period in XML tags

Question

Studying XAML now, I keep seeing XAML tags in the format Object.Attribute. For example:

 
     OutOfBrowserSettings Sh         


        

Answer 1

Found this today in WPF in Action with Visual Studio 2008 by Feldman and Daymon

4.2.3. Using attached properties

You may have noticed an interesting thing about the property values in listing 4.2. Properties such as Width and Padding look like regular XML attributes. But the Left and Top properties' notation is a little different:

Button does not have properties for Left and Top. Unlike Windows Forms, which assumed that everything has an explicit location, the working assumption for WPF is that the parent is responsible for the placement of each control. You'll see this with the other layout types. In the case of a Canvas, each control has to have its explicit location set. Because it is the Canvas layout that requires this information, it is up to the Canvas layout to handle this information.

In "classic" XML (that is, XML that could be validated by a Schema), you'd normally have to introduce an element around each child to specify the properties specific to the parent—something like listing 4.3.

Listing 4.3. A way to set properties for children (but not supported by WPF)

    
        Button1
    

This approach would work but is quite verbose, particularly when you have a lot of nested items. It also implies a hierarchy that doesn't really exist. Rather than requiring more verbose XML and making Canvas follow a structure that it probably doesn't need, XAML introduces a notation that allows properties that belong to the parent to be defined on the child, via the use of the dot notation:

  Button1

This should be read as "When you add the Button to the Canvas, tell the Canvas that the Button should be positioned at Left 40 and Top 40." These properties are called attached properties because they're attached to the child to which they refer, even though they belong to the containing control (the Canvas in this case). You'll see this notation throughout XAML for all sorts of properties. You just need to remember that properties with dots in the middle are really setting values that are used by the containing control. The nice thing is that, when you're editing the properties of the control in the property editor, attached properties are displayed as part of the set of the control's properties