为什么我的矩形未在图片框中绘制？ （拖动）

Question

因此，我尝试通过以某种形式拖动鼠标来绘制矩形，但是我成功了，但是当我尝试在图片框中进行相同的操作时，没有创建矩形。

Private Sub PictureBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseMove

        If fGMouseIsDown And Not PictureBox1.Image Is Nothing Then

            rect.Width = e.X - rect.X
            rect.Height = e.Y - rect.Y
             Invalidate()


        End If
    End Sub

Private Sub PictureBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseDown

        fGMouseIsDown = True
        rect.Location = e.Location
        rect.Width = 0
        rect.Height = 0
        Invalidate()
    End Sub 

Private Sub PictureBox1_Paint(sender As Object, e As PaintEventArgs) Handles PictureBox1.Paint

        e.Graphics.DrawRectangle(Pens.Blue, rect)

End Sub

Answer 1

每个@HansPassant：Invalidate()方法中的PictureBox1_MouseDown()调用使表单无效，而您想使图片框无效。

该通话应改为：

PictureBox1.Invalidate()

此外，请确保以正确的方式拖动；仅当您从左上角转到右下角时，此功能才有效。