How can I tell if my viewcontroller is visible and accepting events?

Question

I have a view that I tell to update when its data changes. But sometimes the data changes when the view isn't visible. So how can I detect that the viewcontroller is visible and accepting events? I could add a boolean that is changed in viewWillAppear and viewWillDisappear, but it seems like there ought to be a way to detect the state directly...

Thanks, Gary

Jonathan Arbogast · Accepted Answer · 2009-05-12 15:53:16Z

12

Short Answer: If you are using a UINavigationController you can use it's visibleViewController so that you don't have to keep track of a separate boolean value.

Long Answer: Typically when I find myself calling reloadData inside of viewWillAppear, it is an indication that my View needs to observe some additional part of my Model. The problem with reloadData is that it is going to reload your entire table. Often times, you really only need to update a small part of the table. My strategy is normally to update only what I need to as it occurs regardless of whether or not a particular view is visible at that time. I know that is a pretty vague response...maybe some sample code of yours would help me be more specific...

answered May 12, 2009 at 15:53

Jonathan Arbogast

9,6504 gold badges37 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Rog Over a year ago

> Typically when I find myself calling reloadData inside of > viewWillAppear, it is an indication that my View needs to observe > some additional part of my Model Agreed.

DrGary Over a year ago

Yup, that's what I was looking for. The line is: 'if(self.navigationController.visibleViewController != self) { ...}'. BTW, I used this in a UIViewController in a UITabBarController.

tmadsen · Accepted Answer · 2009-05-12 08:00:54Z

1

if it's a tableview you can do something like:

[(UITableView *)[self view] reloadData];

in the viewController's viewWillAppear. I'm not sure, that's what you're asking but anyways.

answered May 12, 2009 at 8:00

tmadsen

9217 silver badges14 bronze badges

Comments

mfazekas · Accepted Answer · 2009-05-12 10:07:32Z

0

You can probably check the view's window property:

- (BOOL)isVisible
{
  return view.window != NULL;
}

But i think maintaining a BOOL variable is better.

answered May 12, 2009 at 10:07

mfazekas

5,7291 gold badge37 silver badges25 bronze badges

Collectives™ on Stack Overflow

How can I tell if my viewcontroller is visible and accepting events?

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related