Windows 8 Binding

7/30/2019 Windows 8 Binding

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Learn More @ http://www.learnnowonline.comCopyright by Application Developers Training Company

Windows 8 Binding Part 1

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Objectives

Learn to use Binding objects to bind data

sources and targets

Add data converters to manage conversion

during the binding process

Use data templates to modify the layout of

bound data in lists


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Agenda

Introducing Binding

Working with Type Converters

Binding Lists and Data Templates Using Binding and Data Templates


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When to Use Binding?

Display the number of characters in a text box,

in a TextBlock control

Display the value of Slider control in a TextBlock

Display list of customers in ListBox

Display customers photo in Image control

Display and edit customers name in TextBox

Of course, there are an infinite number of

reasons


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Connecting Sources and Targets

Every time you use binding

Must supply source for data, and target

Normally, target is dependency property of some

user interface element


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Connecting Sources and Targets

Binding source: any property of any object

Binding object connects source to binding target

Must be dependency property of some

DependencyObject instance


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Under the Hood

When using binding in XAML Create instance of Binding class, setting various

properties that affect its behavior

XAML provides binding markup extension Hides this fact, but still working with Binding object

Completely transparent if you create Binding object

in code

Can set Mode property of Binding to control

direction of data flow (one/two directions?)


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Value Converters

Value Converter provides instance of class that

implements

Windows.UI.Xaml.Data.IValueConverter

interface

Binding declaratively often requires value

converter


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Value Converters

Select a customer from a ListBox, displaycombined FirstName and LastName fields in

TextBlock

Select an integer, bind to BorderThickness ofBorder

Cant bind directlyBorderThickness is a Thickness

structure Infinite reasons to use a value converter

But only if binding declaratively


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A Few Simple Examples

SimpleBinding1

SimpleBinding2


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Binding Details

Standard Binding markup extension includes

ElementName and Path attributes:

Text="{Binding ElementName=DemoSlider,

Path=Value}"

Path attribute not required:

Text="{Binding Value,

ElementName=DemoSlider}"

Choose whichever you like


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Binding Details

Path property can refer to property, or

property of a property, or indexed property

Need to refer to an attached property?

Grid.Row, for example

Set Path property to (Grid.Row) (in parentheses)

Parentheses force evaluationwont work without

Parentheses not necessary for property of a property


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Binding Details

Binding Markup extension shortcut for child

element syntax:


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Setting the Binding Mode

In demo, data moves from Slider to TextBox

Changes in TextBox have no effect on slider

Binding is one-way: Data moves in one

direction

Set Mode property of Binding to change

OneTime

OneWay

TwoWay


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DEMO

Two-way binding, SimpleBinding3


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A Simple Example

Enter text into TextBox, update TextBlock with

length of the text

Could react to TextChanged event of TextBox

Better: Bind Text property of TextBlock to

Text.Length property of TextBox

Points out that binding can use expressions


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DEMO

SimpleBinding4


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Agenda

Introducing Binding

Working with Type Converters

Binding Lists and Data Templates Using Binding and Data Templates


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Using a Type Converter

Determine source and target data types

Write code to perform the conversion

Perhaps write code to convert back (for two-way

binding)

Sample binds integer from combo box to

BorderThickness property

Whats the problem? Thickness structure has four

values


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Creating the Type Converter

Attempt to bind SelectedValue of ComboBox

to BorderThickness of Border, and doesnt

work

Need type (or value) converter


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Converters

Implement IValueConverter interface

Requires Convert and ConvertBack methods

Parameters: value (System.Object)

targetType (System.Type)

parameter (System.Object)

Language (System.String)


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Handle Null Case

Always possible that value will be null

Code runs at design time!

Always verify that value isnt null before

performing conversion


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Converter Warning

Converter doesnt trap exceptions

Treated as runtime errors

You must trap and handle all runtime errors

Return DependencyProperty.UnsetValue on error

Not handled in this simple demo

Worth considering!


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DEMO

IntegerToThicknessConverter


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Referencing the Type Converter

Need way to refer to type converter in XAML

Like any other resource, declare instance in

resources; Page.Resources in demo

Need namespace reference

xmlns:local="using:Binding"

Then, within Page.Resources:


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Using the Type Converter

Add a setting in Binding markup extension


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Using the Visual Studio Designer

DEMO


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Windows 8 Binding

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