如何在C＃控制台应用程序的行首处允许用户输入？

Question

I know I can use Console.ReadLine() to allow user input but it only allows user input from where the cursor is positioned, I want a way to be able to allow user input from the beginning of the line (over the whole line) and not only from where the cursor is positioned. for example:

for (int i = 1;i <= 5;i++) Console.Write(i+" ");
string x = Console.ReadLine();

This would give the following output:

1 2 3 4 5 _

Where '_' refers to the cursor, this way, the user will be able to write only from the cursor position - he cannot use backspace to delete the former characters too. So how can I allow user input over the whole line while the cursor is not at the beginning of the line?

Answer 1

This is ready to go example with custom input handling. Of cource this is require some tweaks towards performance but it should give you and idea where to begin.

    static void Main(string[] args)
    {
        List<char> outputString = new List<char>();
        outputString = "test".ToCharArray().ToList();
        //If there is something in outputString write it to buffer and set cursor position
        if (outputString.Count > 0)
        {
            Console.Write(outputString.Select(x => x.ToString()).Aggregate((x, y) => x + y));
        }

        while (true)
        {
            //This will read user input but it will not print it to the console window 
            var key = Console.ReadKey(true);
            //Allow user maniputate cursor to the right
            //Here you can add another condition to prevent line overflow or some constrains
            //if(Console.CursorLeft < 30)
            if (key.Key == ConsoleKey.RightArrow && Console.CursorLeft < outputString.Count)
            {
                Console.SetCursorPosition(Console.CursorLeft + 1, Console.CursorTop);
            }
            else if (key.Key == ConsoleKey.LeftArrow && Console.CursorLeft > 0)
            {
                Console.SetCursorPosition(Console.CursorLeft - 1, Console.CursorTop);
            }
            //Here you should add all keys that your input should take, special characters are ok above ASCII number 32 which is space
            else if (key.KeyChar >= 48 && key.KeyChar <= 57 || //Read numbers
                key.KeyChar >= 64 && key.KeyChar <= 90 || //Read capital letters
                key.KeyChar >= 97 && key.KeyChar <= 122 || //Read lower letters
                key.Key == ConsoleKey.Spacebar)
            {
                Console.Write(key.KeyChar);
                if(Console.CursorLeft > outputString.Count)
                {
                    outputString.Add(' ');
                }
                outputString[Console.CursorLeft - 1] = key.KeyChar;
            }
            //This will remove character
            else if (key.Key == ConsoleKey.Backspace && Console.CursorLeft > 1)
            {
                ClearCurrentConsoleLine();
                outputString.RemoveAt(Console.CursorLeft - 1);
                var currentLeft = Console.CursorLeft;
                Console.CursorLeft = 0;
                Console.Write(outputString.Select(x => x.ToString()).Aggregate((x,y) => x + y));
                Console.CursorLeft = currentLeft - 1;
            }
            //This ends input loop
            //You can add more keys to break current loop with OR condition
            else if (key.Key == ConsoleKey.Enter)
            {
                break;
            }
        }
        //Display result and wait for any key
        Console.WriteLine(outputString.Select(x => x.ToString()).Aggregate((x, y) => x + y));
        Console.ReadKey();
    }

    //Clears current console line and sets cursor at where it was before
    public static void ClearCurrentConsoleLine()
    {
        int currentLineCursorTop = Console.CursorTop;
        int currentLineCursorLeft = Console.CursorLeft;
        Console.SetCursorPosition(0, Console.CursorTop);
        Console.Write(new string(' ', Console.WindowWidth));
        Console.SetCursorPosition(currentLineCursorLeft, currentLineCursorTop);
    }

Answer 2

You could use Console.CursorLeft = 0; for this. The advantage in comparison to Console.SetCursorPosition is, that you don't have to evaluate the y-coordinate, so that the cursor stays in the current line.

I want to make an example for this (in both cases we want the cursor to go to the beginning of the line):

Console.SetCursorPosition(0, Console.CursorTop); //With SetCursorPosition
Console.CursorLeft = 0; //With CursorLeft

However, I don't think there's an elegant way of letting the user delete the chars written by the program. You could still constantly check wether the user presses Backshift and then delete the last character and move the cursor back, while you'd have to check that asynchronously what wouldn't result in a nice solution.