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问题:
I'm trying to create a UISlider
that lets you choose from an array of numbers. Each slider position should be equidistant and the slider should snap to each position, rather than smoothly slide between them. (This is the behavior of the slider in Settings
> General
> Text Size
, which was introduced in iOS 7.)
The numbers I want to choose from are: -3, 0, 2, 4, 7, 10, and 12.
(I'm very new to Objective-C, so a complete code example would be much more helpful than a code snippet. =)
回答1:
Some of the other answers work, but this will give you the same fixed space between every position in your slider. In this example you treat the slider positions as indexes to an array which contains the actual numeric values you are interested in.
@interface MyViewController : UIViewController {
UISlider *slider;
NSArray *numbers;
}
@end
@implementation MyViewController
- (void)viewDidLoad {
[super viewDidLoad];
slider = [[UISlider alloc] initWithFrame:self.view.bounds];
[self.view addSubview:slider];
// These number values represent each slider position
numbers = @[@(-3), @(0), @(2), @(4), @(7), @(10), @(12)];
// slider values go from 0 to the number of values in your numbers array
NSInteger numberOfSteps = ((float)[numbers count] - 1);
slider.maximumValue = numberOfSteps;
slider.minimumValue = 0;
// As the slider moves it will continously call the -valueChanged:
slider.continuous = YES; // NO makes it call only once you let go
[slider addTarget:self
action:@selector(valueChanged:)
forControlEvents:UIControlEventValueChanged];
}
- (void)valueChanged:(UISlider *)sender {
// round the slider position to the nearest index of the numbers array
NSUInteger index = (NSUInteger)(slider.value + 0.5);
[slider setValue:index animated:NO];
NSNumber *number = numbers[index]; // <-- This numeric value you want
NSLog(@"sliderIndex: %i", (int)index);
NSLog(@"number: %@", number);
}
I hope that helps, good luck.
Edit: Here's a version in Swift 4 that subclasses UISlider with callbacks.
class MySliderStepper: UISlider {
private let values: [Float]
private var lastIndex: Int? = nil
let callback: (Float) -> Void
init(frame: CGRect, values: [Float], callback: @escaping (_ newValue: Float) -> Void) {
self.values = values
self.callback = callback
super.init(frame: frame)
self.addTarget(self, action: #selector(handleValueChange(sender:)), for: .valueChanged)
let steps = values.count - 1
self.minimumValue = 0
self.maximumValue = Float(steps)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
@objc func handleValueChange(sender: UISlider) {
let newIndex = Int(sender.value + 0.5) // round up to next index
self.setValue(Float(newIndex), animated: false) // snap to increments
let didChange = lastIndex == nil || newIndex != lastIndex!
if didChange {
let actualValue = self.values[newIndex]
self.callback(actualValue)
}
}
}
回答2:
If you have regular spaces between steps, you can use it like this for 15
value:
@IBAction func timeSliderChanged(sender: UISlider) {
let newValue = Int(sender.value/15) * 15
sender.setValue(Float(newValue), animated: false)
}
回答3:
The answer is essentially the same at this answer to UISlider with increments of 5
To modify it to work for your case, you'll need to create a rounding function that returns only the values you want. For example, you could do something simple (though hacky) like this:
-(int)roundSliderValue:(float)x {
if (x < -1.5) {
return -3;
} else if (x < 1.0) {
return 0;
} else if (x < 3.0) {
return 2;
} else if (x < 5.5) {
return 4;
} else if (x < 8.5) {
return 7;
} else if (x < 11.0) {
return 10;
} else {
return 12;
}
}
Now use the answer from the previous post to round the value.
slider.continuous = YES;
[slider addTarget:self
action:@selector(valueChanged:)
forControlEvents:UIControlEventValueChanged];
Finally, implement the changes:
-(void)valueChanged:(id)slider {
[slider setValue:[self roundSliderValue:slider.value] animated:NO];
}
回答4:
Similar approach as PengOne, but I did manual rounding to make it more clear what was happening.
- (IBAction)sliderDidEndEditing:(UISlider *)slider {
// default value slider will start at
float newValue = 0.0;
if (slider.value < -1.5) {
newValue = -3;
} else if (slider.value < 1) {
newValue = 0;
} else if (slider.value < 3) {
newValue = 2;
} else if (slider.value < 5.5) {
newValue = 4;
} else if (slider.value < 8.5) {
newValue = 7;
} else if (slider.value < 11) {
newValue = 10;
} else {
newValue = 12;
}
slider.value = newValue;
}
- (IBAction)sliderValueChanged:(id)sender {
UISlider *slider = sender;
float newValue = 0.0;
if (slider.value < -1.5) {
newValue = -3;
} else if (slider.value < 1) {
newValue = 0;
} else if (slider.value < 3) {
newValue = 2;
} else if (slider.value < 5.5) {
newValue = 4;
} else if (slider.value < 8.5) {
newValue = 7;
} else if (slider.value < 11) {
newValue = 10;
} else {
newValue = 12;
}
// and if you have a label displaying the slider value, set it
[yourLabel].text = [NSString stringWithFormat:@"%d", (int)newValue];
}
回答5:
This worked for my particular case, using @IBDesignable:
Requires even, integer intervals:
@IBDesignable
class SnappableSlider: UISlider {
@IBInspectable
var interval: Int = 1
override init(frame: CGRect) {
super.init(frame: frame)
setUpSlider()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setUpSlider()
}
private func setUpSlider() {
addTarget(self, action: #selector(handleValueChange(sender:)), for: .valueChanged)
}
@objc func handleValueChange(sender: UISlider) {
let newValue = (sender.value / Float(interval)).rounded() * Float(interval)
setValue(Float(newValue), animated: false)
}
}