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This chapter is from the book

Creating Your First Windows Store App

Let’s be fearless. In this section, I guide you through building your first Windows Store app. Doing a Hello World app would be predictable and boring. Therefore, I suggest that we do something a little more advanced.

I’ll show you how you can create an app which enables you to take pictures. When you click the Take Picture command in the app bar, you can take a picture, and then the picture is displayed in the app (see Figure 1.6, which shows a picture of my dog Rover).

Figure 1.6

Figure 1.6. Your first Windows Store app

Creating the Visual Studio Project

The first step is to create the Microsoft Visual Studio Project. I used Visual Studio 2012 to create almost all of the code samples for this book. In most cases, I used the free version of Visual Studio—Visual Studio 2012 Express for Windows 8—which you can download from Microsoft.com.

Go ahead and launch Visual Studio. Next, select the menu option File, New Project. On the left-side of the New Project dialog, select JavaScript and select the Blank App project template. Enter the name App1 for your project and click the OK button (see Figure 1.7).

Figure 1.7

Figure 1.7. Using the Visual Studio New Project dialog

After you create your project, you can see all of the files for your project in the Solution Explorer window (Figure 1.8). When you create a new Windows Store app, you get a default.html file (in the root of your project), a default.js file (in the js folder), and a default.css file (in the css folder). These three files are the starting point for your app.

Figure 1.8

Figure 1.8. Windows Store app default files

Declaring App Capabilities

Before we can jump into writing code, there is one other thing which we must do first. We are building an app which takes pictures. That is scary. Potentially, an app could take pictures of you without your knowledge and send the pictures back to an evil hacker lurking on the Internet (or Steve Ballmer sitting behind his desk at Microsoft).

When your app does something scary, you must declare that your app will do this scary thing up front so the user can consent. You declare the capabilities of your app in your application manifest file. You can open the editor for your application manifest by double-clicking the package.appxmanifest file in the Solution Explorer window.

Click the Capabilities tab to view all of the declared capabilities of your application. For example, if you want your app to be able to record from the computer microphone, then you need to select the Microphone capability, or if you want your app to be able to save new photos in the user’s Pictures library, then you need to select the Pictures Library capability. For our app, we need to enable the Webcam capability so we can take pictures (see Figure 1.9).

Figure 1.9

Figure 1.9. Enabling the capability to take pictures

When a user first runs our app, the user will need to consent to allowing the app to access the Webcam (see Figure 1.10). The user only needs to consent once.

Figure 1.10

Figure 1.10. Asking for consent to access your webcam

Creating the HTML Page

When you create a Windows Store app, you get a default.html file in the root of your application. This is the first page which is opened when you run your app. Let’s go ahead and customize this page for our picture app (see Listing 1.1).

Listing 1.1. Modified default.html Page

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title>App1</title>

    <!-- WinJS references -->
    <link href="//Microsoft.WinJS.1.0/css/ui-dark.css" rel="stylesheet" />
    <script src="//Microsoft.WinJS.1.0/js/base.js"></script>
    <script src="//Microsoft.WinJS.1.0/js/ui.js"></script>

    <!-- App1 references -->
    <link href="/css/default.css" rel="stylesheet" />
    <script src="/js/default.js"></script>
</head>
<body>

    <img id="imgPhoto" src="/images/placeholder.png" />

    <!-- AppBar Control -->
    <div id="appBar1"
        data-win-control="WinJS.UI.AppBar">
        <button data-win-control="WinJS.UI.AppBarCommand"
            data-win-options="{
                id:'cmdTakePicture',
                label:'Take Picture',
                icon:'camera',
                tooltip:'Take Picture'
            }">
        </button>
    </div>
</body>
</html>

The HTML page in Listing 1.1 has been modified so it contains new content in the body of the page. First, notice that the page contains an IMG tag with the ID imgPhoto. We’ll display the photo which we take from the camera here.

Notice, furthermore, that the page contains a DIV tag with a data-win-control="WinJS.UI.AppBar" attribute. This is an example of a WinJS control. This control renders an app bar which contains a command for taking a picture (see Figure 1.11).

Figure 1.11

Figure 1.11. The Take Picture command in the app bar

Creating the Style Sheet

When you create a new Windows Store app, you also get a default style sheet named default.css which is located in the css folder. This file contains default style rules for handling Windows Store apps in different view states.

For our app, I’ve modified the default.css to format the appearance of the photo which appears in the IMG tag like this:

#imgPhoto {
    display:block;
    margin: 15px auto;
    border: 10px solid white;
    max-width: 90%;
    max-height: 90%;
}

Creating the JavaScript File

The third file that we need to modify is the JavaScript file named default.js which is located in the js folder. This file contains all of the code associated with the default.html page.

We are going to delete all of the default content of this file and start over. The complete contents of the modified version of default.js are contained in Listing 1.2.

Listing 1.2. The default.js JavaScript File

(function () {
    "use strict";

    // Aliases
    var capture = Windows.Media.Capture;

    // Executed immediately after page content is loaded
    function init() {
        // Process all of the controls
        WinJS.UI.processAll().done(function () {
            // References to DOM elements
            var cmdTakePicture = document.getElementById("cmdTakePicture");
            var imgPhoto = document.getElementById("imgPhoto");

            // Handle Take Picture command click
            cmdTakePicture.addEventListener("click", function () {
                var captureUI = new capture.CameraCaptureUI();
                captureUI.photoSettings.format = capture.CameraCaptureUIPhotoFormat.png;

                captureUI.captureFileAsync(capture.CameraCaptureUIMode.photo).done(function (photo) {
                    if (photo) {
                        // Use HTML5 File API to create object URL to refer to the photo file
                        var photoUrl = URL.createObjectURL(photo);

                        // Show photo in IMG element
                        imgPhoto.src = photoUrl;
                    }
                });
            });
        });
    }

    document.addEventListener("DOMContentLoaded", init);
})();

There is a lot of interesting stuff happening in the JavaScript code in Listing 1.2. Let’s walk through the code.

First, I’ve created an init() function which is executed when the DOMContentLoaded event is raised. The DOMContentLoaded event is a standard DOM event which is raised when a browser finishes parsing an HTML document.

I put all of my code into the init() function so the code won’t be executed until the DOM is ready. Otherwise, if I attempted to access any of the HTML elements in the page, I would get an exception because the elements would not yet exist.

The first thing that I do within the init() method is call the WinJS.UI.processAll() method. This method processes all of the controls in a page. In particular, it converts the DIV tag with the data-win-control="WinJS.UI.AppBar" attribute into an actual app bar.

Next, I set up an event handler for the Take Picture command. When you click the Take Picture command in the app bar, an instance of the Windows.Media.Capture.CameraCaptureUI class is created. The CameraCaptureUI class is an example of a Windows Runtime class.

The CameraCaptureUI.captureFileAsync() method displays the screen for taking a picture (see Figure 1.12). When you click the OK button, the done() method is called and the picture is displayed in the page.

Figure 1.12

Figure 1.12. The camera capture UI screen

An object URL is created for the photo blob (the actual image data) returned by the captureFileAsync() method by calling the URL.createObjectURL() method. This createObjectURL() method is part of the HTML5 File API.

The photo is displayed in the HMTL page with the following lines of code:

// Show photo in IMG element
imgPhoto.src = photoUrl;

And that is all there is to it! We built an app which enables us to take pictures from our computer and display the pictures in an HTML page.

Notice that our JavaScript file contains a combination of standard JavaScript methods, HTML5 methods, Windows Library for JavaScript methods, and Windows Runtime methods. This is normal for all of the JavaScript files which you create when creating a Windows Store app.

Running the App

After you create the app, you can run it by hitting the green Run button in the Visual Studio toolbar (see Figure 1.13) or just hit the F5 key.

Figure 1.13

Figure 1.13. Running a Windows Store style app

Assuming that your laptop or tablet has a camera, you can start taking pictures.

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