Question

The error is not every time.
i had try to clean and rebuild app,but it is also.

error:

 *** Assertion failure in -[UIWindowController 
    transition:fromViewController:toViewController:target:didEndSelector:], 
   /SourceCache/UIKit_Sim/UIKit-2372/UIWindowController.m:211

 *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', 
     reason: 'Attempting to begin a modal transition from 
     <UINavigationController: 0x9190730> to <UINavigationController: 0x83a9dc0> 
     while a transition is already in progress. Wait for viewDidAppear/viewDidDisappear
     to know the current transition has completed'

 *** First throw call stack:
 (0x213d012 0x1e85e7e 0x213ce78 0x191bf35 0x10b8d05 0xeb74f3 0xeb7777 0x10be033f   
  0xeb77b7 0x104f0 0x1e996b0 0x18c6035 0x20c0f3f 0x20c096f 0x20e3734 0x20e2f44 
  0x20e2e1b 0x36437e3 0x3643668 0xdcd65c 0x1133f2 0x25c5)
  libc++abi.dylib: terminate called throwing an exception

BaseController.h:

 @class LoginViewController;
 @interface BaseController:UIViewController
 //...
 @end

BaseController.m

 @implement BaseController
 //...
 -(void)showLoginForm
 {
    UIViewController* loginx =(UIViewController*) [[LoginViewController alloc] init];
    UINavigationController* navx = [[UINavigationController alloc] initWithRootViewController:loginx];
    [navx.navigationBar setBackgroundImage:[UIImage imageNamed:@"title_bar.png"] forBarMetrics:UIBarMetricsDefault];
    //added
    //i can use @try to catch it       
    [self presentModalViewController:navx animated:YES];//<====it is error

    [loginx release];
    [navx release];
 }

LoginViewController:

 @interface LoginViewController:BaseController
 //...
 @end

otherViewController:
i will judge the user is login or not in this controller.if it is not login,i will call showLoginForm

  //@interface otherViewController:BaseController
  //......
 -(void)viewDidLoad
  {
     //make a thread to call isLogin
  }
 -(void)isLogin
  { 
      BOOL logined = YES;
      //......
      if(!logined)//i take this on MainThread,it has error also.
         [super showLoginForm];
  }

MainViewController:(it is the Main ViewController to show otherViewController)

 //@interface MainViewController:BaseController
  //......

 -(void)buttonAction
 {
     otherViewController* other = [[otherViewController alloc] init];
     UINavigationController* navigation = [[UINavigationController alloc] initWithRootViewController:other];
      [self presentModalViewController:navigation animated:YES];
     //release
  }

so ,Who knows how this is going on?

Answer 1

In otherViewController.m you should move the code that calls the isLogin method to

- (void)viewDidAppear:(BOOL)animated

This will make sure that the transition for the presentation of the otherViewController will have finished when [self presentModalViewController:navx animated:YES]; is called.