Asp.net 随机字符串生成器在多个调用中创建相同的字符串

我已经构建了一个随机字符串生成器，但是我遇到了一个问题，如果我多次调用该函数（比如在Page_Load方法中），该函数将返回相同的字符串两次

这是密码

Public Class CustomStrings
    ''' <summary>'
    ''' Generates a Random String'
    ''' </summary>'
    ''' <param name="n">number of characters the method should generate</param>'
    ''' <param name="UseSpecial">should the method include special characters? IE: # ,$, !, etc.</param>'
    ''' <param name="SpecialOnly">should the method include only the special characters and excludes alpha numeric</param>'
    ''' <returns>a random string n characters long</returns>'
    Public Function GenerateRandom(ByVal n As Integer, Optional ByVal UseSpecial As Boolean = True, Optional ByVal SpecialOnly As Boolean = False) As String

        Dim chars As String() ' a character array to use when generating a random string'
        Dim ichars As Integer = 74 'number of characters to use out of the chars string'
        Dim schars As Integer = 0 ' number of characters to skip out of the characters string'

        chars = { _
         "A", "B", "C", "D", "E", "F", _
         "G", "H", "I", "J", "K", "L", _
         "M", "N", "O", "P", "Q", "R", _
         "S", "T", "U", "V", "W", "X", _
         "Y", "Z", "0", "1", "2", "3", _
         "4", "5", "6", "7", "8", "9", _
         "a", "b", "c", "d", "e", "f", _
         "g", "h", "i", "j", "k", "l", _
         "m", "n", "o", "p", "q", "r", _
         "s", "t", "u", "v", "w", "x", _
         "y", "z", "!", "@", "#", "$", _
         "%", "^", "&", "*", "(", ")", _
         "-", "+"}


        If Not UseSpecial Then ichars = 62 ' only use the alpha numeric characters out of "char"'
        If SpecialOnly Then schars = 62 : ichars = 74 ' skip the alpha numeric characters out of "char"'

        Dim rnd As New Random()
        Dim random As String = String.Empty
        Dim i As Integer = 0
        While i < n
            random += chars(rnd.[Next](schars, ichars))
            System.Math.Max(System.Threading.Interlocked.Increment(i), i - 1)
        End While
        rnd = Nothing
        Return random
    End Function
End Class

答案是这样的

    Dim rnd1 As New CustomStrings
    Dim rnd2 As New CustomStrings

    Dim str1 As String = rnd1.GenerateRandom(5) 
    Dim str2 As String = rnd2.GenerateRandom(5) 

    rnd1 = Nothing
    rnd2 = Nothing

g*3Jq
g*3Jq

第二次我叫它的时候，它会

3QM0$
3QM0$

---

我错过了什么？我希望生成的每个随机字符串都是唯一的。

原因是，当您构造

random

类的实例时，它会从时钟中为自己播种，但如果您快速连续地调用它，则该时钟的精度不足以在每次调用中生成新的种子

换言之，这：

Random r = new Random();
int i = r.Next(1000);
r = new Random();
int j = r.Next(1000);

在

i

和

j

中产生相同值的概率非常高

您需要做的是：

• 创建并缓存

  Random

  实例，使其与每次调用使用的实例相同（但不幸的是，该类不是线程安全的，因此至少为每个线程保留一个缓存副本）
• 用每次调用都会发生变化的内容对其进行种子设定（这相当困难，因为用顺序值对其进行种子设定会产生可预测的随机数）

下面是一个示例程序，它为每个线程创建一个单独的

Random

实例，并从全局随机对象中为这些实例种子。同样，这可能会产生可预测的序列

using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace SO2755146
{
    public class Program
    {
        public static void Main()
        {
            List<Task> tasks = new List<Task>();
            for (int index = 0; index < 1000; index++)
                tasks.Add(Task.Factory.StartNew(() => Console.Out.WriteLine(RNG.Instance.Next(1000))));
            Task.WaitAll(tasks.ToArray());
        }
    }

    public static class RNG
    {
        private static Random _GlobalSeed = new Random();
        private static object _GlobalSeedLock = new object();

        [ThreadStatic]
        private static Random _Instance;

        public static Random Instance
        {
            get
            {
                if (_Instance == null)
                {
                    lock (_GlobalSeedLock)
                    {
                        _Instance = new Random(_GlobalSeed.Next());
                    }
                }
                return _Instance;
            }
        }
    }
}

使用系统；
使用System.Collections.Generic；
使用System.Threading.Tasks；
名称空间SO2755146
{
公共课程
{
公共静态void Main（）
{
列表任务=新列表（）；
对于（int-index=0；index<1000；index++）
tasks.Add（Task.Factory.StartNew（（）=>Console.Out.WriteLine（RNG.Instance.Next（1000）））；
Task.WaitAll（tasks.ToArray（））；
}
}
公共静态类RNG
{
private static Random_GlobalSeed=new Random（）；
私有静态对象_GlobalSeedLock=新对象（）；
[线程静态]
私有静态随机实例；
公共静态随机实例
{
得到
{
if（_Instance==null）
{
锁（_GlobalSeedLock）
{
_Instance=newrandom（_GlobalSeed.Next（））；
}
}
返回_实例；
}
}
}
}

如果您只想从时钟中为每个随机实例设定种子，但至少要为每个线程生成随机序列，可以将其简化为：

using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace SO2755146
{
    public class Program
    {
        public static void Main()
        {
            List<Task> tasks = new List<Task>();
            for (int index = 0; index < 1000; index++)
                tasks.Add(Task.Factory.StartNew(() => Console.Out.WriteLine(RNG.Instance.Next(1000))));
            Task.WaitAll(tasks.ToArray());
        }
    }

    public static class RNG
    {
        [ThreadStatic]
        private static Random _Instance;

        public static Random Instance
        {
            get
            {
                if (_Instance == null)
                    _Instance = new Random();

                return _Instance;
            }
        }
    }
}

使用系统；
使用System.Collections.Generic；
使用System.Threading.Tasks；
名称空间SO2755146
{
公共课程
{
公共静态void Main（）
{
列表任务=新列表（）；
对于（int-index=0；index<1000；index++）
tasks.Add（Task.Factory.StartNew（（）=>Console.Out.WriteLine（RNG.Instance.Next（1000）））；
Task.WaitAll（tasks.ToArray（））；
}
}
公共静态类RNG
{
[线程静态]
私有静态随机实例；
公共静态随机实例
{
得到
{
if（_Instance==null）
_Instance=newrandom（）；
返回_实例；
}
}
}
}

---

这可能会使两个线程开始时彼此非常接近，以相同的值作为种子，因此存在一个折衷。

我做了一些更改，对我来说似乎很好。我不喜欢使用关键字作为变量名。请注意，我移动了随机语句：

Public Class Form1

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

    Dim myCS As New CustomStrings
    Dim l As New List(Of String)

    For x As Integer = 1 To 10
        Dim s As String = myCS.GenerateRandom(5)
        l.Add(s)
    Next

    For x As Integer = 0 To l.Count - 1
        Debug.WriteLine(l(x))
    Next
    'Debug output
    'YGXiV
    'rfLmP
    'OVUW9
    '$uaMt
    '^RsPz
    'k&91k
    '(n2uN
    'ldbQQ
    'zYlP!
    '30kNt
End Sub

Public Class CustomStrings

    Private myRnd As New Random()
    Public Function GenerateRandom(ByVal n As Integer, _
                                   Optional ByVal UseSpecial As Boolean = True, _
                                   Optional ByVal SpecialOnly As Boolean = False) As String

        Dim ichars As Integer = 74 'number of characters to use out of the chars string'
        Dim schars As Integer = 0 ' number of characters to skip out of the characters string'

        Dim chars() As Char = New Char() {"A"c, "B"c, "C"c, "D"c, "E"c, "F"c, _
                                          "G"c, "H"c, "I"c, "J"c, "K"c, "L"c, _
                                          "M"c, "N"c, "O"c, "P"c, "Q"c, "R"c, _
                                          "S"c, "T"c, "U"c, "V"c, "W"c, "X"c, _
                                          "Y"c, "Z"c, "0"c, "1"c, "2"c, "3"c, _
                                          "4"c, "5"c, "6"c, "7"c, "8"c, "9"c, _
                                          "a"c, "b"c, "c"c, "d"c, "e"c, "f"c, _
                                          "g"c, "h"c, "i"c, "j"c, "k"c, "l"c, _
                                          "m"c, "n"c, "o"c, "p"c, "q"c, "r"c, _
                                          "s"c, "t"c, "u"c, "v"c, "w"c, "x"c, _
                                          "y"c, "z"c, "!"c, "@"c, "#"c, "$"c, _
                                          "%"c, "^"c, "&"c, "*"c, "("c, ")"c, _
                                          "-"c, "+"c}


        If Not UseSpecial Then ichars = 62 ' only use the alpha numeric characters out of "char"'
        If SpecialOnly Then schars = 62 : ichars = 74 ' skip the alpha numeric characters out of "char"'

        Dim rndStr As String = String.Empty
        Dim i As Integer = 0
        While i < n
            rndStr += chars(Me.myRnd.Next(schars, ichars))
            System.Math.Max(System.Threading.Interlocked.Increment(i), i - 1)
        End While
        Return rndStr
    End Function
End Class

End Class

公共类表单1
私有子按钮1\u单击（ByVal sender作为System.Object，ByVal e作为System.EventArgs）处理按钮1。单击
将myCS设置为新的自定义字符串
Dim l作为新列表（字符串）
对于x作为整数=1到10
Dim s As String=myCS.generateradom（5）
l、 加
下一个
对于x为整数=0到l。计数为-1
调试写入线（l（x））
下一个
'调试输出
"YGXiV
“rfLmP
“OVUW9
“$uaMt
“^RsPz
'k&91k
"(n2uN)
“ldbQQ
“zYlP！
'30kNt
端接头
公共类自定义字符串
私有myRnd作为新的Random（）
公共函数生成器域（ByVal n为整数_
可选的ByVal UseSpessional作为布尔值=True_
可选的ByVal（特别是Boolean=False）作为字符串
Dim ichars As Integer=74'字符字符串中要使用的字符数'
Dim schars As Integer=0“要从字符串中跳过的字符数”
Dim chars（）As Char=New Char（）{“A”c，“B”c，“c”c，“D”c，“E”c，“F”c_
“G”c，“H”c，“I”c，“J”c，“K”c，“L”c_
“M”c，“N”c，“O”c，“P”c，“Q”c，“R”c_
“S”c，“T”c，“U”c，“V”c，“W”c，“X”c_
“Y”c、“Z”c、“0”c、“1”c、“2”c、“3”c、_
“4”c、“5”c、“6”c、“7”c、“8”c、“9”c、_
“a”c，“b”c，“c”c，“d”c，“e”c，“f”c_
“g”c，“h”c，“i”c，“j”c，“k”c，“l”c_
“m”c，“n”c，“o”c，“p”c，“q”c，“r”c_
“s”c，“t”c，“u”c，“v”c，“w”c，“x”c_
“y”c，“z”c，“！”c，“@”c，“#”c，“$”c_
“%”c、“^”c、“*”c、“（”c“）”c、_
“-”c“+”c}
如果不使用特殊字符，则ichars=62'仅使用“char”中的字母数字字符'
如果是特殊情况，则schars=62:ichars=74'跳过“char”中的字母数字字符'
作为Stri的Dim rndStr
Private Function GetNewSeed() As Integer
    Dim arrBytes As Byte() = Guid.NewGuid().ToByteArray()  '16 bytes
    Dim seedNum As Integer = 0
    ' Boil GUID down 4 bytes at a time (size of int) and merge into Integer value
    For i As Integer = 0 To arrBytes.Length - 1 Step 4
        seedNum = seedNum Xor BitConverter.ToInt32(arrBytes, i)
    Next
    Return seedNum
End Function

Dim rnd1 As New Random( GetNewSeed )

Session["seedRandom"] = 1;

private string getRandAlphaNum()
{
   int seed_value = (int)DateTime.Now.Ticks;
   seed_value = seed_value + Int32.Parse(Session["seedRandom"].ToString());
   //change the Session variable by incrementing its value to 1 after creating seed value.
   Session["seedRandom"] = Int32.Parse(Session["seedRandom"].ToString()) + 1;

   Random rand = new Random(seed_value);
   .....
   .....
}