UIApplication sharedAppication error: program seems to be accessing wrong file

问题

in my MainViewController implementation, I need to access variables from two different classes. one of the classes is the AppDelegate and the other is the FlipsideViewController. the way I accessed these was through this code:

-(void)someMethod
{
MyApplicationAppDelegate *appDelegate = (MyApplicationAppDelegate *)[[UIApplication sharedApplication] delegate];
FlipsideViewController *viewController = (FlipsideViewController *)[[UIApplication sharedApplication] delegate];

then I have an array I access from my application delegate, and some instance variables that return values from an instance of UISwitch from the flipsideViewController:

NSMutableArray* array = [[NSMutableArray alloc] initWithArray:(NSMutableArray *)appdelegate.originalArray];
for (id element in array)
{
    if ([[element attribute] isEqualToString:@"someAttribute"] && [viewController.switch1 isOn] == YES)
    {
    //preform function
    }
}

I keep getting the error message "-[MyApplicationAppDelegate switch1]: unrecognized selector sent to instance. terminating app due to uncaught exception"

回答1:

[[UIApplication sharedApplication] delegate]; will always return the (singleton) instance of MyApplicationAppDelegate class and you cannot simply cast it to FlipsideViewController*. to access flipsidecontroller value (assuming it is stored in your appdelegate) you can define a property and call it:

-(void)somemethod{
     MyApplicationAppDelegate *appDelegate = (MyApplicationAppDelegate *)[[UIApplication sharedApplication] delegate];
     FlipsideViewController *viewController = appDelegate.flipsideController;
}

来源：https://stackoverflow.com/questions/2075352/uiapplication-sharedappication-error-program-seems-to-be-accessing-wrong-file