UIPageViewController索引错误

Question

I am trying to open 3 ViewControllers ("VC1", "VC2" "VC3") from a UIPageViewController but I get errors which I don't understand.
I am not very familiar with x-code yet.

This is my code from PagingViewController.h :

#import <UIKit/UIKit.h>

@interface PagingViewController : UIViewController <UIPageViewControllerDataSource, UIPageViewControllerDelegate>

@property (assign, nonatomic) NSInteger index;

@property int defaultIndex;

@property NSArray *viewControllers;
@property UIPageControl *pageController;
@property UIPageViewController *pageViewController;

@property UIViewController *VC1;
@property UIViewController *VC2;
@property UIViewController *VC3;

@end

This is the code from "PagingViewController.m":

#import "PagingViewController.h"

@interface PagingViewController ()

@end

@implementation PagingViewController



- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController {


//    self.index--;
//    if(self.index<0)
//    {
//        self.index=0;
//    }
    return [self viewControllerAtIndex:self.index--];

}
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {

    //self.index++;

    return [self viewControllerAtIndex:self.index++];

}
- (UIViewController *)viewControllerAtIndex:(NSUInteger)index {

    return self.viewControllers[index];


}



- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController {
    // The number of items reflected in the page indicator.
    return 3;
}

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController {
    // The selected item reflected in the page indicator.
    return self.defaultIndex;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.pageViewController.dataSource = self;
    self.pageViewController.delegate = self;

    self.index = 1;

    self.VC1 = [self.storyboard instantiateViewControllerWithIdentifier:@"VC1"];
    self.VC2 = [self.storyboard instantiateViewControllerWithIdentifier:@"VC2"];
    self.VC3 = [self.storyboard instantiateViewControllerWithIdentifier:@"VC3"];

    self.viewControllers = @[self.VC1, self.VC2, self.VC3];

    //self.index = 1;

    //  [self performSelector:@selector(loadingNextView) withObject:nil afterDelay:2.0f];

    [self.pageViewController setViewControllers:self.viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];
    [self addChildViewController:self.pageViewController];

    self.view.gestureRecognizers = self.pageViewController.gestureRecognizers;

    [self.view addSubview:self.pageViewController.view];
    [self.pageViewController didMoveToParentViewController:self];

    //NSArray *viewControllers = [NSArray arrayWithObject:self.VC1];
    //[self setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];


}


- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

And this is the error report from the console:

2014-02-17 18:34:05.560 PageViewC und TableVC-20140217[4493:70b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'
*** First throw call stack:
(
    0   CoreFoundation                      0x0173c5e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x014bf8b6 objc_exception_throw + 44
    2   CoreFoundation                      0x016eebcc -[__NSArrayM insertObject:atIndex:] + 844
    3   CoreFoundation                      0x016ee870 -[__NSArrayM addObject:] + 64
    4   UIKit                               0x00343d7b -[UIViewController _addChildViewController:performHierarchyCheck:notifyWillMove:] + 417
    5   UIKit                               0x00355874 -[UIViewController(UIContainerViewControllerProtectedMethods) addChildViewController:] + 68
    6   PageViewC und TableVC-20140217      0x00002b4c -[PagingViewController viewDidLoad] + 1180
    7   UIKit                               0x00341318 -[UIViewController loadViewIfRequired] + 696
    8   UIKit                               0x003415b4 -[UIViewController view] + 35
    9   UIKit                               0x002699fd -[UIWindow addRootViewControllerViewIfPossible] + 66
    10  UIKit                               0x00269d97 -[UIWindow _setHidden:forced:] + 312
    11  UIKit                               0x0026a02d -[UIWindow _orderFrontWithoutMakingKey] + 49
    12  UIKit                               0x0027489a -[UIWindow makeKeyAndVisible] + 65
    13  UIKit                               0x00227cd0 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1851
    14  UIKit                               0x0022c3a8 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 824
    15  UIKit                               0x0024087c -[UIApplication handleEvent:withNewEvent:] + 3447
    16  UIKit                               0x00240de9 -[UIApplication sendEvent:] + 85
    17  UIKit                               0x0022e025 _UIApplicationHandleEvent + 736
    18  GraphicsServices                    0x036e32f6 _PurpleEventCallback + 776
    19  GraphicsServices                    0x036e2e01 PurpleEventCallback + 46
    20  CoreFoundation                      0x016b7d65 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53
    21  CoreFoundation                      0x016b7a9b __CFRunLoopDoSource1 + 523
    22  CoreFoundation                      0x016e277c __CFRunLoopRun + 2156
    23  CoreFoundation                      0x016e1ac3 CFRunLoopRunSpecific + 467
    24  CoreFoundation                      0x016e18db CFRunLoopRunInMode + 123
    25  UIKit                               0x0022badd -[UIApplication _run] + 840
    26  UIKit                               0x0022dd3b UIApplicationMain + 1225
    27  PageViewC und TableVC-20140217      0x000033dd main + 141
    28  libdyld.dylib                       0x01d7a70d start + 1
    29  ???                                 0x00000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Thanks a lot for helping! Daniel

UPDATE

Meanwhile I have set up 'VC1' properly as a class. And after following the advice to activate the Breakpoint navigator (which I set up as "All Exceptions" 'Break on Throw') the Run stopped at this line in the main section ('return UIApplication ... see below)

int main(int argc, char * argv[])
{
    @autoreleasepool {
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));

    }

This is the new error message in the console:

2014-02-18 17:23:02.967 PageViewC und TableVC-20140217[5907:70b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'
*** First throw call stack:
(
    0   CoreFoundation                      0x0173c5e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x014bf8b6 objc_exception_throw + 44
    2   CoreFoundation                      0x016eebcc -[__NSArrayM insertObject:atIndex:] + 844
    3   CoreFoundation                      0x016ee870 -[__NSArrayM addObject:] + 64
    4   UIKit                               0x00343d7b -[UIViewController _addChildViewController:performHierarchyCheck:notifyWillMove:] + 417
    5   UIKit                               0x00355874 -[UIViewController(UIContainerViewControllerProtectedMethods) addChildViewController:] + 68
    6   PageViewC und TableVC-20140217      0x00002acc -[PagingViewController viewDidLoad] + 1180
    7   UIKit                               0x00341318 -[UIViewController loadViewIfRequired] + 696
    8   UIKit                               0x003415b4 -[UIViewController view] + 35
    9   UIKit                               0x002699fd -[UIWindow addRootViewControllerViewIfPossible] + 66
    10  UIKit                               0x00269d97 -[UIWindow _setHidden:forced:] + 312
    11  UIKit                               0x0026a02d -[UIWindow _orderFrontWithoutMakingKey] + 49
    12  UIKit                               0x0027489a -[UIWindow makeKeyAndVisible] + 65
    13  UIKit                               0x00227cd0 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1851
    14  UIKit                               0x0022c3a8 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 824
    15  UIKit                               0x0024087c -[UIApplication handleEvent:withNewEvent:] + 3447
    16  UIKit                               0x00240de9 -[UIApplication sendEvent:] + 85
    17  UIKit                               0x0022e025 _UIApplicationHandleEvent + 736
    18  GraphicsServices                    0x036e32f6 _PurpleEventCallback + 776
    19  GraphicsServices                    0x036e2e01 PurpleEventCallback + 46
    20  CoreFoundation                      0x016b7d65 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53
    21  CoreFoundation                      0x016b7a9b __CFRunLoopDoSource1 + 523
    22  CoreFoundation                      0x016e277c __CFRunLoopRun + 2156
    23  CoreFoundation                      0x016e1ac3 CFRunLoopRunSpecific + 467
    24  CoreFoundation                      0x016e18db CFRunLoopRunInMode + 123
    25  UIKit                               0x0022badd -[UIApplication _run] + 840
    26  UIKit                               0x0022dd3b UIApplicationMain + 1225
    27  PageViewC und TableVC-20140217      0x0000335d main + 141
    28  libdyld.dylib                       0x01d7a70d start + 1
    29  ???                                 0x00000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

Answer 1

The error message says you're trying to insert a nil object. First thing I'd check is whether the view controllers in the storyboard are set up with the correct identifiers ('VC1'... etc).