How do I Create a Default Slider Value Programmatically?

Question

The "current value" default I have set in interface builder for my sliders seems to be bypassed completely, and when I run the app, the sliders start from where I last had them set the last time I ran the app.

I would like the sliders to start from their default value AND recall the position they were last in, before switching to a different view.

Here is the code that allows the slider values to be saved:

viewController.m

- (void)viewWillAppear:(BOOL)animated{
    [_firstSlider setValue:[[NSUserDefaults standardUserDefaults] floatForKey:@"firstSliderValue"]];
}

- (IBAction)firstSliderValueChange:(id)sender {
    [[NSUserDefaults standardUserDefaults] setFloat:[_firstSlider value] forKey:@"firstSliderValue"];
}

Thank You!

That doesn't make sense. How can a slider have both its default value and its saved value at the same time? — Dave Batton, Jun 09 '15 at 21:25
To clarify, I would like to initialize a "default value" at the start of running the app, so the sliders will always start at "0" for example, but also retain their value after switching between views. The above code accomplished the later problem, but now I don't know how to initialize a value for when the app first opens. — PlateReverb, Jun 09 '15 at 21:28
My code was based on the solution from this question: http://stackoverflow.com/questions/24170781/maintaining-slider-position-in-xcode-when-switching-views — PlateReverb, Jun 09 '15 at 21:57

ajay_nasa · Answer 1 · 2015-07-28T07:49:03.133

1

Just add this [[NSUserDefaults standardUserDefaults]removeObjectForKey:@"YourKey"]; as @psobko said in AppDelegate like:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    [[NSUserDefaults standardUserDefaults] removeObjectForKey:@"YourKey"];
    return YES;
}

edited Jul 28 '15 at 07:49

answered Jul 28 '15 at 07:09

ajay_nasa

2,278
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Dave Batton · Answer 2 · 2015-06-09T22:16:57.650

Don't use NSUserDefaults to store the value between views. That's not what it's for. Just pass the slider value from one view to another. You may need to do this in -prepareForSegue:sender:.

Use NSUserDefaults when you want to save and restore a value between fresh launches of the app.

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"ShowAnotherSlider"]) {
        DBAnotherViewController *destinationViewController = (DBAnotherViewController *)segue.destinationViewController;
        destinationViewController.sliderStartValue = self.slider.value;
    }
}

Notice that I'm setting a property on the destination view controller, not setting the slider value directly.

@property (nonatomic, strong) CGFloat sliderStartValue;

The destination view controller's view probably isn't loaded at this point, so the slider property is nil. Set this other property instead, and then when the view gets loaded (-viewDidLoad) you can update the slider with that value.

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.slider.value = self.sliderStartValue;
}

Thanks for the info. I am a beginner, and based my code on the solution given in this question (http://stackoverflow.com/questions/24170781/maintaining-slider-position-in-xcode-when-switching-views). Would you mind giving me any example code of what I might put in `-prepareForSegue:sender:` to accomplish this? — PlateReverb, Jun 09 '15 at 22:01
Except this way you're adding unnecessary complexity. You need to expose the property and pass the correct value in each ViewController the user might go through before coming back to the ViewController with the slider. This creates problems like not knowing whether the `sliderStartValue` property has been set and setting an incorrect initial slider value. — psobko, Jun 09 '15 at 23:05

psobko · Answer 3 · 2015-06-09T22:15:26.003

0

Just remove the object for the key when the app is launching again:

[[NSUserDefaults standardUserDefaults] removeObjectForKey:@"firstSliderValue"];

You can do this in the AppDelegate or wherever else makes sense.

edited Jun 09 '15 at 22:15

answered Jun 09 '15 at 21:37

psobko

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No. That would work. But it would be bad code. Don't fix a problem with a new problem. – Dave Batton Jun 09 '15 at 22:06
It does work! Actually, `[[NSUserDefaults standardUserDefaults] setFloat: 0.05 forKey:@"firstSliderValue"];` is basically what I was looking for. I realize this is not the best way to solve the problem, but it works for now. If someone could show an example of the better solution, that would be great. – PlateReverb Jun 09 '15 at 22:13
Yeah it's not the ideal solution but I thought it was important that someone provided an answer showing why the original solution wasn't working. The best way to go about this would be to create a model object which would have something like "whateverSliderValueRepresents" as a property and access it from whichever view controllers and other classes need it. You can create a global variable and access it through your `AppDelegate` or a shared instance (https://www.cocoanetics.com/2009/05/the-death-of-global-variables/). – psobko Jun 09 '15 at 22:25

TheJack · Answer 4 · 2015-06-09T23:21:23.973

As Dave Batton said, NSUserDefaults is for defaults on fresh launches of the app. If I understand your question correctly, it appears to me that you are overwriting your default value in firstSliderValueChange. That is why this happens:

the sliders start from where I last had them set the last time I ran the app.

Either store your defaults and in-app values separately or pass them between views.

EDIT: The code mentioned in your comment below doesn't pass values. It persists values.

Problem: Say you originally have set a slider value default of 0. When you run the app for the first time, you see the slider at 0. Now you move the slider to, say, 5. Then this method is called:

- (IBAction)firstSliderValueChange:(id)sender {
    [[NSUserDefaults standardUserDefaults] setFloat:[_firstSlider value] forKey:@"firstSliderValue"];
}

Now the default value is no longer 0. It is 5. And that persists between app launches, since you are using NSUserDefaults.

Solution: Save the dynamic slider value some place else - not in NSUserDefaults. Since you have multiple view controllers, one way is this:

//viewController.m
@interface
@property (strong, nonatomic) IBOutlet UISlider *mySlider;
@end

-(void)prepareForSegue: (UIStoryboardSegue *)segue sender:(id)sender {
if([segue.identifier isEqualToString: @"segueIdentifer"]) {
    otherViewController *ovc = (otherViewController *)segue.destinationViewController;
    ovc.dynamicSliderValue = self.mySlider.value;
    }
}

And:

//otherViewController.h
@interface
@property(assign) CGFloat dynamicSliderValue;
@end

Now, whenever you switch back to your first view controller's view, simply access this property, and update the slider accordingly. Note - I am sure there are many other ways of doing this!

I based my code on the answer to this other question: http://stackoverflow.com/questions/24170781/maintaining-slider-position-in-xcode-when-switching-views which was the only place I found that showed how to pass the values between views. Could you please explain a better way that would allow me to retain the default value when the app opens? — PlateReverb, Jun 09 '15 at 22:04
When I switch back to the first controller's view, how do I access this property and update the slider's value? — PlateReverb, Jun 10 '15 at 02:59
@PlateReverb look up unwind segues. Basically, a custom method will be called specifically when you return to your original view controller. In this method, update the slider value using the setValue method. — TheJack, Jun 13 '15 at 06:17
@PlateReverb did this solve your problem? You could also use delegation as shown [here](http://stackoverflow.com/questions/15814426/best-way-to-pass-data-from-child-modal-vc-to-the-parent-view-controller) and [here](https://www.youtube.com/watch?v=XZWT0IV8FrI) . If my (or anyone else's) answers helped you, I would suggest upvoting/marking them as answers! — TheJack, Jun 23 '15 at 19:31

How do I Create a Default Slider Value Programmatically?

4 Answers4