C＃：通过变量引用类

Question

I'm trying to get the hang of using variables in C#, but have hit a roadblock. The following doesn't work.

public static void SetBG(string s)
{
    Console.BackgroundColor = ConsoleColor.s;
}

A very simple method that should set the console's background color according to what the programmer sent through the s variable. If I used SetBG("Red"); , it should go through, but it doesn't. This is because System.ConsoleColor' does not contain a definition for 's' .

How can I do this in C#?

Answer 1

This is not the correct way to do this, and it looks like there are two main concepts you're having trouble with, and understanding them will help you do this correctly.

Firstly, s is a variable in your current class. ConsoleColor.s would refer to the s variable in the ConsoleColor class (it does not have one, hence your error). This is called scope , or encapsulation , and allows us to reuse common words/names without conflict.

Secondly, your code will be compiled before it is run, and ConsoleColor.s (assuming there was such a thing) would no longer say ConsoleColor.s . Instead, it would point to a place in memory where a value is stored representing "s". The s being passed to your method will be a string, such as "Red" or "Blue". There is no connection between such a string and a slot in memory for a differnt object to store it's values.

To do what you are trying to do, you need to take the name of the color and translate it into a color. One way to do this would be with a series of if / else statements checking the contents of the string and assigning the appropriate color if it matches a color name.
Fortunately, there is an easier way. You can simply parse the string into a ConsoleColor !

Following the example from MSDN you can do this:

Console.BackgroundColor = (ConsoleColor) Enum.Parse(typeof(ConsoleColor), s);

Answer 2

Console.BackgroundColor = (ConsoleColor)Enum.Parse(typeof (ConsoleColor), s);

Answer 3

ConsoleColor is an enum. You'll have to cast s .

public static void SetBG(string s){
   Console.BackgroundColor = (ConsoleColor) Enum.Parse(typeof(ConsoleColor), s);
}

Answer 4

This is because ConsoleColor is an enumeration, try

 Console.BackgroundColor = (ConsoleColor) Enum.Parse(typeof(ConsoleColor), s);

You should consider handling if the string is not valid (eg s="Ship") with something like this

 ConsoleColor colorValue;
 if (Enum.TryParse(s, out colorValue))
 {        
     Console.BackgroundColor = colorValue;
 }

Answer 5

ConsoleColor colour;
if (ConsoleColor.TryParse(s, out colour))
{
   Console.BackgroundColor = colour;
}

Answer 6

Just to add to everyone else's use of the Enum.Parse method , as of .NET 4.0 you can use the Enum.TryParse generic method to better handle invalid values:

public static void SetBG(string s)
{
    ConsoleColor color;

    if (!Enum.TryParse<ConsoleColor>(s, out color))
        throw new ArgumentException("s");

    Console.BackgroundColor = color;
}