Calling [table reloadData] removes table's position change from [uiview animatewithduration] - ios

Question

There is a button that horizontally shifts my table.
- (void)togglePreferencePageVisibility:(id)sender {
int translation = [self preferencesVisible] ? -PREFERENCE_TRANSLATION_HEIGHT : PREFERENCE_TRANSLATION_HEIGHT;
//animate tableview down
[UIView animateWithDuration:0.3
delay:0
options: UIViewAnimationCurveEaseOut
animations:^{
_table.center = CGPointMake(_table.center.x, _table.center.y+translation);
}
completion:^(BOOL finished){
}];
}
When I call [_table reloadData], the table reverts to its original position. I tried manually readjusting the table position, like so
NSLog(#"before %#", NSStringFromCGRect(_table.frame));
[_table reloadData];
_table.frame = CGRectMake(initialTablePosition.x, initialTablePosition.y+PREFERENCE_TRANSLATION_HEIGHT, _table.frame.size.width, _table.frame.size.height);
NSLog(#"after %#", NSStringFromCGRect(_table.frame));
but no luck. Also the frame's have the same y position before and after.

Answer 1

You need to also adjust the auto layout constraints using the NSLayoutConstraint class. You can add, remove or change the values of NSLayoutConstraints. This is a VERY common question on stack overflow right now, due to the change from iOS 7 to iOS 8.
If you do not adjust the layout constraints then the view will be repositioned back to its original location. reloadData redraws the UITableView which causes the view hierarchy to reexamine its positions e.t.c.
As an example of making a view with a width constraint narrower:
CGRect frame = myView.frame;
frame.size.width -= 100;
//Next line now needed in iOS 8
myWidthConstraint.constant -= 100;
[UIView animateWithDuration:0.5 animations:^{
[myView setFrame:frame];
}];
EDIT: moving back example:
CGRect frame = myView.frame;
frame.size.width += 100;
//Next line now needed in iOS 8
myWidthConstraint.constant += 100;
[UIView animateWithDuration:0.5 animations:^{
[myView setFrame:frame];
}];

Answer 2

When using auto layout, you should not set any frames. If you do, when the view needs to redraw itself, the frame will be reset to the frame defined by its constraints. You should add an IBOutlet to a constraint between your table view and the top (or bottom what ever works for your use) of its superview (I'll call it topCon in the example below).
- (void)togglePreferencePageVisibility:(id)sender {
int translation = [self preferencesVisible] ? -PREFERENCE_TRANSLATION_HEIGHT : PREFERENCE_TRANSLATION_HEIGHT;
//animate tableview down
self.topCon.constant += translation; // this might need to be "-=" depending on whether your constraint is to the top or bottom
[UIView animateWithDuration:0.3
delay:0
options: UIViewAnimationCurveEaseOut
animations:^{
[self.view layoutIfNeeded];
}
completion:^(BOOL finished){
}];
}