C＃WinForms中的动态组合框列表数据绑定

Question

Have read a lot this resource and really like it, but now i met problem which i can't neither resolve by myself nor find similar solution. I'm using C# winforms and linqtosql. In my userforms I use additional view-class to bind list for comboboxes to let users be able to get and use a name-list of objects while being forbidden to get a whole object itself. (This is not question whether it is a good practice, no matter.)

For example(this is not real code, just for look): ORM classes:

public class Contract
{
    public string ID { get; set; }
    public string Name { get; set; }
    public Contractor Contractor { get; set; }
    public string ContractorID { get; set; }
}
public class Contractor
{
    public string ID { get; set; }
    public string Name { get; set; }
    public string Phone { get; set; }
}

This is additional view-class which is mapping for sqlserver view Contractor_List (SELECT c.ID, c.Name FROM Contractors c)

public class Contractor_List
{
    public string ID { get; set; }
    public string Name { get; set; }
}

UserForm:

public class ContractForm : Form
{
    void Init()
    {
        TextBox nameBox = new TextBox();
        ComboBox contractorBox = new ComboBox();
        BindingSource contractSource = new BindingSource();
        contractSource.DataSource = typeof (Contract);

        nameBox.DataBindings.Add("Text", contractSource, "Name", false, DataSourceUpdateMode.OnValidation);
        contractorBox.DataBindings.Add("SelectedValue", contractSource, "ContractorID", false, DataSourceUpdateMode.OnValidation);


        BindingSource contractorListSource = new BindingSource();
        contractorListSource.DataSource = typeof (Contractor_List);

        contractorBox.DisplayMember = "Name";
        contractorBox.ValueMember = "ID";
    }

}

OK. My idea is to load contractorBox.DataSource (it's binding source) when contractorBox.SelectedValue is set. I found that SelectedValue is not overridable, so I decided to inherit combobox and to create in it a new property called “ID” and do following stuff instead In form:

contractorBox.DataBindings.Add("ID", contractSource, "ContractorID");

In Control (this is real code):

    object _id;
    bool _listInitialized;
    public object ID
            {
                get
                {
                    return _id;

                }
                set
                {
                    if (!_listInitialized)
                    {
                        var bindingSource = DataSource as BindingSource;
                        if (bindingSource != null)
                        {
                            var t = (bindingSource.DataSource as Type);
                            var rst = … //Getting List
                            if (rst!=null)
                            {
                                bindingSource.DataSource = rst;
                                _listInitialized = true;
                                SelectedValueChanged += delegate {
                                    if (SelectedValue != ID)
                                    {
                                        ID = SelectedValue;
                                    }
                                };
                            }
                        }
                    }
                    else
                    {
                        _id = value;
                        if (SelectedValue != ID)
                        {
                            SelectedValue = value;
                        }
                    }

                }
            }

So, this code works fine. I can load form, Contract object and list of contractors and get right contractor name in combobox. But. I have problem with backing Binding of “ID” property. When contractor in combobox is changed Contract object doesn't update (neither ContractorID , no Contractor Itself) while ID , SelectedValue and SelectedItem of combobox change properly. Why? What have I do to make this working.

Answer 1

Hah. So Simple Solution.

public new object SelectedValue
{
    get
    {
        return base.SelectedValue;

    }
    set
    {
        if (!DesignMode)
        {
            if (!_listInitialized)
            {
                var bindingSource = DataSource as BindingSource;
                if (bindingSource != null)
                {
                    var t = (bindingSource.DataSource as Type);
                    var rst = ...///how you get your type list
                    if (rst != null)
                    {
                        bindingSource.DataSource = rst;
                        _listInitialized = true;
                    }
                }
            }
            else
            {
                base.SelectedValue = value;
            }
        }
    }
}

May be will be helpful for someone.