UIView Animaton 重置为开始

Question

我正在尝试运行动画，以便滚动视图的 contentoffset 不断向下滚动。

但是，每次重复后，它都会从原始位置开始动画，并且不会继续。

[UIView beginAnimations:nil context:NULL];
[UIView setAnimationBeginsFromCurrentState: YES];
[UIView setAnimationDuration:1.0];
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIView setAnimationRepeatCount: 100];

CGPoint contentOffset = scrollView.contentOffset;
contentOffset.y += 50;
scrollView.contentOffset = contentOffset;

scrollView.transform = CGAffineTransformIdentity;  
[UIView commitAnimations];

有什么想法吗？

Answer 1

您为什么尝试手动滚动视图？不会用这个方法吗

- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated

？

无论如何，我相信您的动画未按预期工作的原因是因为您设置了重复计数，而不是每次都实际重新渲染动画。如果您想解决此问题，可以通过创建包装动画并通过上下文指针传递参数的方法，在动画回调中再次设置动画。

- (void) animateContentOffsetByAmount:(CGFloat)amount numberRemaining:(int)num {
    if (num == 0) return;

    [UIView setAnimationDelegate:self];
    [UIView setAnimationDidStopSelector:
        @selector(scrollAnimationStoppedWithID:finished:context:)];

    //NSArray released in callback
    NSArray* contextArray = [NSArray arrayWithObjects:
      [NSNumber numberWithFloat:amount],
      [NSNumber numberwithInt:num], nil]
    [UIView beginAnimations:nil context:contextArray];
    [UIView setAnimationBeginsFromCurrentState: YES];
    [UIView setAnimationDuration:1.0];
    [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];

    CGPoint contentOffset = scrollView.contentOffset;
    contentOffset.y += amount;
    scrollView.contentOffset = contentOffset;

    scrollView.transform = CGAffineTransformIdentity;  
    [UIView commitAnimations];
}

- (void) scrollAnimationStoppedWithID:(NSString*)id
        finished:(NSNumber*)finished context:(void*)context {
    NSArray* contextArray = (NSArray*)context;
    CGFloat amount = [(NSNumber*)[contextArray objectAtIndex:0] floatValue];
    int count = [(NSNumber*)[contextArray objectAtIndex:1] intValue];
    count = count - 1;
    [contextArray release];
    [self animateContentOffsetByAmount:amount numberRemaining:count]
}

然后在你的代码中，只需调用

[self animateContentOffsetByAmount:50 numberRemaining:100];