Getting started article

getting-started.md

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+---
+nav-title: "Getting Started With NativeScript"
+title: "Getting Started With NativeScript"
+description: "NativeScript Documentation: Getting Started"
+position: 12
+---
+
+# Getting Started With NativeScript
+NativeScript framework enable developers to use pure JavaScript language to build native mobile applications running on the major mobile platforms - Apple iOS, Google Android. The applications UI stack is built using native UI components and because of that no compromises with the User Experience of the applications are done.
+
+## How It Works
+The native script architectures can be generally explained with this diagram:
+![architecture diagram]( .\img\architecture.png "architecture diagram")
+
+* **Native OS** - At the bottom level is the native OS (Android, iOS and soon Windows).
+* **NativeScript runtime** runs the JavaScript code of your application. The runtime also provides a way to call all the native APIs of the platform the app is running on. This means that you have access to all the native capabilities of the platform. 
+* **NativeScript Modules** are a set of platform-agnostic libraries that are build on top of the runtime. These modules are wrap the platform specific code, providing a common API.
+* **Application Code** - your application's code. Building an application on top of the NativeScript modules means that you will not have write platform-specific code. This should be the case most of the time. However, you still have the option to reach the native API trough the NativeSctipt runtime.
+
+## Requirements 
+Currently NativeScript can run on the following platforms:
+
+* Android 4.2+ (equivalent to Android API level 17+)
+* iOS 7.1+ 
+
+For NativeScript development you have the following options:
+
+* Using the [NativeScript Command-Line Interface](https://github.com/NativeScript/nativescript-cli)
+with a IDE or text editor of your choice.
+* Using [AppBuilder](http://docs.telerik.com/platform/appbuilder/nativescript/index) where you have all the features of [Telerik Platform](http://www.telerik.com/platform) at your disposal.
+
+## Example
+In the following example we will start with a empty NativeScript project and build a simple hello word sample application.
+
+### Creating Blank Project
+Let's start by creating a blank project. As we mentioned you can either use the [NativeScript CLI](https://github.com/NativeScript/nativescript-cli) or NativeScript Blank project template in AppBuilder(available for JavaScript or TypeScript). 
+Form here on we will be working in the `App` folder inside the project. 
+
+### Adding UI
+The project we just created has a single empty page. The UI of the page is defined declaratively in the 'main-page.xml' file. In the project there are also `main-page.js` (or `main-page.ts`) and `main-page.css` files that will hold applications code and styles for this page. 
+
+Let's add some UI in `main-page.xml`:
+```XML
+<?xml version="1.0" encoding="UTF-8" ?>
+<Page>
+  <StackPanel>
+    <Label text="Tap the button" style="horizontal-align: center"/>
+    <Button text="TAP" />
+    <Label text="message" textWrap="true" style="horizontal-align: center"/>
+  </StackPanel>
+</Page>
+```
+We have added a title label, a button and a message label that we are going to use in the next section. 
+Here is the result:
+![step1 android](img/getting-started/step1-android.png "step1 android")![step1 ios](img/getting-started/step1-ios.png "step1 ios")
+
+*Note: UI declaration is covered in depth in the [UI with XML](ui-with-xml.md) article.*
+
+### Creating a View-Model
+[MVVM](http://en.wikipedia.org/wiki/Model_View_ViewModel) pattern is the preferred approach when developing mobile applications with NativeScript. In this section we will create and bind a view-model to the page we already have. 
+The view-model will hold simple counter which will be used to update a message each time the user taps on the button.  
+
+Create a `view-models` folder and `main-view-model.js` ( or `main-view-model.ts` if you are using TypeScript) file in it:
+``` JavaScript
+var observable = require("data/observable");
+
+var counter = 42;
+var mainViewModel = new observable.Observable();
+mainViewModel.set("message", counter + " taps left");
+mainViewModel.tapAction = function () {
+    counter--;
+    if (counter <= 0) {
+        mainViewModel.set("message", "Hoorraaay! You unlocked the NativeScript clicker achievement!");
+    }
+    else {
+        mainViewModel.set("message", counter + " taps left");
+    }
+};
+exports.mainViewModel = mainViewModel;
+```
+``` TypeScript
+import observable = require("data/observable");
+
+export class HelloWorldModel extends observable.Observable {
+    private counter: number;
+    constructor() {
+        super();
+
+        this.counter = 42;
+        this.set("message", this.counter + " taps left");
+    }
+
+    public tapAction() {
+        this.counter--;
+        if (this.counter <= 0) {
+            this.set("message", "Hoorraaay! You unlocked the NativeScript clicker achievement!");
+        }
+        else {
+            this.set("message", this.counter + " taps left")
+        }
+    }
+}
+export var mainViewModel = new HelloWorldModel();
+```
+
+The view-model is an instance of `Observable` type so that the UI can receive notification whenever the `message` property is set.
+
+Now that we have the main-view-model we will set it as a `bindingContext` of the main-page. We will do this by handling the `pageLoaded` event:
+
+main-page.xml:
+```XML
+<Page loaded="pageLoaded"/>
+    ...
+</Page>
+```
+
+main-page.js (or main-page.ts):
+```JavaScript
+var vmModule = require("./view-models/main-view-model");
+function pageLoaded(args) {
+    var page = args.object;
+    page.bindingContext = vmModule.mainViewModel;
+}
+exports.pageLoaded = pageLoaded;
+
+```
+```TypeScript
+import observable = require("data/observable");
+import pages = require("ui/page");
+import vmModule = require("./view-models/main-view-model");
+
+// Event handler for Page "loaded" event attached in main-page.xml
+export function pageLoaded(args: observable.EventData) {
+    // Get the event sender
+    var page = <pages.Page>args.object;
+    page.bindingContext = vmModule.mainViewModel;
+}
+```
+
+The last thing we need to do is to bind the UI elements in the XML to the view-model:
+main-page.xml
+``` XML
+<?xml version="1.0" encoding="UTF-8" ?>
+<Page loaded="pageLoaded">
+  <StackPanel>
+    <Label text="Tap the button" style="horizontal-align: center"/>
+    <Button text="TAP" tap="{{ tapAction }}"/>
+    <Label text="{{ message }}" textWrap="true" style="horizontal-align: center"/>
+  </StackPanel>
+</Page>
+```
+
+Here is the result:
+![step2 android](img/getting-started/step2-android.png "step2 android")![step2 ios](img/getting-started/step2-ios.png "step2 ios")
+
+We used data-binding for the `tap` event of the button and the `text` of the message-label.
+*Note: Binding is covered in depth in the [Data Binding](bindings.md) article.*
+
+### Adding Styles
+The final step in this tutorial will be to style the application. Styling in NativeScript is done with a subset of the CSS syntax.
+For each page, the NativeScript runtime will automatically load and apply the CSS file that has the same name as the XML file for the page.
+
+We will add the CSS in `main-page.css`:
+```CSS
+.title {
+    font-size: 30;
+    horizontal-align: center;
+    margin:20;
+}
+
+button {
+    font-size: 42;
+    horizontal-align: center;
+}
+
+.message {
+    font-size: 20;
+    color: #284848;
+    margin:10 40;
+    horizontal-align: center;
+}
+```
+
+Finally - replace the inline styles in the `main-page.xml` with `cssClass` attribute, so that the CSS classes we defined are applied:
+```XML
+<?xml version="1.0" encoding="UTF-8" ?>
+<Page loaded="pageLoaded">
+  <StackPanel>
+    <Label text="Tap the button" cssClass="title"/>
+    <Button text="TAP" tap="{{ tapAction }}" />
+    <Label text="{{ message }}" cssClass="message" textWrap="true"/>
+  </StackPanel>
+</Page>
+```
+
+Here is the result:
+![step3 android](img/getting-started/step3-android.png "step3 android")![step3 ios](img/getting-started/step3-ios.png "step3 ios")
+
+*Note: CSS Styling is covered in depth in the [Styling](styling.md) article.*
+
+## Next Steps
+Read the advanced topics below or refer to the [Api Reference](ApiReference/) to continue wit NativeScript development:
+
+* [Application](application-management.md)
+* [Navigation](navigation.md)
+* [Layouts](layouts.md)
+* [Styling](styling.md)
+* [Binding](bindings.md)
+* [UI with XML](ui-with-xml.md)
+* [UI Views](ui-views.md)
+* [UI Dialogs](ui-dialogs.md)
+* [Location](location.md)
+* [Modules](modules.md)