What is Xamarin? >>
Structure of Applications
The
Collective objects which are appears in
the Xamarin.Forms is known as Visual elements. There are main 03 Categories.
- Layout
- Page
- Views
Xamarin.Forms API defines classes named VisualElement, Page, Layout, and View. These classes and descendants of those classes form the
backbone of Xamarin.Forms user
–interface. VisualElement is important class in the Xamarin.Forms. A
Visual-element object is anything that occupies space in the screen.
Xamarin.Forms
application consists of one page or multiple pages. Pages occupies all of the
screen. Some applications consists of one page and other pages allow to
navigate in multiple pages.
On each page
visual elements arrange in parent- child heirachy. Some layouts have a single
child, but many layouts have multiple children that the layout arranges within
itself. These children can be other layouts or views. Different types of
layouts arrange children in a stack, in a two-dimensional grid, or in a more freeform manner.
The views in
Xamarin.Forms familiar types of presentations and objects such as : text,
bitmaps, buttons, text-entry fields, sliders, switches, progress bars, date and
time pickers, and etc. These are normally known as widgets or controls in in
the programming environement.
Now let see
how to create new application using Visual Studio and Xamarin Studio.
In Visual
Studio, select the menu option File > New > Project. At the left of the
New Project dialog, select Visual C# and then Cross-Platform. In the center
part of the dialog you’ll see several available solution templates, including
three for Xamarin.Forms:
· Blank
App (Xamarin.Forms Portable)
· Blank
App (Xamarin.Forms Shared)
· Class
Library (Xamarin.forms)
To create a
new Xamarin.Forms solution in Xamarin Studio, select File > New >
Solution from the menu, and at the left of the New Project dialog, under
Multiplatform select App, pick Forms App, and press the Next button. Toward the
bottom of the next screen are a pair of radio buttons labeled Shared Code.
These buttons allow you to choose one of the following options:
- Use Portable Class Library
- Use Shared
Library
Portable in
this refers to Portable Class Library (PCL) .In here all the common application
code become a dynamic – link –library that can referred by all the individual
platforms.
Shared in
here means the Shared Asset Project
(SAP) it contain the loose code that are shared among the platform projects and
it become a essential part of platform projects.
Select Blank App (Xamarin.Forms Portable) in Visual
Studio and Portable Class Library in Xamarin studio. And after that give
project name then select the disk location that in the dialog in Visual Studio
or the dialog which appears after clicking the next button in Xamarin studio.
If the
project is run in Visual Studio there are six project running and one of them
are common project rest five are application projects.
Lets assume that our
project name is Hello;
·
An
Application project for Android is Hello.Droid.
·
An
Application project for ios is Hello.ios.
·
An
Application project for Universal
Windows Platform of Windows 10 and Windows Mobile 10 is Hello.UWP.
·
An
Application project for Windows 8.1 is Hello.Windows.
·
An
Application project for Windows phone 8.1 is Hello.WinPhone.
When you
create the Xamarin.Forms solutions Xamarin.Forms libraries
are automatically downloaded from the NuGet package manager.
Visual
Studio and Xamarin Studio store these libraries in the directory called Package In Visual Studio, in the Solution
Explorer at the far right of the screen, right-click the solution name and select Manage NuGet Packages for
Solution. The dialog that appears contains electable items at the upper left
that let you see what NuGet packages
are installed in the solution and let you install others. You can also select
the Update item to update the Xamarin.Forms library.
In
Xamarin.Studio, you can select the tool icon to the right of the solution name
in the Solution list and select Update NuGet
Packages.
Checking the Project Configuration
Before you
continue your development check whether the configuration is done in correct
manner . To check that in Visual Studio :
·
Select
the Build à Configuration
Manager menu item.
·
In
the Configuration Manager dialog,
you’ll see the PCL project and the five application projects.
·
Make
sure the Build box is checked for
all the projects and the Deploy box
is checked for all the application projects.
·
Take
note of the Platform column: If the
Hello project is listed, it should be flagged as Any CPU. The Hello.Droid project should also be flagged as Any CPU.
·
For
the Hello.iOS project, choose either iPhone
or iPhoneSimulator depending on how
you’ll be testing the program.
·
For
the Hello.UWP project, the project configuration must be x86 for deploying to the Windows desktop or an on-screen emulator,
and ARM for deploying to a
phone.
If the
project in Visual Studio is not compiling or deploying you must have to check
the settings in the Configuration Manager dialog.May be some invalid
Configuration become active or PCL project may
be not included.
In Xamarin
Studio you can deploying to the iphone or iphone simulator through Project à Active Configuration menu item.
In Visual
Studio you have to show the tool bar in ios and android.these tool bar can be
select from the among emulators and
devices and allow you to manage the emulators. And make sure wheather you has been check these items :
·
Views
à Toolbars à ios
·
Views
à Toolbar à
Android
In Visual
Studio their is Solution Explore,
right-click any of the five application projects and select the Set As StartUp Project item from the menu. You
can then select to deploy to either an emulator or a real device. To build and
run the program, select the menu item Debug
à Start Debugging.
In the
Solution list in Xamarin Studio, click the little tool icon that appears to the
right of a selected project and select Set As Startup Project from the menu.
You can then pick Run à Start Debugging from the main menu.
If all
processes taken places in correct manner
skeleton application will be created in the template will be run and it will be
display a message.
There are
different color schema for different platform in iOS and Windows ark there is text in the light
background in Android light color text
in the dark background. Windows 8.1 and Windows Phone 8.1 have same as in the
Android.
Inside the Files
The program
created inside the Xamarine.Forms is very simple as a result we have
opportunity to understand the code files and interrelationship of each other
and how they work.
Lets try to
understand the code which is related to things that we are seen in the
screen.This is know as App class in
the HelloProject we created.If the project is created in the Visual Studio App class is defined in the App.cs file but in
Xamarin Studio it is Hello.cs file.
using System;
using System.Collections.Generic;
using System.Linq; using System.Text;
using Xamarin.Forms;
namespace Hello{
public class App : Application{
public App(){
// The
root page of your application
MainPage = new ContentPage{
Content = new StackLayout{
VerticalOptions =LayoutOptions.Center,
Children = {
new Label {
HorizontalTextAlignment = TextAlignment.Center,Text = "Welcome to Xamarin Forms!"
}
}
}
};
}
protected override void OnStart()
{
// Handle when your app starts
}
protected override void OnSleep()
{
// Handle when your app sleeps
}
protected override void OnResume()
{
// Handle when your app resumes
}
}
}
The code
that the Xamarin.Forms template has generated here shows one very simple
approach to defining this constructor: The ContentPage
class derives from Page and is very common in singlepage Xamarin.Forms applications. It occupies most of the
phone’s screen with the exception of the status bar at the top of the Android
screen, the buttons on the bottom of the Android screen, and the status bar at
the top of the Windows Phone screen.
The ContentPage class defines a property
named Content that you set to the content of the page. Generally this content
is a layout that in turn contains a bunch of views, and in this case it’s set
to a StackLayout, which arranges its
children in a stack.
This StackLayout has only one child, which
is a Label. The Label class derives from View and is used in Xamarin.Forms
applications to display up to a paragraph of text.
For your own
single-page Xamarin.Forms applications, you’ll generally be defining your own
class that derives from ContentPage.
The constructor of the App class then sets an instance of the class that you
define to its MainPage property.
The iOS Project
The ios project
contain the classes that are derive from the UIApplicationDeligate (A class
used to receive events raised by a UIApplication.)
FormsApplicationDelegate
this is a alternative class which is define by Xamarin.Forms.Platform.iOS
library.
And there is
AppDelegate.cs file in Hello.ios project
which contain all using using
directives and comments.
using Foundation;
using UIKit;
namespace Hello.iOS
{
[Register("AppDelegate")]
public
partial class AppDelegate
: global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
public override bool FinishedLaunching(UIApplication app,
NSDictionary options) {
global::Xamarin.Forms.Forms.Init();
LoadApplication(new App());
return base.FinishedLaunching(app,
options);
}
}
}
The Android Project
In the Android application, the typical MainActivity class must be derived from a Xamarin.Forms class named
FormsApplicationActivity, defined in
the Xamarin.Forms.Platform.Android assembly, and the Forms.Init call requires some additional information:
using Android.App;
using Android.Content.PM;
using Android.OS;
namespace Hello.Droid
{
[Activity(Label =
"Hello", Icon = "@drawable/icon", MainLauncher = true,
ConfigurationChanges = ConfigChanges.ScreenSize |
ConfigChanges.Orientation)]
Public
class MainActivity :
global::Xamarin.Forms.Platform.Android.FormsApplicationActivity
{
protected
override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
global::Xamarin.Forms.Forms.Init(this,bundle);
LoadApplication(new App());
}
}
}
The Windows Project
In the UWP
project (Universal Windows Project), look first in the App.xaml.cs file tucked underneath the App.xaml file in the project file list. In the OnLaunched method you will see the call to Forms.Init using the event arguments:
Xamarin.Forms.Forms.Init(e);
Now look at
the MainPage.xaml.cs file tucked
underneath the MainPage.xaml file in
the project file list. This file defines the customary MainPage class, but it actually derives from a Xamarin.Forms class
specified as the root element in the MainPage.xaml
file. A newly instantiated App class is passed to the LoadApplication method defined by this base class:
namespace Hello.UWP
{
public sealed partial class MainPage
{
public MainPage()
{
this.InitializeComponent();
LoadApplication(new Hello.App());
}
}
}
PCL or SAP
When you
create your first application in Visual Studio there are 02 template to be
selected:
·
Blank App (Xamarin.Forms Portable)
·
Blank App (Xamarin.Forms Shared)
In Xamarin
Studio :
·
Use
Portable Class Library
·
Use Shared Library
In Xamarin Studio
first option is to create a portable
class library and then create a Shared Asset Project which only create the
shared code. Original application solution consist the PCL template.And now we
create the second solution (Assume that the application that we make is Hello)
as HelloSAP with the SAP template.
After you
create all these things all are look like same but there is one extra item in
in HelloSAP that is App.cs.file.
With both
the PCL and SAP approaches, code is shared among the five applications, but in
decidedly different ways: With the PCL approach, all the common code is bundled
into a dynamic-link library that each application project references and binds
to at run time.
With the SAP
approach, the common code files are effectively included with each of the five
application projects at build time. By default, the SAP has only a single file
named App.cs, but effectively it’s as if this HelloSap project did not exist
and instead there were five different copies of this file in the five application
projects.
iOS and the
Android have the some what same features of the .Net but it not 100% equal to
the .Net that the Windows used. This means that any .Net classes
accessed by the shared code might be somewhat different depending on the
platform.
In the
projects generated by the Xamarin.Forms template, the various application
projects define symbols that you can use with these directives.
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