Listen on ESC while reading Console line

Question

I want to read an users input into a string while still reacting on ESC press at any time, but without defining a system wide hotkey.

So when the user types e. g. "Test Name" but instead of confirming with ENTER presses ESC he should be led back into main menu.

Console.Write("Enter name: ")
if (Console.ReadLine().Contains(ConsoleKey.Escape.ToString()))
{
    goto MainMenu;
}
return Console.ReadLine();

Thats the simplest way I could think of, but since ESC is not seen by Console.ReadLine() it is not working.

Found a rather complex way to react on ESC when pressed before starting to enter text here, but I want it to work at any time.

Solution 1

You will probably have to forego the use of ReadLine and roll your own using ReadKey:

static void Main(string[] args)
{
    Console.Clear();
    Console.Write("Enter your name and press ENTER.  (ESC to cancel): ");
    string name = readLineWithCancel();

    Console.WriteLine("\r\n{0}", name == null ? "Cancelled" : name);

    Console.ReadLine();
}

//Returns null if ESC key pressed during input.
private static string readLineWithCancel()
{
    string result = null;

    StringBuilder buffer = new StringBuilder();

    //The key is read passing true for the intercept argument to prevent
    //any characters from displaying when the Escape key is pressed.
    ConsoleKeyInfo info = Console.ReadKey(true);
    while (info.Key != ConsoleKey.Enter && info.Key != ConsoleKey.Escape)
    {
        Console.Write(info.KeyChar);
        buffer.Append(info.KeyChar);
        info = Console.ReadKey(true);
    } 

    if (info.Key == ConsoleKey.Enter)
    {
        result = buffer.ToString();
    }

    return result;
}

This code is not complete and may require work to make it robust, but it should give you some ideas.

Solution 2

A bit improved version of Chris Dunaway's one :

    public static bool CancelableReadLine(out string value)
    {
        value = string.Empty;
        var buffer = new StringBuilder();
        var key = Console.ReadKey(true);
        while (key.Key != ConsoleKey.Enter && key.Key != ConsoleKey.Escape)
        {
            if (key.Key == ConsoleKey.Backspace && Console.CursorLeft > 0)
            {
                var cli = --Console.CursorLeft;
                buffer.Remove(cli, 1);
                Console.CursorLeft = 0;
                Console.Write(new String(Enumerable.Range(0, buffer.Length + 1).Select(o => ' ').ToArray()));
                Console.CursorLeft = 0;
                Console.Write(buffer.ToString());
                Console.CursorLeft = cli;
                key = Console.ReadKey(true);
            }
            else if (Char.IsLetterOrDigit(key.KeyChar) || Char.IsWhiteSpace(key.KeyChar))
            {
                var cli = Console.CursorLeft;
                buffer.Insert(cli, key.KeyChar);
                Console.CursorLeft = 0;
                Console.Write(buffer.ToString());
                Console.CursorLeft = cli + 1;
                key = Console.ReadKey(true);
            }
            else if (key.Key == ConsoleKey.LeftArrow && Console.CursorLeft > 0)
            {
                Console.CursorLeft--;
                key = Console.ReadKey(true);
            }
            else if (key.Key == ConsoleKey.RightArrow && Console.CursorLeft < buffer.Length)
            {
                Console.CursorLeft++;
                key = Console.ReadKey(true);
            }
            else
            {
                key = Console.ReadKey(true);
            }
        }

        if (key.Key == ConsoleKey.Enter)
        {
            Console.WriteLine();
            value = buffer.ToString();
            return true;
        }
        return false;
    }
}

I didn't test it much, but at least works for me.

Comments

[AstronAUT]

That is not working for me: when the while loop is entered Console.ReadLine() is stoping the thread until ENTER is pressed.

[AstronAUT]

Thank you for your response. Looks more efficient than mine, although I had to add support for backspace ;)

[derekantrican]

This doesn't seem to work with the backspace key. It moves the cursor back, but doesn't delete the letter