(newImage2, ulCorner2)

        If i = 5 Then
            ' Create image. 
            Dim newImage3 As Image = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")

            ' Create Point for upper-left corner of image. 
            Dim ulCorner3 As New Point(250, 250)

            ' Draw image to screen.
            e.Graphics.DrawImage(newImage3, ulCorner3)
        End If

    End Sub

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        i = 5
        Me.Refresh()
    End Sub
End Class

刚刚在这里尝试了这段代码：

 Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        i = 5
        Me.Invalidate()
 End Sub

刚刚测试过的新类：

Public Class Form2
    Dim newImage As Image = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")
    Dim newImage2 As Image = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")
    Dim newImage3 As Image = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")

    Private bgImage As Bitmap
    Private srcImages As Image()

    Protected Overrides Sub OnPaint(e As System.Windows.Forms.PaintEventArgs)

        Dim img As Bitmap = Me.bgImage

        If (img Is Nothing) Then
            Me.bgImage = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height)
            img = Me.bgImage
        End If

        If (Not Me.srcImages Is Nothing) Then
        End If

        MyBase.OnPaint(e)

    End Sub

    Private Sub _Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.srcImages = New Image(3 - 1) {}
        Me.srcImages(0) = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")
        Me.srcImages(1) = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")
        Me.srcImages(2) = Image.FromFile("C:\Users\itpr13266\Desktop\Pic\article-tip.gif")
    End Sub

    Private Sub _Disposed(sender As Object, e As EventArgs) Handles MyBase.Disposed
        If (Not Me.srcImages Is Nothing) Then
            For Each img As Image In Me.srcImages
                If (Not img Is Nothing) Then
                    img.Dispose()
                End If
            Next
            Me.srcImages = Nothing
        End If
        If (Not Me.bgImage Is Nothing) Then
            Me.bgImage.Dispose()
            Me.bgImage = Nothing
        End If
    End Sub

    Private Sub _Resize(sender As Object, e As EventArgs) Handles MyBase.SizeChanged, MyBase.Resize
        If (Not Me.bgImage Is Nothing) Then
            Me.bgImage.Dispose()
            Me.bgImage = Nothing
        End If
    End Sub

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        Me.Invalidate()
    End Sub
End Class

Answer 1

第一个片段没有显示需要任何帮助的证据。 Paint事件处理程序中的任何内容都不依赖于类的状态，因此没有理由强制重绘。默认绘画已经足够好了。

第二个片段通过人工i变量执行。在这种情况下，您总是会调用Me.Invalidate()，这会将表单的整个客户区域标记为需要重新绘制。然后，当没有更重要的事情需要完成时，UI最终会获得Paint事件。使用Me.Refresh()也可以起作用，但是很苛刻，而且非常罕见。我想不出一个好的例子。

请注意Invalidate()如何重载，您可以只标记窗口的一部分以重新绘制。这是一种使绘画更有效的优化。

如上所述，您的程序在使用一段时间后可能会崩溃。您必须调用加载的图像的Dispose（）方法。看一下VB.NET 使用语句。您需要预先加载图像，以便在绘画时不会发生，并且不会重复发生。强烈建议遵循Winforms编程教程或书籍以避免这类陷阱。

Answer 2

调用Me.Invalidate()会使控件的整个表面无效并导致重绘控件。

我还建议您不在每个绘制周期中加载图片。 您可以在表单加载事件中加载源图像，并在表单处理时将其销毁。

Public Class Form1

    Protected Overrides Sub OnPaint(e As System.Windows.Forms.PaintEventArgs)

        Dim img As Bitmap = Me.bgImage

        If (img Is Nothing) Then
            Me.bgImage = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height)
            img = Me.bgImage
        End If

        'TODO: Draw and paint.
        If (Not Me.srcImages Is Nothing) Then

        End If

        MyBase.OnPaint(e)

    End Sub

    Private Sub _Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.srcImages = New Image(3 - 1) {}
        Me.srcImages(0) = Image.FromFile("...")
        Me.srcImages(1) = Image.FromFile("...")
        Me.srcImages(2) = Image.FromFile("...")
    End Sub

    Private Sub _Disposed(sender As Object, e As EventArgs) Handles MyBase.Disposed
        If (Not Me.srcImages Is Nothing) Then
            For Each img As Image In Me.srcImages
                If (Not img Is Nothing) Then
                    img.Dispose()
                End If
            Next
            Me.srcImages = Nothing
        End If
        If (Not Me.bgImage Is Nothing) Then
            Me.bgImage.Dispose()
            Me.bgImage = Nothing
        End If
    End Sub

    Private Sub _Resize(sender As Object, e As EventArgs) Handles MyBase.SizeChanged, MyBase.Resize
        If (Not Me.bgImage Is Nothing) Then
            Me.bgImage.Dispose()
            Me.bgImage = Nothing
        End If
    End Sub

    Private bgImage As Bitmap
    Private srcImages As Image()

End Class