iOS 开发：应用内实现 更新提醒

目前绝大多数的应用都可以实现应用更新后，打开应用就能得到更新提醒。这有利于用户的更新。

关于如何实现的方式，很多人希望Xcode本身能够提供相应的API来实现对应用版本的查找，但就目前来看，还没有这样的API。因此，目前的解决办法有两种：

1、自己架设服务器，当应用更新后，就在自己的服务器中更新版本信息，然后让应用连接服务器来查找版本信息，与当前应用版本核对，如果更新则提示

2、利用App Store的Search-api，通过相应的api，request可以得到相应的应用信息，关键是JSON格式的，因此就很方面对版本信息进行提取然后比对。下面是网址：

http://www.apple.com/itunes/affiliates/resources/documentation/itunes-store-web-service-search-api.html

可以看到，只要使用https://itunes.apple.com/lookup?id=595176741 这样的url进行request，id要换成所在应用的id，然后就可以得到JSON格式的信息。

下面是以应用 3D量角器为例可以得到如下JSON信息：

{

"resultCount":1,

"results": [

{"kind":"software", "features":["iosUniversal"], "supportedDevices":["iPodTouchourthGen", "iPad2Wifi", "iPad23G", "iPhone4"], "isGameCenterEnabled":false, "artistViewUrl":"https://itunes.apple.com/us/artist/hongkun-song/id595176744?uo=4", "artworkUrl60":"http://a86.phobos.apple.com/us/r1000/091/Purple2/v4/0a/db/51/0adb5130-5d18-0b98-d1cc-3ddd114b10d5/icon57_57.png",

"screenshotUrls":["http://a1960.phobos.apple.com/us/r1000/108/Purple/v4/ea/52/80/ea52802a-c7d9-1dca-defe-937fb61bbc3e/mzl.ghupvxyw.png", "http://a1740.phobos.apple.com/us/r1000/110/Purple2/v4/58/40/64/584064d8-1d3b-6704-3bf7-3b1c771d25c1/mzl.ydpovfzk.png", "http://a180.phobos.apple.com/us/r1000/100/Purple2/v4/22/01/90/22019008-314d-07e7-49e4-2359983058c0/mzl.hefjpqiw.png", "http://a1862.phobos.apple.com/us/r1000/107/Purple/v4/ee/23/a6/ee23a69f-768f-5fe8-9444-298a26330faa/mzl.sxiofdqt.png", "http://a980.phobos.apple.com/us/r1000/102/Purple/v4/cd/2c/9f/cd2c9fff-8dac-b75d-f260-c223ea8d2b33/mzl.trozlblw.png"],

"ipadScreenshotUrls":["http://a651.phobos.apple.com/us/r1000/079/Purple/v4/e9/ab/55/e9ab55ab-6b7c-04ab-034e-833c113be412/mzl.ganeacuj.1024x1024-65.jpg", "http://a247.phobos.apple.com/us/r1000/107/Purple/v4/f3/87/60/f3876038-162a-7df4-87e5-54b6a5b14b78/mzl.vxycagic.1024x1024-65.jpg", "http://a831.phobos.apple.com/us/r1000/093/Purple2/v4/8b/b3/77/8bb37753-e3d5-9f45-ecfb-bf09cdb660f0/mzl.ncygstwb.1024x1024-65.jpg", "http://a376.phobos.apple.com/us/r1000/078/Purple/v4/f3/4e/36/f34e362f-dee0-0903-436e-034ba94a6f79/mzl.ecchwkyv.1024x1024-65.jpg", "http://a1624.phobos.apple.com/us/r1000/079/Purple/v4/db/12/9d/db129d6b-107b-fa80-f472-a8c7809ef513/mzl.xjmeijfn.1024x1024-65.jpg"], "artworkUrl512":"http://a1435.phobos.apple.com/us/r1000/076/Purple/v4/d1/36/f5/d136f5d0-3962-9ba1-95b2-3ca0ba3be9ec/mzl.zzqaoikx.jpg", "artistId":595176744, "artistName":"Hongkun Song", "price":1.99, "version":"2.0",

"description":"Measure actual angles from a distance? This magical App makes impossible happen!\n\nJust throw your plastic protractor away if you have an iPhone! I think you would never have to use traditional protractors any more! Since here is a much better tool for you to measure angles, that is your iOS device and of course, with the amazing app 3D Protractor!\n\n3D Protractor! A super tool for you to measure all kinds of angles in the 3D space by moving and rotating your iOS device or using the camera!\n\nDon\u2019t limit your imagination of measuring angles to just measuring the angle between two lines on a plane! This was an old thinking. 3D Protractor breaks it! In fact,it is so powerful that it can do following five jobs:\n1,Line-Line Angle Measurement. It can measure the angle of any two lines in the space,include the angle on a plane.\n2,Slope Angle Measurement. \n3,Dihedral Angle Measurement.\n4,Line-Face Angle Measurement.\n\n5,Camera Angle Measurement. It is a super cool feature! It can measure actual angles of any objects in front by the device's camera. Unbelievable! Actual angle! \n\nYou might feel a little bit confused at first after reading the above professional descriptions. This App uses 3D models to make it really easy for you to understand and use.\nEveryone can use it. Students can use it to do their homework. Teachers can use it to teach geometry especially solid geometry, which makes a really good teaching tool. Engineers can use it to measure any angles they need to know at work. And of course, there are many many more usages in our daily life.\n\n3D Protractor! Re-invention of protractor! \nA great app to make measuring angle easy and more accurate! \nA great app to change the world of angle measurement!\n\nPS. 1、If you measure an angle in a long time,the precision may be lower.\n2、This version has no Ads!", "currency":"USD", "genres":["Utilities", "Education"], "genreIds":["6002", "6017"], "releaseDate":"2013-01-26T07:54:39Z", "sellerName":"Hongkun Song", "bundleId":"com.manmanlai.-D-Protractor", "trackId":595176741, "trackName":"3D Protractor", "primaryGenreName":"Utilities", "primaryGenreId":6002,

"releaseNotes":"1、Add Camera Angle Measurement Feature; \nIt is a super cool feature! It can measure actual angles of any objects in front by the device's camera. Unbelievable! Actual angle!\n2、Add radian number display; \nTap the number, then you would see the transition between degree and radian number. \n3、Add traditional chinese version; \n4、Fix some bugs;", "formattedPrice":"$1.99", "wrapperType":"software", "trackCensoredName":"3D Protractor", "trackViewUrl":"https://itunes.apple.com/us/app/3d-protractor/id595176741?mt=8&uo=4", "contentAdvisoryRating":"4+", "artworkUrl100":"http://a1435.phobos.apple.com/us/r1000/076/Purple/v4/d1/36/f5/d136f5d0-3962-9ba1-95b2-3ca0ba3be9ec/mzl.zzqaoikx.jpg", "languageCodesISO2A":["ZH", "EN"], "fileSizeBytes":"14633609", "averageUserRatingForCurrentVersion":5.0, "userRatingCountForCurrentVersion":2, "trackContentRating":"4+", "averageUserRating":4.5, "userRatingCount":8}]

}

可以看出，包括更新的内容都有，这就非常好办了。具体的实现方式这里写一下获取的方法：

[cpp]

[plain]

<span style="font-size:24px;">NSString *query = [NSString stringWithFormat:@"https://itunes.apple.com/lookup?id=%@", AppID];

query = [query stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSData *jsonData = [[NSString stringWithContentsOfURL:[NSURL URLWithString:query] encoding:NSUTF8StringEncoding error:nil] dataUsingEncoding:NSUTF8StringEncoding];

NSError *error = nil;

NSDictionary *results = jsonData ? [NSJSONSerialization JSONObjectWithData:jsonData options:0 error:&error] : nil;</span>

获取了NSDictionary 的results，之后一切都好办。代码中特地加入UTF8String编码，不用也可以。当然，网页上说All JSON results are encoded as UTF-8。

另外，要获得App的版本号，如下

App版本： [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleShortVersionString"];

App Build版本： [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleVersion"];