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添加一个TextBox控件（比如叫TextBox1）。
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类似于Lable控件的功能，你可以修改TextBox控件的Text属性来达到目的：
不是在设计器里修改，而是在代码中用“TextBox1.Text="你想要显示的字符串";”这样的语句，这样就可以在程序运行时改变显示的内容。
设置或者取消星号，你可以通过代码修改TextBox1的PasswordChar属性，跟上面的是类似的：
在其他的控件的事件中比如Button的Click事件中修改——“TextBox1.PasswordChar="";//不显示***”
“TextBox1.PasswordChar="*（或者任何你想要的字符）";//显示为***”
至于什么时候改就完全随你的意思了。
这个类继承自Panel，把它加到你的项目里面，先运行一下，然后从工具箱里把它拖到窗体上，然后再向里面添加其它控件就可以了，支持Shift加选，Alt减选
Imports System.Linq
Imports System.Collections
Public Class MyPanel
Inherits Panel
' 选择模式，相交还是包含
Enum SelectMode
Intersects
Contains
End Enum
Dim down As New Point(-1, -1)
Dim rect As Rectangle
Dim selected As New List(Of Control)
Dim editting As IEnumerable(Of Control)
Dim mode As SelectMode = SelectMode.Contains
Dim shift, alt As Boolean
Public Sub New()
Me.DoubleBuffered = True
End Sub
Protected Overrides Sub OnMouseDown(e As MouseEventArgs)
MyBase.OnMouseDown(e)
down = e.Location
editting = selected.ToArray().ToList()
OnMouseMove(e)
End Sub
Protected Overrides Sub OnMouseMove(e As MouseEventArgs)
MyBase.OnMouseMove(e)
If e.Button = Windows.Forms.MouseButtons.Left Then
Dim loc As New Point(Math.Min(down.X, e.X), Math.Min(down.Y, e.Y))
Dim size As New Size(Math.Abs(down.X - e.X), Math.Abs(down.Y - e.Y))
rect = New Rectangle(loc, size)
Dim cs As New List(Of Control)
For Each c In Controls
cs.Add(c)
Next
Dim a = cs.Where(Function(n As Control) (mode = SelectMode.Contains And rect.Contains(n.Bounds)) Or (mode = SelectMode.Intersects And rect.IntersectsWith(n.Bounds)))
If shift Then editting = a.Union(selected) Else If alt Then editting = selected.Except(a) Else editting = a
Invalidate()
End If
End Sub
Protected Overrides Sub OnMouseUp(e As MouseEventArgs)
MyBase.OnMouseUp(e)
down = New Point(-1, -1)
selected = editting.ToList()
editting = Nothing
Invalidate()
End Sub
Protected Overrides Function ProcessKeyPreview(ByRef m As Message) As Boolean
Dim KeyCode As Keys = CInt(m.WParam) And CInt(Keys.KeyCode)
Dim d As Boolean
If m.Msg = H100 Or m.Msg = H104 Then d = True Else If m.Msg = H101 Or m.Msg = H105 Then d = False Else Return MyBase.ProcessKeyPreview(m)
If KeyCode = Keys.ShiftKey Then
shift = d
ElseIf KeyCode = Keys.Menu Then
alt = d
End If
Return MyBase.ProcessKeyPreview(m)
End Function
Protected Overrides Sub OnPaint(e As PaintEventArgs)
MyBase.OnPaint(e)
For Each c As Control In IIf(editting Is Nothing, selected, editting)
e.Graphics.DrawRectangle(New Pen(Color.Gray) With {.DashStyle = Drawing2D.DashStyle.DashDot}, c.Left - 1, c.Top - 1, c.Width + 1, c.Height + 1)
Next
If (down.X 0) Then e.Graphics.DrawRectangle(New Pen(Color.Gray) With {.DashStyle = Drawing2D.DashStyle.DashDot}, rect)
End Sub
End Class
文本框控件就是TextBox，只有一个，至于你说的txtScore，txtAvg，txtMax,txtMin。。。。这些都是实例，你把文本框控件拖到窗体，然后起这些名字就可以了。
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
ComboBox1.Items.Add("米")
ComboBox1.Items.Add("分米")
ComboBox1.Items.Add("厘米")
ComboBox1.DropDownStyle = ComboBoxStyle.DropDownList
End Sub
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
Select Case ComboBox1.SelectedIndex
Case 0
TextBox1.Text = "1"
Case 1
TextBox1.Text = "10"
Case 2
TextBox1.Text = "100"
Case Else
TextBox1.Text = ""
End Select
End Sub
End Class