Why does GetType on string property throw NullReferenceException?
When I call GetType on an int or DateTime property, I get the expected results, but on the string property, I get a NullReferenceException (?):
private int PropInt { get; set; }
private DateTime PropDate { get; set; }
private string propString { get; set; }
WriteLine(PropInt.GetType().ToString()); // Result : System.Int32
WriteLine(PropDate.GetType().ToString()); // Result : System.DateTime
WriteLine(propString.GetType().ToString()); // Result : NullReferenceException (?!)
Can someone explain why? How is a string pointer different from an int-prop?
If the value is a property null
, you will get a NullReferenceException when trying to access object methods or properties, for example GetType()
. Primitive types such as int
and DateTime
are value types and therefore cannot contain a value null
, so GetType()
will not tolerate more than any of their other member functions.
source to share
Because the string is a reference type where the rest are not. DateTime and Int must have default values, they cannot be null.
What you need to understand is that the compiler creates a variable to store information. In C # 3.0, you don't need to explicitly declare it, but it still exists, so it creates a DateTime variable and an int variable and initializes them to their default values so as not to throw a compiler error. With a string, you don't have to do this (initialize the default) because it's a reference type.
source to share
The initial propString is null. We cannot execute null method. If you initialize propString: propString = "" then you can execute GetType () without exception
Code without exception:
private int PropInt { get; set; }
private DateTime PropDate { get; set; }
private string propString { get; set; }
propString = ""; // propString != null
WriteLine(PropInt.GetType().ToString()); // Result : System.Int32
WriteLine(PropDate.GetType().ToString()); // Result : System.DateTime
WriteLine(propString.GetType().ToString()); // Result : System.String
source to share