如何在 VB.Net PictureBox 上动态创建覆盖

Question

我在表单form1 上有一个VB.Net PictureBox floorPlanImage。

我将图片加载到图片框中：

    floorPlanImage.image = my.resources.ResourceManager.GetObject("level8") 'this is actually dynamic, and this part works

我正在尝试创建一个叠加层来突出显示图像的某个区域：

    Public Sub highlightPrintArea(ByVal x1 As Integer, ByVal y1 As Integer, ByVal x2 As Integer, ByVal y2 As Integer)
    '**** DOES NOT WORK
    Dim g As Graphics = Me.CreateGraphics
    Dim r As Rectangle = New Rectangle(x1, y1, x2 - x1, y2 - y1) 'these are args passed in to the function
    Dim pen As Pen = New Pen(Color.FromArgb(128, 32, 100, 200), 1) 'semi-transparent
    Dim b As Brush = New SolidBrush(pen.Color)

    g.FillRectangle(b, r)
    end sub

我需要在运行时动态地执行此操作，例如在单击按钮时。上面的函数好像没有画矩形。

但是，如果我有一个 Handles floorPlanImage.Paint 如下所示的函数，那么矩形将按照我的预期绘制：

Private Sub floorPlanImage_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles floorPlanImage.Paint
    '**** Works, but does not suit my workflow
    Dim g As Graphics = e.Graphics
    Dim r As Rectangle = New Rectangle(100, 100, 100, 100)
    Dim pen As Pen = New Pen(Color.FromArgb(128, 32, 100, 200), 1)
    Dim b As Brush = New SolidBrush(pen.Color)

    g.FillRectangle(b, r)
End Sub

问题（终于）

如何修改我的 onclick 函数以正确地将矩形覆盖在我的 PictureBox 上？

Answer 1

在 onclick 事件中，您需要将位置/点保存到成员变量并设置一个标志，以便应用知道您保存了一个位置。要更新图片框，请调用 Invalidate 和 Update。

floorPlanImage.Invalidate()
floorPlanImage.Update()

在 onpaint 事件中测试你有一个点的标志，然后使用保存的点来绘制覆盖。

Private Sub floorPlanImage_Paint(ByVal sender As Object, ByVal e As  System.Windows.Forms.PaintEventArgs) Handles floorPlanImage.Paint
    If hasPoint

       'Draw with saved point
    End If
End Sub