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Binding.Format Event

Occurs when the property of a control is bound to a data value.

[Visual Basic]
Public Event Format As ConvertEventHandler
[C#]
public event ConvertEventHandler Format;
[C++]
public: __event ConvertEventHandler* Format;

[JScript] In JScript, you can handle the events defined by a class, but you cannot define your own.

Event Data

The event handler receives an argument of type ConvertEventArgs containing data related to this event. The following ConvertEventArgs properties provide information specific to this event.

Property Description
DesiredType Gets the data type of the desired value.
Value Gets or sets the value of the ConvertEventArgs object.

Remarks

The Format event occurs when data is pushed from the data source into the control. You can handle the Format event to convert unformatted data from the data source into formatted data for display. When data is pulled from the control into the data source, the Parse event occurs to unformat the displayed value, then the Format event occurs to reformat the data for display. This ensures that the bound control displays correctly formatted data regardless of whether the user enters formatted or unformatted data in the control.

The Format and Parse events allow you to create custom formats for displaying data. For example, if the data in a table is of type Decimal, you can display the data in the local currency format by setting the Value property of the ConvertEventArgs object to the formatted value in the Format event. You must consequently unformat the displayed value in the Parse event.

The Format event occurs whenever the Current value of the BindingManagerBase changes, which includes:

  • The first time the property is bound.
  • Any time the Position changes.
  • Whenever the data-bound list is sorted or filtered, which is accomplished when a DataView supplies the list.

The Format event also occurs after the Parse event. For example, when a control loses focus, its contents are parsed. Immediately afterwards, as new data is pushed into the control, the Format event occurs allowing the new contents to be formatted.

For more information about handling events, see Consuming Events.

Example

The following example creates a Binding, adds a ConvertEventHandler delegate to both the Parse and Format events, and adds the Binding to the BindingsCollection of a TextBox control through the DataBindings property. The DecimalToCurrencyString event delegate, added to the Format event, formats the bound value (a Decimal type) as currency using the ToString method. The CurrencyStringToDecimal event delegate, added to the Parse event, converts the value displayed by the control back to the Decimal type.

[Visual Basic] 
Private Sub DecimalToCurrencyString(sender As Object, cevent As _
ConvertEventArgs)
   ' The method converts only to string type. Test this using the DesiredType.
   If Not cevent.DesiredType Is GetType(String) Then
      Exit Sub
   End If

   ' Use the ToString method to format the value as currency ("c").
   cevent.Value = CType(cevent.Value, Decimal).ToString("c")
End Sub

Private Sub CurrencyStringToDecimal(sender As Object, cevent As _
ConvertEventArgs)
   ' The method converts back to decimal type only.
   If Not cevent.DesiredType Is GetType(Decimal) Then
      Exit Sub
   End If

   ' Converts the string back to decimal using the static ToDecimal method.
   cevent.Value = Decimal.Parse(cevent.Value.ToString, _
   NumberStyles.Currency, nothing)
End Sub

Private Sub BindControl
   ' Creates the binding first. The OrderAmount is a Decimal type.
   Dim b As Binding = New Binding _
      ("Text", ds, "customers.custToOrders.OrderAmount")
   ' Add the delegates to the event
   AddHandler b.Format, AddressOf DecimalToCurrencyString
   AddHandler b.Parse, AddressOf CurrencyStringToDecimal
   text1.DataBindings.Add(b)
End Sub

[C#] 
private void DecimalToCurrencyString(object sender, ConvertEventArgs cevent)
{
   // The method converts only to string type. Test this using the DesiredType.
   if(cevent.DesiredType != typeof(string)) return;

   // Use the ToString method to format the value as currency ("c").
   cevent.Value = ((decimal) cevent.Value).ToString("c");
}

private void CurrencyStringToDecimal(object sender, ConvertEventArgs cevent)
{
   // The method converts back to decimal type only. 
   if(cevent.DesiredType != typeof(decimal)) return;

   // Converts the string back to decimal using the static Parse method.
   cevent.Value = Decimal.Parse(cevent.Value.ToString(),
   NumberStyles.Currency, null);
}

private void BindControl()
{
   // Creates the binding first. The OrderAmount is a Decimal type.
   Binding b = new Binding
      ("Text", ds, "customers.custToOrders.OrderAmount");
   // Add the delegates to the event.
   b.Format += new ConvertEventHandler(DecimalToCurrencyString);
   b.Parse += new ConvertEventHandler(CurrencyStringToDecimal);
   text1.DataBindings.Add(b);
}


[C++] 
private:
void DecimalToCurrencyString(Object* /*sender*/, ConvertEventArgs* cevent)
{
   // The method converts only to string type. Test this using the DesiredType.
   if(cevent->DesiredType != __typeof(String)) return;

   // Use the ToString method to format the value as currency ("c").
   cevent->Value = (*__try_cast<Decimal*>(cevent->Value)).ToString(S"c");
}

void CurrencyStringToDecimal(Object* /*sender*/, ConvertEventArgs* cevent)
{
   // The method converts back to decimal type only. 
   if(cevent->DesiredType != __typeof(Decimal)) return;

   // Converts the string back to decimal using the static Parse method.
   cevent->Value = __box(Decimal::Parse(cevent->Value->ToString(),
   NumberStyles::Currency, 0));
}

void BindControl()
{
   // Creates the binding first. The OrderAmount is a Decimal type.
   Binding* b = new Binding
      (S"Text", ds, S"customers.custToOrders.OrderAmount");
   // Add the delegates to the event.
   b->Format += new ConvertEventHandler(this, &Form1::DecimalToCurrencyString);
   b->Parse += new ConvertEventHandler(this, &Form1::CurrencyStringToDecimal);
   text1->DataBindings->Add(b);
}


[JScript] 
private function DecimalToCurrencyString(sender, cevent : ConvertEventArgs)
{
   // The method converts only to string type. Test this using the DesiredType.
   if(cevent.DesiredType != String.GetType()) return;

   cevent.Value = (Decimal(cevent.Value)).ToString("c"); 
}

private function CurrencyStringToDecimal(sender, cevent : ConvertEventArgs)
{
   // The method converts only to decimal type. 
   if(cevent.DesiredType != Decimal.GetType()) return;

   // Converts the string back to decimal using the static Parse method.
   cevent.Value = Decimal.Parse(cevent.Value.ToString(),
   NumberStyles.Currency, null);
}

private function BindControl()
{
   // Creates the binding first. The OrderAmount is a Decimal type.
   var b : Binding = new Binding
      ("Text", ds, "Suppliers.CompanyName");
   // Add the delegates to the event.
   b.add_Format(DecimalToCurrencyString);
   b.add_Parse(CurrencyStringToDecimal);
   text1.DataBindings.Add(b);
}

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also

Binding Class | Binding Members | System.Windows.Forms Namespace | Parse | OnFormat

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