Creating a custom databound control with postbacks

Creating a custom databound control with postbacks

/// <summary>
/// Creating a custom databound control with postbacks
/// --------------------------------------------------
/// This class provides you the basis for a databound custom control
/// and shows you where to place logic to ensure the data is saved in
/// the ViewState and the dynamically created child controls work
/// as intended
/// </summary>
class MyControl : Control
    private object datasource;
    //CF: A list we are using for example
    private RadioButtonList _List;

    //CF: Define this as whatever you want if this control is databound
    //    This object should not be persisted as you are relying on ViewState
    public object DataSource
        get { return datasource; }
        set { datasource = value; }

    //CF: This variable holds the number of items that were databound
    //    It is used on post back to recreate the items that are stored in the ViewState
    private int NumberOfItems
            if (ViewState["NumberOfItems"] == null)
                return 0;
            return (int) ViewState["NumberOfItems"];
        set { ViewState["NumberOfItems"] = value; }

    protected override void OnInit(EventArgs e)

        //CF: The controls must be created here otherwise the postback data will not be loaded!!!

        //CF: If your control requires ControlState uncomment this line

    protected override void CreateChildControls()
        //CF: Only create the list and it's items here it will be populated on databinding, or via viewstate
        _List = new RadioButtonList();
        for (int i = 0; i < NumberOfItems; i++)
            ListItem item = new ListItem();

        //CF: Setting additional properties of the controls should be done *after* 
        //    they are added to Controls collection. This will "dirty" the ViewState
        //    and ensure their value is persisted
        //    Ensure you give your dynamic controls an ID, to associate them to their 
        //    ViewState data
        _List.ID = "list";

    protected override void OnDataBinding(EventArgs e)
        //CF: You need to set the number of items here
        NumberOfItems = DataSource.Count;

        //CF: As the list was already created in OnInit() with no items, it must be recreated here

        //CF: Now we loop through each item and databind it's actual value
        for (int i = 0; i < NumberOfItems; i++)
            ListItem item = _List.Items[i];
            //TODO: Obtain the value from the DataSource and set the Controls properties

    //CF: If necessary override Render() to specify custom control rendering, otherwise leave it as it is
    //protected override void Render(HtmlTextWriter writer)
    //  //TODO: Do stuff

    //CF: If you are using control state uncomment the following 2 paragraphs and customise them 
    //    as necessary. If you need to save multiple objects it is probably best to wrap them up
    //    in a struct/class.
    //    Remember all objects must be Serializable.
    protected override void LoadControlState(object savedState)
        object[] state = (object[]) savedState;
        MyObject = state[1];

    protected override object SaveControlState()
        object[] state = new object[2];
        state[0] = base.SaveControlState();
        state[1] = MyObject;
        return state;
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