Convert Nullable<Boolean> to Generic type

Question

Assume this method:

public T GetParameterValue<T>(string ParamName) {

if(typeof(T) == typeof(Boolean?) && Request.QueryString.AllKeys.Contains(ParamName)) {

                Boolean? istrue = null;

                if(Request.QueryString.GetValues(ParamName).FirstOrDefault() == "1")
                    istrue = true;
                else if(Request.QueryString.GetValues(ParamName).FirstOrDefault() == "0")
                    istrue = false;

                return (T)Convert.ChangeType(istrue, typeof(T));
            }

//Other types implementation

}

So this method always rise an exception in return line:

Invalid cast from 'System.Boolean' to 'System.Nullable`1[[System.Boolean, 
mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]'.

I don't understand where is the problem I don't use Boolean I use Boolean?

this is my call line:

Product.IsAllow= GetParameterValue<Boolean?>("IsAllow");

So what is your idea about it?

Answer 1

You can use

return (T)(object)istrue;

I would not use this kind of code at all though. Simply create a method that specifically parses each data type (e.g. bool? GetBooleanParameter(string name)). You're not gaining anything with the generics here and only making the code more cumbersome.