Silverlight 2.0 promises to bring much of the goodness of WPF to the browser. So how does one of my favourite WPF features - data binding - fare in the new Silverlight 2.0 beta 1 world? To help answer this question I drew up the following summary:
| Similarities | Differences |
|---|---|
| Binding Object – the Binding object is present in both SL 2.0 and WPF. Many simple binding scenarios will probably work between the two without modification, but if you’re using the more complex properties of the Binding object in WPF you’ll need to revisit that for Silverlight 2.0 code. The INotifyPropertyChanged interface is also used for change notifications on data objects to be propagated back up to the binding infrastructure. | Binding Object – although the Binding object exists in SL 2.0 and WPF the SL 2.0 version is very pared-back compared to WPF, having only 5 properties: Converter, ConverterCulture, ConverterParameter, Mode and Source, in contrast to the 20 or so relevant properties the WPF binding object exposes or inherits from its base types. One of the most key properties on the WPF binding object – the path isn’t even a property at all on the Silverlight equivalent. Instead it is specified as a constructor property. Also the Path in SL 2 can’t drill down into indexes or attached properties the way it can in WPF, however you can still access sub-properties on objects. Josh has some screen-shots from Reflector showing the difference in size of the two types. |
| Data Context – the concept of a Data Context for a control which is propagated from a parent control down to child controls is shared between WPF and Silverlight 2 beta 1. As with WPF the FrameworkElement type adds the DataContext property in Silverlight 2.0 beta 1. | Binding Markup Extension – although syntactically quite similar (albeit with less properties) bindings in Silverlight are quite different internally to their WPF counterparts because they don’t use a managed Binding Markup Extension. In fact, from what we can see of Silverlight 2.0 beta 1 there ARE no markup extensions of any kind. The Silverlight documentation discusses them here but they don’t appear anywhere in the object model. Presumably the implementations of the various markup extensions are hard-wired into the Silverlight runtime. |
| Converters – One of my favourite extensibility points of WPF has been completely migrated to Silverlight 2.0 beta 1 (possibly due to the simplicity of the IValueConverter interface). A converter and converter parameter can be supplied as part of a binding. | Binding to Other Elements – one common scenario is to bind two pieces of WPF UI to each-other. For example binding a slider to the “zoom” on a ScaleTransform. This is done by setting the ElementName property to the name of the element in the current name scope. Silverlight 2.0 beta 1 doesn’t support ElementName as a parameter when binding. This limitation can be worked around fairly easily by creating a simple object with a single property of the type you wish to glue together (double is probably the most common scenario) and then implementing INotifyPropertyChanged on that type. This approach is described in more detail here. |
| Data Templates – Both WPF and Silverlight 2.0 beta 1 share the concept of templates that can be applied to data. One area where SL 2 differs is that in WPF you can specify a template by the type of object the template applies to (by setting the DataType property). If this is set and no key is supplied (and the Datatemplate is appropriately scoped) the template becomes the default appearance for that type of data item in WPF. The DataTemplate type in Silverlight 2.0 beta 1 doesn’t include this property so all data templates are “keyed” in resource dictionaries or entered in-line. | Data Triggers – Data templates in Silverlight 2.0 beta 1 don’t have data triggers like their WPF counterparts. This can be worked around using a converter, but requires more code than a data trigger would. Given the changes introduced by the new Silverlight control templating model data triggers going missing are the least of your worries. |
| TemplateBinding – TemplateBinding is fundamental to styling of controls, and thus has also made its way over from WPF to Silverlight. | |
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