How can you set a default input value in a .net console app?
Here is some make-believe code:
Console.Write("Enter weekly cost: ");
string input = Console.ReadLine("135"); // 135 is the default. The user can change or press enter to accept
decimal weeklyCost = decimal.Parse(input);
Of course, I don't expect it to be this simple. I am betting on having to do some low-level, unmanaged stuff; I just don't know how.
I know I can replace no input with the default. That's not what I am asking about. I am trying to LEARN what's involved in achieving the behavior I described: giving the user an editable default. I'm also not worried about input validation; my question has nothing to do with that.
The only difference between the Read() and ReadLine() is that Console. Read is used to read only single character from the standard output device, while Console. ReadLine is used to read a line or string from the standard output device. Program 1: Example of Console.
The default keyword returns the "default" or "empty" value for a variable of the requested type. For all reference types (defined with class , delegate , etc), this is null . For value types (defined with struct , enum , etc) it's an all-zeroes value (for example, int 0 , DateTime 0001-01-01 00:00:00 , etc).
ReadLine method to read each line in the file, replaces every sequence of four spaces with a tab character, and uses the Console. WriteLine method to write the result to the output file.
I believe that you will have manage this manually by listening to each key press:
Quickly thown together example:
// write the initial buffer
char[] buffer = "Initial text".ToCharArray();
Console.WriteLine(buffer);
// ensure the cursor starts off on the line of the text by moving it up one line
Console.SetCursorPosition(Console.CursorLeft + buffer.Length, Console.CursorTop - 1);
// process the key presses in a loop until the user presses enter
// (this might need to be a bit more sophisticated - what about escape?)
ConsoleKeyInfo keyInfo = Console.ReadKey(true);
while (keyInfo.Key != ConsoleKey.Enter)
{
switch (keyInfo.Key)
{
case ConsoleKey.LeftArrow:
...
// process the left key by moving the cursor position
// need to keep track of the position in the buffer
// if the user presses another key then update the text in our buffer
// and draw the character on the screen
// there are lots of cases that would need to be processed (backspace, delete etc)
}
keyInfo = Console.ReadKey(true);
}
This is quite involved - you'll have to keep ensure the cursor doesn't go out of range and manually update your buffer.
Here's a simple solution:
public static string ConsoleReadLineWithDefault(string defaultValue)
{
System.Windows.Forms.SendKeys.SendWait(defaultValue);
return Console.ReadLine();
}
It's not complete however. Some characters in the SendWait input string have special meaning so you have to escape them (eg. +, (, ), etc.) See: http://msdn.microsoft.com/en-us/library/system.windows.forms.sendkeys.aspx for a complete description.
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