NSUserDefaults適合存儲輕量級的本地數據,比如要保存一個登陸界面的數據,用戶名、密碼之類的,個人覺得使用NSUserDefaults是首選。下次再登陸的時候就可以直接從NSUserDefaults裏面讀取上次登陸的信息咯。
因爲如果使用自己建立的plist文件什麼的,還得自己顯示創建文件,讀取文件,很麻煩,而是用NSUserDefaults則不用管這些東西,就像讀字符串一樣,直接讀取就可以了。
NSUserDefaults支持的數據格式有:NSNumber(Integer、Float、Double),NSString,NSDate,NSArray,NSDictionary,BOOL類型。很實用吧
NSUserDefaults很方便,讀取也很容易。下面給出一個示例看看如何使用:(PS:更詳細的也可以參考官方文檔哈)
ViewController.h文件中主要是放幾個控件,用於顯示存儲的數據:
- #import <UIKit/UIKit.h>
- @interface ViewController : UIViewController
- {
- IBOutlet UILabel *txtInteger;
- IBOutlet UILabel *txtFloat;
- IBOutlet UILabel *txtDouble;
- IBOutlet UILabel *txtNSString;
- IBOutlet UILabel *txtNSDate;
- IBOutlet UILabel *txtNSArray;
- IBOutlet UILabel *txtNSDictionary;
- }
- @end
saveNSUserDefaults:用於將各種類型數據保存到NSUserDefaults中
readNSUserDefautls:用於從NSUserDefaults中讀取各種類型的數據。在viewDidLoad中調用這兩個方法就可以看出結果咯
- #import "ViewController.h"
- @interface ViewController ()
- @end
- @implementation ViewController
- - (void)viewDidLoad
- {
- [super viewDidLoad];
- [self saveNSUserDefaults]; //調用此方法將各種數據存儲到NSUserDefautls中,在下面定義
- [self readNSUserDefaults]; //調用此方法從NSUserDefautls中讀取各種數據,在下面定義
- }
- - (void)viewDidUnload
- {
- [txtNSString release];
- txtNSString = nil;
- [txtNSDate release];
- txtNSDate = nil;
- [txtNSArray release];
- txtNSArray = nil;
- [txtNSDictionary release];
- txtNSDictionary = nil;
- [txtInteger release];
- txtInteger = nil;
- [txtFloat release];
- txtFloat = nil;
- [txtDouble release];
- txtDouble = nil;
- [super viewDidUnload];
- // Release any retained subviews of the main view.
- }
- - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
- {
- return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
- }
- - (void)dealloc {
- [txtNSString release];
- [txtNSDate release];
- [txtNSArray release];
- [txtNSDictionary release];
- [txtInteger release];
- [txtFloat release];
- [txtDouble release];
- [super dealloc];
- }
- //保存數據到NSUserDefaults
- -(void)saveNSUserDefaults
- {
- NSString *myString = @"enuola";
- int myInteger = 100;
- float myFloat = 50.0f;
- double myDouble = 20.0;
- NSDate *myDate = [NSDate date];
- NSArray *myArray = [NSArray arrayWithObjects:@"hello", @"world", nil];
- NSDictionary *myDictionary = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"enuo", @"20", nil] forKeys:[NSArray arrayWithObjects:@"name", @"age", nil]];
- //將上述數據全部存儲到NSUserDefaults中
- NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
- //存儲時,除NSNumber類型使用對應的類型意外,其他的都是使用setObject:forKey:
- [userDefaults setInteger:myInteger forKey:@"myInteger"];
- [userDefaults setFloat:myFloat forKey:@"myFloat"];
- [userDefaults setDouble:myDouble forKey:@"myDouble"];
- [userDefaults setObject:myString forKey:@"myString"];
- [userDefaults setObject:myDate forKey:@"myDate"];
- [userDefaults setObject:myArray forKey:@"myArray"];
- [userDefaults setObject:myDictionary forKey:@"myDictionary"];
- //這裏建議同步存儲到磁盤中,但是不是必須的
- [userDefaults synchronize];
- }
- //從NSUserDefaults中讀取數據
- -(void)readNSUserDefaults
- {
- NSUserDefaults *userDefaultes = [NSUserDefaults standardUserDefaults];
- //讀取數據到各個label中
- //讀取整型int類型的數據
- NSInteger myInteger = [userDefaultes integerForKey:@"myInteger"];
- txtInteger.text = [NSString stringWithFormat:@"%d",myInteger];
- //讀取浮點型float類型的數據
- float myFloat = [userDefaultes floatForKey:@"myFloat"];
- txtFloat.text = [NSString stringWithFormat:@"%f",myFloat];
- //讀取double類型的數據
- double myDouble = [userDefaultes doubleForKey:@"myDouble"];
- txtDouble.text = [NSString stringWithFormat:@"%f",myDouble];
- //讀取NSString類型的數據
- NSString *myString = [userDefaultes stringForKey:@"myString"];
- txtNSString.text = myString;
- //讀取NSDate日期類型的數據
- NSDate *myDate = [userDefaultes valueForKey:@"myDate"];
- NSDateFormatter *df = [[NSDateFormatter alloc] init];
- [df setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
- txtNSDate.text = [NSString stringWithFormat:@"%@",[df stringFromDate:myDate]];
- //讀取數組NSArray類型的數據
- NSArray *myArray = [userDefaultes arrayForKey:@"myArray"];
- NSString *myArrayString = [[NSString alloc] init];
- for(NSString *str in myArray)
- {
- NSLog(@"str= %@",str);
- myArrayString = [NSString stringWithFormat:@"%@ %@", myArrayString, str];
- [myArrayString stringByAppendingString:str];
- // [myArrayString stringByAppendingFormat:@"%@",str];
- NSLog(@"myArrayString=%@",myArrayString);
- }
- txtNSArray.text = myArrayString;
- //讀取字典類型NSDictionary類型的數據
- NSDictionary *myDictionary = [userDefaultes dictionaryForKey:@"myDictionary"];
- NSString *myDicString = [NSString stringWithFormat:@"name:%@, age:%d",[myDictionary valueForKey:@"name"], [[myDictionary valueForKey:@"age"] integerValue]];
- txtNSDictionary.text = myDicString;
- }
- @end
好了,運行一下,可以看到xib文件中的各種數據已經綁定上了吧?
再次運行的時候,可以把viewDidLoad中的 [self saveNSUserDefaults]; 這一行註釋掉,讓程序直接讀取而不存儲數據,發現以前保存的數據仍然可以讀取到界面上。
嘻嘻,很簡單吧,就這樣就可以是實現數據的存儲了。
下面講一下原理:
你可能會問一個問題:NSUserDefautls將數據存儲在什麼地方了???我都沒有顯示的指定路徑???很疑惑吧。。。。
用NSUserDefaults存儲的數據下次程序運行的時候依然存在,它把數據存儲在什麼地方了?如何能夠清除?
/UsersLibrary/Application Support/iPhoneSimulator/4.1/Applicati*****/29788E40-AF47-45A0-8E92-3AC0F501B7F4/,(這個是應用程序對應在mac上的位置)
這個下面有/Library/Prefereces,裏面有個plist文件,存儲的就是你的userDefaults
想要刪掉的話,用removeObjectForKey或者刪掉沙盒,也就是你的應用程序然後重新安裝。