Objective-C学习篇第九弹:归档与解档

Foundation框架的归档功能

将对象存储转换为二进制序列的过程成为归档、打包或编码，逆变换称为解档、解码或对象还原。

可以使用NSKeyedArchiver和NSKeyedUnarchiver完成对象的归档和解档操作，而他们都是抽象类NSCoder的子类。

所有可以归档的对象都必须要适用于协议NSCoding。协议NSCoding在Foundation/NSObject.h中定义，NSObject自身并不采用该协议。NSString、NSDictionary等Foundation框架的主要类都适用协议NSCoding。

协议NSCoding按照如下方式声明:

@protocol NSCoding

- (void)encodeWithCoder:(NSCoder *)coder
- (id)initWithCoder:(NSCoder *)coder

归档方法的定义

协议NSCoding中，函数encodeWithCoder：定义了归档自身的方法。

- (void)encodeWithCoder:(NSCoder *)coder
{
[super encodeWithCoder:coder];
//超类需要适用NSCoding协议
[coder encodeObject:对象 forKey:关键词字符串];
[coder encodeInt:实数变量 forKey:关键词字符串];
}

如果超类不适用协议NSCoding，则不能调用encodeWithCoder：方法。

类自身对包含的实例变量归档。在类没有自己的实例变量且超类中定义了方法encodeWithCoder：的情况下，该方法就不需要在定义了。

通过使用NSString字符串作为键值，可以指定归档解档的内容。让某个类实例归档时，它的实例变量必须指定成不同的键值。在单个对象内部，如果超类使用了一个键值，那么子类中就不能使用该键值。键值只需在同一个类内区分出来即可，不同的类可使用相同的键值。

当对象图有闭环时，同一个对象会重复要求归档，实际上已归档的对象是不用重复归档的。

解档方法的定义

- (instancetype)initWithCoder:(NSCoder *)coder
{
self = [super initWithCoder:coder];
//超类不适应于协议NSCoding时，
//建议使用 self = [super init];
if (self) {
self.name = [coder decodeObjectForKey: 键值];
self.age = [coder decodeIntForKey: 键值];
}
return self;
}

归档示例程序:

main.m

#import <Foundation/Foundation.h>
#import "Person.h"

int main(int argc, const char * argv[]) {

@autoreleasepool {
Person * p = [[Person alloc] init];
p.name = @"lu";
p.age = 18;
p.weight = 100.0;

BOOL isSuccess = [NSKeyedArchiver archiveRootObject:p toFile:@"/Users/lu/Desktop/test.plist"];
if (isSuccess) {
NSLog(@"归档成功");
} else {
NSLog(@"归档失败");
}
}
return 0;

}

解档示例程序：

main.m

int main(int argc, const char * argv[]) {
@autoreleasepool {

//解档
Person * p = [NSKeyedUnarchiver unarchiveObjectWithFile:@"/Users/lu/Desktop/test.plist"];
NSLog(@"%@",p.name);
NSLog(@"%d",p.age);
NSLog(@"%f",p.weight);

}
return 0;
}

若类中实例变量为其他类对象，则还需要在其他类中实现encodeWithCoder：和initWithCoder：方法。

示例程序:

Dog.m

#import "Dog.h"

@implementation Dog

- (void)encodeWithCoder:(NSCoder *)coder
{
[coder encodeObject:self.name forKey:@"name"];
[coder encodeInt:self.age forKey:@"age"];
}

- (instancetype)initWithCoder:(NSCoder *)coder
{
self = [super init];
if (self) {
self.name = [coder decodeObjectForKey:@"name"];
self.age = [coder decodeIntForKey:@"age"];
}
return self;
}
@end

student.m

#import "Student.h"
#import "Dog.h"

@implementation Student

//归档
- (void)encodeWithCoder:(NSCoder *)coder
{
[coder encodeObject:self.name forKey:@"name"];
[coder encodeInt:self.score forKey:@"score"];
[coder encodeInt:self.number forKey:@"number"];
[coder encodeObject:self.dog forKey:@"dog"];
}
//解档
- (instancetype)initWithCoder:(NSCoder *)coder
{
self = [super init];
if (self) {
self.name = [coder decodeObjectForKey:@"name"];
self.score = [coder decodeIntForKey:@"score"];
self.number = [coder decodeIntForKey:@"number"];
self.dog = [coder decodeObjectForKey:@"dog"];
}
return self;
}

@end

main.m

int main(int argc, const char * argv[]) {

@autoreleasepool {

Student * stu = [[Student alloc] init];
stu.name = @"di";
stu.score = 70;
stu.number = 20;

Dog * d = [[Dog alloc] init];
d.name = @"Chen";
d.age = 10;
stu.dog = d;
//归档
BOOL isSuccess = [NSKeyedArchiver archiveRootObject:stu toFile:@"/Users/lu/Desktop/Stu.txt"];
if (isSuccess) {
NSLog(@"Yes");
}
else {
NSLog(@"NO");
}
//解档
Student * stu3 = [NSKeyedUnarchiver unarchiveObjectWithFile:@"/Users/lu/Desktop/Stu.txt"];
NSLog(@"%@", stu3.name);
NSLog(@"%d", stu3.score);
NSLog(@"%d", stu3.number);
NSLog(@"%@", stu3.dog.name);
NSLog(@"%d", stu3.dog.age);

}
return 0;
}

对多个对象进行归档，可以先将多个对象存储于NSArray、NSMutableArray、NSDictionary或NSMutableDictionary中，再进行归档。

示例程序：

NSArray * stuArray = @[stu, stu1, stu2];
BOOL isSuccess = [NSKeyedArchiver archiveRootObject:stuArray toFile:@"/Users/lu/Desktop/stuArray.txt"];
if (isSuccess) {
NSLog(@"Yes");
}
else {
NSLog(@"NO");
}

最后一种方式利用NSData对多个对象进行归档解档

示例程序

main.m

#import <Foundation/Foundation.h>
#import "Person.h"

int main(int argc, const char * argv[]) {
@autoreleasepool {

Person * p = [[Person alloc] init];
p.name = @"dou";
p.age = 22;
p.weight = 120.00;

Person * p2 = [[Person alloc] init];
p2.name = @"dashu";
p2.age = 24;
p2.weight = 140.3;

NSMutableData * data = [NSMutableData data];

//        根据二进制流创建NSkeyedArchiver对象
NSKeyedArchiver * archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
//        对对象进行归档操作
[archiver encodeObject:p forKey:@"person1"];
[archiver encodeObject:p2 forKey:@"person2"];
//        结束归档
/*** -[NSKeyedArchiver dealloc]: warning: NSKeyedArchiver deallocated without having had -finishEncoding called on it.
归档如果没有结束 finishEncoding就不会归档成功，产生文件无法打开    The data couldn't be read because it isn't in the correct format.
*/
[archiver finishEncoding];

BOOL isSuccess = [data writeToFile:@"/Users/lu/Desktop/Data.plist" atomically:YES];
if (isSuccess) {
NSLog(@"归档成功！");
} else {
NSLog(@"归档失败");
}

//解档
NSData * data = [NSData dataWithContentsOfFile:@"/Users/lu/Desktop/Data.plist"];
NSKeyedUnarchiver * unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
Person * p = [unarchiver decodeObjectForKey:@"person1"];
Person * p2 = [unarchiver decodeObjectForKey:@"person2"];
//结束解档 解档没有finishDecoding无影响
//        [unarchiver finishDecoding];
NSLog(@"%@", p.name);
NSLog(@"%d", p.age);
NSLog(@"%f", p.weight);

NSLog(@"%@", p2.name);
NSLog(@"%d", p2.age);
NSLog(@"%f", p2.weight);
}
return 0;
}

总结

这一篇文章我们就说了OC中的归档和解档的相关概念和操作，其实说白了就是将对象写入到文件，和从文件中读取对象。