string.Replace (or other string modification) not working

Solution 1:

Strings are immutable. The result of string.Replace is a new string with the replaced value.

You can either store result in new variable:

var newString = someTestString.Replace(someID.ToString(), sessionID);

or just reassign to original variable if you just want observe "string updated" behavior:

someTestString = someTestString.Replace(someID.ToString(), sessionID);

Note that this applies to all other string functions like Remove, Insert, trim and substring variants - all of them return new string as original string can't be modified.

Solution 2:

someTestString = someTestString.Replace(someID.ToString(), sessionID);

that should work for you

Solution 3:

strings are immutable, the replace will return a new string so you need something like

string newstring = someTestString.Replace(someID.ToString(), sessionID);

Solution 4:

You can achieve the desired effect by using

someTestString = someTestString.Replace(someID.ToString(), sessionID);

As womp said, strings are immutable, which means their values cannot be changed without changing the entire object.