iOS：从viewDidAppear更改视图

Question

I'm playing around with view life cycles & am having trouble changing a view from the load of a different view.

In my ViewController.hi have:

-(void)viewDidAppear:(BOOL)animated{
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    ViewController2 *viewController = (ViewController2 *)[storyboard instantiateViewControllerWithIdentifier:@"ViewController2"];
    [self presentViewController:viewController animated:YES completion:nil];
}

However this only causes the view to be between ViewController, and ViewController2 appearing with animation (in a loop).

I used the code in viewDidLoad however neither of the view's loaded (from reading you cannot change view until the viewWillAppear)

Update: When using the code in viewWillAppear , whose view is not in the window hierarchy error is thrown.

How does one change the view from view setup stage?

Using the above code, inside & out of GCD, in viewDidLoad , viewWillAppear & viewDidAppear either results in an infinite loop of animated showing of the ViewController2, or crash on 2nd attempt of segue (result from the loop).

Answer 1

EDITED:

I'm not sure exactly what you're trying to do, but assuming you are wanting the first viewcontroller to appear and then the second viewcontroller to immediately animate on top of the first one, you should be able to accomplish using several options:

First you could just wrap your calls in a dispatch_async call:

dispatch_async(dispatch_get_main_queue(), ^{

    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    ViewController2 *viewController = (ViewController2 *)[storyboard 
    instantiateViewControllerWithIdentifier:@"ViewController2"];

    [self presentViewController:viewController animated:YES completion:nil];
});

Or you could use a show modally segue:

- (void)viewDidLoad {
  [super viewDidLoad];

  dispatch_async(dispatch_get_main_queue(), ^{

        [self performSegueWithIdentifier:@"myModalSegue" sender:self];
  });
}

Or you could use a navigation controller and use a standard show segue (formally push). This one doesn't require the dispatch_async:

- (void)viewDidLoad {
  [super viewDidLoad];

  [self performSegueWithIdentifier:@"myshowsegue" sender:self];
}

I've posted working examples of all three on: github

Answer 2

It is better to exchange views in loadView method.

- (void)loadView {
    CGRect rect = [[UIScreen mainScreen] applicationFrame];
    MyView *view = [[MyView alloc] initWithFrame:rect];
    [view setAutoresizingMask:UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth];
    self.view = view;
}