How to store an retrieve float from NSUserDefaults

问题

I'm having trouble storing and retrieving a float in NSUserDefauts. I store the value, but when I retrieve it, it returns 0.

here's what I tried and didn't work:

[pref setFloat:3.0f forKey:@"key"];
float value = [pref floatForKey:@"key"]; //value=0

[pref setFloat:3 forKey:@"key"];
float value = [pref floatForKey:@"key"];//value=0

[pref setObject:[NSNumber numberWithFloat:3] forKey:@"key"];
float value = [[pref objectForKey:@"key"]floatValue];//value=0

[pref setObject:[NSNumber numberWithFloat:3.0f] forKey:@"key"];
float value = [[pref objectForKey:@"key"]floatValue];//value=0

What am I doing wrong here? I've tried these 4 pieces of code but they all return zero when retrieving the float from NSUserDefaults.

Any help is appreciated. Thanks!

回答1:

The first example in your code is fine, assuming that this line:

NSUserDefaults *pref = [NSUserDefaults standardUserDefaults];

Appears before it. As I suggested in my comment, the behaviour you are seeing suggests that pref is nil.

回答2:

Save

-(void) saveFloatToUserDefaults:(float)x forKey:(NSString *)key {
    NSUserDefaults * userDefaults = [NSUserDefaults standardUserDefaults];
    [userDefaults setFloat:x forKey:key];
    [userDefaults synchronize];
}

Load

-(float) loadFloatFromUserDefaultsForKey:(NSString *)key {
    NSUserDefaults * userDefaults = [NSUserDefaults standardUserDefaults];
    return [userDefaults floatForKey:key];
}

How-To

[self saveFloatToUserDefaults:5.241 forKey:@"myFloat"];
float x = [self loadFloatFromUserDefaultsForKey:@"myFloat"];

回答3:

[[NSUserDefaults standardUserDefaults]setObject:[NSNumber numberWithFloat:3] forKey:@"key"];

回答4:

Try this:

For Storing

-(void)sliderAction:(id)sender

{
   [[NSUserDefaults standardUserDefaults] setFloat:fontSlider.value forKey:@"keyFontSize"];
    [[NSUserDefaults standardUserDefaults] synchronize];
}

2.For retriving

-(void)retrive
{
   NSLog(@"%f",[storedata floatForKey:@"keyFontSize"]);
}

回答5:

NSUserDefaults special cases floats as well as a few other native "C" types.

[[NSUserDefaults standardUserDefaults] setFloat:3 forKey:@"key"];

float value = [[NSUserDefaults standardUserDefaults] floatForKey:@"key"];
NSLog(@"value: %.0f", value);

NSLog output:
value: 3

回答6:

NSUserDefaults *pref = [NSUserDefaults standardUserDefaults];
if (pref) {
   [[NSUserDefaults standardUserDefaults] setFloat:3 forKey:@"key"];

   //for accessing
   float value = [pref floatForKey:@"key"]; //if key does not exist, value will be zero
}

回答7:

Well, no one seems to have explicitly resolved the issue the OP had.
The OP had declared NSUserDefaults in the .h file and was just trying to access it in the .m file without actually alloc'ing the pref instance.
For the sake of the beginner programmer, this means in .h declare the instance:
NSUserDefaults * pref;

and in your .m method, put this before trying to access it:

pref = [NSUserDefaults standardUserDefaults];

It seems obvious to some, but can catch you out every now and then. You will ideally put this somewhere like viewDidLoad, but if you're accessing methods in that class via something like a shared instance, then in the methods you might benefit from putting

if(!pref){ 
pref = [NSUserDefaults standardUserDefaults];
}

before you need to access it, just to make sure it's been allocated memory.
Hope this helps somebody!

来源：https://stackoverflow.com/questions/9957055/how-to-store-an-retrieve-float-from-nsuserdefaults

标签

iphone

objective-c

ios

xcode

nsuserdefaults