c# - Nested classes? Properties with properties?

Question

I would like to create a class with properties that have subproperties...

In other words, if I did something like:

Fruit apple = new Fruit();

I would want something like:

apple.eat(); //eats apple
MessageBox.Show(apple.color); //message box showing "red"
MessageBox.Show(apple.physicalProperties.height.ToString()); // message box saying 3

I would think it would be done like:

class Fruit{
    public void eat(){
        MessageBox.Show("Fruit eaten");
    }
    public string color = "red";
    public class physicalProperties{
        public int height = 3;
    }

}

...but, if that were working, I wouldn't be on here...

`apple` doesn't have `physicalProperties` now, only `Fruit` does. It's just a type now. And you definitely can't access its `height`, because `physicalProperties` doesn't have a `height`, only its instances do. — harold, Dec 23 '11 at 09:04
LOL! Did anyone else notice the personification of the apple in this example? i.e. "since when can apples eat stuff?" :P — Chiramisu, Jun 28 '12 at 01:25

Scott Rippey · Accepted Answer · 2011-12-23T09:09:24.413

7

So close! Here's how your code should read:

class Fruit{
    public void eat(){
        MessageBox.Show("Fruit eaten");
    }
    public string color = "red";
    public class PhysicalProperties{
        public int height = 3;
    }
    // Add a field to hold the physicalProperties:
    public PhysicalProperties physicalProperties = new PhysicalProperties();
}

A class just defines the signature, but nested classes don't automatically become properties.

As a side note, there's also a couple things I'd recommend, to follow .NET's "best practices":

Don't nest classes unless necessary
All Public members should be Properties instead of Fields
All Public members should be PascalCase, not camelCase.

I'm sure there's plenty of documentation on best practices too, if you're so inclined.

edited Dec 23 '11 at 09:09

answered Dec 23 '11 at 09:02

Scott Rippey

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Don't you need to create a instance else height won't be accessible – V4Vendetta Dec 23 '11 at 09:09
If I'm not supposed to nest classes, how do I add properties to the properties? – mowwwalker Dec 23 '11 at 09:12
@Walkemeo Nested classes is just referring to the namespace ... I shouldn't have even brought it up, it's more of a preference. Read more here: http://stackoverflow.com/questions/804453/using-inner-classes-in-c-sharp – Scott Rippey Dec 23 '11 at 09:21
1

@Walkerneo - You can define the class outside the "Fruit" class, but still create an instance of it within the Fruit class. Much as String is defined elsewhere, but you still have a String instance in the Fruit class. – Rawling Dec 23 '11 at 09:26
Also, what if I want that property to return a value if none of its members are called? – mowwwalker Dec 23 '11 at 10:23
@Walkerneo I'm not sure I correctly understand your question. If none of its members are called, then `apple.physicalProperties` returns a `PhysicalProperties` instance, the same way `apple.color` returns a `String` instance. – Scott Rippey Dec 27 '11 at 20:39

score 2 · Answer 2 · answered Dec 23 '11 at 09:03

2

class Fruit{
    public void eat(){
        MessageBox.Show("Fruit eaten");
    }
    public string color = "red";
    //you have declared the class but you havent used this class
    public class physicalProperties{
        public int height = 3;

    }
    //create a property here of type PhysicalProperties
    public physicalProperties physical;
}

answered Dec 23 '11 at 09:03

Haris Hasan

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This should give a Null Reference exception for height – V4Vendetta Dec 23 '11 at 09:11
@V4Vendetta, it sure does! Now what? – mowwwalker Dec 23 '11 at 09:11
Check my answer, instantiate in the constructor of Fruit – V4Vendetta Dec 23 '11 at 09:13
The field needs to be initialized or you'll get `null-reference` exceptions. `public physicalProperties physical = new physicalProperties();` – Scott Rippey Dec 23 '11 at 09:15

score 0 · Answer 3 · answered Dec 23 '11 at 09:04

Can you extrapolate the class, then reference it?

class Fruit{
    public void eat(){
        MessageBox.Show("Fruit eaten");
    }
    public string color = "red";
    public physicalProperties{
        height = 3;
    }

}

public class physicalProperties{
        public int height = 3;
    }

score 0 · Answer 4 · answered Dec 23 '11 at 09:06

class Fruit{
    public class physicalProperties{
        public int height = 3;
    }
}

Fruit.physicalProperties does indeed declare another type, but:

It will be private, only available to the members of Fruit unless you declare it public.
Creating a type does not create an instance of that type, or member of Fruit to allow users of Fruit to access it.

You need to add:

class Fruit {
  private physicalProperties props;
  public physicalProperties PhysicalProperties { get; private set; }

and in the (default) constructor of Fruit assign PhysicalProperties an instance of physicalProperties.

V4Vendetta · Answer 5 · 2011-12-23T09:15:27.080

0

You will need to expose the property as it is contained for the instance of the class physicalProperties so maybe you could do like

public Fruit()
{
    physical = new physicalProperties();
}

And a property which gives it back

public int Height { get { return physical.height;}}

OR

public physicalProperties physical;

so that you can do apple.physical.height

edited Dec 23 '11 at 09:15

answered Dec 23 '11 at 09:07

V4Vendetta

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score 0 · Answer 6 · answered Dec 23 '11 at 09:18

class Fruit{
    public void eat(){
        MessageBox.Show("Fruit eaten");
    }
    public string color = "red";
    public class physicalProperties{
        public int height = 3;
    }
    // create a new instance of the class so its public members
    // can be accessed
    public physicalProperties PhysicalProperties = new physicalProperties();
}

You can then access the sub-properties like so:

Fruit apple = new Fruit();
MessageBox.Show(apple.PhysicalProperties.height.ToString());

c# - Nested classes? Properties with properties?

6 Answers6