NoesisGUI
Documentation Index

Binding

http://msdn.microsoft.com/en-us/library/system.windows.data.binding.aspx

http://i.msdn.microsoft.com/ms617928.DataBindingMostBasic(en-us,VS.100).png

Binding allows the connection of an object's property to any data source (property from other object, database, XML file, etc...). Current implementation only supports the connection between object properties.

Methods
Name Sup Comments
ShouldSerializePath No  
ShouldSerializeSource No  
ShouldSerializeValidationRules No  
Dependency Properties
Name Att Sup Comments
XamlNamespaceManagerPropert Yes No  
Properties
Name Sup Comments
AsyncState No  
BindsDirectlyToSource No  
Converter Yes  
ConverterCulture No  
ConverterParameter Yes  
ElementName Yes  
IsAsync No  
Mode Yes  
NotifyOnSourceUpdated No  
NotifyOnTargetUpdated No  
NotifyOnValidationError No  
Path Yes  
RelativeSource Yes  
Source Yes  
UpdateSourceExceptionFilter No  
UpdateSourceTrigger No  
ValidatesOnDataErrors No  
ValidatesOnExceptions No  
ValidationRules No  
XPath No  
Routed Events
Name Att Sup Comments
SourceUpdatedEvent Yes No  
TargetUpdatedEvent Yes No  

In a binding there are 3 main elements: a Target, a Source and a Path to the value in the Binding Source

  • The Target is always a Dependency Property
  • The Source can be a Dependency Property, or a "normal" property from an object that implements the INotifyChange interface
  • The Path is created from a string that tells how to reach the binding value in the Source

The Binding object is stored in the Target as an expression, so a call to DependencyObject::ReadLocalValue over a local binding will return an object that can be casted to BindingExpression.

Source

The source of a Binding can be expressed in several ways:

  • ElementName: The source search traverses the tree upwards looking in the namescopes until the root is reached
  • Source: Explicit set of the source, for example using a DynamicResource extension
  • RelativeSource: Useful when the source is relative (an ancestor) to the target object. The relative source can be:
  • Self: Set the source equal to the target object
  • AncestorType: Gets an ancestor matching the specified type
  • AncestorLevel: To know how many ancestors (of type AncestorType if indicated) have to skipped to reach the desired source
  • TemplatedParent: To get the source from the target's templated parent.
  • DataContext: Is explained later in this document
<Button Background="Red" Foreground="{Binding RelativeSource={RelativeSource Self}, Path=Background}"/>
<Button Background="{Binding RelativeSource={RelativeSource AncestorType={x:Type Border}, AncestorLevel=2}, Path=Background}"/>
<Button Background="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Background}"/>

Return value

When a binding can't be resolved for any reason (invalid property path, source not found, converter not available, etc...) it returns the FallbackValue if set. If there is no FallbackValue, the binding returns a DependencyProperty::UnsetValue and when this value is evaluated in the DependencyObject, the default value of the target property is stored.

Binding modes

Data flow in a binding can be modified with the Binding::Mode property. There are 4 flow modes:

  • OneWay: Updates the binding target property when the binding source changes
  • TwoWay: Updates either the source property or the target property when the other changes
  • OneWayToSource: Updates the source property when the target property changes
  • OneTime: Updates the binding target when the application starts or when the data context changes

Update timing

For TwoWay or OneWayToSource bindings the moment when the target is updated can be controller with the UpdateSourceTrigger property. It has 3 possible values:

  • PropertyChanged: It's the most common. The source is updated immediately after a target property change
  • LostFocus: The update is done when the target object loses focus. It's the default behavior for TextBox::Text property
  • Explicit: The update is done by code, calling BindingExpression::UpdateSource method
  • Default: The value is read from the target property Metadata (FrameworkPropertyMetaData::DefaultUpdateSourceTrigger)

Type Converters

Target and Source values can have different types. To allow the assignment of values of different types, an intermediate conversion is done by a converter (an object that implements IValueConverter interface).

The converter can be specified by the user (even when target and source types are the same). If the types are different and the user doesn't specify a converter, the binding object instantiates a DefaultValueConverter which internally uses Core::TypeConverters from source and target types. Internally, the DefaultValueConverter first instantiates the target type converter, and if the conversion can't be done it makes a second try with the source type converter; if the second one also fails, then the binding can't resolve.

String Format

When the target property is a String, the user can also specify a StringFormat property to indicate how to format the bound value (the StringFormat is only applied in the Source to Target data flow). If StringFormat is specified, the DefaultValueConverter is not utilized in the Source to Target data flow, but for user setted converters the converter is evaluated first and then the StringFormat is applied to the resulting value.

There are several formatting types for StringFormat:

  • Numeric format
  • Currency C: Implemented as number + 2 decimals + Euro symbol, but number is lacking thousands separator
  • Decimal D: Implemented
  • Scientific E: Implemented
  • Fixed Point F: Implemented
  • General G: Implemented
  • Number N: Implemented as Fixed Point
  • Percent P: Implemented
  • Round Trip R: Currently not implemented
  • Hexadecimal H: Implemented
  • Date and Time format: currently not implemented
  • Enum format: currently not implemented

DataContext

When several properties are binding to a common source the DataContext property of FrameworkElement and FrameworkContentElement can be set to allow the children in the same tree to resolve using the same source.

<DockPanel DataContext="{Binding Source={StaticResource Blog}}">
  <Label Content="{Binding Path=Name}"/>
  <Label Content="{Binding Path=Author}"/>
</DockPanel>

TemplateBinding

http://msdn.microsoft.com/en-us/library/system.windows.templatebindingextension.aspx

TemplateBinding is an ligthweight Binding version equivalent to using RelativeSource=TemplatedParent

Properties
Name Sup Comments
Converter No  
ConverterParameter No  
Property Yes   
<Button Background="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Background}"/>
<Button Background="{TemplateBinding Background}"/>
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