如何使用animateWithDuration淡化标签的背景色

Question

I'm trying to fade a label's background color by using animateWithDuration, but my code isn't working out. Here's what I've got:

.h (in @interface...)

IBOutlet UILabel *labelColor;

.m (in viewDidLoad method)

[labelColor setBackgroundColor:[UIColor colorWithRed:55/255.0 green:191/255.0 blue:122/255.0 alpha:0.3]];

if (labelColor.alpha >= 0.3) {
    [UIView animateWithDuration:1 animations:^{
        labelColor.alpha = 0.3;
        labelColor.alpha = 1.0;
    }];
} else if (labelColor.alpha == 1.0) {
    labelColor.alpha = 0.3;
}

The color shows up at 0.3 alpha, but doesn't fade from 0.3 to 1.0. I'm trying to make it so the label's color fades from 0.3 to 1.0 in a continuous loop, resetting the alpha to 0.3 as the it hits 1.0.

Any help on how to achieve this is appreciated.

Answer 1

There are a few problems with your current code:

(1) Your else statement will never be called since if labelColor.alpha == 1.0 it will also be >= .3

(2) Having both labelColor.alpha = 0.3; and labelColor.alpha = 1.0; within your animation block means that only the second line (ie labelColor.alpha = 1.0; ) will dictate the animation

(3) You haven't set up a loop as you'd like

(4) You haven't animated the fade out

If I'm in fact understanding what it is you're trying to accomplish, you could continuously fade the entire UILabel in and out like so:

- (void)performLabelFade {
    // If the label is faded out, fade it in
    if (labelColor.alpha == .3) {
        [UIView animateWithDuration:1 animations:^{
            labelColor.alpha = 1.0;
        } completion:^(BOOL finished) {
            // Repeat the current method (i.e. like a loop)
            [self performLabelFade];
        }
    }
    // Else if the label is faded in, fade it out
    else if (labelColor.alpha == 1.0) {
        [UIView animateWithDuration:1 animations:^{
            labelColor.alpha = 0.3;
        } completion:^(BOOL finished) {
            // Repeat the current method (i.e. like a loop)
            [self performLabelFade];
        }
    }
}

Answer 2

You should set your initial conditions outside of the animation block.

labelColor.alpha = 0.3;
[UIView animateWithDuration:1 animations:^{
    labelColor.alpha = 1.0;
}];

---

Side note : This will fade the alpha value of the entire UILabel , not just the background colour. If you want the text to stick around while your background fades, you should be using something more along these lines:

labelColor.backgroundColor = [UIColor colorWithRed:55/255.0 green:191/255.0 blue:122/255.0 alpha:0.3];
[UIView animateWithDuration:1 animations:^{
    labelColor.backgroundColor = [UIColor colorWithRed:55/255.0 green:191/255.0 blue:122/255.0 alpha:1.0];
}];