注意：将UILabel的contentMode属性更改为UIViewContentModeScaleToFill会修复此问题,但是我仍然不明白为什么在不更改contentMode属性的情况下增加大小的原因.

#import "FooView.h"
 
@interface FooView ()
@property (strong,nonatomic) UILabel   *label;
@property (assign,nonatomic) BOOL       resized;
@end
 
@implementation FooView
 
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor lightGrayColor];
 
        self.label = [[UILabel alloc] initWithFrame:(CGRect){0,frame.size}];
        self.label.backgroundColor = [UIColor greenColor];
        [self addSubview:self.label];
        _resized = false;
 
        UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(changeSize)];
        tapRecognizer.numberOfTapsrequired = 1;
        [self addGestureRecognizer:tapRecognizer];
    }
    return self;
}
 
- (void)changeSize {
    [UIView animateWithDuration:0.8
                          delay:0.0
                        options:UIViewAnimationOptionCurveEaseIn
                     animations:^{
                         CGRect bounds = self.label.bounds;
                         if (self.resized) {
                             bounds.size.height *= 2;
                             bounds.size.width  *= 2;
                         } else {
                             bounds.size.width  /= 2;
                             bounds.size.height /= 2;
                         }
                         self.label.bounds = bounds;
                     }
                     completion:^(BOOL finished) {
                         self.resized = !self.resized;
                     }];
}
 
@end