How can I access some (private) properties of an object?

Question

I have

public class Item
{
    public string description { get; set; }
    public string item_uri { get; set; }
    public thumbnail thumbnail { get; set; }
}

and

public class thumbnail 
{

 private string url { get; set; }
 private string width { get; set; }
 private string height { get; set; }
}

If I create an object of Item like this

 Item item = new Item ();

How can I access the variables url, width and height?

Thanks!

Answer 1

You have two options:

1. Make the properties public instead of private.
2. Use reflection to access the properties.

I recommend using (1).

Note that you also need to initialise item.thumbnail:

Item item = new Item ();
item.thumbnail = new thumbnail();

If you require that the thumbnail property is always set, you could add a constructor to class Item as follows (where I have also removed the setter for thumbnail and capitalised the name of the Thumbnail class. Class names should begin with a capital letter):

public class Item
{
    public Item(Thumbnail thumbnail)
    {
        if (thumbnail == null)
            throw new ArgumentNullException("thumbnail");

        this.thumbnail = thumbnail;
    }

    public string description { get; set; }
    public string item_uri { get; set; }
    public thumbnail thumbnail { get; }
}

---

Using Reflection to get and set the private properties

To use reflection, here's an example. Given a class like this:

public class Test
{
    private int PrivateInt
    {
        get;
        set;
    }
}

You can set and get its PrivateInt property like so:

Test test = new Test();
var privateInt = test.GetType().GetProperty("PrivateInt", BindingFlags.Instance | BindingFlags.NonPublic);

privateInt.SetValue(test, 42); // Set the property.

int value = (int) privateInt.GetValue(test); // Get the property (will be 42).

---

Simplify with helper methods

You could simplify this by writing a couple of generic helper methods like so:

public static T GetPrivateProperty<T>(object obj, string propertyName)
{
    return (T) obj.GetType()
                  .GetProperty(propertyName, BindingFlags.Instance | BindingFlags.NonPublic)
                  .GetValue(obj);
}

public static void SetPrivateProperty<T>(object obj, string propertyName, T value)
{
    obj.GetType()
       .GetProperty(propertyName, BindingFlags.Instance | BindingFlags.NonPublic)
       .SetValue(obj, value);
}

Then the example with the Test class would be like this:

Test test = new Test();

SetPrivateProperty(test, "PrivateInt", 42);
int value = GetPrivateProperty<int>(test, "PrivateInt");

Answer 2

Properties are members that provide a flexible mechanism to read, write, or compute the values of private fields

So I think you should declare them as public

public class thumbnail 
{

 public string url { get; set; }
 public string width { get; set; }
 public string height { get; set; }
}

May be you can have private class variables and then you can access them via these public properties.