效果图

原理

就是持有两个视图，并且两个视图同时改变origin.y
动画结束之后，判断哪个视图是在上面并且看不到的，
则将该视图移动到底部，并且该视图展示下一跳内容
在开始下一轮动画

代码

- (void)startAnimationWithDuration:(CGFloat)duration
{
    self.duration = duration;
    [self changeAnimation];
}

- (void)changeAnimation
{
    CGRect rect1 = self.label1.frame;
    CGPoint point1 = rect1.origin;
    point1.y -= CGRectGetHeight(self.bounds);
    rect1.origin = point1;
    
    CGRect rect2 = self.label2.frame;
    CGPoint point2 = rect2.origin;
    point2.y -= CGRectGetHeight(self.bounds);
    rect2.origin = point2;
    
    self.currentIndex = (self.currentIndex + 1)%self.titleArray.count;
    NSString *crrentTitle = self.titleArray[self.currentIndex];
    [UIView animateWithDuration:0.5 animations:^{
        self.label1.frame = rect1;
        self.label2.frame = rect2;
    } completion:^(BOOL finished) {
        if (CGRectGetMinY(self.label1.frame) < - CGRectGetHeight(self.bounds) / 2) {
            self.label1.frame = self.bottomRect;
            self.label1.text = crrentTitle;
        } else {
            self.label2.frame = self.bottomRect;
            self.label2.text = crrentTitle;
        }
    }];
    [self performSelector:@selector(changeAnimation) withObject:nil afterDelay:3.5];
}

demo
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