对模型对象进行归档

FourLines.h

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>


@interface FourLines : NSObject <NSCoding,NSCopying>{
    NSString *field1;
    NSString *field2;
    NSString *field3;
    NSString *field4; 
}

@property (nonatomic,retain)NSString *field1;
@property (nonatomic,retain)NSString *field2;
@property (nonatomic,retain)NSString *field3;
@property (nonatomic,retain)NSString *field4;

@end

FourLines.m

#import "FourLines.h"

#define kField1Key    @"Field1"
#define kField2Key    @"Field2"
#define kField3Key    @"Field3"
#define kField4Key    @"Field4"

@implementation FourLines

@synthesize field1;
@synthesize field2;
@synthesize field3;
@synthesize field4;

/**
 将对象编码到文档中
 */
#pragma mark NSCoding
-(void)  encodeWithCoder:(NSCoder *)enCoder{
    
    [enCoder encodeObject:field1 forKey:kField1Key];
    [enCoder encodeObject:field2 forKey:kField2Key];
    [enCoder encodeObject:field3 forKey:kField3Key];
    [enCoder encodeObject:field4 forKey:kField4Key];
}

/**
 通过对文档进行解码来常见一个新对象。
 */
-(id)initWithCoder:(NSCoder *)decoder{
    if (self = [super init]) {
        field1 = [[decoder decodeObjectForKey:kField1Key] retain];
        field2 = [[decoder decodeObjectForKey:kField2Key] retain];
        field3 = [[decoder decodeObjectForKey:kField3Key] retain];
        field4 = [[decoder decodeObjectForKey:kField4Key] retain];
    }
    return self;
}

#pragma mark -
#pragma mark NSCopying
-(void)copyWithZone:(NSZone *)zone{
    FourLines *copy = [[[self class] allocWithZone:zone] init ];
    copy.field1 = [[self.field1 copyWithZone:zone] autorelease];
    copy.field2 = [[self.field2 copyWithZone:zone] autorelease];
    copy.field3 = [[self.field3 copyWithZone:zone] autorelease];
    copy.field4 = [[self.field4 copyWithZone:zone] autorelease];
    
    return copy;
}
@end

PersistenceViewController.h

#import <UIKit/UIKit.h>

#define kFileName    @"data.list"
#define kFileName    @"archive"
#define kDataKey    @"Data"

@interface PersistenceViewController : UIViewController {
    UITextField *field1;
    UITextField *field2;
    UITextField *field3;
    UITextField *field4;
}
@property (nonatomic,retain)IBOutlet UITextField *field1;
@property (nonatomic,retain)IBOutlet UITextField *field2;
@property (nonatomic,retain)IBOutlet UITextField *field3;
@property (nonatomic,retain)IBOutlet UITextField *field4;

- (NSString *)dataFilePath;
-(void)applicationWillResignActive:(NSNotification *)notification;

@end

PersistenceViewController.m

#import "PersistenceViewController.h"
#import "FourLines.h"

@implementation PersistenceViewController
@synthesize field1;
@synthesize field2;
@synthesize field3;
@synthesize field4;

//用于返回数据文件的完整路径名，它通过查找Document目录并对对其附加kFilename累执行该操作。
-(NSString *)dataFilePath{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    return [documentsDirectory stringByAppendingFormat:kFileName];
}

#pragma mark -

/*
// The designated initializer. Override to perform setup that is required before the view is loaded.
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}
*/

/*
// Implement loadView to create a view hierarchy programmatically, without using a nib.
- (void)loadView {
}
*/



// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
//在该方法中，我们做了一下操作
/**
    1,检查数据文件是否存在
    2，数据文件存在，使用该引用订阅UIApplicationWillReSignActiveNotification.
    3,我们使用NSNotificationCenter的默认实例，以及addObserver：select：name：object方法。我们传递一个observer即self、这就意味着
 PersistenceViewController是需要通知的对象。
 */
- (void)viewDidLoad {
    NSString *filePath = [self dataFilePath];
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
        NSArray *array = [[NSArray alloc] initWithContentsOfFile:filePath];
        field1.text = [array objectAtIndex:0];
        field2.text = [array objectAtIndex:1];
        field3.text = [array objectAtIndex:2];
        field4.text = [array objectAtIndex:3];
        
        [array release];
        
        NSData *data = [[NSMutableData alloc] initWithContentsOfFile:[self dataFilePath]];
        
        NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
        
        FourLines *fourLine = [unarchiver decodeObjectForKey:kDataKey];
        
        [unarchiver finishDecoding];
        
        field1.text = fourLine.field1;
        field2.text = fourLine.field2;
        field3.text = fourLine.field3;
        field4.text = fourLine.field4;
        
        [unarchiver release];
        [data release];
        
    }
    
    UIApplication *app = [UIApplication sharedApplication];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(applicationWillResignActive:)
                                            name:UIApplicationWillResignActiveNotification
                                               object:app];
    [super viewDidLoad];
}

/**
    
 */
-(void)applicationWillResignActive:(NSNotification *)notification{
    NSMutableArray *array = [[NSMutableArray alloc] init ];
    [array addObject:field1.text];
    [array addObject:field2.text];
    [array addObject:field3.text];
    [array addObject:field4.text];
    
    [array writeToFile: [self dataFilePath] atomically:YES];
    [array release];
    
    FourLines *fourLine = [[FourLines alloc] init];
    fourLine.field1 = field1.text;
    fourLine.field2 = field2.text;
    fourLine.field3 = field3.text;
    fourLine.field4 = field4.text;
    
    NSMutableData *data = [[NSMutableData alloc] init];
    NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
    [archiver encodeObject:fourLine
                    forKey:kDataKey];
    [archiver finishEncoding];
    [data writeToFile:[self dataFilePath] atomically:YES];
    [fourLine release];
    [archiver release];
    [data release];
    
}



/*
// Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
*/

- (void)didReceiveMemoryWarning {
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];
    
    // Release any cached data, images, etc that aren't in use.
}

- (void)viewDidUnload {
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
    self.field1 = nil;
    self.field2 = nil;
    self.field3 = nil;
    self.field4 = nil;
    [super viewDidUnload];
}


- (void)dealloc {
    [field1 release];
    [field2 release];
    [field3 release];
    [field4 release];
    [super dealloc];
}

@end