Animate text Content in iOS - Equivalent for Android ValueAnimator

Question

I am working on an iOS 7+ app and would like to animated change the content of an UILabel. I do not want do do any graphical animation like fade out old con

Answer 1

Since I found no tailored solution for this I created my own: A simple Animator Class which handles the Easing:

// MyValueAnimation.h
typedef void (^MyAnimationBlock)(double animationValue);

@interface MyValueAnimation : NSObject

- (void)startAnimation:(MyAnimationBlock)animationBlock runtime:(NSUInteger)runtime delay:(NSUInteger)delay;

@end


// MyValueAnimation.m
#import "MyValueAnimation.h"

// Number of seconds between each animation step
#define kStepSize 0.05

@interface MyValueAnimation () {
    NSTimer *timer;            
    NSUInteger totalRunTime;    // Total duration of the animation (delay not included)
    NSUInteger currentRuntime;  // Time the animation is already running
    MyAnimationBlock animationBlock;
}
@end

@implementation MyValueAnimation

- (void)startAnimation:(MyAnimationBlock)block runtime:(NSUInteger)runtime delay:(NSUInteger)delay {
    if (timer != nil)
        [timer invalidate];

    timer = nil;
    totalRunTime = runtime;
    animationBlock = block;
    currentRuntime = 0;

    if (block != nil) {
        if (delay > 0) {
            // Wait to delay the start. Convert delay from millis to seconds
            double delaySeconds = (double)delay / 1000.0;
            timer = [NSTimer scheduledTimerWithTimeInterval:delaySeconds target:self selector:@selector(delayTick:) userInfo:nil repeats:false];
        } else {
            // Run the animation
            timer = [NSTimer scheduledTimerWithTimeInterval:kStepSize target:self selector:@selector(animationTick:) userInfo:nil repeats:true];
        }
    }
}

- (void)delayTick:(NSTimer *)delayTimer {
    // End of delay -> run animation
    [delayTimer invalidate];
    timer = [NSTimer scheduledTimerWithTimeInterval:kStepSize target:self selector:@selector(animationTick:) userInfo:nil repeats:true];
}

- (void)animationTick:(NSTimer *)animationTimer {
    NSUInteger step = 1000 * kStepSize;  // step size/length in milli seconds
    currentRuntime += step;
    double progress = MIN((double)currentRuntime / (double)totalRunTime, 1.0);

    // Progress is a value between 0 and 1. The easing function maps this
    // to the animationValue which is than used inside the animationBlock
    // to calculate the current value of the animiation
    double animationValue = [self customEaseOut:progress];

    if (animationBlock != nil)
        animationBlock(animationValue);

    if (progress >= 1.0) {
        // Animation complete
        [timer invalidate];
        timer = nil;
    }        
}

- (double)customEaseOut:(double)t {
    // Use any easing function you like to animate your values...
    // http://rechneronline.de/function-graphs/
    // http://sol.gfxile.net/interpolation/
    return (1 - pow(1-t, 2));
}

@end 


// =============================================================

// Some code using the animation
- (void)animateValueFrom:(double)fromValue to:(double)toValue {
    if (valueAnimation == nil)
        valueAnimation = [[MyValueAnimation alloc] init];

    MyAnimationBlock animationBlock = ^(double animationValue) {
        double currentValue = fromValue + ((toValue - fromValue) * animationValue);

        someLabel.text = [NSString stringWithFormat:"%dV", currentValue];        
    };

    [valueAnimation startAnimation:animationBlock runtime:1500 delay:500];
}

Maybe not the prettiest solution but it works :-)