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DataControlField.ExtractValuesFromCell Method

  • Reference

Definition

Namespace:
System.Web.UI.WebControls
Assembly:
System.Web.dll

Extracts the value of the data control field from the current table cell and adds the value to the specified IDictionary collection.

public:
 virtual void ExtractValuesFromCell(System::Collections::Specialized::IOrderedDictionary ^ dictionary, System::Web::UI::WebControls::DataControlFieldCell ^ cell, System::Web::UI::WebControls::DataControlRowState rowState, bool includeReadOnly);
public virtual void ExtractValuesFromCell (System.Collections.Specialized.IOrderedDictionary dictionary, System.Web.UI.WebControls.DataControlFieldCell cell, System.Web.UI.WebControls.DataControlRowState rowState, bool includeReadOnly);
abstract member ExtractValuesFromCell : System.Collections.Specialized.IOrderedDictionary * System.Web.UI.WebControls.DataControlFieldCell * System.Web.UI.WebControls.DataControlRowState * bool -> unit
override this.ExtractValuesFromCell : System.Collections.Specialized.IOrderedDictionary * System.Web.UI.WebControls.DataControlFieldCell * System.Web.UI.WebControls.DataControlRowState * bool -> unit
Public Overridable Sub ExtractValuesFromCell (dictionary As IOrderedDictionary, cell As DataControlFieldCell, rowState As DataControlRowState, includeReadOnly As Boolean)

Parameters

dictionary
IOrderedDictionary

An IOrderedDictionary.

cell
DataControlFieldCell

A DataControlFieldCell that contains the text or controls of the DataControlField.

rowState
DataControlRowState

One of the DataControlRowState values.

includeReadOnly
Boolean

true to indicate that the values of read-only fields are included in the dictionary collection; otherwise, false.

Examples

The following code example demonstrates how to implement the ExtractValuesFromCell method for a control that derives from the DataControlField class. The RadioButtonField class renders a data-bound radio button for every row in a GridView control. When the ExtractValuesFromCell method is called, the method attempts to determine whether the current value of the RadioButton object contained in the cell is selected or cleared, and adds the value to the IDictionary collection. This code example is part of a larger example provided for the DataControlField class.

// This method is called by the ExtractRowValues methods of 
// GridView and DetailsView. Retrieve the current value of the 
// cell from the Checked state of the Radio button.
public override void ExtractValuesFromCell(IOrderedDictionary dictionary,
                                           DataControlFieldCell cell,
                                           DataControlRowState rowState,
                                           bool includeReadOnly)
{

  // Determine whether the cell contains a RadioButton 
  // in its Controls collection.
  if (cell.Controls.Count > 0) {
    RadioButton radio = cell.Controls[0] as RadioButton;

    object checkedValue = null;
    if (null == radio) {
      // A RadioButton is expected, but a null is encountered.
      // Add error handling.
      throw new InvalidOperationException
          ("RadioButtonField could not extract control.");
    }
    else {
        checkedValue = radio.Checked;
    }

    // Add the value of the Checked attribute of the
    // RadioButton to the dictionary.
    if (dictionary.Contains(DataField))
      dictionary[DataField] = checkedValue;
    else
      dictionary.Add(DataField, checkedValue);
  }
}

' This method is called by the ExtractRowValues methods of
' GridView and DetailsView. Retrieve the current value of the 
' cell from the Checked state of the Radio button.
Public Overrides Sub ExtractValuesFromCell( _
    ByVal dictionary As IOrderedDictionary, _
    ByVal cell As DataControlFieldCell, _
    ByVal rowState As DataControlRowState, _
    ByVal includeReadOnly As Boolean)
    ' Determine whether the cell contain a RadioButton 
    ' in its Controls collection.
    If cell.Controls.Count > 0 Then
        Dim radio As RadioButton = CType(cell.Controls(0), RadioButton)

        Dim checkedValue As Object = Nothing
        If radio Is Nothing Then
            ' A RadioButton is expected, but a null is encountered.
            ' Add error handling.
            Throw New InvalidOperationException( _
                "RadioButtonField could not extract control.")
        Else
            checkedValue = radio.Checked
        End If


        ' Add the value of the Checked attribute of the
        ' RadioButton to the dictionary.
        If dictionary.Contains(DataField) Then
            dictionary(DataField) = checkedValue
        Else
            dictionary.Add(DataField, checkedValue)
        End If
    End If
End Sub

Remarks

The ExtractValuesFromCell method is implemented by types derived from DataControlField to associate the current field with a value, if applicable. The field/value pair is stored in the dictionary collection that is passed to the method. The ExtractValuesFromCell method is called by the ExtractRowValues method of data controls such as DetailsView and GridView.

Call this method when you are writing a custom data-bound control that uses DataControlFieldCell objects to assemble a set of cells and their associated values. Implement this method when you are writing a class derived from DataControlField that displays user data or data-bound data. Not all derived types implement the ExtractValuesFromCell method, because not all fields display user data. For example, the ButtonField control displays a button and has no user data.

Applies to

See also