iOS网络开发——JSON数据解码(使用NSJSONSerialization)

下面我们通过一个案例MyNotes学习一下NSJSONSerialization的用法。这里重新设计数据结构为JSON格式，

其中备忘录信息Notes.json文件的内容如下：

{"ResultCode":0,"Record":[
{"ID":"1","CDate":"2012-12-23","Content":"发布iOSBook0","UserID":"tony"},
{"ID":"2","CDate":"2012-12-24","Content":"发布iOSBook1","UserID":"tony"},
{"ID":"3","CDate":"2012-12-25","Content":"发布iOSBook2","UserID":"tony"},
{"ID":"4","CDate":"2012-12-26","Content":"发布iOSBook3","UserID":"tony"},
{"ID":"5","CDate":"2012-12-27","Content":"发布iOSBook4","UserID":"tony"}]}

事实上，NSJSONSerialization使用起来更为简单，只要能确定你的项目使用了iOS 5 SDK就可以了。修改视图
控制器MasterViewController的viewDidLoad方法，具体代码如下：

- (void)viewDidLoad
{
	[super viewDidLoad];
	self.navigationItem.leftBarButtonItem = self.editButtonItem;
	
	self.detailViewController = (DetailViewController *)
	[[self.splitViewController.viewControllers lastObject] topViewController];
	[[NSNotificationCenter defaultCenter] addObserver:self
										  selector:@selector(reloadView:)
										  name:@"reloadViewNotification"
										  object:nil];
	
	//路径,实际开发中要请求服务器端
	NSString* path = [[NSBundle mainBundle] pathForResource:@"Notes" ofType:@"json"];
	NSData *jsonData = [[NSData alloc] initWithContentsOfFile:path];
	NSError *error;
	//options参数指定了解下JSON的模式:
	//NSJSONReadingMutableContainers -指定解析返回的是可变的数组或字典.(这个常量是合适的选择)
	//NSJSONReadingMutableLeaves。指定叶节点是可变字符串。
	//NSJSONReadingAllowFragments。指定顶级节点可以不是数组或字典
	id jsonObj = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&error];
	
	if (!jsonObj || error) {
		NSLog(@"JSON解码失败");
	}
	self.listData = [jsonObj objectForKey:@"Record"];
}

此外，NSJSONSerialization还提供了JSON编码的方法：dataWithJSONObject:options:error:和
writeJSONObject:toStream:options:error:。