How to write a custom templatefield-like DataControlField

I am using a GridView to display data where one of the data columns has type DateTimeOffset. In order to display dates & times in the user's timezone, I save the user's timezone preference to his or her profile (property value key "TimezoneOffset"), and need to access it when formatting dates & times.

If I were to use templatefield, then I would need to write:

<abbr class="datetimeoffset">
<%#
    ((DateTimeOffset)Eval("CreatedDate"))
    .ToOffset(new TimeSpan(-((Int32)Profile.GetPropertyValue("TimezoneOffset"))
                            .ToRepresentativeInRange(-12, 24), 0, 0)).ToString("f") %>
</abbr>

which is too complicated and not reusable.

I tried adding a TimeSpan property to the code-behind (to at least move that out of the data binding expression), but apparently properties of the view's code-behind are inaccessible within <%# ... %>.

Therefore, I think that I need to write a custom DataControlField to format dates & times in the user's timezone.

I have started with:

public class DateTimeOffsetField : DataControlField
{
    private TimeSpan userOffsetTimeSpan;

    protected override DataControlField CreateField()
    {
        return new DateTimeOffsetField();
    }

    protected override void CopyProperties(DataControlField newField)
    {
        base.CopyProperties(newField);
        ((DateTimeOffsetField)newField).userOffsetTimeSpan = userOffsetTimeSpan;
    }

    public override bool Initialize(bool sortingEnabled, System.Web.UI.Control control)
    {
        bool ret = base.Initialize(sortingEnabled, control);
        int timezoneOffset = ((Int32)HttpContext.Current.Profile.GetPropertyValue("TimezoneOffset")).ToRepresentativeInRa开发者_StackOverflow社区nge(-12, 24);
        userOffsetTimeSpan = new TimeSpan(-timezoneOffset, 0, 0);
        return ret;
    }
}

But now I am stuck. How do I output the HTML <abbr class="datetimeoffset"><%# ((DateTimeOffset)Eval("CreatedDate")).ToOffset(userOffsetTimeSpan).ToString("f") %></abbr> for each cell?

EDIT: I have been reading an article titled Cutting Edge: Custom Data Control Fields. So far I have added:

    public override void InitializeCell(DataControlFieldCell cell, DataControlCellType cellType, DataControlRowState rowState, int rowIndex)
    {
        base.InitializeCell(cell, cellType, rowState, rowIndex);

        if (cellType == DataControlCellType.DataCell)
        {
            InitializeDataCell(cell, rowState, rowIndex);
        }
    }

    protected virtual void InitializeDataCell(DataControlFieldCell cell, DataControlRowState rowState, int rowIndex)
    {
        System.Web.UI.Control control = cell;

        if (control != null && Visible)
        {
            control.DataBinding += new EventHandler(OnBindingField);
        }
    }

    protected virtual void OnBindingField(object sender, EventArgs e)
    {
        var target = (System.Web.UI.Control)sender;

        if (target is TableCell)
        {
            TableCell tc = (TableCell)target;
        }
    }

but whereas the article sets the Text property of the TableCell instance, I would like to render a partial view into the table cell. Is that possible?

I figured it out. Here is what I ended up with:

// DateTimeOffsetField.cs
public class DateTimeOffsetField : BoundField
{
    private TimeSpan userOffsetTimeSpan;

    protected override DataControlField CreateField()
    {
        return new DateTimeOffsetField();
    }

    protected override void CopyProperties(DataControlField newField)
    {
        base.CopyProperties(newField);
        ((DateTimeOffsetField)newField).userOffsetTimeSpan = userOffsetTimeSpan;
    }

    public override bool Initialize(bool sortingEnabled, System.Web.UI.Control control)
    {
        bool ret = base.Initialize(sortingEnabled, control);
        int timezoneOffset = ((Int32)HttpContext.Current.Profile.GetPropertyValue("TimezoneOffset")).ToRepresentativeInRange(-12, 24);
        userOffsetTimeSpan = new TimeSpan(-timezoneOffset, 0, 0);
        return ret;
    }

    protected override void OnDataBindField(object sender, EventArgs e)
    {
        base.OnDataBindField(sender, e);

        var target = (Control)sender;

        if (target is TableCell)
        {
            var tc = (TableCell)target;
            var dataItem = DataBinder.GetDataItem(target.NamingContainer);
            var dateTimeOffset = (DateTimeOffset)DataBinder.GetPropertyValue(dataItem, DataField);
            tc.Controls.Add(new TimeagoDateTimeOffset { DateTimeOffset = dateTimeOffset.ToOffset(userOffsetTimeSpan) });
        }
    }
}

TimeagoDateTimeOffset.cs:

[DefaultProperty("DateTimeOffset")]
[ToolboxData("<{0}:TimeagoDateTimeOffset runat=server></{0}:TimeagoDateTimeOffset>")]
public class TimeagoDateTimeOffset : WebControl
{
    [Bindable(true)]
    [Category("Appearance")]
    [DefaultValue("")]
    [Localizable(true)]
    public DateTimeOffset DateTimeOffset
    {
        get { return (DateTimeOffset)ViewState["DateTimeOffset"]; }
        set { ViewState["DateTimeOffset"] = value; }
    }

    protected override void RenderContents(HtmlTextWriter writer)
    {
        writer.BeginRender();
        writer.AddAttribute(HtmlTextWriterAttribute.Class, "timeago", false);
        writer.AddAttribute(HtmlTextWriterAttribute.Title, DateTimeOffset.ToString("o"));
        writer.RenderBeginTag("abbr");
        writer.Write(DateTimeOffset.ToString("d"));
        writer.RenderEndTag();
        writer.EndRender();
    }
}