[iOS开发]JSONModel源码学习
Posted Billy Miracle
tags:
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JSONModel对外给出了许多常见的初始化方法：
- (instancetype)initWithDictionary:(NSDictionary *)dict error:(NSError **)err;
- (instancetype)initWithData:(NSData *)data error:(NSError **)error;
// Create a new model instance and initialize it with the JSON from a text parameter.
// The method assumes UTF8 encoded input text.
- (instancetype)initWithString:(NSString *)string error:(JSONModelError **)err;
// Create a new model instance and initialize it with the JSON from a text parameter using the given encoding.
- (instancetype)initWithString:(NSString *)string usingEncoding:(NSStringEncoding)encoding error:(JSONModelError **)err;
接下来，我们看一看实现代码：
- (instancetype)initWithData:(NSData *)data error:(NSError *__autoreleasing *)err
//check for nil input
if (!data)
if (err) *err = [JSONModelError errorInputIsNil];
return nil;
//read the json
JSONModelError* initError = nil;
id obj = [NSJSONSerialization JSONObjectWithData:data
options:kNilOptions
error:&initError];
if (initError)
if (err) *err = [JSONModelError errorBadJSON];
return nil;
//init with dictionary
id objModel = [self initWithDictionary:obj error:&initError];
if (initError && err) *err = initError;
return objModel;
- (id)initWithString:(NSString*)string error:(JSONModelError**)err
JSONModelError* initError = nil;
id objModel = [self initWithString:string usingEncoding:NSUTF8StringEncoding error:&initError];
if (initError && err) *err = initError;
return objModel;
- (id)initWithString:(NSString *)string usingEncoding:(NSStringEncoding)encoding error:(JSONModelError**)err
//check for nil input
if (!string)
if (err) *err = [JSONModelError errorInputIsNil];
return nil;
JSONModelError* initError = nil;
id objModel = [self initWithData:[string dataUsingEncoding:encoding] error:&initError];
if (initError && err) *err = initError;
return objModel;
我们发现，这几个初始化方法最终实际上都还是调用了
- (id)initWithDictionary:(NSDictionary*)dict error:(NSError**)err;
在看实现前，我们先看一看：
#pragma mark - associated objects names
static const char * kMapperObjectKey;
// 关联对象kMapperObjectKey
// 保存自定义的mapper
static const char * kClassPropertiesKey;
// 关联对象kClassPropertiesKey
// 用来保存所有属性信息的NSDictionary
static const char * kClassRequiredPropertyNamesKey;
// 关联对象kClassRequiredPropertyNamesKey
// 用来保存所有属性的名称NSSet
static const char * kIndexPropertyNameKey;
大致过程为：
首先，在这个模型类的对象被初始化的时候，遍历自身到所有的父类（直到JSONModel为止），获取所有的属性，并将其保存在一个字典里。获取传入字典的所有key，将这些key与保存的所有属性进行匹配。如果匹配成功，则进行kvc赋值。
此外，在load方法里，定义了它的支持：
+ (void)load
static dispatch_once_t once;
dispatch_once(&once, ^
@autoreleasepool
//兼容的对象属性
allowedJSONTypes = @[
[NSString class], [NSNumber class], [NSDecimalNumber class], [NSArray class], [NSDictionary class], [NSNull class], //immutable JSON classes
[NSMutableString class], [NSMutableArray class], [NSMutableDictionary class] //mutable JSON classes
];
//兼容的基本类型属性
allowedPrimitiveTypes = @[
@"BOOL", @"float", @"int", @"long", @"double", @"short",
@"unsigned int", @"usigned long", @"long long", @"unsigned long long", @"unsigned short", @"char", @"unsigned char",
//and some famous aliases
@"NSInteger", @"NSUInteger",
@"Block"
];
//转换器
valueTransformer = [[JSONValueTransformer alloc] init];
//自己的类型
JSONModelClass = NSClassFromString(NSStringFromClass(self));
);
接下来我们来看看它的实现：
- (id)initWithDictionary:(NSDictionary*)dict error:(NSError**)err
//check for nil input
// 第一步： 先是判断传入的字典是否为空，如果为空返回为空的错误
if (!dict)
if (err) *err = [JSONModelError errorInputIsNil];
return nil;
//invalid input, just create empty instance
//第二步：再判断传入的数据是否是字典类型，如果不是字典类型不正确的错误
if (![dict isKindOfClass:[NSDictionary class]])
if (err) *err = [JSONModelError errorInvalidDataWithMessage:@"Attempt to initialize JSONModel object using initWithDictionary:error: but the dictionary parameter was not an 'NSDictionary'."];
return nil;
//create a class instance
//第三步：核心的代码，通过init方法初始化映射property
self = [self init];
if (!self)
//super init didn't succeed
if (err) *err = [JSONModelError errorModelIsInvalid];
return nil;
//check incoming data structure
//第四步：检查映射结构是否能从我们传入的dict中找到对应的数据，如果不能找到，就返回nil，并且抛出错误
if (![self __doesDictionary:dict matchModelWithKeyMapper:self.__keyMapper error:err])
return nil;
//import the data from a dictionary
//第五步：根据传入的dict进行数据的赋值，如果赋值没有成功，就返回nil，并且抛出错误。
if (![self __importDictionary:dict withKeyMapper:self.__keyMapper validation:YES error:err])
return nil;
//run any custom model validation
//第六步：根据本地的错误来判断是否有错误，如果有错误，就返回nil，并且抛出错误。
if (![self validate:err])
return nil;
//model is valid! yay!
//第七步：返回self，model有效，耶嘿！
return self;
我们看一下其中的第三步：
//第三步：核心的代码，通过init方法初始化映射property
self = [self init];
看一下它的实现：
- (id)init
self = [super init];
if (self)
//do initial class setup
[self __setup__];
return self;
调用了__setup__方法。我们来看它的实现：
- (void)__setup__
//if first instance of this model, generate the property list
// 第一步：
// 先是通过AssociateObject来判断是否进行过映射property的缓存，
// 如果没有就使用“__inspectProperties”方法进行映射property的缓存
if (!objc_getAssociatedObject(self.class, &kClassPropertiesKey))
// 进行映射property的缓存
[self __inspectProperties];
//if there's a custom key mapper, store it in the associated object
// 第二步：判断一下，当前的keyMapper是否存在和是否进行映射过，如果没有进行映射就使用AssociateObject方法进行映射
id mapper = [[self class] keyMapper];
if ( mapper && !objc_getAssociatedObject(self.class, &kMapperObjectKey) )
//第三步：进行AssociateObject映射
objc_setAssociatedObject(
self.class,
&kMapperObjectKey,
mapper,
OBJC_ASSOCIATION_RETAIN // This is atomic
);
key mapper主要是用来针对某些json字段名和model数据名不一致的情况。
比如"com.app.test.name":"xxx"，"test_name":"xxx"这样的情况，可能对应的model数据字段名为name，那如何讲着两个值进行映射，就通过key mapper来完成。
接下来解析一下__inspectProperties方法，介绍怎么进行映射property的缓存。先看实现：
//inspects the class, get's a list of the class properties
//检查类，获取类属性的列表
//它的任务是保存所有需要赋值的属性。
- (void)__inspectProperties
//JMLog(@"Inspect class: %@", [self class]);
NSMutableDictionary* propertyIndex = [NSMutableDictionary dictionary];
//temp variables for the loops
Class class = [self class];
NSScanner* scanner = nil;
NSString* propertyType = nil;
// inspect inherited properties up to the JSONModel class
while (class != [JSONModel class])
//JMLog(@"inspecting: %@", NSStringFromClass(class));
// 先是获取当前class的property列表和个数
unsigned int propertyCount;
objc_property_t *properties = class_copyPropertyList(class, &propertyCount);
//loop over the class properties
// 遍历property
for (unsigned int i = 0; i < propertyCount; i++)
// 创建一个解析和判断每个property的局部变量JSONModelClassProperty
JSONModelClassProperty* p = [[JSONModelClassProperty alloc] init];
//get property name
objc_property_t property = properties[i];
const char *propertyName = property_getName(property);
// 获取property的名称给当前这个局部变量
p.name = @(propertyName);
//JMLog(@"property: %@", p.name);
//get property attributes
// 获取这个property的属性
// 通过property_getAttributes获取property的encode string，解析encode string可以解析出具体property的类型
const char *attrs = property_getAttributes(property);
NSString* propertyAttributes = @(attrs);
NSArray* attributeItems = [propertyAttributes componentsSeparatedByString:@","];
//ignore read-only properties
//忽略只读属性
if ([attributeItems containsObject:@"R"])
continue; //to next property
// 扫描property属性
scanner = [NSScanner scannerWithString: propertyAttributes];
//JMLog(@"attr: %@", [NSString stringWithCString:attrs encoding:NSUTF8StringEncoding]);
[scanner scanUpToString:@"T" intoString: nil];
[scanner scanString:@"T" intoString:nil];
//check if the property is an instance of a class
//解析一个类，检查属性是否为类的实例
if ([scanner scanString:@"@\\"" intoString: &propertyType])
[scanner scanUpToCharactersFromSet:[NSCharacterSet characterSetWithCharactersInString:@"\\"<"]
intoString:&propertyType];
//JMLog(@"type: %@", propertyClassName);
// 设置property的类型
p.type = NSClassFromString(propertyType);
// 判断并设置property的是否是可变的
p.isMutable = ([propertyType rangeOfString:@"Mutable"].location != NSNotFound);
// 判断property的是否我们允许的json类型
p.isStandardJSONType = [allowedJSONTypes containsObject:p.type];
//read through the property protocols
// 解析protocol的string
while ([scanner scanString:@"<" intoString:NULL])
NSString* protocolName = nil;
[scanner scanUpToString:@">" intoString: &protocolName];
if ([protocolName isEqualToString:@"Optional"])
p.isOptional = YES;
else if([protocolName isEqualToString:@"Index"])
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
p.isIndex = YES;
#pragma GCC diagnostic pop
objc_setAssociatedObject(
self.class,
&kIndexPropertyNameKey,
p.name,
OBJC_ASSOCIATION_RETAIN // This is atomic
);
else if([protocolName isEqualToString:@"Ignore"])
p = nil;
else
p.protocol = protocolName;
[scanner scanString:@">" intoString:NULL];
//check if the property is a structure
// 检查property是否为structure
else if ([scanner scanString:@"" intoString: &propertyType])
[scanner scanCharactersFromSet:[NSCharacterSet alphanumericCharacterSet]
intoString:&propertyType];
p.isStandardJSONType = NO;
p.structName = propertyType;
//the property must be a primitive
// 属性必须是基本类型，比如int float等
else
//the property contains a primitive data type
//该属性包含基元数据类型
[scanner scanUpToCharactersFromSet:[NSCharacterSet characterSetWithCharactersInString:@","]
intoString:&propertyType];
//get the full name of the primitive type
//获取基元类型的全名
propertyType = valueTransformer.primitivesNames[propertyType];
if (![allowedPrimitiveTypes containsObject:propertyType])
//type not allowed - programmer mistaken -> exception
//类型不允许 - 程序员错误 - >异常
@throw [NSException exceptionWithName:@"JSONModelProperty type not allowed"
reason:[NSString stringWithFormat:@"Property type of %@.%@ is not supported by JSONModel.", self.class, p.name]
userInfo:nil];
NSString *nsPropertyName = @(propertyName);
// 判断property是不是Optional
if([[self class] propertyIsOptional:nsPropertyName])
p.isOptional = YES;
// 判断property是不是Ignored
if([[self class] propertyIsIgnored:nsPropertyName])
p = nil;
Class customClass = [[self class] classForCollectionProperty:nsPropertyName];
if (customClass)
p.protocol = NSStringFromClass(customClass);
//few cases where JSONModel will ignore properties automatically
//在少数情况下，JSONModel 会自动忽略属性
if ([propertyType isEqualToString:@"Block"])
p = nil;
//add the property object to the temp index
//将属性对象添加到临时索引
// 通过kvc去设置相应的值
if (p && ![propertyIndex objectForKey:p.name])
[propertyIndex setValue:p forKey:p.name];
// generate custom setters and getter
//生成自定义设置器和获取器
if (p)
NSString *name = [p.name stringByReplacingCharactersInRange:NSMakeRange(0, 1) withString:[p.name substringToIndex:1].uppercaseString];
// getter
SEL getter = NSSelectorFromString([NSString stringWithFormat:@"JSONObjectFor%@", name]);
if ([self respondsToSelector:getter])
p.customGetter = getter;
// setters
p.customSetters = [NSMutableDictionary new];
SEL genericSetter = NSSelectorFromString([NSString stringWithFormat:@"set%@WithJSONObject:", name]);
if ([self respondsToSelector:genericSetter])
p.customSetters[@"generic"] = [NSValue valueWithBytes:&genericSetter objCType:@encode(SEL)];
for (Class type in allowedJSONTypes)
NSString *class = NSStringFromClass([JSONValueTransformer classByResolvingClusterClasses:type]);
if (p.customSetters[class])
continue;
SEL setter = NSSelectorFromString([NSString stringWithFormat:@"set%@With%@:", name, class]);
if ([self respondsToSelector:setter])
p.customSetters[class] = [NSValue valueWithBytes:&setter objCType:@encode(SEL)];
free(properties);
iOS开发解决 jsonModel 属性跟系统的重复