将数据写入本地

在iOS中一般将数据写入本地, 可以分为两大类第一类是简单对象另一类是复杂对象对于简单对象我们直接进行写入和获取就可以对于复杂对象我们利用的是归档和反归档(归档和反归档是对于复杂对象的存储和获取)

要将数据写入本地首先我们先来了解一下沙盒(SandBox)
沙盒中包含三个文件夹:

Document(文件文档用来给用户存储数据的文件夹)
Library(资源程序员用这个文件夹存储数据信息)
Library文件夹又包含两个文件夹:
CaChes(缓存数据的文件夹)
Preferences(存储用户信息的例如; NSUserDefaults)
tmp(临时目录下载的临时文件)

沙盒是由以上三个文件夹组成的其中Document文件夹就是用户用来存储数据用的用户将可以将数据存放到这个文件夹里

下面我们来用沙盒存储数据:

简单数据的存储(字符串数组字典 NSData)
// 字符串的存储
// 1. 创建沙盒路径
NSArray *pathArray = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
// 2. 创建一个字符串将这个字符串存到沙盒中
NSString *str = @"离别是今晚的康桥, I/O file";
// 3. 拼接字符串路径
NSString *path = [[pathArray firstObject] stringByAppendingPathComponent:@"poet.txt"];
NSError *error = nil;
// 4. 将字符串写入本地
BOOL isSuc = [str writeToFile:path atomically:YES encoding:NSUTF8StringEncoding error:&error];
if (isSuc) {
NSLog(@"存储失败");
} else {
NSLog(@"存储成功");
}
// 5. 读取字符串
NSError *readError = nil;
NSString *readStr = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:&readError];
NSLog(@"%@", readStr);

// 将数组写入本地
// 这里 我们就用之前创建的沙盒来做就可以
NSArray *array = @[@"十年", @"陀飞轮", @"十面埋伏", @"遥远的她"];
// 拼接数组路径
NSString *arrayPath = [[pathArray firstObject]stringByAppendingPathComponent:@"musicName.plist"];
// 将数组写入本地
BOOL isSuce = [array writeToFile:arrayPath atomically:YES];
if (isSuce) {
 NSLog(@"存储失败");
} else {
 NSLog(@"存储成功");
}
// 读取数组
NSArray *array1 = [NSArray arrayWithContentsOfFile:arrayPath];
NSLog(@"%@", array1);

// 字典写入本地
NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"十年", @"陈奕迅", @"大地", @"beyond", @"可乐", @"赵", nil];
// 拼接字典路径
NSString *dicPath = [[pathArray firstObject] stringByAppendingPathComponent:@"music.plist"];
// 将字典写入本地
BOOL isDic = [dic writeToFile:dicPath atomically:YES];
if (isDic) {
 NSLog(@"存储成功");
} else {
 NSLog(@"存储失败");
}
// 读出字典
NSDictionary *secDic = [NSDictionary dictionaryWithContentsOfFile:dicPath];
NSLog(@"%@", secDic);

// 将NSData类型写入本地
UIImage *image = [UIImage imageNamed:@"u=881185622,577705802&fm=206&gp=0"];
// 需要将图转化为二进制(NSData类型)
// UIImageJPEGRepresentation  UIImagePNGRepresentation(<#UIImage * _Nonnull image#>)
NSData *imageData = UIImageJPEGRepresentation(image, 0.1);
// 拼接路径
NSLog(@"%@", imageData);
NSString *dataPath = [[pathArray firstObject] stringByAppendingPathComponent:@"image.a"];
// 写入本地
BOOL isData = [imageData writeToFile:dataPath atomically:YES];
if (isData) {
 NSLog(@"写入成功");
} else {
 NSLog(@"写入失败");
}
// 读取NSData
NSData *newData = [NSData dataWithContentsOfFile:dataPath];
UIImage *newImage = [UIImage imageWithData:newData];
NSLog(@"%@", newImage);

总结一下通过上面将数据写入本地的例子可以看出简单数据写入本地主要分为这几步:
(1) 创建沙盒路径
(2) 创建一个你要存储的对象
(3) 拼接路径
(4) 写入本地
(5) 从本地读取数据

下面来说一下怎么将复杂对象存储到本地所谓复杂对象就是指在实际应用中我们用到的model数据将复杂数据存储到本地要用到归档将复杂数据从本地中读出来要用到反归档
1 我们创建一个自定义的类(继承与 NSObject)

#import <Foundation/Foundation.h>
// 1. 将需要归档的类  签订协议 签订   NSCoding协议         

@interface Book : NSObject   <NSCoding>

@property (nonatomic, copy)   NSString *bookName;
@property (nonatomic, copy) NSString *bookPrice;
@property (nonatomic, copy) NSString *writer;
@property (nonatomic, copy) NSString *bookAddress;
@property (nonatomic, copy) NSString *bookType;

@end


#import "Book.h"

@implementation Book
// 2. 签订协议后 必须实现 下面两个方法
// 初始化是 读取数据的
- (instancetype)initWithCoder:(NSCoder *)aDecoder {
self = [super init];
if (self) {
    _bookName = [aDecoder decodeObjectForKey:@"bookName"];
    _bookPrice = [aDecoder decodeObjectForKey:@"bookPrice"];
    _writer = [aDecoder decodeObjectForKey:@"writer"];
    _bookAddress = [aDecoder decodeObjectForKey:@"bookAddress"];
    _bookType = [aDecoder decodeObjectForKey:@"bookType"];
}
return self;
}
// 写入数据的方法 赋值
- (void)encodeWithCoder:(NSCoder *)aCoder {
[aCoder encodeObject:_bookName forKey:@"bookName"];
[aCoder encodeObject:_bookPrice forKey:@"bookPrice"];
[aCoder encodeObject:_writer forKey:@"writer"];
[aCoder encodeObject:_bookAddress forKey:@"bookAddress"];
[aCoder encodeObject:_bookType forKey:@"bookType"];
}



@end


Book *book = [Book new];
book.bookName = @"傲慢与偏见";
book.bookPrice = @"18.5";
book.writer = @"josejjs";
book.bookType = @"story";
book.bookAddress = @"English";

NSString *bookPath = [[pathArray firstObject] stringByAppendingPathComponent:@"book.plist"];
BOOL isBook = [NSKeyedArchiver archiveRootObject:book toFile:bookPath];
if (isBook) {
    NSLog(@"写入成功");
} else {
    NSLog(@"写入失败");
}

// 2. 反归档(取出对象 反归档走的是初始化)
Book *book1 = [NSKeyedUnarchiver unarchiveObjectWithFile:bookPath];
NSLog(@"%@", book1.bookName);