如何编写自定义模板字段的DataControlField

Question

我正在使用GridView来显示其中一个数据列的类型为DateTimeOffset的数据。为了在用户的时区显示日期&次，我将用户的时区首选项保存到他或她的配置文件（属性值键“TimezoneOffset”），并且在格式化日期&次时需要访问它。

如果我是用模板列，然后我需要写：

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

这也太复杂，不能重复使用。

我试着给代码隐藏添加一个TimeSpan属性（至少将它移出数据绑定表达式），但显然在<%# ... %>内无法访问视图的代码隐藏属性。

因此，我认为我需要编写一个自定义DataControlField来格式化用户时区中的日期&次。

我已经开始用：

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")).ToRepresentativeInRange(-12, 24); 
     userOffsetTimeSpan = new TimeSpan(-timezoneOffset, 0, 0); 
     return ret; 
    } 
} 

但现在我卡住了。如何为每个单元格输出HTML <abbr class="datetimeoffset"><%# ((DateTimeOffset)Eval("CreatedDate")).ToOffset(userOffsetTimeSpan).ToString("f") %></abbr>？

编辑：我一直在阅读一篇文章，标题为Cutting Edge: Custom Data Control Fields。到目前为止，我还补充说：

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; 
     } 
    } 

但而文章设置TableCell实例的Text财产，我想呈现的局部视图到表格单元格。那可能吗？

Answer 1

我想通了。以下是我结束了：

// 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(); 
    } 
}