Question

我有一个简单的程序，您可以使用FillEllipse和FillRectangle在屏幕上绘制。我的问题是，当您将另一个窗口拖过屏幕的一小部分时，该部分将被删除。将另一个窗口拖过，放开并将其拖回时会发生这种情况。有什么方法可以解决这个问题吗？

Dim MyFormObject As Graphics = Me.CreateGraphics
        Select Case shape
            Case "Ellipse"
                MyFormObject.FillEllipse(brush, e.X - CInt(brushWidth / 2), e.Y - CInt(brushHeight / 2), brushWidth, brushHeight)
            Case "Rectangle"
                MyFormObject.FillRectangle(brush, e.X - CInt(brushWidth / 2), e.Y - CInt(brushHeight / 2), brushWidth, brushHeight)
        End Select

Answer 1

你可以在你的表单上放置一个PictureBox控件，然后绘制它，当其他窗口涂在它上面时它不会被删除：

在form_load上执行此操作一次：

pictureBox1.Image = new Bitmap(Width, Height);

画画：

Graphics.FromImage(pictureBox1.Image).FillRectangle(Brushes.Black, 0, 0, 100, 100);
pictureBox1.Refresh();

Answer 2

您需要在Paint事件中完成所有绘图，每次重新绘制控件时都会触发。

Answer 3

以下代码允许您使用鼠标绘制矩形（单击并拖动）。将PictureBox添加到表单。

Public Class Form1
  Private mpntMouseDown As Point

  Private Sub Form1_Load(sender As Object, e As System.EventArgs) Handles Me.Load
    Dim w As Integer = PictureBox1.Width
    Dim h As Integer = PictureBox1.Height
    Dim bmp As New Bitmap(w, h, System.Drawing.Imaging.PixelFormat.Format32bppArgb)
    Using g As Graphics = Graphics.FromImage(bmp)
      Dim rct As New RectangleF(0, 0, w, h)
      Dim b As Brush = New System.Drawing.Drawing2D.LinearGradientBrush(rct, Color.White, Color.Blue, 0)
      g.FillRectangle(b, rct)
      g.DrawEllipse(Pens.Blue, New RectangleF(CInt(0.1 * w), CInt(0.2 * h), CInt(0.8 * w), CInt(0.6 * h)))
      g.FillEllipse(Brushes.Yellow, New RectangleF(CInt(0.1 * w) + 1, CInt(0.2 * h) + 1, CInt(0.8 * w) - 2, CInt(0.6 * h) - 2))
      Dim sft As New StringFormat
      sft.Alignment = StringAlignment.Center
      sft.LineAlignment = StringAlignment.Center
      g.DrawString("Sample Image", New Font(System.Drawing.FontFamily.GenericSerif, 14, FontStyle.Italic, GraphicsUnit.Point), Brushes.Red, rct, sft)
    End Using
    PictureBox1.Image = bmp
  End Sub

  Private Sub PictureBox1_MouseDown(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseDown
    If e.Button = Windows.Forms.MouseButtons.Left Then
      mpntMouseDown = e.Location
    End If
  End Sub

  Private Sub PictureBox1_MouseUp(sender As Object, e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseUp
    If mpntMouseDown = Nothing Then Exit Sub
    Using g As Graphics = Graphics.FromImage(PictureBox1.Image, Bitmap)
      Dim rct As New Rectangle
      If mpntMouseDown.X < e.X Then
        rct.X = mpntMouseDown.X
        rct.Width = e.X - mpntMouseDown.X + 1
      Else
        rct.X = e.X
        rct.Width = mpntMouseDown.X - e.X + 1
      End If
      If mpntMouseDown.Y < e.Y Then
        rct.Y = mpntMouseDown.Y
        rct.Height = e.Y - mpntMouseDown.Y + 1
      Else
        rct.Y = e.Y
        rct.Height = mpntMouseDown.Y - e.Y + 1
      End If
      g.DrawRectangle(Pens.Black, rct)
    End Using
    mpntMouseDown = Nothing
    PictureBox1.Invalidate()
  End Sub
End Class

Answer 4

@SLaks已经告诉过你在OnPaint方法中做所有绘画。这里有更多信息。如果您尝试在表单上绘图，则会覆盖OnPaint方法，并使用传递给方法的Graphics实例绘制所有绘图。以下是有关该主题的更多信息：

http://www.bobpowell.net/creategraphics.htm

http://www.bobpowell.net/picturebox.htm

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

    e.Graphics.FillEllipse(Brushes.Red, Me.ClientRectangle)
End Sub

Answer 5

只是一个洞察力，真正帮助我在vb.net中绘制的是这个例子vbnettuthut.blogspot.com它显示了一个完整的例子来绘制平滑和快速的工作示例和源代码

绘图图形在VB.net中消失

5 个答案: