[iOS]如何向 appstore 查询已发布 APP 的信息？

如果我们需要实现版本的 app 自动更新，那么我们需要获取当前运行程序的版本信息和 appstore 里发布的最新版本信息。

当前运行程序的版本信息，可以在 mainBundle 里面获取：

NSDictionary *infoDict = [[NSBundle mainBundle] infoDictionary];
    NSString *currentVersion = [infoDict objectForKey:@"CFBundleVersion"];

而 appstore 里发布的最新版本信息获取稍微复杂一些，有两种方案，思路都是一样的：
其一：在某个服务器上存储最新发布的版本信息，需要的时候向该服务器查询；
其二：在需要的时候向 appstore 查询；

在这里我来介绍第二种方法：向 appstore 查询应用程序信息，包括作者，版本，app 介绍页面地址等信息。
英文好的同学可以参考 apple 的文档：www.apple.com/itunes/affiliates/resources/documentation/itunes-store-web-service-search-api.html

具体步骤如下：
1，用 POST 方式发送请求： http://itunes.apple.com/search?term=你的应用程序名称&entity=software
更加精准的做法是根据 app 的 id 来查找：

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 13.0px Menlo; color: #cf2a24}
http://itunes.apple.com/lookup?id=你的应用程序的ID 2，从获得的 response 数据中解析需要的数据。因为从 appstore 查询得到的信息是 JSON 格式的，所以需要经过解析。解析之后得到的原始数据就是如下这个样子的：

{
    resultCount = 1;
    results =     (
                {
            artistId = 301724683;
            artistName = Citibank;
            artistViewUrl = "http://itunes.apple.com/us/artist/citibank/id301724683?uo=4";
            artworkUrl100 = "http://a5.mzstatic.com/us/r1000/117/Purple/a1/85/a9/mzl.hvwnfdkw.png";
            artworkUrl512 = "http://a5.mzstatic.com/us/r1000/117/Purple/a1/85/a9/mzl.hvwnfdkw.png";
            artworkUrl60 = "http://a2.mzstatic.com/us/r1000/099/Purple/67/86/7e/mzi.utfdvrgy.png";
            averageUserRating = "3.5";
            averageUserRatingForCurrentVersion = 5;
            contentAdvisoryRating = "4+";
            currency = USD;
            description = "Description of you app.";
            features =             (
                iosUniversal
            );
            fileSizeBytes = 4141195;
            genreIds =             (
                6015
            );
            genres =             (
                Finance
            );
            ipadScreenshotUrls =             (
                "http://a1.mzstatic.com/us/r1000/095/Purple/e0/a6/17/mzl.pbbxcjzt.1024x1024-65.jpg",
                "http://a3.mzstatic.com/us/r1000/036/Purple/cc/14/98/mzl.dyairego.1024x1024-65.jpg"
            );
            isGameCenterEnabled = 0;
            kind = software;
            languageCodesISO2A =             (
                EN
            );
            price = 0;
            primaryGenreId = 6015;
            primaryGenreName = Finance;
            releaseDate = "2011-01-24T06:14:35Z";
            releaseNotes = "* View Real-time streaming prices for U.S. Treasuries \n\n* Open and Save your Citi Research in your favorite PDF Reader and Library such as iBooks\n\n* Search for your favorite videos";
            screenshotUrls =             (
                "http://a3.mzstatic.com/us/r1000/066/Purple/17/51/fb/mzl.zywiavgn.png",
                "http://a5.mzstatic.com/us/r1000/026/Purple/73/85/97/mzl.csmdtndk.png"
            );
            sellerName = "Citibank, N.A.";
            sellerUrl = "http://";
            supportedDevices =             (
                all
            );
            trackCensoredName = "Citi Velocity";
            trackContentRating = "4+";
            trackId = 414697122;
            trackName = "Citi Velocity";
            trackViewUrl = "http://itunes.apple.com/us/app/citi-velocity/id414697122?mt=8&uo=4";
            userRatingCount = 5;
            userRatingCountForCurrentVersion = 1;
            version = "1.4";
            wrapperType = software;
        }
    );
}

然后从中取得 results 数组即可，具体代码如下所示：

NSDictionary *jsonData = [dataPayload JSONValue];
    NSArray *infoArray = [jsonData objectForKey:@"results"];
    NSDictionary *releaseInfo = [infoArray objectAtIndex:0];
    NSString *latestVersion = [releaseInfo objectForKey:@"version"];
    NSString *trackViewUrl = [releaseInfo objectForKey:@"trackViewUrl"];

如果你拷贝 trackViewUrl 的实际地址，然后在浏览器中打开，就会打开你的应用程序在 appstore 中的介绍页面。当然我们也可以在代码中调用 safari 来打开它。

UIApplication *application = [UIApplication sharedApplication];
    [application openURL:[NSURL URLWithString:trackViewUrl]];