Create tableHeaderView that always fills the frame of the visible table? - ios

Question

I need to implement the ability to display a label perfectly centered on screen with nothing else visible, but this needs to be done in a UITableView. The setup is a UISpiltViewController that has a UITableViewController for the detail view controller, and when no item is selected on the left I want to display a message stating that on the right, and when the user selects an item that label should instantly disappear and reveal the table. (Just like the Mail app.)
I already have this set up and it's working ok, but for some reason it's not always staying centered on screen, and it isn't a very good solution - there are some minor oddities for example you can partially see the top of the table while the rotation is occurring. I am just creating a UILabel, setting its frame to fill the visible area, then setting the table's tableHeaderView to that label, and finally disabling the ability to scroll the table. And upon rotation, the frame has to be updated to fill the visible area again. That's where the oddities occur, because it's not updating until after the rotation completes.
My question is, what is a better approach to implement this behavior? Is there some way I can prevent having to update the frame after rotation, would it be possible to use Auto Layout for the tableHeaderView?
//Setting the tableHeaderView
self.tableView.tableHeaderView = self.label;
//Creating the UILabel
- (UILabel *)label {
_label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, self.tableView.bounds.size.width,
self.tableView.bounds.size.height
- self.navigationController.navigationBar.frame.size.height
- self.tabBarController.tabBar.frame.size.height
- MIN([UIApplication sharedApplication].statusBarFrame.size.height,
[UIApplication sharedApplication].statusBarFrame.size.width))];
_label.text = #"Nothing Selected";
_label.textAlignment = NSTextAlignmentCenter;
_label.backgroundColor = self.tableView.backgroundColor;
return _label;
}
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation {
if (_label) {
_label.frame = CGRectMake(0, 0, self.tableView.bounds.size.width,
self.tableView.bounds.size.height
- self.navigationController.navigationBar.frame.size.height
- self.tabBarController.tabBar.frame.size.height
- MIN([UIApplication sharedApplication].statusBarFrame.size.height,
[UIApplication sharedApplication].statusBarFrame.size.width));
self.tableView.tableHeaderView = nil;
self.tableView.tableHeaderView = _label;
}
}

Answer 1

Is your detail controller a UITableViewController? If so, that makes things harder since any subviews you add (your label) become part of the table. It would be easier if you use a UIViewController, and alternately hide the label or table view when you need to. The label can be any size, and use centerX and centerY constraints to keep it centered. If you do it that way, you won't have to do anything on rotation.

Answer 2

You don't have to set the label as the headerView of your UITableView.
You can simply add the label to self.view. Even if you are running inside a UITableViewController, each UIViewController always has a view property.
Add the label to self.view and toggle the visibility of the label and the tableView as needed.This is much easier, than trying to fiddle the label in the tableview - hierarchy ;)
EDIT
As pointed out by #rdelmar, the UITableViewController indeed does not have a separate view which contains the tableview, but rather uses the tableview as it's view directly. -.-
Sorry. I did assume the two views were separated.
All I can say is follow #rdelmar s advice, and stop using UITableViewController. It forces you to do things the default way, and if you want to customized it you WILL have a bad time :(
EDIT 2
Ok so you have 2 options:
1) Do the following:
[_label setAutoResizingMask:(UIViewAutoResizingFlexibleWidth | UIViewAutoResizingFlexibleHeight)];
in your label getter. That way, you don't have to care about screen rotation anymore. The label will always fit its parents bounds.
2) Use UIViewController and treat the label as a sibling of the tableView. <- Better approach but requires more refactoring from your current state.

Answer 3

As pointed out by Cabus, the solution is to set the autoresizingMask of the label to UIViewAutoResizingFlexibleWidth | UIViewAutoResizingFlexibleHeight. That way, the label will always fit its parent. This can be done while using the label for the tableHeaderView, and there's no longer a need for detecting orientation changes.