Question

我想点击一个按钮，创建一个新的图片框控件。因此，每次我点击它，它都会添加另一个新的图片框控件。这些图片框都具有相同的功能，如能够移动它们并在它们上绘制。但是按钮只会生成一个，之后不再使用以下代码。我错过了什么？

 Public Class Form1
        Dim xpos As New Integer
        Dim ypos As New Integer
        Dim pos As New Point
        Dim x As Integer
        Dim y As Integer
        Dim canvas As New PictureBox
        Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

            Dim i As Integer = 0
            i = i + 1
            canvas.Name = "canvas" & i
            canvas.BackColor = Color.White
            canvas.BorderStyle = BorderStyle.FixedSingle
            canvas.Image = Nothing
            canvas.Height = TextBox1.Text
            canvas.Width = TextBox2.Text
            AddHandler canvas.MouseDown, AddressOf PictureBox1_MouseDown
            AddHandler canvas.MouseMove, AddressOf PictureBox1_MouseMove
            Controls.Add(canvas)

        End Sub
        Private Sub PictureBox1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
            xpos = Cursor.Position.X - canvas.Location.X
            ypos = Cursor.Position.Y - canvas.Location.Y
        End Sub

        Private Sub PictureBox1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
            If e.Button = Windows.Forms.MouseButtons.Left Then
                pos = MousePosition
                pos.X = pos.X - xpos
                pos.Y = pos.Y - ypos
                canvas.Location = pos
            End If
        End Sub

        Private Sub PictureBox1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)

        End Sub

        Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        End Sub
    End Class

Answer 1

   Dim canvas As New PictureBox

您的代码中存在多个错误，但这是最严重的错误。 As New语法确保您始终创建PictureBox对象，但它只会是一个对象。当然，一个变量无法跟踪多个图片框。

您需要做的是在点击按钮时创建一个新的。跟踪您创建的图片框通常是个好主意。所以正确的代码如下：

   Dim canvases As New List(Of PictureBox)

   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
       Dim canvas = New PictureBox
       canvases.Add(canvas)
       canvas.Name = "canvas" & canvases.Count.ToString()
       '' etc...
   End Sub

    Private Sub PictureBox1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
        Dim canvas = DirectCast(sender, PictureBox)
        xpos = Cursor.Position.X - canvas.Location.X
        ypos = Cursor.Position.Y - canvas.Location.Y
    End Sub

请注意 sender 参数如何为您提供一个返回正在被鼠标的图片框对象的引用。在任何其他事件处理程序中执行相同的操作。

Answer 2

每当创建新画布时增加计数器：

 Public Class Form1
    Dim counter As New Integer
    ...

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        counter += 1
        canvas.Name = "canvas" & counter.ToString()
        ...

访问鼠标当前正在移动的画布：

    Private Sub PictureBox1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs)
        If e.Button = Windows.Forms.MouseButtons.Left Then
            pos = MousePosition
            pos.X = pos.X - xpos
            pos.Y = pos.Y - ypos
            DirectCast(sender, PictureBox).Location = pos
        End If
    End Sub

在Visual Basic中创建新的窗体控件

2 个答案: