为什么NSUserDefaults无法保存NSMutableDictionary?
我试图用NSUserDefaults
保存一个NSMutableDictionary
。 我阅读了很多关于这个主题的post…我也发现了一个选项,工作; 然而不幸的是,它只工作了一次,然后开始只保存(空)。 有人有提示吗?
谢谢
代码保存:
[[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:dictionary] forKey:@"Key"]; [[NSUserDefaults standardUserDefaults] synchronize];
加载代码:
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc]init]; NSData *data = [[NSUserDefaults standardUserDefaults]objectForKey:@"Key"]; dictionary = [NSKeyedUnarchiver unarchiveObjectWithData:data];
将对象添加到NSMutableDictionary
代码:
[dictionary setObject:[NSNumber numberWithInt:0] forKey:@"Key 1"]; [dictionary setObject:[NSNumber numberWithInt:1] forKey:@"Key 2"]; [dictionary setObject:[NSNumber numberWithInt:2] forKey:@"Key 3"];
代码到NSLog()值:
for (NSString * key in [dictionary allKeys]) { NSLog(@"key: %@, value: %i", key, [[dictionary objectForKey:key]integerValue]); }
而且关键是(空):
NSLog(@"%@"[dictionary allKeys]);
从Apple的NSUserDefaults objectForKey
的文档:
即使您最初设置的值是可变的,返回的对象也是不可变的。
该行:
dictionary = [NSKeyedUnarchiver unarchiveObjectWithData:data];
丢弃之前创build的NSMutableDictionary
并返回一个NSDictionary
。
将加载更改为:
NSData *data = [[NSUserDefaults standardUserDefaults]objectForKey:@"Key"]; dictionary = [NSKeyedUnarchiver unarchiveObjectWithData:data];
完整的例子,在这个例子中也不需要使用NSKeyedArchiver
:
NSDictionary *firstDictionary = @{@"Key 4":@4}; [[NSUserDefaults standardUserDefaults] setObject:firstDictionary forKey:@"Key"]; NSMutableDictionary *dictionary = [[[NSUserDefaults standardUserDefaults] objectForKey:@"Key"] mutableCopy]; dictionary[@"Key 1"] = @0; dictionary[@"Key 2"] = @1; dictionary[@"Key 3"] = @2; for (NSString * key in [dictionary allKeys]) { NSLog(@"key: %@, value: %@", key, [dictionary objectForKey:key]); }
NSLog输出:
键:键2,值:1
键:键1,值:0
键:键4,值:4
键:键3,值:2