martes, 31 de marzo de 2015

Creando un lector de codigo de barras en Andriod - Android SDK: Create a Barcode Reader

En este tutorial usamos el ZXing libreria de Zebra para desarrollar una aplicacion de lector de codigo de barras para andriod.

In Eclipse, create a new Android project. Enter your chosen application, project, and package names. Let Eclipse create a blank activity for you, with the name of your choice for both the activity and its layout.
New Project
Open your main layout file. With the default settings, Eclipse starts your layout with aRelative Layout object, which you can leave as is. Inside of it, replace the existing content (typically a Text View) with a button.
After the button, add two Text Views in which we will output scanning information.
Add the button text string to your "res/values/strings" XML file.
The user will press the button to scan. When the app receives a result from the barcode scanning operation, it will display the scan content data and format name in the two Text Views.
ZXing is an open source library that provides access to tested and functional barcode scanning on Android. Many users will already have the app installed on their devices, so you can simply launch the scanning Intents and retrieve the results. In this tutorial we are going to use the Scanning via Intent method to make scanning easier. This method involves importing a couple of classes into your app and lets ZXing take care of instances where the user does not have the scanner installed. If the user doesn't have the barcode scanner installed, they'll be prompted to download it.
Tip: Since ZXing is open source, you can import the source code into your projects in its entirety. However, this is really only advisable if you need to make changes to its functionality. You can also compile the project and include its JAR file in your own apps if you prefer. For most purposes, using Scanning via Intent is a reliable and easy to implement options, plus your users will have access to the most recent version of the ZXing app.
In Eclipse, add a new package to your project by right-clicking the "src" folder and choosing "New", then "Package", and entering "" as the package name.
New Package
Eclipse offers several ways to import existing code into your projects. For the purposes of this tutorial, you'll probably find it easiest to simply create the two required classes and copy the code from ZXing. Right-click your new package, choose "New" then "Class" and enter "IntentIntegrator" as the class name. You can leave the other default settings the way they are. Once you've created this class, do the same for the other class we'll be importing, giving it "IntentResult" as its class name.
New Class
Copy the code from both classes in the ZXing library and paste it into the class files you created. These are IntentIntegrator and IntentResult. Refer to the source code download if you're in any doubt about where the various files and folders should be or what should be in them.
Project Package
You can now import the ZXing classes into your main Activity class.
Go ahead and add the other import statements we'll use for this tutorial. Bear in mind that Eclipse may have already added some for you.
Feel free to have a look at the content of the two ZXing classes. It's fairly straightforward, but the details of the barcode scanning processing are carried out elsewhere in the library. These two classes really act as an interface to the scanning functionality.
Let's implement scanning when the user clicks the button we added. In your app's main activity class, the default onCreate method entered by Eclipse should look something like this.
Above this method, add the following instance variables to represent the button and two Text Views we created in the layout file.
In onCreate, after the existing code, instantiate these variables using the ID values we specified in the XML.
Next, add a listener to the button so that we can handle presses.
Extend the opening line of the class declaration to implement the OnClickListenerinterface.
Now we can respond to button clicks by starting the scanning process. Add anonClick method to your activity class.
Check whether the scanning button has been pressed inside this method.
Inside this conditional block, create an instance of the Intent Integrator class we imported.
Now we can call on the Intent Integrator method to start scanning.
At this point, the scanner will start if it's installed on the user's device. If not, they'll be prompted to download it. The results of the scan will be returned to the main activitywhere scanning was initiated, so we'll be able to retrieve it in the onActivityResultmethod.
Tip: When you call the initiateScan method, you can choose to pass a collection of the barcode types you want to scan. By default, the method will scan for all supported types. These include UPC-A, UPC-E, EAN-8, EAN-13, QR Code, RSS-14, RSS Expanded, Data Matrix, Aztec, PDF 417, Codabar, ITF, Codes 39, 93, and 128. The ZXing library also includes barcode scanning options that we're not going to cover in this tutorial. You can check the project out at Google Code for more info.
When the user clicks the scan button, the barcode scanner will launch. When they scan a barcode, it will return the scanned data to the onActivityResult method of the calling activity. Add the method to your main activity class.
Inside the method, try to parse the result into an instance of the ZXing Intent Result class we imported.
As with any data being retrieved from another app, it's vital to check for null values. Only proceed if we have a valid result.
If scan data is not received (for example, if the user cancels the scan by pressing the back button), we can simply output a message.
Back in the if block, let's find out what data the scan returned. The Intent Resultobject provides methods to retrieve the content of the scan and the format of the data returned from it. Retrieve the content as a string value.
Retrieve the format name, also as a string.
Now your program has the format and content of the scanned data, so you can do whatever you want with it. For the purpose of this tutorial, we'll just write the values to the Text Views in our layout.
Run your app on a device instead of an emulator so that you can see the scan functioning. Try scanning a book or any other barcode you might have.
App During Scanning

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