An interface can contain methods, properties, events or indexers. It cannot contain fields.
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| interface IMoo{ // Methods void Moo(); // Field not allowed - compile-time error string Name; |
Instead of a field, you can use a property.
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| interface IMoo{ // Methods void Moo(); // Name as a property is OK string Name { get; set; } |
Interfaces don’t allow fields because they consist of a contract that is a list of methods, whose implementation is provided by a class. Properties are implemented as methods (get and set accessors), so they fit this model. But fields are just data locations, so it doesn’t make sense to include them in an interface.