unable to switch from multiple views - iphone

Question

I have a simple app with only location services and 3 (almost empty) different views, and from some reason I can't get from view 1 to view 2 - app crashes and I get an exception. View 1 is the original .xib file, the two others are just views that I added later. It's weird cause I can switch between all of them (1->3, 2->1, 2->3, etc..) just not from 1->2.
I use this code in #1 view controller m. file:
- (IBAction) switchToMaps : (id)sender //this is the one that doesnt work
{
MyMap *mapsView = [[MyMap alloc] initWithNibName:nil bundle:nil];
[self presentModalViewController:mapsView animated:YES];
}
- (IBAction) switchToThird : (id)sender
{
ThirdView *third = [[ThirdView alloc] initWithNibName:nil bundle:nil];
[self presentModalViewController:third animated:YES];
}
and as another example, here is the code from the 2nd view controller (MyMaps.m):
- (IBAction) switchBack : (id)sender
{
LastLocationViewController *firstView = [[LastLocationViewController alloc] initWithNibName:nil bundle:nil];
[self presentModalViewController:firstView animated:YES];
}
- (IBAction) switchFront : (id)sender
{
ThirdView *lastView = [[ThirdView alloc] initWithNibName:nil bundle:nil];
[self presentModalViewController:lastView animated:YES];
}
I know it's super vague, but any ideas what can cause this? I have no idea how to debug this...I even put breakpoints at the beginning of each IBAction method, and when it crashes, it doesnt even stop there....before I added this code, this app (which has only location) worked totally fine.
Any ideas?? Thanks!!

Answer 1

if your view does not load from any nib file then you should do like
MyMap *mapsView = [[MyMap alloc] init];
and
ThirdView *lastView = [[ThirdView alloc] init];
and in your back method
- (IBAction) switchBack : (id)sender
{
// LastLocationViewController *firstView = [[LastLocationViewController alloc] initWithNibName:nil bundle:nil]; // because you are allocating new memory to your last view
// [self presentModalViewController:firstView animated:YES];
[self dismissModalViewControllerAnimated:YES];
}
- (IBAction) switchFront : (id)sender
{
// ThirdView *lastView = [[ThirdView alloc] initWithNibName:nil bundle:nil];
// [self presentModalViewController:lastView animated:YES];
[self dismissModalViewControllerAnimated:YES];
}

Answer 2

My hunch is that you're throwing an exception because
MyMap *mapsView = [[MyMap alloc] initWithNibName:nil bundle:nil];
is failing to load a nib. Without seeing your console output it's impossible to say for sure. So a few things to try:
Comment out [self presentModalViewController:mapsView animated:YES];, see if it still crashes.
Explicitly name the nib you expect to load. The nib loader assumes the nib is named exactly the same as the view controller if you pass in nil. So if you don't have a match, you'll end up with an exception (Like this [[MyMap alloc] initWithNibName:#"NibNameWithoutExtension" bundle:nil];)
Set a breakpoint at [self present... and then hover your mouse over "mapsView" after execution pauses. If the popup thing shows you mapsView is nil, you know your trouble is trying to pass a nil object to -presentModalViewController:animated:. If your breakpoint never hits because you throw an exception first, well, there you go, the trouble is a line above.
edit:
One more thing. If your nib has a button that's wired to an action that no longer exists, that would definitely get you in trouble. Inspect each button and make sure no actions are labeled in yellow, indicating a mismatch between the button's target and the actions it's reporting to IB. This would definitely account for the breakpoint behavior you described.