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vb.net 关于PictureBox和Panel滚动条问题 未将对象引用设置到对象的实例。 RRS feed

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  • Question
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    代码：

    本来利用的是PictureBox的AutoSize属性 再放到一个Panel里面得以增加滚动条

        Private Sub Panel1_Paint(ByVal sender As System.Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Panel1.Paint
            PictureBox.Size = New Point(PictureBox.Image.Width, PictureBox.Image.Height)
        End Sub

    有时可以读取 而有时不行

    报错时Panel周围ScrollBar的区域出现红线

    System.NullReferenceException: 未将对象引用设置到对象的实例。
       在 Personal_Tools.Form_ClipPic.Panel1_Paint(Object sender, PaintEventArgs e) 位置 *（本人已删除） :行号 23
       在 System.Windows.Forms.Control.OnPaint(PaintEventArgs e)
       在 System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e, Int16 layer)
       在 System.Windows.Forms.Control.WmPaint(Message& m)
       在 System.Windows.Forms.Control.WndProc(Message& m)
       在 System.Windows.Forms.ScrollableControl.WndProc(Message& m)
       在 System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       在 System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       在 System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

    2015年1月16日 14:50
    |

答案

  • Question
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    1. 可能你贴错代码了，下面应该是Size而不是Point, Point 只是一个坐标

     PictureBox.Size = New Point(PictureBox.Image.Width, PictureBox.Image.Height)

    2. 其实panel的大小应该已经固定，我们需要在 picturebox的size变化的时候处理下picturebox的位置， 比如我们想要它一直居中，则可以尝试以下方式。

        Private Sub PictureBox1_Resize(sender As Object, e As EventArgs) Handles PictureBox1.Resize
        Me.Panel1.VerticalScroll.Value = 0
        Me.Panel1.HorizontalScroll.Value = 0
        If Me.PictureBox1.Image IsNot Nothing Then


            Dim picSize As Size = Me.PictureBox1.Image.Size
            Dim panSize As Size = Me.Panel1.Size
            If picSize.Height < panSize.Height Then
                Me.PictureBox1.Location = New Point(Me.PictureBox1.Location.X, (panSize.Height - picSize.Height) / 2)
            Else
                Me.PictureBox1.Location = New Point(Me.PictureBox1.Location.X, 0)
            End If
            If picSize.Width < panSize.Width Then
                Me.PictureBox1.Location = New Point((panSize.Width - picSize.Width) / 2, Me.PictureBox1.Location.Y)
            Else
                Me.PictureBox1.Location = New Point(0, Me.PictureBox1.Location.Y)
            End If

        End If
    End Sub

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    2015年1月19日 4:51
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    版主