What is causing my EXC_BAD_ACCESS? (iPhone SDK) - ios

Question

- (IBAction)startSignin:(id)sender {
Login *aview = [[Login alloc] init];
aview.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self.navigationController presentModalViewController:aview animated:YES];
[_window addSubview:aview.view];
[aview release];
}
What is causing my EXC BAD ACCESS?
Every time it loads Login, It crashes whenever i press a button or something on that page.
*** Call stack at first throw:
(
0 CoreFoundation 0x00dc25a9 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x00f16313 objc_exception_throw + 44
2 CoreFoundation 0x00d7aef8 +[NSException raise:format:arguments:] + 136
3 CoreFoundation 0x00d7ae6a +[NSException raise:format:] + 58
4 UIKit 0x000c6709 -[UIViewController _loadViewFromNibNamed:bundle:] + 295
5 UIKit 0x000c4134 -[UIViewController loadView] + 120
6 UIKit 0x000c400e -[UIViewController view] + 56
7 UIKit 0x00037d42 -[UIWindow addRootViewControllerViewIfPossible] + 51
8 Test 0x00001b3c -[TestAppDelegate application:didFinishLaunchingWithOptions:] + 220
9 UIKit 0x00014c89 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1163
10 UIKit 0x00016d88 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 439
11 UIKit 0x00021617 -[UIApplication handleEvent:withNewEvent:] + 1533
12 UIKit 0x00019abf -[UIApplication sendEvent:] + 71
13 UIKit 0x0001ef2e _UIApplicationHandleEvent + 7576
14 GraphicsServices 0x00ffb992 PurpleEventCallback + 1550
15 CoreFoundation 0x00da3944 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
16 CoreFoundation 0x00d03cf7 __CFRunLoopDoSource1 + 215
17 CoreFoundation 0x00d00f83 __CFRunLoopRun + 979
18 CoreFoundation 0x00d00840 CFRunLoopRunSpecific + 208
19 CoreFoundation 0x00d00761 CFRunLoopRunInMode + 97
20 UIKit 0x000167d2 -[UIApplication _run] + 623
21 UIKit 0x00022c93 UIApplicationMain + 1160
22 Test 0x00001a29 main + 121
23 Test 0x000019a5 start + 53
)
terminate called throwing an exceptionCurrent language: auto; currently objective-c

Answer 1

This is frequently caused by accessing an object after it is released. This is a good point to familiarize yourself with the debugger, too. Set a break point on the first line of the button action method, and step through it to find out which line is bad.
This time, i suspect it is your call to addSubview:, the presentModal… will take care of presenting the view.