Question if Directly set IsActive

Question

Original Invader.cs code from video

namespace TreehouseDefense
{
    class Invader
    {
      private readonly Path _path;
      private int _pathStep = 0;

      public MapLocation Location => _path.GetLocationAt(_pathStep); 

      public int Health {get; private set;} = 2;

      public bool HasScored {get {return _pathStep >= _path.Length;}}

      public bool IsNeutralised => Health <= 0;

      public bool IsActive => !(IsNeutralised || HasScored);

      public Invader(Path path)
      {
        _path = path;
      }

      public void Move() => _pathStep += 1;

      public void DecreaseHealth(int factor)
      {
        Health -= factor; 
      }

    }
}

why console will return Invader.cs(16,32): error CS0236: A field initializer cannot reference the nonstatic field, method, or property TreehouseDefense.Invader.IsNeutralised' Invader.cs(16,49): error CS0236: A field initializer cannot reference the nonstatic field, method, or propertyTreehouseDefense.Invader.HasScored'

if I directly put

public bool IsActive = !(IsNeutralised || HasScored);

I think that although I didnt make it into property which allows other classes to get, this bool should can be set in this way, does it?

Answer 1 · 2017-07-20T22:50:10Z

July 20, 2017 10:50pm

You want this to be a property, not a field.

The compiler error is reminding you that you cannot use instance fields or properties to initialize other instance fields. But even if this was possible you would not want it. You want IsActive to be a calculated property that will reflect the current state of the invader every time you check it. If you initialzed this as field, it would always reflect that state it was in as it was constructed, which would not be useful to the program later.

Welcome to the Treehouse Community

Looking to learn something new?

JingChi Liang

JingChi Liang

Question if Directly set IsActive

1 Answer

Steven Parker

Steven Parker

You want this to be a property, not a field.