如何在另一个控制器下调出模态视图控制器？

Question

I have a navigation problem. I want to create the following navigation structure:

Start on screen A. When a button is pressed, screen B animates up as a modal view controller, covering A. In the first scenario, when screen B is dismissed it slides down revealing screen C, which is a new modal view controller now covering screen A. When C is dismissed, it slides down to reveal screen A again. In the second scenario when screen B is dismissed it reveals modal screen D covering screen A.

My biggest problem is that I can't find a way to display the model dialogs C or D behind B before it is dismissed, and until something takes place in B, I don't know if I should be creating C or D, so I can't parent B off of C to start with. Additionally, even if I could do that I can't get the animations to work as I described in the problem statement.

Any ideas how I might make this scenario work?

Answer 1

Strategy one: if it would suit your app, consider using navigation controllers rather than modals. NSNavigationController has a handy method:

- (void)setViewControllers:(NSArray *)viewControllers animated:(BOOL)animated

which lets you reorganise the view controller stack, with or without animation. So perhaps changing the stack to insert the new VC below the top (current one) without animation would work. Then your Done button (or similar) pops the top VC to reveal the new one underneath.

Strategy two: this is a little more experimental and may not work, but you may get away with doing 'just in time' view controller insertion. For example, for VC A, implement viewWillAppear. This method usually gets called right at the start of the animation of a UI above it being dismissed, and may be a good place to insert a new VC (ie show modal without animation) because the dismiss animation for the above VC has just begun. As I say, your mileage may vary.

Answer 2

see the Apple docs

"Any view controller object can present any other single view controller modally. This is true even for view controllers that were themselves presented modally. In other words, you can chain modal view controllers together as needed, presenting new modal view controllers on top of other modal view controllers as needed."

So you can present NavigationControllers modally.

However, you can't switch the root view controller of a navigation controller easily (one possibility is here ).

An alternative would be to present the NavigationController modally but push two ViewControllers on it from the get-go so the user sees the second one(screen B), then goes back to the first(screen C) and then dismisses the modal NavigationController going back to screen A.

Answer 3

It appears that this is not possible using the standard modal view controller scenario. The only solution I could find was to make this into a single view controller and use custom animations. Since this was not particularly desirable, we ended up changing the navigation structure.