为什么当两个对象相同时我的C＃代码找不到？

Question

This is a method for recursively searching through a binary tree that is filled with objects of the various child classes of the class Photo.

public void SearchForIdentical(Photo searched)
{
    SearchForIdentical(ref root, searched);
}

void SearchForIdentical(ref TreeNode current, Photo searched)
{
    try
    {
        if(current != null)
        {
            if(current.content.Equals(searched))
            {
                throw new PhotoAlreadyExistsException(searched);
            }
            SearchForIdentical(ref current.left, searched);
            SearchForIdentical(ref current.right, searched);
        }
    }
    catch (PhotoAlreadyExistsException e)
    {
        Console.WriteLine("This photo already exists! Try a new one!");
    }
}

A 'photo' is defined by the value of its various arguments and properties (the child classes don't necessarily all have the same kind of arguments and properties). If the user types in a new photo, that is fully identical in all its arguments and properties with an existing one, this method should notice it, and throw an exception.

The problem is, it never happens. When I debugged it, it seemed the program never assigns true to the premise current.content.Equals(searched) , even when the two object is exactly identical.

What could be the problem?

Answer 1

If you never override the Equals() method in the Photo class to do the comparisons of the properties you've described, your code will be doing an object reference equality comparison.

This would explain why when the properties are identical, the Equals() method returns false .