使用foreach作为对序列遍历list(或array)

本文关键字：list array 遍历 foreach 使用 | 更新日期: 2023-09-27 18:10:53

我正在创建一个简单的程序，从Customers.txt文件中读取用户名和密码，并验证它是否正确。txt的格式为用户名和密码的序列用逗号分隔(忽略安全问题):

JaneDoe

JohnDoe, 1234年,5678年…

是否可以创建一个foreach循环来迭代strArray[]并检查对{strArray[0], strArray[1]}然后{strArray[2], strArray[3]}等等，以查看用户是否输入了正确的凭据?

private void enter_click_Click(object sender, RoutedEventArgs e)
{
    StreamReader reader1 = new StreamReader("Customers.txt");
    string text = reader1.ReadToEnd();
    reader1.Close();
    string[] Strarray = text.Split(',');
    StreamReader reader2 = new StreamReader("Admin.txt");
    string text2 = reader2.ReadToEnd();
    reader2.Close();
    string[] AdminArray = text2.Split(',');
    if (username_txt.Text == AdminArray[0] && passwordBox1.Password == AdminArray[1])
    {
        AdminPage admin = new AdminPage();
        admin.Activate();
        admin.Show();
        method.CheckDate();
        return;
    }
    if (username_txt.Text == Strarray[0] && passwordBox1.Password == Strarray[1])
        {
            ATM_Screen atm = new ATM_Screen();
            atm.Activate();
            atm.Show();
            method.CheckDate();
            return;
        }

使用foreach作为对序列遍历list(或array)

是的，你可以这样做:

var usernames = Strarray.Where((s, i) => { return i % 2 == 0; });
var passwords = Strarray.Where((s, i) => { return i % 2 != 0; });
var userPasswords = usernames.Zip(passwords, (l, r) => new { username = l, password = r });
foreach(var userPassword in userPasswords) {
    if (userPassword.username == "rob" && userPassword.password == "robspassword") {
    }
}

根据注释编辑:

您可以为多个有效凭据执行此操作:

var allowedCredentials = new List<Tuple<String, String>> { 
    new Tuple<String, String>("Rob", "Robspassword"), 
    new Tuple<String, String> ("SomeoneElse", "SomeoneElsespassword" 
};
var inputCredentials = new List<string> { "Rob","Robspassword","Rob","Notrobspassword" };
var usernames = inputCredentials.Where((s, i) => { return i % 2 == 0; });
var passwords = inputCredentials.Where((s, i) => { return i % 2 != 0; });
var userPasswords = usernames.Zip(passwords, (l, r) => new { username = l, password = r });
foreach(var userPassword in userPasswords) {
    if (allowedCredentials.Any(ac => ac.Item1 == userPassword.username 
           && ac.Item2 == userPassword.password)
    {
        //Valid
    }
}

使用foreach很难从序列中获得元素对:

  • 你可以正常地遍历序列，在奇数迭代中记住第一个元素，在每个偶数迭代中执行操作
  • 您可以先使用LINQ和索引将序列转换成成对，或者压缩偶数和奇数一半。

收集对方法:

 string name;
 bool even = false;
 foreach(var text in items)
 {
     if (even)
     {
         var password = item;
         // check name, password here 
     }
     else
     { 
         name = text;
     }
     even = !even;
  }

Zip-based方法

  foreach(var pair in items
        .Where((v,id)=>id % 2 == 1) // odd - names
        .Zip(items.Where((v,id)=>id % 2 == 0), // even - passwords
          (name,password)=> new { Name = name, Password = password}))
  {
     // check pair.Name, pair.Password
  }

注意:使用常规的for循环，增量为2会更容易。

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