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Figure 14-6. Silverlight screen coordinates system You are probably expecting to be able to position elements in Silverlight similar to the following code: <TextBlock Left="10" Top="20"></TextBlock> However, elements are positioned using the Canvas.Left and Canvas.Top properties (unless positioned through some other means such as a Grid): <TextBlock Canvas.Left="10" Canvas.Top="20"></TextBlock> Canvas.Left and Canvas.Top are a special type of property called an attached property. The Left and Top properties are actually attached to the Canvas element. This means you are positioning the TextBlock relative to the Canvas element. This is an important concept to understand and brings you to the subject of attached and dependency properties.

At times, applications need to retrieve a collection of child objects directly. To do this, you need to create a root collection object. For instance, the application may have a WPF UI consisting of a ListBox control that displays a collection of Contact objects. If the root object is a collection of child Contact objects, the UI developer can simply bind the collection to the ListBox (with an appropriate data template), and the user can edit all the objects in the list.

Anywhere When casting away const or casting to a constant Conversions between compiletime compatible types Conversions with runtime check in inheritance hierarchies Force conversion between incompatible types

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When the indexer is the target of an assignment, the set accessor is called, and receives two items of data, as follows: An implicit parameter, named value, where value holds the data to be stored One or more index parameters that represent where it should be stored emp[0] = "Doe"; Index Value Parameter Your code in the set accessor must examine the index parameters, determine where the data should be stored, and then store it. The syntax and meaning of the set accessor are shown in Figure 6-18. The left side of the figure shows the actual syntax of the accessor declaration. The right side shows the semantics of the accessor if it were written using the syntax of a normal method. The figure on the right shows that the set accessor has the following semantics: It has a void return type. It uses the same parameter list as that in the indexer declaration. It has an implicit value parameter named value, of the same type as the indexer.

The envelope is the root element of the message XML. It contains the message body and message header elements. The body element is required for all SOAP messages. It contains qualified XML for the request and response messages. The header contains optional extended information for the SOAP message. The WS- specification settings are stored in the header. The SOAP fault information, if present, is retrieved from the envelope and returned by the Fault property as an Exception class. The Context property enables you to modify the SOAP message contents within a custom WSE filter or to process the SOAP message contents within a SoapReceiver processing class.