Objective-C JSON操作

Objective-C 操作JSON 主要使用的是 NSJSONSerialization 这个类

NSJSONSerialization 包含了以下五个类函数

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

<span style="font-size:18px;">+ (BOOL)isValidJSONObject:(id)obj;</span>

将JSON数据写为NSData数据，其中opt参数的枚举如下，这个参数可以设置，也可以不设置，如果设置，则会输出视觉美观的JSON数据，否则输出紧凑的JSON数据。

<span style="font-size:18px;">+ (NSData *)dataWithJSONObject:(id)obj options:(NSJSONWritingOptions)opt error:(NSError **)error;</span>

这个方法是解析中数据的核心方法，data是JSON数据对象，可以设置一个opt参数，具体用法如下：

<span style="font-size:18px;">typedef NS_OPTIONS(NSUInteger, NSJSONReadingOptions) {
    //将解析的数组和字典设置为可变对象
    NSJSONReadingMutableContainers = (1UL << 0),
    //将解析数据的子节点创建为可变字符串对象
    NSJSONReadingMutableLeaves = (1UL << 1),
    //允许解析对象的最上层不是字典或者数组
    NSJSONReadingAllowFragments = (1UL << 2)
}</span>

<span style="font-size:18px;">+ (id)JSONObjectWithData:(NSData *)data options:(NSJSONReadingOptions)opt error:(NSError **)error;</span>

将JSON数据写入到输出流，返回的是写入流的字节数

<span style="font-size:18px;">+ (NSInteger)writeJSONObject:(id)obj toStream:(NSOutputStream *)stream options:(NSJSONWritingOptions)opt error:(NSError **)error;</span>

从输入流读取JSON数据

<span style="font-size:18px;">+ (id)JSONObjectWithStream:(NSInputStream *)stream options:(NSJSONReadingOptions)opt error:(NSError **)error;</span>

<span style="font-size:18px;">NSMutableDictionary *dictionary = [[NSMutableDictionary alloc]init];
        [dictionary setValue:@"xiaominfc" forKey:@"username"];
        [dictionary setValue:@"1991-03-26" forKey:@"birthday"];
        [dictionary setValue:[NSNumber numberWithInteger:23] forKey:@"age"];
        NSArray *arrayOfAnthonysChildren = [[NSArray alloc]initWithObjects:@"Java",@"Objective-C",@"Python",@"C++", nil];
        [dictionary setValue:arrayOfAnthonysChildren forKey:@"program_language"];
        
        if([NSJSONSerialization isValidJSONObject:dictionary]){
            NSLog(@"it is a JSONObject!");
        }
        //use dataWithJSONObject fun
        
        NSError *error = nil;
        NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dictionary options:NSJSONWritingPrettyPrinted error:&error];
        if([jsonData length] > 0 && error == nil) {
            NSString *jsonString = [[NSString alloc]initWithData:jsonData encoding:NSUTF8StringEncoding];
            NSLog(@"data:%@",jsonString);
            
        }
        
        //use JSONObjectWithData fun
        
        NSString *jsonDataString = @"{\"username\":\"xiaominfc\",\"city\":\"深圳\"}";
        NSData *data = [jsonDataString dataUsingEncoding:NSUTF8StringEncoding];
        id jsonObject = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&error];
        if ([jsonObject isKindOfClass:[NSDictionary class]]) {
            NSDictionary *jsonDictionary = (NSDictionary*)jsonObject;
            NSLog(@"username:%@ And city:%@",[jsonDictionary valueForKey:@"username"],[jsonDictionary valueForKey:@"city"]);
        }
        
        //use writeJSONObject fun
        
        NSString *filePath = @"/Users/xiaominfc/text.txt";
        
        NSOutputStream *outStream = [[NSOutputStream alloc]initToFileAtPath:filePath append:NO];
        [outStream open];
        NSInteger length = [NSJSONSerialization writeJSONObject:dictionary toStream:outStream options:NSJSONWritingPrettyPrinted error:&error];
        NSLog(@"write %ld bytes",(long)length);
        [outStream close];
        
        //use JSONObjectWithStream
        NSInputStream *inStream = [[NSInputStream alloc]initWithFileAtPath:filePath];
        [inStream open];
        id streamObject = [NSJSONSerialization JSONObjectWithStream:inStream options:NSJSONReadingAllowFragments error:&error];
        if ([streamObject isKindOfClass:[NSDictionary class]]) {
            NSDictionary *jsonDictionary = (NSDictionary*)streamObject;
            NSNumber *ageNumber = (NSNumber*)[jsonDictionary valueForKey:@"age"];
            NSLog(@"username:%@ And age:%d",[jsonDictionary valueForKey:@"username"],[ageNumber intValue]);
        }
        [inStream close];</span>