实时捕获用户输入错误

Question

我制作了这个简单的控制台应用程序，它要求用户输入用户名和密码。 然后将数据保存在数据库中。对于 Db 中的每一列，我为数据类型分配了有限数量的值。例如，密码 (varchar(5)( 最多必须包含 5 个字符。

using System;
namespace MyConto
{
public class NewUser
{
public static void NewUserRegistration()
{
Console.Write("Username: ");
string user = Console.ReadLine();
Console.Write("Password: ");
string pass = Console.ReadLine();     
}
}
}

现在，如何实时(？？(检查用户在控制台中写入的内容？甚至有可能吗？ 例如，一条消息，警告用户如果将"password"写为密码字符串太长。

谢谢

Answer 1

添加验证方法，如下所示：

private bool isValid(string input)
{
//my validation logic
}

并像这样使用：

...
string user = Console.ReadLine();
if (!isValid(user))
{
///my logic for warning the user that input is invalid
}
...

Answer 2

我假设"实时"是指您不希望用户在看到消息之前按 Enter 键 - 因此一旦他们键入第 6 个字符，它就会告诉他们它太长了。 你不能用 Console.ReadLine(( 来做这件事，你可以用 Console.ReadKey((来做这件事，尽管这需要付出很多努力......但只是为了好玩：

class Program
{
static void Main(string[] args)
{
//First clear the screen.  We need to have absolute knowledge of what's on 
//the screen for this to work.
Console.Clear();
//hide the cursor as it has no real bearing on much....
Console.CursorVisible = false;
var user = GetLimitedInput("UserName?", 0, 10, true);
var password = GetLimitedInput("Password?", 4, 5, false);
Console.Clear();
Console.WriteLine($"User is {user} and password is {password}");
}

private static string GetLimitedInput(string prompt, 
int lineToShowPromptOn, int maxChars, bool showChars)
{
//set cursor to the suggested position
Console.SetCursorPosition(0, lineToShowPromptOn);
//output the prompt.
Console.WriteLine(prompt);
Console.SetCursorPosition(0, lineToShowPromptOn + 1);
var finished = false;
var inputText = string.Empty;
while (!finished)
{
if (Console.KeyAvailable)
{
//remembr old input so we can re-display if required.
var oldInput = inputText;
var key = Console.ReadKey();
//check for CTRL+C to quit
if (key.Modifiers.HasFlag(ConsoleModifiers.Control) && key.KeyChar=='c')
{
inputText = string.Empty;
finished = true;
}
//allow backspace
else if (key.KeyChar == 'b')
{
if (inputText.Length > 0)
{
inputText = inputText.Substring(0, inputText.Length - 1);
}
}
//check for return & finish if legal input.
else if (key.KeyChar == 'r')
{
if (inputText.Length<=maxChars)
{
finished = true;
}
}
else
{
//really we should check for other modifier keys (CTRL, 
//ALT, etc) but this is just example.
//Add text onto the input Text
inputText += key.KeyChar;
}
if (inputText.Length > maxChars)
{
//Display error on line under current input.
Console.SetCursorPosition(0, lineToShowPromptOn + 2);
Console.WriteLine("Too many characters!");
}
else
{
//if not currently in an 'error' state, make sure we
//clear any previous error.
Console.SetCursorPosition(0, lineToShowPromptOn + 2);
Console.WriteLine("                     ");
}
//if input has changed, then refresh display of input.
if (inputText != oldInput)
{
Console.SetCursorPosition(0, lineToShowPromptOn + 1);
//do we show the input?
if (showChars)
{
//We write it out to look like we're typing, and add 
//a bunch of spaces as otherwise old input may be        
//left there.
Console.WriteLine(inputText+"            ");
}
else
{
//show asterisks up to length of input.
Console.WriteLine(new String('*', inputText.Length)+"            ");
}
}
}
}
return inputText;
}       
}

注意：这有很多缺陷，但仅用于说明目的:)

Answer 3

如果你想继续询问用户，直到他给出一个有效的密码，你可以做这样的事情：

string ObtainPassword()
{
string password;
string passwordErrorMessage;
while(true)
{
Console.Write("Password: ");
password = Console.ReadLine();
passwordErrorMessage = ValidatePassword(password);
if (passwordErrorMessage == null)
return password;
Console.WriteLine($"rn*** {passwordErrorMessage}");
}
}

密码验证方法如下所示：

string ValidatePassword(string password)
{
if(password.Length > 5) return "Password is too long";
//Add other validations here as needed
return null;
}

Answer 4

我最终得到了这个：

using System;
namespace MyConto
{
public class NewUser
{
public static void NewUserRegistration()
{
Console.Write("Username: ");
string user = Console.ReadLine();
Console.Write("Password: ");
string pass = Console.ReadLine();
while (pass.Length > 5)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Insert a valid password (max 5 chars)n");
Console.ForegroundColor = ConsoleColor.White;
Console.Write("Password: ");
pass= Console.ReadLine();
}     
}
}
}