private string? typeOfContract
{
get { return (string?)ViewState["typeOfContract"]; }
set { ViewState["typeOfContract"] = value; }
}
Later in the code I use it like this:
typeOfContract = Request.QueryString["type"];
I am getting the following error at the declaration of typeOfContract line stating:
The type 'string' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'System.Nullable<T>'
Any ideas? Basically, I want to make sure that "type" exists in the QueryString before performing an action.
String is a reference type, so you don't need to (and cannot) use Nullable<T> here. Just declare typeOfContract as string and simply check for null after getting it from the query string. Or use String.IsNullOrEmpty if you want to handle empty string values the same as null.
You are making it complicated. string is already nullable. You don't need to make it more nullable. Take out the ? on the property type.
Please note that in upcoming version of C# which is 8, the answers are not true.
All the reference types are non-nullable by default and you can actually do the following:
public string? MyNullableString;
this.MyNullableString = null; //Valid
However,
public string MyNonNullableString;
this.MyNonNullableString = null; //Not Valid and you'll receive compiler warning.
The important thing here is to show the intent of your code. If the "intent" is that the reference type can be null, then mark it so otherwise assigning null value to non-nullable would result in compiler warning.
To the moderator who is deleting all the answers, don't do it. I strongly believe this answer adds value and deleting would simply keep someone from knowing what is right at the time. Since you have deleted all the answers, I'm re-posting answer here. The link that was sent regarding "duplicates" is simply an opening of some people and I do not think it is an official recommendation.
String is a reference type, so you don't need to (and cannot) use Nullable<T> here. Just declare typeOfContract as string and simply check for null after getting it from the query string. Or use String.IsNullOrEmpty if you want to handle empty string values the same as null.
string cannot be the parameter to Nullable because string is not a value type. String is a reference type.
string s = null;
is a very valid statement and there is not need to make it nullable.
private string typeOfContract
{
get { return ViewState["typeOfContract"] as string; }
set { ViewState["typeOfContract"] = value; }
}
should work because of the as keyword.
string cannot be the parameter to Nullable because string is not a value type. String is a reference type.
string s = null;
is a very valid statement and there is not need to make it nullable.
private string typeOfContract
{
get { return ViewState["typeOfContract"] as string; }
set { ViewState["typeOfContract"] = value; }
}
should work because of the as keyword.
You are making it complicated. string is already nullable. You don't need to make it more nullable. Take out the ? on the property type.
String is a reference type, so you don't need to (and cannot) use Nullable<T> here. Just declare typeOfContract as string and simply check for null after getting it from the query string. Or use String.IsNullOrEmpty if you want to handle empty string values the same as null.
You are making it complicated. string is already nullable. You don't need to make it more nullable. Take out the ? on the property type.
string cannot be the parameter to Nullable because string is not a value type. String is a reference type.
string s = null;
is a very valid statement and there is not need to make it nullable.
private string typeOfContract
{
get { return ViewState["typeOfContract"] as string; }
set { ViewState["typeOfContract"] = value; }
}
should work because of the as keyword.
String is a reference type, so you don't need to (and cannot) use Nullable<T> here. Just declare typeOfContract as string and simply check for null after getting it from the query string. Or use String.IsNullOrEmpty if you want to handle empty string values the same as null.
For nullable, use ? with all of the C# primitives, except for string.
The following page gives a list of the C# primitives: http://msdn.microsoft.com/en-us/library/aa711900(v=vs.71).aspx
Please note that in upcoming version of C# which is 8, the answers are not true.
All the reference types are non-nullable by default and you can actually do the following:
public string? MyNullableString;
this.MyNullableString = null; //Valid
However,
public string MyNonNullableString;
this.MyNonNullableString = null; //Not Valid and you'll receive compiler warning.
The important thing here is to show the intent of your code. If the "intent" is that the reference type can be null, then mark it so otherwise assigning null value to non-nullable would result in compiler warning.
To the moderator who is deleting all the answers, don't do it. I strongly believe this answer adds value and deleting would simply keep someone from knowing what is right at the time. Since you have deleted all the answers, I'm re-posting answer here. The link that was sent regarding "duplicates" is simply an opening of some people and I do not think it is an official recommendation.
For nullable, use ? with all of the C# primitives, except for string.
The following page gives a list of the C# primitives: http://msdn.microsoft.com/en-us/library/aa711900(v=vs.71).aspx
Source: Stackoverflow.com