無法更新使用NSUserDefauts值初始化的NSMutableDictionary

Question

我使用NSUserDefaults來保存NSMutableDictionary。但是，當我從NSUserDefaults中檢索值時，我無法修改/更新要保存值的NSMutableDictionary的值。

需要一些建議如何做到這一點？

Answer 1

您總是從NSUserDefaults獲得NSDictionary的非可變實例。爲了使它們變得可變，你需要做這樣的事情：

dict = [[NSUserDefaults standardUserDefaults] objectForKey:@"myKey"]; 
myMutableDict = [dict mutableCopy]; 
// Note that the retain count is +1, so you will need to 
// release or autorelease myMutableDict later on. 

Answer 2

你也可以保存爲plist。

這是你如何寫一個的plist：

NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString * docDirectory = [paths objectAtIndex:0]; 
NSString * dataFilePath = [docDirectory stringByAppendingPathComponent:@"YourFile.dat"] 

NSMutableDictionary * newLocalPlist = [[NSMutableDictionary alloc] init]; 

// add your prefs here 

[newLocalPlist writeToFile:dataFilePath atomically:YES]; 
[newLocalPlist release]; 

這就是你如何從plist中寫着：

NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString * docDirectory = [paths objectAtIndex:0]; 
NSString * dataFilePath = [docDirectory stringByAppendingPathComponent:@"YourFile.dat"] 
NSMutableDictionary * lastLocalPlist = [[[NSMutableDictionary alloc] initWithContentsOfFile:dataFilePath] autorelease];