iOS中有五種持久化數據的方式：屬性列表、對象歸檔、NSUserDefault、SQLite3和Core Data

本文章講述通過屬性列表的方式持久化數據，這個方法也是我們平時最經常用到的方式。比如應用程序的配置和個性化的設置，一般都是通過屬性列表（properties list） plist文件來存儲和讀取的。   [objc]   FOUNDATION_EXPORT NSArray *NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory directory, NSSearchPathDomainMask domainMask, BOOL expandTilde);   這個函數的作用：創建一個目錄搜索路徑的列表。 創建一個路徑字符串列表指定域中指定的目錄。列表中的順序，你應該搜索目錄。 PS： 通過此方法返回的目錄可能不存在。這種方法只是給你請求目錄的適當位置。根據應用的需求，它可能是開發者創建合適的目錄或者在任何兩者之間。 下面是一個把數據以plist的形式保存到本地的自定義類 [objc]  //   //  Plist.h   //  PlistDemo   //   //  Created by swplzj on 13-11-20.   //  Copyright (c) 2013年 swplzj. All rights reserved.   //      #import <Foundation/Foundation.h>      @interface Plist : NSObject      - (void)modifyData:(NSString *)dataKey Value:(NSString *)dataValue;   - (void)deleteDataWithDataKey:(NSString *)key;      @end     [objc]  //   //  Plist.m   //  PlistDemo   //   //  Created by swplzj on 13-11-20.   //  Copyright (c) 2013年 swplzj. All rights reserved.   //      #import "Plist.h"      @implementation Plist      - (id)init   {       if (self = [super init]) {           NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);           //獲取完整路徑           NSString *documentsDirectory = [paths objectAtIndex:0];           NSLog(@"homeDirectory = %@", documentsDirectory);           NSString *plistPath = [documentsDirectory stringByAppendingPathComponent:@"student.plist"];           //判斷是否已經創建文件           if ([[NSFileManager defaultManager] fileExistsAtPath:plistPath]) {               NSLog(@"student.plist文件已經存在！");           }else {               //plist文件沒有被創建               NSMutableDictionary *rootDic = [[NSMutableDictionary alloc] init];               NSMutableDictionary *subDic = [[NSMutableDictionary alloc] init];               [rootDic setObject:subDic forKey:@"student"];               [subDic release];               //寫入到文件               [rootDic writeToFile:plistPath atomically:YES];               [rootDic release];           }       }              return self;   }      //把數據寫入到plist文件中   - (void)modifyData:(NSString *)dataKey Value:(NSString *)dataValue   {       //獲取路徑       NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:@"student.plist"];       NSMutableDictionary *rootDic = [[[NSMutableDictionary alloc] initWithContentsOfFile:path] mutableCopy];       NSMutableDictionary *studentInfo = [rootDic objectForKey:@"student"];       NSString *name = [studentInfo objectForKey:dataKey];       name = dataValue;       [studentInfo setValue:name forKey:dataKey];       //寫入到文件       [rootDic writeToFile:path atomically:YES];       NSLog(@"Key - Value: %@ - %@",dataKey, dataValue );       [rootDic release];   }      //根據key來刪除某一行的數據   - (void)deleteDataWithDataKey:(NSString *)key   {       //獲取路徑       NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:@"student.plist"];       NSMutableDictionary *rootDic = [[[NSMutableDictionary alloc] initWithContentsOfFile:path] mutableCopy];       NSMutableDictionary *studentInfo = [rootDic objectForKey:@"student"];       [studentInfo removeObjectForKey:key];       NSLog(@"Delete data key - value: %@ - %@", key, [studentInfo objectForKey:key]);       [rootDic setValue:studentInfo forKey:@"student"];       //寫入到文件       [rootDic writeToFile:path atomically:YES];       [rootDic release];   }      @end     在RootViewController裡面的代碼 [objc]  //   //  RootViewController.m   //  PlistDemo   //   //  Created by swplzj on 13-11-20.   //  Copyright (c) 2013年 swplzj. All rights reserved.   //      #import "RootViewController.h"   #import "Plist.h"      @interface RootViewController ()      @property (retain, nonatomic) Plist *plistFile;      @property (retain, nonatomic) IBOutlet UITextField *keyTF;   @property (retain, nonatomic) IBOutlet UITextField *valueTF;   @property (retain, nonatomic) IBOutlet UITextField *deleteKeyTF;   @end      @implementation RootViewController      - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil   {       self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];       if (self) {           // Custom initialization       }       return self;   }      - (void)viewDidLoad   {       [super viewDidLoad];       // Do any additional setup after loading the view from its nib.       _plistFile = [[Plist alloc] init];   }      - (void)didReceiveMemoryWarning   {       [super didReceiveMemoryWarning];       // Dispose of any resources that can be recreated.   }      - (IBAction)addOrModifyBtnClicked:(id)sender {       if (![_keyTF.text isEqualToString:@""] && ![_valueTF.text isEqualToString:@""]) {           [_plistFile modifyData:_keyTF.text Value:_valueTF.text];        }   }      - (IBAction)deleteBtnClicked:(id)sender {       if (![_deleteKeyTF.text isEqualToString:@""]) {           [_plistFile deleteDataWithDataKey:_deleteKeyTF.text];       }   }      - (void)dealloc {       [_plistFile release];       [_keyTF release];       [_valueTF release];       [_deleteKeyTF release];       [super dealloc];   }   @end