Methods gets called when app goes to the background - ios

Question

my app consists of a table view controller and a view controller. when i press a cell in the table view, the toolbar at that view slips with animation down outside the screen and when i'm in the view controller and press back, the toolbar bar slips upwards to it's original position. My problem is, i figured out a bug that when i'm in the view controller and press the home button to exit the app and then come back. the app resumes where i left but when i go back to the table view, the toolbar shifts upwards beyond it's original position. the sliding of the toolbar works fine when i'm in the app before exiting. so there's like something is being called to reset the toolbar to it's origin and thus adding the additional y-axis point to shift more upwards. does anybody know what are those methods?
Code:
i have this in the viewWillAppear method of the view controller:
[UIView animateWithDuration:0.7 animations:^{
self.navigationController.toolbar.center = CGPointMake(self.navigationController.toolbar.center.x, self.navigationController.toolbar.center.y + self.navigationController.toolbar.frame.size.height);
} completion:^(BOOL finished){
self.navigationController.toolbar.hidden = YES;
}];
and in the same view when it needs to disappear i added this in the viewWillDisappear:
[[self.navigationController toolbar] setHidden:NO];
[UIView animateWithDuration:1 animations:^{
self.navigationController.toolbar.center = CGPointMake(self.navigationController.toolbar.center.x, self.navigationController.toolbar.center.y - self.navigationController.toolbar.frame.size.height);
} completion:^(BOOL finished){
}];
i tried this as another way to animate the hiding of the toolbar but there is no animation:
- (void) viewWillAppear:(BOOL)animated
{
[self.picker setHidden:YES];
[self.navigationController setToolbarHidden:YES animated:YES];
}
- (void) viewWillDisappear:(BOOL)animated
{
[self.navigationController setToolbarHidden:NO animated:YES];
[self.course setValue:self.nameTextField.text forKey:#"courseName"];
[self.course setValue:[NSNumber numberWithInt:[self.creditsTextfield.text integerValue]] forKey:#"courseCredits"];
[self.course setValue:[NSNumber numberWithInt:[self.chaptersTextfield.text integerValue]] forKey:#"courseChapters"];
[self.course setValue:self.gradeTextfield.text forKey:#"courseGrade"];
}

Answer 1

For one thing, you should use frame instead of center, but replace the viewWillDisappear animation line with this:
self.navigationController.toolbar.frame = CGRectMake(0,0,self.navigationController.toolbar.frame.size.width, self.navigationController.toolbar.frame.size.height);
and tell me what happens...
That should fix your problem.

Answer 2

Since you are using the toolbar belonging to a UINavigationController (and not a standalone UIToolbar instantiated and added to a UIView by your own controller), it's better to use the methods that UINavigationController exposes, because you don't know how it manages and move its UIToolbar.
Try to put just this in viewWillAppear:, instead of the entire animation block
[self.navigationController setToolbarHidden:NO animated:YES];
and this in viewWillDisappear:
[self.navigationController setToolbarHidden:YES animated:YES];

Answer 3

i fixed it! i aded the following lines of code in viewWillDisappear:
self.navigationController.toolbar.center = CGPointMake(self.navigationController.toolbar.center.x, 458);
self.navigationController.toolbar.center = CGPointMake(self.navigationController.toolbar.center.x, self.navigationController.toolbar.center.y + self.navigationController.toolbar.frame.size.height);
since the problem seems that when the app goes background then foreground the toolbar resets to it's original position and thus after navigating back to the table view the toolbar is shifted beyond it's original position. therefore the first line i added resets the toolbar to it's original position while still hidden then shift it down. after that the block of animation is done. i did this so that the animation works on the following cases:
1. the user enters the detail view from the table view then goes back to the tableview without exiting the app.
2. the user enters the detail view from the tableview then exits the app and then resume the app and goes back to the table view.