在之前介绍的数据存储方法中,不管是NSUserDefaults还是plist文件都不能对自定义对象进行存储,OC提供的解归档恰好解决了这个问题
本片文章对 iOS13 以后的版本 归档和解档 进行介绍。老版本的解归档见这篇文章:【iOS】文件(对象数据)的归档和解档,参考这篇文章对比学习会对解归档有更好的理解
在iOS中,对象的序列化和反序列化分别使用NSKeyedArchiver和NSKeyedUnarchiver两个类,我们可以把一个类对象进行序列化然后保存到文件中,使用时再读取文件,把内容反序列化出来。这个过程通常也被称为 对象的编码(归档)和解码(解档)
归档一般保存自定义对象、自定义对象数组,由于自定义对象不具有归档的性质,所以只有遵循了NSCoding协议的类才可以归档
由于决大多数支持存储数据的Foundation和Cocoa Touch类都遵循了NSCoding协议,因此,对于大多数OC提供的类来说,归档相对而言还是比较容易实现的。
对象归档的文件是保密的,在磁盘上无法查看文件中的内容,而属性列表是明文的,可以查看。通过文件归档产生的文件是不可见的,如果打开归档文件的话,内容是乱码的;ta不同于属性列表和plist文件是可见的,正因为不可见的缘故,使得这种持久性的数据保存更有可靠性
iOS 13中需要支持NSSecureCoding 协议
(父协议为NSCoding
)才能支持归档
NSCoding 协议
的方法@interface Person : NSObject <NSSecureCoding>
@property (nonatomic, copy)NSString* name;
@property (nonatomic, assign)int age;
@property (nonatomic, assign)double weight;
@end
@implementation Person
//NSCoder是一个抽象类
//归档的协议方法
//将归档对象序列化
- (void)encodeWithCoder:(NSCoder *)coder {
[coder encodeObject: self.name forKey: @"name"];
[coder encodeInt: self.age forKey: @"age"];
[coder encodeDouble: self.weight forKey: @"weight"];
}
//解档的协议方法
//将解档对象反序列化
- (instancetype)initWithCoder:(NSCoder *)coder {
self = [super init];
if (self) {
self.name = [coder decodeObjectForKey: @"name"];
self.age = [coder decodeIntForKey: @"age"];
self.weight = [coder decodeDoubleForKey: @"weight"];
}
return self;
}
@end
//NSSecureCoding的协议方法
+ (BOOL)supportsSecureCoding {
return YES;
}
+ (nullable NSData *)archivedDataWithRootObject:(id)object requiringSecureCoding:(BOOL)requiresSecureCoding error:(NSError **)error;
Person* person = [[Person alloc] init];
person.name = @"XY";
person.age = 20;
person.weight = 125.0;
//归档成二进制数据流
NSError* error;
NSData* data1 = [NSKeyedArchiver archivedDataWithRootObject: person requiringSecureCoding: YES error: &error];
if (error) {
NSLog(@"归档错误:%@", error);
return 0;
}
//写入指定路径(一般写入到沙盒,这里方便演示存到一个新的文件夹)
[data1 writeToFile: @"/Users/jakey/Desktop/CS/Xcode/NSKeyedArchiverTest/test.archiver" atomically: YES];
Person对象被序列化后就会被保存在下方的文件中,但无法直接打开
通过终端命令打开后,可以看到内容是经过加密的,保证了数据的安全性
+ (nullable id)unarchivedObjectOfClass:(Class)cls fromData:(NSData *)data error:(NSError **)error;
//解档此二进制数据
error = nil;
NSData* data2 = [NSData dataWithContentsOfFile: @"/Users/jakey/Desktop/CS/Xcode/NSKeyedArchiverTest/test.archiver"];
Person* unarchiverPerson = (Person *)[NSKeyedUnarchiver unarchivedObjectOfClass: [Person class] fromData: data2 error: &error];
if (error) {
NSLog(@"解档错误:%@", error);
}
NSLog(@"unarchiverPerson:%@", unarchiverPerson);
将多个对象归档在同一个文件中:
Person* person1 = [[Person alloc] init];
person1.name = @"XY";
person1.age = 20;
person1.weight = 125.0;
Dog* dog1 = [[Dog alloc] init];
dog1.name = @"Bruce";
person1.dog = dog1;
Person* person2 = [[Person alloc] init];
person2.name = @"Jacky";
person2.age = 21;
person2.weight = 130.0;
Dog* dog2 = [[Dog alloc] init];
dog2.name = @"Oudy";
person2.dog = dog2;
//创建归档对象
NSKeyedArchiver* archiver = [[NSKeyedArchiver alloc] initRequiringSecureCoding: NO];
//进行归档(编码)操作
[archiver encodeObject: person1 forKey: @"personOne"];
[archiver encodeObject: person2 forKey: @"personTwo"];
//将归档(序列化)后的数据写入指定文件中
[archiver.encodedData writeToFile: @"/Users/jakey/Desktop/CS/Xcode/NSKeyedArchiverTest/test.archiver" atomically: YES];
//结束归档
[archiver finishEncoding];
//解档
NSData* data = [NSData dataWithContentsOfFile: @"/Users/jakey/Desktop/CS/Xcode/NSKeyedArchiverTest/test.archiver"];
NSKeyedUnarchiver* unarchiver = [[NSKeyedUnarchiver alloc] initForReadingFromData: data error: nil];
unarchiver.requiresSecureCoding = NO;
Person* unchiverPerson1 = [unarchiver decodeObjectForKey: @"personOne"];
NSLog(@"%@ %d %lf %@", unchiverPerson1.name, unchiverPerson1.age, unchiverPerson1.weight, unchiverPerson1.dog.name);
Person* unchiverPerson2 = [unarchiver decodeObjectForKey: @"personTwo"];
NSLog(@"%@ %d %lf %@", unchiverPerson2.name, unchiverPerson2.age, unchiverPerson2.weight, unchiverPerson2.dog.name);
现对于Person
类,设置一个自定义对象dog
属性,那么这个内层的Dog
类也需要实现NSSecureCoding 协议
,否则程序会崩溃:
上面也提到过,OC提供的类(比如这里的name
)已经遵循了此协议,因此无需手动操作,但自定义的Dog
类要手动添加协议函数:
@interface Dog : NSObject <NSSecureCoding>
@property (nonatomic, strong)NSString* name;
@end
- (void)encodeWithCoder:(NSCoder *)coder {
[coder encodeObject: self.name forKey: @"dogName"];
}
- (instancetype)initWithCoder:(NSCoder *)coder {
self = [super init];
if (self) {
self.name = [coder decodeObjectForKey: @"dogName"];
}
return self;
}
+ (BOOL)supportsSecureCoding {
return YES;
}
以下是复合类解归档完整代码:
#import <Foundation/Foundation.h>
#import "Person.h"
#import "Dog.h"
int main(int argc, const char * argv[]) {
@autoreleasepool {
Person* person1 = [[Person alloc] init];
person1.name = @"XY";
person1.age = 20;
person1.weight = 125.0;
Dog* dog1 = [[Dog alloc] init];
dog1.name = @"Bruce";
person1.dog = dog1;
Person* person2 = [[Person alloc] init];
person2.name = @"Jacky";
person2.age = 21;
person2.weight = 130.0;
Dog* dog2 = [[Dog alloc] init];
dog2.name = @"Oudy";
person2.dog = dog2;
//创建归档对象
NSKeyedArchiver* archiver = [[NSKeyedArchiver alloc] initRequiringSecureCoding: NO];
//进行归档操作
[archiver encodeObject: person1 forKey: @"personOne"];
[archiver encodeObject: person2 forKey: @"personTwo"];
//将归档(序列化)后的数据写入指定文件中
[archiver.encodedData writeToFile: @"/Users/jakey/Desktop/CS/Xcode/NSKeyedArchiverTest/test.archiver" atomically: YES];
//结束归档
[archiver finishEncoding];
//解档
NSData* data = [NSData dataWithContentsOfFile: @"/Users/jakey/Desktop/CS/Xcode/NSKeyedArchiverTest/test.archiver"];
NSKeyedUnarchiver* unarchiver = [[NSKeyedUnarchiver alloc] initForReadingFromData: data error: nil];
unarchiver.requiresSecureCoding = NO;
Person* unchiverPerson1 = [unarchiver decodeObjectForKey: @"personOne"];
NSLog(@"%@ %d %lf %@", unchiverPerson1.name, unchiverPerson1.age, unchiverPerson1.weight, unchiverPerson1.dog.name);
Person* unchiverPerson2 = [unarchiver decodeObjectForKey: @"personTwo"];
NSLog(@"%@ %d %lf %@", unchiverPerson2.name, unchiverPerson2.age, unchiverPerson2.weight, unchiverPerson2.dog.name);
return 0;
}
运行结果如下:
如果需要归档的类是某个自定义类的子类时,就需要在归档和解档之前实现父类的解档和归档方法:[super encodeWithCoder: coder];
和[super initWithCoder: coder];
其实还可以使用MJExtension第三方库实现解归档,这样就可以不用写复杂的NSCoding协议
,只需要一行代码调用写好的宏MJExtensionCodingImplementation就可以实现
MJExtension也和JSONModel、YYModel一样,支持 JSON数据<->Model
的转换同时也支持解归档,它们在代码量级上、性能优化上各有优缺点,详见这篇文章:
【YYModel,MJExtension,JSONModel对比】
具体的学习,小编日后了解!