将数据模型(数组)转换为json字符串

    //1. 初始化可变字符串，存放最终生成json字串

    NSMutableString *datajsonString = [[NSMutableString alloc] initWithString:@[""];

    

    for(GoodsModel *model in dataArray){

        

        //2. 遍历数组，取出键值对并按json格式存放

        NSString *string;

        NSNumber *boolNumber=[NSNumber numberWithBool:model.isCustom];

        //相应键值对

        string  = [NSString stringWithFormat:

                   @"{\"goodsId\":\"%@\",\"name\":\"%@\",\"price\":\"%f\",\"count\":\"%f\",\"isCustom\":\"%@\"},",model.goodsID,model.goodsName,model.goodsSalePrice,model.orderCount,boolNumber];

        

        [datajsonString appendString:string];

        

    }

    // 3. 获取末尾逗号所在位置

    NSUInteger location = [datajsonString length]-1;

    

    NSRange range       = NSMakeRange(location, 1);

    

    // 4. 将末尾逗号换成结束的]}

    [datajsonString replaceCharactersInRange:range withString:@""]];