Deriving from ComboBox | 易学教程

问题

I need to derive a class from ComboBox and change its Items property. Here is my code:

public class MyComboBox2 : ComboBox
{
    private MyObjectCollection MyItems;

    public MyComboBox2()
    {
        MyItems = new MyObjectCollection(this);
    }

    //new public ComboBox.ObjectCollection Items
    new public MyObjectCollection Items
    {
        get {
            return MyItems;
        }
    }


}

public class MyObjectCollection : ComboBox.ObjectCollection
{
    public MyObjectCollection(ComboBox Owner) : base(Owner)
    {

    }

    new public int Add(Object j)
    {
        base.Add(j);
        return 0;
    }


}

As you can see, I am creating a new class MyComboBox2 derived from ComboBox. This class is supposed to have a new Items property, which would be of type MyObjectCollection rather than ComboBox.ObjectCollection. I have a comboBox called myComboBox21 on the form of type MyComboBox2. When I want to add a new object to my ComboBox, I would execute code like this: myComboBox21.Items.Add("text"); In this case, I end up executing the Add method of MyObjectCollection that I implemented myself. However, the ComboBox on the form does not end up containing value 'text'. I am attaching screenshot of debugger showing ComboBox values. MyComboBox21 contains Items Property (which does contain "text", as shown in screenshot "2.png"), and it contains base.Items (which does not contain "text" as shown in "1.png"). So, apparently, MyComboBox21 contains its own Items property (which I can insert to), and its base class's Items property, which gets displayed in the Windows Form. What can I do so that I can successfully add to comboBox with my own method? Since my ComboBox has 2 Items properties, can I specify which Items property's values should be shown in ComboBox?

回答1:

Just by looking very quickly on the code:

The original Item index is declared as

     virtual Object this[int index] {...}

Does the new keyword maybe be exchanged by override in your implementation in order to make the runtime pick the intended code?

来源：https://stackoverflow.com/questions/25835441/deriving-from-combobox

标签

.net

winforms

inheritance

combobox