嵌套类？ 属性与属性？

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...

Answer 1

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.

Answer 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;
}

Answer 3

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;
    }

Answer 4

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

Fruit.physicalProperties does indeed declare another type, but:

1. It will be private, only available to the members of Fruit unless you declare it public .
2. 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 .

Answer 5

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

Answer 6

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());