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。