从NSUserDefaults返回的值是不可改变的,即便是你在存储的时候使用的是可变的值。例如你使用mutablestring做为“MyStringDefault”的值,当你做使用stringForKey:方法获取的值,这个值仍然是不可变的。
NSUserDefaults是单例,同时也是线程安全的
在使用NSUserDefaults的时候,
先看下下面的代码
NSDictionary* defaults = [[NSUserDefaults standardUserDefaults]dictionaryRepresentation];
NSLog(@"Defaults: %@", defaults);
是用来获取设备上的所有的NSUserDefaults的设置。
上面代码输出了
Defaults: {
AppleITunesStoreItemKinds= (
eBook,
document,
"software-update",
booklet,
"itunes-u",
newsstand,
artist,
podcast,
"podcast-episode",
software
);
AppleKeyboards= (
"zh_Hans-Pinyin@sw=Pinyin;hw=US",
"en_US@hw=US;sw=QWERTY"
);
AppleKeyboardsExpanded= 1;
AppleLanguages= (
"zh-Hans",
en,
fr,
de,
ja,
nl,
it,
es,
pt,
"pt-PT",
da,
fi,
nb,
sv,
ko,
"zh-Hant",
ru,
pl,
tr,
uk,
ar,
hr,
cs,
el,
he,
ro,
sk,
th,
id,
"en-GB",
ca,
hu,
vi
);
如果想单独看某个key的设置,例如:
NSArray *array = [[NSUserDefaults standardUserDefaults]objectForKey:@"AppleKeyboards"];
NSLog(@"Keyboards: %@", array);
会输出
AppleKeyboards= (
"zh_Hans-Pinyin@sw=Pinyin;hw=US",
"en_US@hw=US;sw=QWERTY"
);
在看下面的代码
if([[NSUserDefaults standardUserDefaults]objectForKey:@"message"]==nil){
[[NSUserDefaults standardUserDefaults]setObject:@"This_is_my_default_message" forKey:@"message"];
}
代码意思是判断NSUserDefaults的“message”key 在dictionaryRepresentation中是否存在,如果不存在就
设置“message”key为This_is_my_default_message。
在加上句[[NSUserDefaultsstandardUserDefaults] synchronize];,这样这个设置就存到默认参数中了。
也见过别人把默认参数的设置写到applicationDidFinishLaunching注册的,
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
NSDictionary *defaultValues =[NSDictionary dictionaryWithObjectsAndKeys:
@"This_is_my_default_message",@"message",
nil];
[[NSUserDefaults standardUserDefaults]registerDefaults:defaultValues];
[[NSUserDefaultsController sharedUserDefaultsController]setInitialValues:defaultValues];
}
当然写到applicationDidFinishLaunching中注册和不写到里面效果是一样的,只是代码的优美问题
用户轻量级的数据持久化,主要用于保存用户程序的配置等信息,以便下次启动程序后能恢复上次的设置。
该数据实际上是以“键值对”形式保存的(类似于NSDictionary),因此我们需要通过key来读取或者保存数据(value)。
具体使用如下:
1、获取一个NSUserDefaults引用:
NSUserDefaults *userDefaults= [NSUserDefaults standardUserDefaults];
2、保存数据
[userDefaults setInteger:1 forKey:@"segment"];
[userDefaults synchronize];
3、读取数据
int i= [userDefaults integerForKey:@"segment"];
4、其他数据的存取
The NSUserDefaults
classprovides convenience methods for accessing common types such asfloats, doubles, integers, Booleans, and URLs. A default objectmust be a property list, that is, an instance of (or forcollections a combination of instancesof): NSData
,NSString
, NSNumber
, NSDate
, NSArray
,or NSDictionary
.If you want to store any other type of object, you should typicallyarchive it to create an instance of NSData
.
保存数据:
NSData *objColor= [NSKeyedArchiver archivedDataWithRootObject:[UIColor redColor]];
[[NSUserDefaults standardUserDefaults]setObject:objColor forKey:@"myColor"];
读取数据:
NSData *objColor= [[NSUserDefaults standardUserDefaults]objectForKey:@"myColor"];
UIColor *myColor =[NSKeyedUnarchiver unarchiveObjectWithData:objColor];
5、应用实例
-(UITableViewCell *)tableView:(UITableView *)tableViewcellForRowAtIndexPath:(NSIndexPath *)indexPath
{
......
[cellSwitch setTag:indexPath.row];
[cellSwitch addTarget:self action:@selector(SwitchAction:)forControlEvents:UIControlEventValueChanged];
//retrieving cell switch value
NSUserDefaults *switchV= [NSUserDefaults standardUserDefaults];
int i=indexPath.row;
NSString *str= [[NSString alloc]initWithFormat:@"switch%d",i];
cellSwitch.on =([switchV integerForKey:str]==1)?YES:NO;
......
return cell;
}
-(void)SwitchAction:(id)sender
{
int i=[sender tag];
NSString *str= [[NSString alloc]initWithFormat:@"switch%d",i];
// save cell switch value
NSUserDefaults *switchV= [NSUserDefaults standardUserDefaults];
isOnOff =([sender isOn]== 1)?1:0;
[switchV setInteger:isOnOff forKey:str];
[switchV synchronize]; //调用synchronize函数将立即更新这些默认值。
[str release];
}
NSUserDefaults可以存取一些短小的信息。
比如存入再读出一个字符串到NSUserDefaults:
- NSString *string = [NSString stringWithString @"hahaha"];
- NSUserDefaults *ud = [NSUserDefaults standardUserDefaults];
- [ud setObject:string forKey:@"myKey"];
- NSString *value;
- value = [ud objectForKey:"myKey"];
但是并不是所有的东西都能往里放的。NSUserDefaults只支持: NSString, NSNumber, NSDate,NSArray, NSDictionary.
如果把一个自定义的类存到一个NSArray里,然后再存到NSUserDefaults里也是不能成功的。不信可以试试,如果你成功的请告诉我。
那怎么办呢?
我找到的方法是,让这个自定义类实现协议中的- (id) initWithCoder: (NSCoder *)coder方法和-(void) encodeWithCoder: (NSCoder*)coder方法(obj-c的协议protocol就是java的接口interface,就是C++的纯虚函数),然后把该自定义的类对象编码到NSData中,再从NSUserDefaults中进行读取。
粘代码:
假设有这样一个简单的类对象
- @interface BusinessCard : NSObject {
- NSString *_firstName;
- NSString *_lastName;
- }
- @property (nonatomic, retain) NSString *_firstName;
- @property (nonatomic, retain) NSString *_lastName;
- @end;
-
- @implementation BusinessCard
- @synthesize _firstName, _lastName;
- - (void)dealloc{
- [_firstName release];
- [_lastName release];
- [super dealloc];
- }
- - (id) initWithCoder: (NSCoder *)coder
- {
- if (self = [super init])
- {
- self._firstName = [coder decodeObjectForKey:@"_firstName"];
- self._lastName = [coder decodeObjectForKey:@"_lastName"];
- }
- return self;
- }
- - (void) encodeWithCoder: (NSCoder *)coder
- {
- [coder encodeObject:_firstName forKey:@"_firstName"];
- [coder encodeObject:_lastName forKey:@"_lastName"];
-
- }
-
- @end
然后再存取时通过NSData做载体:
- BusinessCard *bc = [[BusinessCard alloc] init];
- NSUserDefaults *ud = [NSUserDefaults standardUserDefaults];
- NSData *udObject = [NSKeyedArchiver archivedDataWithRootObject:bc];
- [ud setObject:udObject forKey:@"myBusinessCard"];
- [bc release];
- udObject = nil;
- udObject = [ud objectForKey:@"myBusinessCard"];
- bc = [NSKeyedUnarchiver unarchiveObjectWithData:udObject] ;
-
-
-
以上的代码时由另一个程序中截取的,没有测试过,但意思就是这样了。
如果一个自定义类中由另一个自定义类对象,那么所有嵌套的类都要实现。