How to access to parentViewController after presen

问题:

I need to access to parentViewController after presentMoalViewController. This is my method that I call in the firstViewController to view the secondViewController:

- (void)viewData {

    SecondViewController *viewCtrl = [self.storyboard instantiateViewControllerWithIdentifier:@"select_data"];
    UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:viewCtrl];
    navigationController.navigationBar.barStyle = UIBarStyleBlack;

    UIBarButtonItem *saveButton = [[[UIBarButtonItem alloc] initWithTitle:@"Save" style:UIBarButtonItemStyleDone target:viewCtrl action:@selector(saveData)] autorelease];
    viewCtrl.navigationItem.rightBarButtonItem = salvaButton;

    UIBarButtonItem *undoButton = [[[UIBarButtonItem alloc] initWithTitle:@"Undo" style:UIBarButtonItemStyleBordered target:viewCtrl action:@selector(backView)] autorelease];
    viewCtrl.navigationItem.leftBarButtonItem = annullaButton;

    [self presentModalViewController:navigationController animated:YES];

}

When I click on saveButton, I try to access to parentViewController in this way, but it not work:

- (void) saveData {

    FirstViewController *parentView = (FirstViewController*)[[self navigationController] presentingViewController];
    parentView.dataString = [[NSMutableString alloc] initWithFormat:@"new string"];
    [parentView performSelectorInBackground:@selector(myMethod) withObject:nil];

    [self dismissModalViewControllerAnimated:YES];

}

回答1:

It would be much better if you used a delegate/protocol in your second viewController that the first viewController could set itself as. You can find more info here Pass data back to the previous controller or simply doing a search. This design pattern is used virtually everywhere in iOS programming.

The big advantage is that then your second viewController becomes independent of whoever presented it, and can be easily reused. The technical term would be 'decoupling'.

回答2:

Last time I did this I used notifications:

[[NSNotificationCenter defaultCenter] postNotificationName:@"saveData" object:dataString];

in your parent vc view didload:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(saveDataNow:) name:@"saveData" object:nil];

回答3:

For navigationController you can declare a property called something like myController, then you have to initiate your navigationController like this:

UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:viewCtrl];
navigationController.navigationBar.barStyle = UIBarStyleBlack;
navigationController.myController = self;

UIBarButtonItem *saveButton = [[[UIBarButtonItem alloc] initWithTitle:@"Save" style:UIBarButtonItemStyleDone target:viewCtrl action:@selector(saveData)] autorelease];
viewCtrl.navigationItem.rightBarButtonItem = salvaButton;

UIBarButtonItem *undoButton = [[[UIBarButtonItem alloc] initWithTitle:@"Undo" style:UIBarButtonItemStyleBordered target:viewCtrl action:@selector(backView)] autorelease];
viewCtrl.navigationItem.leftBarButtonItem = annullaButton;

[self presentModalViewController:navigationController animated:YES];

In your parentViewController Class you declare your Method

- (void) saveData {

FirstViewController *parentView = (FirstViewController*)[[self navigationController] presentingViewController];
parentView.dataString = [[NSMutableString alloc] initWithFormat:@"new string"];
[parentView performSelectorInBackground:@selector(myMethod) withObject:nil];

[self dismissModalViewControllerAnimated:YES];
}

In your navigationController you can then call [myController saveData]; This should work, if you have any questions, feel free to ask!

回答4:

You can access your parent view controller using following-

- (void) saveData {
NSMutableArray *activeControllerArray = [self.navigationController.viewControllers mutableCopy];
FirstViewController *parentView;
for(int i = 0, i <[activeControllerArray  count], i++) {
    if([[activeControllerArray objectAtIndex:i] isKindOfClass:[FirstViewController class]) {
        parentView= [activeViewController objectAtIndex:i];
        break;
     }
}

parentView.dataString = [[NSMutableString alloc] initWithFormat:@"new string"];
[parentView performSelectorInBackground:@selector(myMethod) withObject:nil];

[self dismissModalViewControllerAnimated:YES];

}