Compiler Error CS0120

An object reference is required for the nonstatic field, method, or property 'member'

In order to use a non-static field, method, or property, you must first create an object instance. For more information about static methods, see Static Classes and Static Class Members. For more information about creating instances of classes, see Instance Constructors.

The following sample generates CS0120:

// CS0120_1.cs  
public class MyClass  
{  
   // Non-static field  
   public int i;   
   // Non-static method  
   public void f(){}  
   // Non-static property  
   int Prop  
   {  
      get   
      {  
         return 1;   
      }  
   }  

   public static void Main()  
   {  
      i = 10;   // CS0120  
      f();   // CS0120  
      int p = Prop;   // CS0120  
      // try the following lines instead  
      // MyClass mc = new MyClass();  
      // mc.i = 10;  
      // mc.f();  
      // int p = mc.Prop;  
   }  
}  

CS0120 will also be generated if there is a call to a non-static method from a static method, as follows:

// CS0120_2.cs  
// CS0120 expected  
using System;  

public class MyClass  
{  
   public static void Main()  
   {  
      TestCall();   // CS0120  
      // To call a non-static method from Main,  
      // first create an instance of the class.  
      // Use the following two lines instead:  
      // MyClass anInstanceofMyClass = new MyClass();  
      // anInstanceofMyClass.TestCall();  
   }  

   public void TestCall()  
   {  
   }  
}  

Similarly, a static method cannot call an instance method unless you explicitly give it an instance of the class, as follows:

// CS0120_3.cs  
using System;  

public class MyClass  
{  
   public static void Main()  
   {  
      do_it("Hello There");   // CS0120  
   }  

   private void do_it(string sText)  
   // You could also add the keyword static to the method definition:  
   // private static void do_it(string sText)  
   {  
      Console.WriteLine(sText);  
   }  
}  

See Also

Classes and Structs