Linux Journal | January 2013 | Issue 225 - ACM Digital Library

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INDEPTHcall in Cordova. I’m only trying todemonstrate that you can. In this case,you’re loading some content from aremote server and putting it inside thequote discussed earlier. Duringdevelopment, I’d simply change thecontent of that file on the server toverify that it changed inside the app.Lines 44–58 are onclick handlers forthe two buttons in the application. Allthese routines do is adjust an arrayindex plus or minus one, as appropriate,and do some bounds checking. Finally,they call display_contact() todisplay the current contact.The display_contact() function (lines59–72) is the last of the Cordovaspecificfunctions in the program.In lines 60–64, you blank out all ofthe contact fields in preparation forsetting them with new values. I foundthat if I didn’t blank them out first,they would persist into the next recordif the next record didn’t happen tohave a value for a given field. In lines65–69, you populate the fields withdata from the current contact record.Note that both phoneNumbers ande-mails are arrays of objects, and thatfor this purpose, you are interestedonly in the first element.And there you have it. There’snothing here that would be unfamiliarto the average Web developer,except a really powerful API. But, I’veonly touched on what this API cando. Figure 2 shows the applicationrunning on my Droid Bionic.I did some hand waving over asubtle problem with this applicationthat many JavaScript, particularly Ajax,developers have encountered. Onmost browsers, your program can’tFigure 2. Sample Application Runningon Android108 / JANUARY <strong>2013</strong> / WWW.LINUXJOURNAL.COM
INDEPTHload from one domain, and then loadcontent or code from another domain.However, this program is standaloneand needed to load content froma potentially arbitrary Web site.Cordova handles this problem by“whitelisting” the domains fromwhich an application is allowed tofetch content. By default, all domainsare blacklisted, and, thus, all networkaccess is disabled. A developer canwhitelist a domain by editing/res/xml/cordova.xml and followingthe examples given for the tag. This is a safe but elegant solutionto a potentially nasty problem.Another interesting possibility is tohave your application load all of itsHTML and JavaScript from a remoteWeb server. This easily can be doneby making a simple change to ./src/{projectname}/{projectname}.java. Thisfile has only 20 lines of real code, andthe necessary change is pretty intuitive.Being able to load content froma remote server actually makesdevelopment easier. I found it easierto do my development on a remote,publicly accessible server, than todevelop on my workstation. This way,I could point my Web browser at theapplication and get all my HTML,CSS and JavaScript working the wayI wanted. Then I got the applicationfully functional on my Android. Onceit was fully functional, I copied theproject to my workstation for thefinal build. Doing it this way is theonly way you’ll be able to test anapplication that makes any Ajax callswithout violating your browser’scross-site scripting security policy.As neat as Cordova is, thereare a few things I didn’t like. As Imentioned earlier, there is no wayto detect automatically whether aprogram is running in a browseror on a device. Also, I found thewhitelisting functionality to be abit buggy, but not in any way thatbroke my application. But, the mostdisheartening thing I found waswhen I tried to use the camera API.Instead of simply snapping a pictureand either returning the data orstoring it, the API actually broughtup the device’s native camera deviceas a pop-up. This was extremelyintrusive and actually broke my firstdemonstration app.I’ve had a lot of fun playing withCordova, and I’ve barely scratchedthe surface of what it can do or beextended to do. This has to be theeasiest way to get into smartphoneapplication development.■Mike Diehl operates Diehlnet Communications, LLC, a small IPphone company. Mike lives in Blythewood, South Carolina, with hiswife and four sons. He can be reached at mdiehl@diehlnet.com.WWW.LINUXJOURNAL.COM / JANUARY <strong>2013</strong> / 109
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Linux Journal | January 2013 | Issue 225 - ACM Digital Library

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