Extending a (ASP.NET) BoundField

Question

I would like to create a control that extends the BoundField that's used within a GridView. What I'd like to do is provide another property named HighlightField that will be similar to the DataField property in that I want to give it the name a data column. Given that data column it would see if the value is true or false and highlight the given text within the given column on the given row.

Some psuedo-code if that doesn't make sense:

<asp:GridView id="grid">
  <Columns>
    <asp:BoundField DataField="Name" />
    <cc:HighlightField DataField="Name" HighlightField="IsHighlighted" />
  </Columns>
</asp:GridView>

And then within the databind or something:

if(this row's IsHighlighted value is true)
  set the CssClass of this datacell  = "highlighted"
(or wrap a span tag around the text)

Ravish pointed me in the correct direction, here's what I ended up with:

public class HighlightedBoundField : BoundField
{
 public string HighlightField
 {
  get { return ViewState["HighlightField"].ToString(); }
  set
  {
   ViewState["HighlightField"] = value;
   OnFieldChanged();
  }
 }

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

  bool isDataRowAndIsHighlightFieldSpecified = cellType == DataControlCellType.DataCell && !string.IsNullOrEmpty(HighlightField);
  if (isDataRowAndIsHighlightFieldSpecified)
  {
   cell.DataBinding += new EventHandler(cell_DataBinding);
  }
 }

 void cell_DataBinding(object sender, EventArgs e)
 {
  TableCell cell = (TableCell)sender;
  object dataItem = DataBinder.GetDataItem(cell.NamingContainer);
  cell.Text = DataBinder.GetPropertyValue(dataItem, DataField).ToString();

  bool highlightThisCellsText = Convert.ToBoolean(DataBinder.GetPropertyValue(dataItem, HighlightField));
  if (highlightThisCellsText)
  {
   cell.CssClass += " highlight";
  }
 }
}

Answer 1

Untested:

public class HighlightBoundField : DataControlField {

    //property to indicate if this field should be highlighted, given the value of this property
    //
    public string HighlightField {
     get {
      object value = ViewState["HighlightField"];

      if (value != null) {
       return Convert.ToString(value);
      }

      return "";
     }

     set {
      ViewState["HighlightField"] = value;
      OnFieldChanged();
     }
    }

    //property to display as text in the cell
    //
    public string DataField {
     get {
      object value = ViewState["DataField"];

      if (value != null) {
       return value.ToString();
      }

      return string.Empty;
     }

     set {
      ViewState["DataField"] = value;

      OnFieldChanged();
     }
    }

    //bound field creation
    //
    protected override DataControlField CreateField() {
     return new BoundField();
    }

    //override the method that is used to populate and format a cell
    //
    public override void InitializeCell(DataControlFieldCell cell, DataControlCellType cellType, DataControlRowState rowState, int rowIndex) {
     base.InitializeCell(cell, cellType, rowState, rowIndex);

     //if this celltype is a data row
     //
     if (cellType == DataControlCellType.DataCell && !string.IsNullOrEmpty(HighlightField)) {
      //create label control to display text
      //
      var lblText = new Label();

      //add event listener for when the label is bound
      //
      lblText.DataBinding += new EventHandler(lblText_DataBinding);

      //add label to controls collection
      //
      cell.Controls.Add(lblText);
     }
    }

    void lblText_DataBinding(object sender, EventArgs e) {
     //retrieve data item and set label text
     //
     Label lblText = (Label) sender;
     object dataItem = DataBinder.GetDataItem(lblText.NamingContainer);
     lblText.Text = DataBinder.GetPropertyValue(dataItem, DataField).ToString();

     //check if value should be highlighted
     //
     if (Convert.ToBoolean(DataBinder.GetPropertyValue(dataItem, HighlightField))) {
      lblText.Style.Add("background-color", "yellow");
     }
    }
}