使用视图控制器容器，子视图会失去父视图。

Question

我是一个新的iOS开发人员，正在写第一个委托应用程序适用于iPhone。

模态调用的父视图控制器拥有六个子项，使用父项中的分段控件进行转换。 我遇到了以下错误：

当调用-[UIViewController transitionFromViewController:toViewController:duration:options:animations:completion:]时，子视图控制器和必须具有共同的父视图控制器

当我按下第二个按钮时，即在显示父项后，我可以按任何按钮，它都能正常工作。 但是，下一次我按下新按钮时，我会收到上面的崩溃错误。 使用NSLogs，我已确定崩溃原因是当前和新子项在按钮按下之间失去了它们的父项。 我不知道为什么。 父项的相关代码如下：

接口代码：

#import <UIKit/UIKit.h>
#import "WorksheetScrollViewController.h"
#import "Worksheet1ViewController.h"
#import "Worksheet2ViewController.h"
#import "Worksheet3ViewController.h"
#import "Worksheet4ViewController.h"
#import "WorksheetEndViewController.h"


@interface WorkSheetParentViewController : UIViewController
{
IBOutlet UISegmentedControl *segControl;
IBOutlet UIBarButtonItem *doneButton;
IBOutlet UIView *childContainerView;

WorksheetScrollViewController *wStart;
Worksheet1ViewController *w1; 
Worksheet2ViewController *w2;
Worksheet3ViewController *w3;
Worksheet4ViewController *w4;
WorksheetEndViewController *wEnd;

UIViewController *currentVC;
UIViewController *newVC;

}


-(void)initToolbar;
-(IBAction) doneButtonPressed:(id)sender;
-(IBAction) segControlChanged:(id)sender;

-(void)swapViewControllers;

实现代码:

- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view from its nib.
wStart = [[WorksheetScrollViewController alloc        ]initWithNibName:@"WorksheetScrollViewController" bundle:nil];

[self addChildViewController:wStart];
wStart.view.frame=childContainerView.bounds;

[childContainerView addSubview:wStart.view];
[wStart didMoveToParentViewController:self];
currentVC = wStart;

}

- (IBAction) segControlChanged:(id)sender

{

NSLog(@"selected tab bar item:%i",segControl.selectedSegmentIndex);
switch (segControl.selectedSegmentIndex) {
    case 0:
        if (!wStart) {
            wStart = [[WorksheetScrollViewController alloc ]initWithNibName:@"WorksheetScrollViewController" bundle:nil];
        }
        newVC = wStart;
        break;

    case 1:
        if (!w1) {
            w1 = [[Worksheet1ViewController alloc ]initWithNibName:@"Worksheet1ViewController" bundle:nil];
        }
        newVC = w1;
        break;

    case 2:
        if (!w2) {
            w2 = [[Worksheet2ViewController alloc ]initWithNibName:@"Worksheet2ViewController" bundle:nil];
        }
        newVC = w2;
       break;

    case 3:
        if (!w3) {
            w3 = [[Worksheet3ViewController alloc ]initWithNibName:@"Worksheet3ViewController" bundle:nil];
        }
        newVC = w3;
        break;

    case 4:
        if (!w4) {
            w4 = [[Worksheet4ViewController alloc ]initWithNibName:@"Worksheet4ViewController" bundle:nil];
        }
        newVC = w4;
        break;

    case 5:
        if (!wEnd) {
            wEnd = [[WorksheetEndViewController alloc ]initWithNibName:@"WorksheetEndViewController" bundle:nil];
        }
        newVC = wEnd;
        break;


    default:
        break;
}
[self  swapViewControllers];


}

-(void)swapViewControllers
{
NSLog(@"top current VC parent = %@",currentVC.parentViewController);
NSLog(@"top new VC parent = %@",newVC.parentViewController);
[currentVC willMoveToParentViewController:nil];
newVC.view.frame=childContainerView.bounds;

[self addChildViewController:newVC];

NSLog(@"current VC parent = %@",currentVC.parentViewController);
NSLog(@"new VC parent = %@",newVC.parentViewController);
[self transitionFromViewController:currentVC
                  toViewController:newVC
                          duration:1.0
                           options:UIViewAnimationOptionTransitionCurlUp
                        animations:nil
                        completion:^(BOOL finished) {
                            [currentVC removeFromParentViewController];
                            [newVC didMoveToParentViewController:self];

                        }];
currentVC = newVC;
NSLog(@"bottom current VC parent = %@",currentVC.parentViewController);
NSLog(@"bottom new VC parent = %@",newVC.parentViewController);

}

按下按钮1，然后按下按钮2的Nslog结果：

2013-08-26 14:49:07.245 Alveolar Gas iPhone[556:707] selected tab bar item:1
2013-08-26 14:49:07.251 Alveolar Gas iPhone[556:707] top current VC parent =      <WorkSheetParentViewController: 0x198da0>
2013-08-26 14:49:07.256 Alveolar Gas iPhone[556:707] top new VC parent = (null)
2013-08-26 14:49:07.437 Alveolar Gas iPhone[556:707] current VC parent = <WorkSheetParentViewController: 0x198da0>
2013-08-26 14:49:07.440 Alveolar Gas iPhone[556:707] new VC parent = <WorkSheetParentViewController: 0x198da0>
2013-08-26 14:49:07.460 Alveolar Gas iPhone[556:707] bottom current VC parent = <WorkSheetParentViewController: 0x198da0>
2013-08-26 14:49:07.462 Alveolar Gas iPhone[556:707] bottom new VC parent = <WorkSheetParentViewController: 0x198da0>
2013-08-26 14:49:13.984 Alveolar Gas iPhone[556:707] selected tab bar item:2
2013-08-26 14:49:33.912 Alveolar Gas iPhone[556:707] top current VC parent = (null)
2013-08-26 14:49:50.038 Alveolar Gas iPhone[556:707] top new VC parent = (null)
2013-08-26 14:55:36.149 Alveolar Gas iPhone[556:707] current VC parent = (null)
2013-08-26 14:55:36.153 Alveolar Gas iPhone[556:707] new VC parent = <WorkSheetParentViewController: 0x198da0>
2013-08-26 14:55:36.160 Alveolar Gas iPhone[556:707] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Children view controllers <Worksheet1ViewController: 0x1ea780> and <Worksheet2ViewController: 0x1403b0> must have a common parent view controller when calling -[UIViewController transitionFromViewController:toViewController:duration:options:animations:completion:]'

- Adam Strait

---

谢谢您的发布。我也在做我的第一个项目，遇到了同样的问题 :) - Shaun

Answer 1

我通过将 currentVC = newVC; 移动到完成块中来解决了这个问题。SwapViewControllers 现在看起来像这样：

-(void)swapViewControllers
{
NSLog(@"top current VC parent = %@",currentVC.parentViewController);
NSLog(@"top new VC parent = %@",newVC.parentViewController);
[currentVC willMoveToParentViewController:nil];
newVC.view.frame=childContainerView.bounds;

[self addChildViewController:newVC];

NSLog(@"current VC parent = %@",currentVC.parentViewController);
NSLog(@"new VC parent = %@",newVC.parentViewController);
[self transitionFromViewController:currentVC
                  toViewController:newVC
                          duration:1.0
                           options:UIViewAnimationOptionTransitionCurlUp
                        animations:nil
                        completion:^(BOOL finished) {
                            [currentVC removeFromParentViewController];
                            [newVC didMoveToParentViewController:self];
                            currentVC = newVC;
                        }];

NSLog(@"bottom current VC parent = %@",currentVC.parentViewController);
NSLog(@"bottom new VC parent = %@",newVC.parentViewController);

}

- Adam Strait