Continuously Update Label Based on UISlider Value - ios

Question

I currently have a series of 5 UISliders that continuously update their respective labels to display what value the user is selecting in an hh:mm:ss format. I have the properties of each slider set to continuous and have their targets set to when the slider is changed (This example would be for just the first slider).
sliderOne.continuous=YES;
[sliderOne addTarget:self action:#selector(sliderOneChanged:) forControlEvents:UIControlEventTouchUpInside];
Each slider's individual label updates the time selected perfectly. Now however, I need to update another label underneath all of these sliders that continuously sums up the value of the sliders.
At the same time, I am also doing some conversions with the value of the slider using two segmented controllers -- a miles/kilometers segmented controller and various distances in another segmented controller. Each conversion results in a time in seconds that is then converted back into the hh:mm:ss format and displayed in the last label when the user selects which combo from the segment controller they want. I have all the math worked out for this, and the label will update correctly when changing segments, but not continuously.
How could I update a label to continuously show the sum of every UISlider as the user changes them?

Answer 1

For a continuous updating, use the UIControlEventValueChanged event along with the continuous property
sliderOne.continuous=YES;
[sliderOne addTarget:self action:#selector(sliderOneChanged:) forControlEvents:UIControlEventValueChanged];

Answer 2

Use KVO to get notified of changes in UISliders and update the UI accordingly. You want to wrap UI updates with dispatch_async to avoid locking the interface.
Using KVO-Notification-Manager it can be something like this (in viewDidLoad or similar):
id token1 = [slider1 addKVOBlockForKeyPath:#"value" options:NSKeyValueObservingOptionNew handler:^(NSString *keyPath, id object, NSDictionary *change) {
dispatch_async(dispatch_get_main_queue(), ^{
whateverSliderNeedsUpdate.value = /* your calculation result */;
});
}];
id token2 = [slider2 /* repeat for as many sliders as you want */];
...
It's important to remove the observers at some point.
- (void)dealloc {
[slider1 removeKVOBlockForToken:token1];
[slider2 ...];
}
If you feel adventurous you can try with ReactiveCocoa.

Answer 3

You could create a method that does all of your math and updates your UILabel with the result. For example:
- (void)updateSumLabel {
// this is obviously very simple
float num1 = [_sliderOne value];
float num2 = [_sliderTwo value];
float sum = num1 + num2;
[_sumLabel setText:[NSString stringWithFormat:#"#f",sum]];
}
The you can call updateSumLabel from any of your existing methods like sliderOneChanged. This is probably the most simple way todo this.