从josn加载数据模型

- (NSArray *)htmls
{
    if (!_htmls) {

    // JSON文件的路径
    NSString *path = [[NSBundle mainBundle] pathForResource:@"help.json" ofType:nil];    
    // 加载JSON文件
    NSData *data = [NSData dataWithContentsOfFile:path]; 
    // 将JSON数据转为NSArray或者NSDictionary
    NSArray *dictArray = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
    // 将字典转成模型
    NSMutableArray *htmlArray = [NSMutableArray array];
    for (NSDictionary *dict in dictArray) {
        Html *html = [Html htmlWithDict:dict];
        [htmlArray addObject:html];
    }
    _htmls = htmlArray;
}
return _htmls;

}
参数说明:

typedef NS_OPTIONS(NSUInteger, NSJSONReadingOptions) {
    NSJSONReadingMutableContainers = (1UL << 0),
    NSJSONReadingMutableLeaves = (1UL << 1),
    NSJSONReadingAllowFragments = (1UL << 2)
} NS_ENUM_AVAILABLE(10_7, 5_0);

typedef NS_OPTIONS(NSUInteger, NSJSONWritingOptions) {
NSJSONWritingPrettyPrinted = (1UL << 0)
} NS_ENUM_AVAILABLE(10_7, 5_0);

/* A class for converting JSON to Foundation objects and converting Foundation objects to JSON.

An object that may be converted to JSON must have the following properties:

- Top level object is an NSArray or NSDictionary
- All objects are NSString, NSNumber, NSArray, NSDictionary, or NSNull
- All dictionary keys are NSStrings
- NSNumbers are not NaN or infinity

/
NS_CLASS_AVAILABLE(10_7, 5_0)
@interface NSJSONSerialization : NSObject {
@private
void reserved[6];
}

 

NSJSONReadingMutableContainers：返回可变容器，NSMutableDictionary或NSMutableArray。

NSJSONReadingMutableLeaves：返回的JSON对象中字符串的值为NSMutableString，目前在iOS 7上测试不好用，应该是个bug，参见：
http://stackoverflow.com/questions/19345864/nsjsonreadingmutableleaves-option-is-not-working

NSJSONReadingAllowFragments：允许JSON字符串最外层既不是NSArray也不是NSDictionary，但必须是有效的JSON Fragment。例如使用这个选项可以解析 @“123” 这样的字符串。参见：
http://stackoverflow.com/questions/16961025/nsjsonserialization-nsjsonreadingallowfragments-reading

• (BOOL)isValidJSONObject:(id)obj;
  // 判断 该实例(obj)是否为JSONObject
  // 需满足下面三个条件
  // 1.obj 是NSArray 或 NSDictionay 以及他们派生出来的子类
  // 2.obj 包含的所有对象是NSString,NSNumber,NSArray,NSDictionary 或NSNull
  // 3.NSNumber的对象不能是NaN或无穷大

• (NSData )dataWithJSONObject:(id)obj options:(NSJSONWritingOptions)opt error:(NSError *)error;

// 将JSONObject的实例转成NSData

• (id)JSONObjectWithData:(NSData )data options:(NSJSONReadingOptions)opt error:(NSError *)error;

// 将NSData类型的实例转成JSONObject

• (NSInteger)writeJSONObject:(id)obj toStream:(NSOutputStream )stream options:(NSJSONWritingOptions)opt error:(NSError *)error;
  // 将一个JSONObject的实例写入到一个输出流中 返回写入的长度

• (id)JSONObjectWithStream:(NSInputStream )stream options:(NSJSONReadingOptions)opt error:(NSError *)error;
  // 从输入流中读取成JSONObject 并返回