iPhone开发数据持久化总结之第2篇—属性文件（.plist） .

实现的功能：1）演示使用属性文件持久化数据。

关键词：数据持久化 属性文件 plist


1、新建一个Sigle View Application，命名为Persistence-file，工程结构如下

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[img]http://dl.iteye.com/upload/attachment/0078/7419/3a9fb508-d179-3c27-9bea-6d86d22f3818.png[/img]
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2、修改ViewController.xib，添加4个Label控件和4个TextField控件，如下：

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[img]http://dl.iteye.com/upload/attachment/0078/7421/bf642f94-20dd-3752-8ea3-e1d7d3b748e1.png[/img]
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3、修改ViewController.h，如下：

#define kFileName @"data.plist"
#import <UIKit/UIKit.h>

@interface ViewController : UIViewController
@property(nonatomic,retain)IBOutlet UITextField *name;
@property(nonatomic,retain)IBOutlet UITextField *gender;
@property(nonatomic,retain)IBOutlet UITextField *age;
@property(nonatomic,retain)IBOutlet UITextField *education;

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

@end

注意，需要连接各个输出口


4、修改ViewController.m，如下：

#import "ViewController.h"

@implementation ViewController
@synthesize name,gender,age,education;

#pragma mark - View lifecycle
- (void)viewDidLoad
{
	// Do any additional setup after loading the view, typically from a nib.
    [super viewDidLoad];
    UIApplication *app = [UIApplication sharedApplication];
    //订阅通知UIApplicationWillResignActiveNotification，进行数据保存操作
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationWillResignActive:) name:UIApplicationWillResignActiveNotification object:app];
    //初始化数据
    [self initData];
}

-(void)initData{
    NSString *filePath = [self dataFilePath];
    NSLog(@"filePath=%@",filePath);

    //从文件中读取数据，首先判断文件是否存在
    if([[NSFileManager defaultManager] fileExistsAtPath:filePath]){
        NSArray *array = [[NSArray alloc]initWithContentsOfFile:filePath];
        name.text = [array objectAtIndex:0];
        gender.text = [array objectAtIndex:1];
        age.text = [array objectAtIndex:2];
        education.text = [array objectAtIndex:3];

        [array release];
    }
}

-(void)applicationWillResignActive:(NSNotification *)nofication{
    NSMutableArray *array = [[NSMutableArray alloc]init];
    [array addObject:name.text];
    [array addObject:gender.text];
    [array addObject:age.text];
    [array addObject:education.text];
    //将数据写入到文件dataFilePath中
    [array writeToFile:[self dataFilePath] atomically:YES];
    [array release];
}

//获得文件路径
-(NSString *)dataFilePath{
    //检索Documents目录
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask,YES);//备注1
    NSString *documentsDirectory = [paths objectAtIndex:0];//备注2
    return [documentsDirectory stringByAppendingPathComponent:kFileName];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
    self.name = nil;
    self.gender = nil;
    self.age = nil;
    self.education = nil;
}

-(void)dealloc{
    [name release];
    [gender release];
    [age release];
    [education release];
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
	[super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
	[super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end

备注1、备注2：
NSDocumentDirectory:常量，表明正在查找Documents目录的路径
NSUserDomainMask:常量，表面将搜索限制与当前应用程序的沙盒中，这样的话只能找到一个Documents目录，因为每个应用程序沙盒中只有一个Documents目录，所以备注2中从paths中取第一个即为当前应用程序的Documents目录的路径


5、编译、运行，在TextField中输入内容，然后退出Simulator，进行测试：

[img]
[img]http://dl.iteye.com/upload/attachment/0078/7423/a97c5739-4ece-3f7d-802a-ce6b070bd92c.png[/img]
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[img]http://dl.iteye.com/upload/attachment/0078/7425/8c8ba656-2068-3208-b29a-d8e3f6e3bfbc.png[/img]
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6、通过上一篇对IOS应用程序沙盒的的介绍，本工程属性文件data.plist，保存的位置是：

/Users/duobianxing/Library/Application Support/iPhone Simulator/5.0/Applications/88528A36-00CB-4900-9762-1FD5D6AC8595/Documents

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[img]http://dl.iteye.com/upload/attachment/0078/7427/05d588f8-af3d-36fa-a5ef-3eeeb2e540c8.png[/img]
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7、总结：

1）可以简单保存静态数据，但是无法将自定义对象序列化到属性列表中

2）该持久化方法与上一篇中介绍的NSUserDefaults实质上都是将数据写入到.plist属性文件中，区别是文件保存的位置不同。