' 导入命名空间
Imports System.Windows.Forms
Imports System.Drawing.Text
Imports System.Drawing
Imports System.Drawing.Drawing2D

public class TextBoxSelectionLength
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If TextBox1.SelectionLength = 0 Then
            MessageBox.Show(TextBox1.Text)
        Else
            MessageBox.Show(TextBox1.SelectedText)
        End If
    End Sub
End Class
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Partial Class Form1
    Inherits System.Windows.Forms.Form

    'Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.Button1 = New System.Windows.Forms.Button
        Me.SuspendLayout()
        '
        'TextBox1
        '
        Me.TextBox1.Location = New System.Drawing.Point(12, 12)
        Me.TextBox1.Multiline = True
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(410, 137)
        Me.TextBox1.TabIndex = 0
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(150, 173)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(131, 23)
        Me.Button1.TabIndex = 1
        Me.Button1.Text = "Display selected text"
        Me.Button1.UseVisualStyleBackColor = True
        '
        'Form1
        '
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 12.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(434, 208)
        Me.Controls.Add(Me.Button1)
        Me.Controls.Add(Me.TextBox1)
        Me.ResumeLayout(False)
        Me.PerformLayout()

    End Sub
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    Friend WithEvents Button1 As System.Windows.Forms.Button

End Class