How to tell if a key exists
I'm working on a small iPhone app, and I am using NSUserDefaults as my data persistence. It only has to keep track of a few things, such as some names and some numbers so I figure I might as well keep it simple.
I found this page for some reference, but I don't think it can answer my question. Basically, I want to be able to check if a value (or a key) already exists in the NSUserDefaults and then do something accordingly.
Some examples: The app starts up, if this is the first time it starts up it outputs an alert saying welcome. To tell if this is first time it has opened it reads the UserDefaults and checks.
Example 2: It says, "Hello [Name]", where Name is something you have entered. If you have opened the app and there is no name, it should say "Hello World." I need to check if you have entered a name already and act accordingly. The name would be stored in NSUserDefaults .
Some help here? I'd really appreciate it!
objectForKey:如果不存在，将返回nil 。
As mentioned above it wont work for primitive types where 0/NO could be a valid value. I am using this code.
NSUserDefaults *defaults= [NSUserDefaults standardUserDefaults];
if([[[defaults dictionaryRepresentation] allKeys] containsObject:@"mykey"]){
NSLog(@"mykey found");
}
The objectForKey: method will return nil if the value does not exist. Here's a simple IF / THEN test that will tell you if the value is nil:
if([[NSUserDefaults standardUserDefaults] objectForKey:@"YOUR_KEY"] != nil) {
...
}
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