= Chapter 11 Notes =

Title: '''The Bindable Infrastructure'''

== Summary ==

This will be our introduction to binding views to properties, i.e. Data Binding.

=== Programming Concepts Summary ===

|| '''Concept''' || '''Page''' ||
|| Property      || 227 ||
|| Xamarin enhances property definition and encapsulates this enhanced property in the {{{BindableProperty}}} class. || 227 ||
|| {{{BindableProperty}}} objects are used to store the data associated with a {{{BindableObject}}} || 22 + Docs online ||

In general there are two extremely important concepts in CS: '''abstraction''' and '''layering'''. 

Properties are an abstraction of implementing getters and setters for a field. The abstraction allows the the user to treat the property like a field (variable), and as such we are abstracting away the details of getters and setters so that the user of a property does not have to remember to use a getter and setter when dealing with a property vs. a normal field variable. 

The class hierarchy project shows the process of layering functionality. Functionality shared by every object is at the top of the inheritance tree, and every object inherits from that object directly or through an inheritance chain. This is demonstrated nicely in the {{{ClassHierarchy}}} program. 

== Programs ==

=== Program ClassHierarchy ===

Page 228.

Concepts:

 1. Shows how to walk the Xamarin.Forms class hierarchy so that we can see how the classes are related. 
 1. General functionality is defined and implemented higher in the hierarchy this includes all functionality (and implementation code) shared by the children. Although this may seem obvious to say, I want to emphasize that this is a '''layering''' technique similar to what you learned in CPTR 328 (Principles of Networking). I.e. different functionality is defined at different layers in the inheritance hierarchy. 

Classes: 

 1. {{{ClassesAndSubclasses}}} is a data class used to build the hierarchy.
 1. {{{TypeInformation}}} adds some functionality needed to interrogate types.
 1. {{{ClassHierarchyPage : ContentPage}}} contains most of the functionality. (Opitonal)

=== Program PropertySettings ===

Page 235.

Concepts:

 1. Exposes the underlying {{{BindableProperty}}} by calling the {{{label1.SetValue(Label.TextProperty, "Some Text");}}} function (defined in {{{BindableObject}}} instead of using the common shortcut method of {{{label1.Text="Some Text");}}}
    a. {{{Label.TextProperty}}} is a {{{BindableProperty}}} defined in the {{{Label}}} class as: 

{{{#!csharp 
public static readonly BindableProperty TextProperty;

public string Text
{
   set { SetValue(Label.TextProperty, value); }
   get { return (string)GetValue(Label.TextProperty); }
}
}}}

Classes: No new classes.

=== Program DynamicVsStaticCode ===

Page 238.

Concepts:

 1. This program shows the motivation for {{{BindableProperty}}} classes. 
 1. For the reasons given, whenever you create a custom view and need to define public properties, your default inclination should be to define them as {{{BindableProperty}}} objects!

Classes: No new classes.

=== AltLabel ===

Page 241.

Concepts:

 1. Extends Label with a {{{BindableProperty}}} named {{{PointSize}}} to allow you to set the font size with a point value. 
 1. Shows how to create a {{{BindableProperty}}} see Page 242.1.

Classes:

 1. {{{AltLabel}}}

=== PointSizedText ===

Page 245.

Concepts:

 1. Demonstrates the use of AltLabel

Classes: No new classes.

=== CountedLabel ===

Page 246

Concepts:

 1. Demos how to create a readonly property, namely wordcount, which of course should not be set!
 1. Re-introduces INPC {{{INotifyPropertyChanged}}} interface and event. 

=== BaskervillesCount ===

Page 249.

Demonstrates the {{{CountedLabel}}} class. 

Classes: {{{CountedLabel}}}