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Rafe Sanders
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2 v v Each cell is represented by some data structure which is then visualized on the screen headshot.source =...; nameentry.text = person.name; entry.text = person. ; birthday.date = person.dob;... nameentry.textchanged += (sender, e) => person.name = nameentry.text; entry.textchanged += (sender, e) => person. = entry.text; 2

3 Source Target Any Object BindableObject Any public property Binding BindableProperty Binding acts as an intermediary moving the data between the source and target Source Path Target Can be any accessible object Public property defined on the source object Must be a BindableProperty 3

4 Person person = new Person() { Name = "Homer Simpson",... }; Entry nameentry = new Entry(); 1 Binding namebinding = new Binding(); namebinding.source = person;... Binding identifies the source of the binding data this is where the data comes from, in this case it's a single person defined in our application Person person = new Person() { Name = "Homer Simpson",... }; Entry nameentry = new Entry(); 2 Binding namebinding = new Binding(); namebinding.source = person; namebinding.path = "Name";... Binding identifies the property path which identifies a property on the source to get the data from, in this case we want to get the value from the Person.Name property 4

Person person = new Person() { Name = "Homer Simpson",... }; Entry nameentry = new Entry(); Binding namebinding = new Binding(); namebinding.source = person; namebinding.

Child") new Binding("Property[Key]") new Binding("Property[1]") new Binding("Item[Key]") new Binding(".") path = "Name"; 3 nameentry.setbinding(entry.

5 Person person = new Person() { Name = "Homer Simpson",... }; Entry nameentry = new Entry(); Binding namebinding = new Binding(); namebinding.source = person; namebinding.path = "Name";... More Path Examples new Binding("Property") new Binding("Property.Child") new Binding("Property[Key]") new Binding("Property[1]") new Binding("Item[Key]") new Binding(".") Person person = new Person() { Name = "Homer Simpson",... }; Entry nameentry = new Entry(); Binding namebinding = new Binding(); namebinding.source = person; namebinding.path = "Name"; 3 nameentry.setbinding(entry.textproperty, namebinding); Binding is associated to the target property using the BindableObject.SetBinding method 5

6 Person person = new Person() { Name = "Homer Simpson",... }; Entry nameentry = new Entry(); Binding namebinding = new Binding(); namebinding.source = person; namebinding.path = "Name"; 3 nameentry.setbinding(entry.textproperty, namebinding); This is passed the specific target property the binding will work with this must be a BindableProperty Person person = new Person() { Name = "Homer Simpson",... }; Entry nameentry = new Entry(); Binding namebinding = new Binding(); namebinding.source = person; namebinding.path = "Name"; 3 nameentry.setbinding(entry.textproperty, namebinding); and the binding which identifies the source and the property on the source to apply 6

<StackLayout Padding="20" Spacing="20"> <StackLayout.Resources> <ResourceDictionary> <Person x:key="homer" Name="Homer Simpson".../> </ResourceDictionary> </StackLayout.

7 <StackLayout Padding="20" Spacing="20"> <StackLayout.Resources> <ResourceDictionary> <Person x:key="homer" Name="Homer Simpson".../> </ResourceDictionary> </StackLayout.Resources> <Entry Text="{Binding Name, Source={StaticResource homer}}" />... </StackLayout> Assigned to Target property {Binding} takes the Path as the first unnamed argument Source supplied through resource v v public class Person { public string Name { get; set; } public string { get; set; } public Gender Gender { get; set; } } 7

8 Person person = new Person() { Name = "Homer Simpson",... };... nameentry.bindingcontext = person; nameentry.setbinding(entry.textproperty, new Binding("Name")); Binding only identifies the Path no source is set; it will then look to the BindingContext on the parent control as the source for the binding data public partial class PersonDetailsPage : ContentPage { public PersonDetailsPage (Person person) { BindingContext = person; InitializeComponent (); } } Can set the BindingContext once on the root page and it is then assigned to ever y control (child) on that page 8

9 Model-View-ViewModel View Data Events ViewModel Data Model How to display information What to display Flow of interaction Business Logic Data objects Model-View-ViewModel Data View ViewModel Model Events Xamarin.Forms Data Binding 9

10 INotifyPropertyChanged INotifyPropertyChanged 10

11 INotifyPropertyChanged INotifyPropertyChanged 11

12 Data Binding XAML Data Binding XAML 12

13 Pros Provides higher testable surface Centralizes the visual & business logic Can reduce converter code used to tie models to UI Takes advant age of binding infrastructure Cons Requires infrastructure, more for some platforms than others Necessitates multiple layers which may not be worth it for smaller apps Bindings can be hard to debug and may not be efficient for large data sets v BooleanToColorConverter ArrayToStringConverter v DoubleToIntegerConverter NotBooleanConverter v IntegerToBooleanConverter 13

14 Menu Button ToolbarItem TextCell other patterns abstractions Dependency Injection Factor y and Singleton Command Navigation Alerts + Prompts Messages 14

15 v Publisher MessagingCenter v Subscriber Subscriber Publisher identifies sending type and parameter type through generic parameters MessagingCenter.Send<MainViewModel, ItemViewModel>( this, "Select", selecteditem); 15

Action to run when "Select" is received // from MainViewModel }); Combination of the sender

between publisher and subscriber Xamarin.

16 MessagingCenter.Subscribe<MainViewModel, ItemViewModel> ( this, "Select", (mainvm, selecteditem) => { // Action to run when "Select" is received // from MainViewModel }); Combination of the sender type, string message, and parameter type is the key for the message recipient these must match between publisher and subscriber Xamarin.Forms has support for dealing with a few, very common platform-specific features Device.OpenUrl to launch external apps based on a URL scheme Page.DisplayAlert to show simple alert messages Timer management using Device.StartTimer 16

17 UI Thread marshaling with Device.BeginInvoke OnMainThread Mapping and Location through Xamarin.Forms.Maps v platform-specific Dialing the phone would require platform-specific code 17

18 abstraction implemented by the target platform which defines the platform-specific functionality public interface IDialer { bool MakeCall(string number); } Shared code defines IDialer interface to represent required functionality PhoneDialerIOS PhoneDialerDroid PhoneDialerWP8 Platform projects implement the shared dialer interface using the platform-specific APIs 1 Define an interface or abstract class in the shared code project (PCL) public interface IDialer { bool MakeCall(string number); } 18

19 2 Provide implementation of abstraction in each platformspecific project class PhoneDialerIOS : IDialer { public bool MakeCall(string number) { // Implementation goes here } } 3 Expose platform-specific implementation using assembly-level attribute in platform-specific project [assembly: Dependency(typeof(PhoneDialerIOS))] 19

20 4 Retrieve and use the dependency anywhere using DependencyService.Get<T> (both shared and platform specific projects can use this API) IDialer dialer = DependencyService.Get<IDialer>(); if (dialer!= null) {... } Summary 20

Mobile Computing. Xamarin Data Binding MVVM Pattern. Data Binding. XAML binding example. Target Views. In simple apps. For complex or big apps

Mobile Computing. Xamarin Data Binding MVVM Pattern. Data Binding. XAML binding example. Target Views. In simple apps. For complex or big apps APM@FEUP Xamarin Data Binding MVVM Pattern 1 Data Binding In simple apps Get and set properties of controls is done explicitly in the code behind entry1.text = Hello, world! ; For complex or big apps This