c＃在类的方法中访问结构成员

Question

i'm trying to write a simple game. I want to design a "movement controller" object, that would handle move instructions from the engine. I would also like for this object to expose a method, that would check its state and return true/false depending if it's ready to move or not. The state will be saved as group of boolean variables. Since there is a lot of them, I decided to group them together in a new struct called "flags". This is how it looks like more or less:

public class movContr
{
    int movId;
    public struct flags
    {
        bool isMoving;
        bool isLocked;
        bool isReady;
        (...)
    }

    public bool CheckReadiness()
    {
        if(flags.isReady==true) return true;
        return false;
    }
}

Now the problem is this won't compile, error being:

error CS0120: An object reference is required to access non-static member

offending line being:

if(flags.isReady==true) return true;

So I guess C# doesn't treat structs like memory blobs that just contains variables in orders, but like some "special" cousin of a class.

Here are my questions:

how should I handle accessing struct class members in its methods? How can I refer in class methods to members of its future instances? I tried this instead:

if(this.flags.isReady==true) return true;

but i get the same error.

Alternatively, if encapsulating my flag variables using 'struct' is not a proper way to do so, what is?

I tried to find an answer myself but since all the keywords I could come up with are very generic, so are the results. Most deal with static members, which are not a solution here since I need multiple, independent instances of movContr class.

Answer 1

You have created a declaration of struct called flags . But it is only declartion, not a concrete value. So, the snippet

if(flags.isReady==true) return true;

tries to access static member ( https://msdn.microsoft.com/en-us/library/98f28cdx.aspx ).

You need to declare a variable of that type in order to use it:

private flags myFlag;

public bool CheckReadiness()
{
     if(myFlag.isReady==true) return true;
      return false;
}

Maybe your confusion comes from C++, where "inline, anonymous" struct is allowed:

struct {
    int some_var
} flags;

flags.some_var = 1;

It is not available in C#

Answer 2

As exception suggests You need to create instance of struck as shown below :-

flags flag;
flag.isReady = true;

For more information :-

http://www.dotnetperls.com/struct

Please notice how, in Main, the struct is created on the stack. No "new" keyword is used. It is used like a value type such as int.

By the way i would suggest you to use auto implemented properties instead of Struck if this is the only use as shown in your code

Ref:- https://msdn.microsoft.com/en-us/library/bb384054.aspx

Answer 3

You can't use flags , because you are only declaring a datatype with "struct flags". You need to create an instance.

and you should declare the fields of the struct as public. otherwise you can't access them.

    int movId;

    // Delace fields as public
    public struct flags
    {
        public bool isMoving;
        public bool isLocked;
        public bool isReady;
    }

    // create a instance
    private flags myFlag;

    public bool CheckReadiness()
    {
        if(this.myFlag.isMoving == true) return true;
        return false;
    }

    // Better Implementation
    public bool CheckReadiness()
    {
        if (this.myFlag.isMoving) return true;
        return false;
    }

    // Best Implementation
    public bool CheckReadiness()
    {
        return (this.myFlag.isMoving);
    }

Answer 4

Instead of creating the struct it might make more sense to have properties.

public class movContr
{
    int movId;

    public bool IsMoving { get; set; }
    public bool IsLocked { get; set; }
    public bool IsReady { get; set; }
        (...)
}

Then instead of calling CheckReadiness you'd just call IsReady .

var temp = new movContr();
if(temp.IsReady)
{
    // It is ready.
}