如何为UITableView节的页脚设置动画

Question

I am trying to animate a UITableView section footer. I have tried the following code:

- (UIView *)tableView:(UITableView *)tableView viewForFooterInSection:(NSInteger)section {
CustomView *footer = [[CustomView alloc]initWithFrame:CGRectZero
                                            labelText:@"I am a label in a footer"];
footer.label.alpha = 0.0f;
[UIView animateWithDuration:5.0f
                      delay:0.0f
                    options:UIViewAnimationOptionCurveLinear
                 animations:^{
                     footer.label.alpha = 1.0f;
                 }
                 completion:nil];

return footer;
}

But the footer displays without animation. What's the correct way to animate a UITableView section footer? I believe it is possible but can't find an answer for it.

Answer 1

Try doing the animation in the tableView:willDisplayFooterView:forSection: method instead. In the method you are using, the view is not inserted into the view hierarchy yet (and thus not in a window), so animations really won't do anything (and they would likely be cancelled by inserting it into a view anyways). The -willDisplay* variants are really where you should configure visible UI properties, since it should be in the view hierarchy at that point, and things like UIAppearance values should have been set so your settings won't be overwritten later.

You can often get away with configuring properties in the cellForRowAtIndexPath: method (or viewForFooter in this case) but not always -- and definitely for animations.