VB 2010 (7) 引用类型
Object 类
https://docs.microsoft.com/zh-cn/dotnet/api/system.object?view=netframework-4.8
Object类是.NET中每个类型的基类——包括值类型和引用类型。本质上，每个变量都是一个对象，都可以作为对象来处理。
由于Object类是所有类型的基础，所以可以将任何变量转换为Object。引用类型将维护它们当前的引用和实现代码，但是会被当做一般类型来处理，而值类型会从它们在堆栈的当前位置上提取，并放入堆上与Object相关的内存位置中。这个过程称为“装箱”，因为我们提取了值，并把它从一个地方移动到另一个地方。
String 类
https://docs.microsoft.com/zh-cn/dotnet/api/system.string?view=netframework-4.8
String.Empty 字段
String类是.NET中特有的，这是唯一不是值类型的基本类型。
String.Compare 方法
https://docs.microsoft.com/zh-cn/dotnet/api/system.string.compare?view=netframework-4.8
String.CompareOrdinal 方法
String.Concat 方法
String.Copy(String) 方法
https://docs.microsoft.com/zh-cn/dotnet/api/system.string.copy?view=netframework-4.8
String.Equals 方法
https://docs.microsoft.com/zh-cn/dotnet/api/system.string.equals?view=netframework-4.8#definition
String.IsNullOrEmpty(String) 方法
String.Substring 方法
String.Split 方法
https://docs.microsoft.com/zh-cn/dotnet/api/system.string.split?view=netframework-4.8#definition
String.Concat 方法
https://docs.microsoft.com/zh-cn/dotnet/api/system.string.concat?view=netframework-4.8#definition
StringBuilder 类
https://docs.microsoft.com/zh-cn/dotnet/api/system.text.stringbuilder?view=netframework-4.8
DBNull 类
https://docs.microsoft.com/zh-cn/dotnet/api/system.dbnull?view=netframework-4.8
Array 类
https://docs.microsoft.com/zh-cn/dotnet/api/system.array?view=netframework-4.8
System.Collections 命名空间
https://docs.microsoft.com/zh-cn/dotnet/api/system.collections?view=netframework-4.8
CType 函数 (Visual Basic)
返回将表达式显式转换为指定的数据类型、对象、结构、类或接口的结果
https://docs.microsoft.com/zh-cn/dotnet/visual-basic/language-reference/functions/ctype-function
Public Class Form1
Dim count As Integer
Private Sub ButtonTest_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonTest.Click
count += 1
'MessageBox.Show("Hello World show " & count.ToString & " times", _
' "Hello World message box", _
' MessageBoxButtons.OK, _
' MessageBoxIcon.Information)
'测试值类型
'ValueType()
'测试引用类型
'RefType()
'试验布尔型数据
'Booltest()
'试验时间数据类型
'Dates()
'试验String类型
StringSamples()
End Sub
'测试值类型
Private Sub ValueType()
Dim ptX As Point = New Point(10, 20)
Dim ptY As Point
ptY = ptX
'ptX变，ptY不会变
ptX.X = 200
TextBox1.Text = "值类型变量：" & vbCrLf & "Pt Y= " & ptY.ToString & vbCrLf
End Sub
'测试引用类型
Private Sub RefType()
Dim objX As System.Text.StringBuilder = New System.Text.StringBuilder("Hello World.")
Dim objY As System.Text.StringBuilder
objY = objX
'objX变化，objY也会变，浅复制（shallow copy）
objX.Replace("World", "Test")
TextBox1.Text = TextBox1.Text & "引用型变量：" & vbCrLf & "objY = " & objY.ToString
End Sub
'试验布尔型数据
Private Sub Booltest()
Dim blnTrue As Boolean = True
Dim blnFalse As Boolean = False
If blnTrue Then
TextBox1.Text = blnTrue & Environment.NewLine
TextBox1.Text &= blnFalse.ToString
End If
End Sub
'时间类型
Private Sub Dates()
Dim dtNow = Now
Dim dtToday = Today
TextBox1.Text = dtNow & Environment.NewLine
TextBox1.Text &= dtToday.ToShortDateString & Environment.NewLine
TextBox1.Text &= DateTime.UtcNow & Environment.NewLine
Dim dtString = #12/13/2009#
TextBox1.Text &= dtString.ToLongDateString
End Sub
'试验String类型
Private Sub stringSamples()
Dim strSample As String = "ABC"
Dim strSample2 = "DEF"
Dim strSample3 = New String("A"c, 20) '调用构造函数，第一个参数是一个字符，第二个是字符串中该字符的重复次数
Dim strline = New String("-", 80)
'子串
Dim MysubString = "Hello World"
TextBox1.Text &= MysubString.Substring(0, 5) & Environment.NewLine '起始位置及长度
TextBox1.Text &= MysubString.Substring(6) & Environment.NewLine '起始位置到末尾
TextBox1.Text &= strline & Environment.NewLine
'分隔
Dim csvString = "Col1,Col2,Col3"
Dim stringArray As String() = csvString.Split(",")
For i = 0 To stringArray.Length - 1
TextBox1.Text &= stringArray(i) & Environment.NewLine
Next
TextBox1.Text &= strline & Environment.NewLine
'字符串连接
Dim start = Now
Dim strRedo = "A simple string "
For index = 1 To 10000
strRedo &= "Making a much larger String."
Next
'DateTime.Subtract方法返回通过从此实例的值减去指定的时间或持续时间得到的值。
TextBox1.Text &= "time to Concatenate strings:" & _
(Now().Subtract(start)).TotalMilliseconds().ToString() & _
" String length:" & strRedo.Length.ToString
TextBox1.Text &= strline & Environment.NewLine
start = Now
Dim strBulider = New System.Text.StringBuilder("A simple string ")
For Index = 1 To 1000000
strBulider.Append("Making a much larger string")
Next
TextBox1.Text &= "Time to concatenate string:" & _
(Now().Subtract(start)).TotalMilliseconds().ToString() & _
" String length:" & strBulider.Length.ToString
TextBox1.Text &= strline & Environment.NewLine
End Sub
End Class