Const String From Settings

Question

I would like to set a const string from Settings.

In case I would like to change in the future the program language, it is quite easy; Just have to modify the appropriate settings!

When trying this:

private const string constString =   
              "-&" + Properties.Settings.Default.constStringText;  

I get this error:

The property or indexer 'Properties.Settings.Default'  
cannot be used in this context because it lacks the get accessor.  

Any idea?

Answer 1

Since you intend to use this as the default value for an optional method argument, that is:

public void Foo(string something = constString)
{
    //do something
}

This constString must be a compile-time constant. From the MSDN page for "Named and Optional Arguments":

A default value must be one of the following types of expressions:

• a constant expression;

• an expression of the form new ValType(), where ValType is a value type, such as an enum or a struct;

• an expression of the form default(ValType), where ValType is a value type.

As such, there really is no way to read a value from a configuration file at runtime then use it for an optional argument.

One workaround would be to instead declare your constString as a readonly field:

private readonly string constString =   
              "-&" + Properties.Settings.Default.constStringText; 

Then make your optional argument required and create a wrapping overload for your method that doesn't take that parameter. That overload in turn calls the old method with the default value resolved at runtime:

public void Foo(string something) //no longer optional
{
    //do something
}

public void Foo()
{
    Foo(constString); //calls the other overload with the default value
}

Answer 2

This error is in 99% of cases related to a wrong namespace. You've probably generated some class in which you are using Properties.Settings.Default

Solution: check namespace in that class file. It must be the same as the name of the tag in App.config (Web.config) where that particular setting is stored.