平滑我的滚动TouchesMoved

Question

我有一个半透明的视图，位于台面上。当我将视图拖到屏幕底部附近时，我想要顺利地滚动它下面的表视图。

我试着模仿：

用户拖动悬停视图靠近屏幕底部，并保持在那里。表视图滚动直到它们松开，或者直到它们到达表的底部。用户放弃悬停视图。

目前我正在做：

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    if (!_hoverViewTouch) {
        return;
    }

    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView:self];
    CGPoint prevLocation = [touch previousLocationInView:self];

    //scroll down.
    if (prevLocation.y < location.y) {
        if (location.y >= _table.frame.size.height - rowHeight) {
            NSArray *cells = [_table visibleCells];
            UITableViewCell *cell = [cells objectAtIndex:round(cells.count / 2)];
            NSIndexPath *indexPath = [_table indexPathForCell:cell];
            [_table scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionTop animated:true];
        }
    }

    CGRect frame = [hoverView frame];
    frame.origin.y = location.y - (hoverView.frame.size.height / 2.0f);
    [hoverView setFrame:frame];
}

然而，它滚动到表格底部的速度是如此之快。我怎样才能放慢速度或者平滑滚动呢？

Answer 1

UITableView的scrollToRowAtIndexPath方法不能控制动画速度。相反，您可以使用CADisplayLink来平稳地更新表视图的contentOffset。

- (void)startAnimatingTable
{
    self.scrollStartDate = [NSDate date];
    self.startContentOffset = self.tableView.contentOffset;
    self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(displayLinkFired:)];
    [self.displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
}

- (void)stopAnimatingTable
{
    [self.displayLink removeFromRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    self.displayLink = nil;
}

- (void)displayLinkFired:(CADisplayLink *)displayLink
{
    NSTimeInterval interval = -[self.scrollStartDate timeIntervalSinceNow];
    CGFloat speed = 100;
    CGFloat yOffset = self.startContentOffset.y + speed * interval;
    self.tableView.contentOffset = CGPointMake(self.startContentOffset.x, yOffset);
}