UITableView viewForHeaderInSection UIView动画问题

Question

I have a custom UIView that has two labels, one of which is animated (it blinks like a cursor and looks quite fly). This view works fine EXCEPT when I try to use it for a tableView's header; the animation doesn't repeat even though I specify UIViewAnimationOptionRepeat .

My class:

@implementation HXTEST {

  UILabel *cursorLabel;
}

#pragma mark - inits

- (id) initForLabel:(UILabel *)forLabel {

  self = [super init];

  if (self) {

    self.translatesAutoresizingMaskIntoConstraints = NO;

    CGRect abba = [forLabel.text boundingRectWithSize:forLabel.frame.size
                                              options:NSStringDrawingUsesFontLeading
                                           attributes:@{ NSFontAttributeName : forLabel.font}
                                              context:[NSStringDrawingContext new]];

    float width = CGRectGetWidth(abba) * 1.005f;

    self->cursorLabel = [UILabel new];

    self->cursorLabel.textColor = forLabel.textColor;
    self->cursorLabel.font = forLabel.font;
    self->cursorLabel.text = @"▏";
    self->cursorLabel.adjustsFontSizeToFitWidth = forLabel.adjustsFontSizeToFitWidth;
    self->cursorLabel.minimumScaleFactor = forLabel.minimumScaleFactor;
    self->cursorLabel.translatesAutoresizingMaskIntoConstraints = NO;

    [self addSubview:forLabel];
    [self addSubview:self->cursorLabel];

    [self addConstraint:[NSLayoutConstraint constraintWithItem:forLabel
                                                          attribute:NSLayoutAttributeLeading
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self
                                                          attribute:NSLayoutAttributeLeft
                                                         multiplier:1.f
                                                           constant:0.f]];

    [self addConstraint:[NSLayoutConstraint constraintWithItem:forLabel
                                                     attribute:NSLayoutAttributeWidth
                                                     relatedBy:NSLayoutRelationEqual
                                                        toItem:nil
                                                     attribute:NSLayoutAttributeNotAnAttribute
                                                    multiplier:1.0f
                                                      constant:width]];

    [self addConstraint:[NSLayoutConstraint constraintWithItem:forLabel
                                                          attribute:NSLayoutAttributeTop
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self
                                                          attribute:NSLayoutAttributeTop
                                                         multiplier:1.f
                                                           constant:0.f]];

    [self addConstraint:[NSLayoutConstraint constraintWithItem:forLabel
                                                          attribute:NSLayoutAttributeBottom
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self
                                                          attribute:NSLayoutAttributeBottom
                                                         multiplier:1.f
                                                           constant:0.f]];

    [self addConstraint:[NSLayoutConstraint constraintWithItem:self->cursorLabel
                                                     attribute:NSLayoutAttributeLeading
                                                     relatedBy:NSLayoutRelationEqual
                                                        toItem:forLabel
                                                     attribute:NSLayoutAttributeTrailing
                                                    multiplier:1.f
                                                      constant:0.f]];

    [self addConstraint:[NSLayoutConstraint constraintWithItem:self->cursorLabel
                                                     attribute:NSLayoutAttributeWidth
                                                     relatedBy:NSLayoutRelationEqual
                                                        toItem:nil
                                                     attribute:NSLayoutAttributeNotAnAttribute
                                                    multiplier:1.f
                                                      constant:forLabel.font.pointSize]];

    [self addConstraint:[NSLayoutConstraint constraintWithItem:self->cursorLabel
                                                     attribute:NSLayoutAttributeTop
                                                     relatedBy:NSLayoutRelationEqual
                                                        toItem:self
                                                     attribute:NSLayoutAttributeTop
                                                    multiplier:1.f
                                                      constant:0.f]];

    [self addConstraint:[NSLayoutConstraint constraintWithItem:self->cursorLabel
                                                     attribute:NSLayoutAttributeBottom
                                                     relatedBy:NSLayoutRelationEqual
                                                        toItem:self
                                                     attribute:NSLayoutAttributeBottom
                                                    multiplier:1.f
                                                      constant:0.f]];
  }

  [UIView animateWithDuration:1.f
                        delay:0.f
                      options:UIViewAnimationOptionRepeat
                   animations:^{

                     self->cursorLabel.alpha = 1.f;
                     self->cursorLabel.alpha = 0.f;
                   }

                   completion:nil];

  return self;
}

@end

Is there something about tableView headers and their presentation? Is there some other combination of UIViewAnimationOptions I should consider? Instead of automatically starting the animation block should I trigger it off some event like the headerView's appearance or some such?

Answer 1

Aha! Although [UIView areAnimationsEnabled] defaults to TRUE , it was for some reason FALSE . I forced it with

[UIView setAnimationsEnabled:YES];

before the animation block and all works now! I don't know why it was off...

Answer 2

Try like this using UIViewAnimationOptionAutoreverse option as well:

void (^animationLabel) (void) = ^{
    blinkLabel.alpha = 0;
};
void (^completionLabel) (BOOL) = ^(BOOL f) {
    blinkLabel.alpha = 1;
};

NSUInteger opts =  UIViewAnimationOptionAutoreverse | 
                   UIViewAnimationOptionRepeat;
[UIView animateWithDuration:1.f delay:0 options:opts
                 animations:animationLabel completion:completionLabel];

Hope it helps!