如何以编程方式选择嵌入式视图的控制器？

Question

I have an embedded container on a view controller, and I would like to change it's content depending on a specific condition. How should I do this, knowing that there can only be one embed segue linked to an embedded container.

I tried to put a view controller between my embedded container and my 2 possible content views, but it won't work because of custom segues (error : "Could not create a segue with class 'null'). I don't understand this error by the way, if someone could tell me more about it :)

I read about some ways to go around this problem by creating a tab view, and switching between the tabs programmatically, or by adding 2 container view and hiding the unwanted one, but these seem to be kind of hacky.

What would be the best practice to do this ? (In swift please)

Thank you for your help

Answer 1

There's two ways to do it, the first is to add two container views on top of each other and set the alpha to 0 for one and 1 for the other and switch the alpha values when you want to change between view controllers. The disadvantage of this is that there will always be two view controllers instantiated. The second way is to change the the type of segue from embed to a custom segue (this will allow you to add more than one segue in the storyboard) that loads or swaps a view controller. Here is the implementation of a segue I implemented that does this, if you can understand it you can implement it in swift.

 (void)perform
//
// Used to seque between the master view controller and its immediate child view controllers and also from the homw view controller
// and all its immediate child controllers.
// At app launch then it is necessary to directly load a particular view controller - this is determined by checking that the source
// view controller has no children. At other times the seque is used to switch from one controller to another.
//
{

    //
    // This seque is for use when there is a container view controller where it is necessary to switch the contained view controllers (storyboards only permit one embed seque).
    //
    //
    //                             embed segue                              segueA
    //             MainVC  --------------------------> ContainerVC -------------------> VCA
    //     (has the view containing
    //       the containded VC)
    //                                                                      sequeB
    //                                                             --------------------> VCB
    //
    //
    // When the app initially launches the OS will automatically execute the embed seque and thus the ContainerVC gets the opportunity in its viewDidLoad to decide which
    // VC to load at that point and then execute either segueA or sequeB. Assuming it calls sequeA then when the seque executes the source will be the ContainerVC and the
    // destination with will VCA. The seque checks to see if the containerVC already has any children, if not then it knows to just add VCA as a child.
    //

    DDLogInfo(@"SEGUE - entered seque");
    UIViewController *container = self.sourceViewController;
    UIViewController *destination = self.destinationViewController;
    if([container.childViewControllers count] == 0)
    {
        DDLogInfo(@"SEGUE - adding intitial VC: %@", [destination description]);
        // The containerVC doesn't yet any any children so just add the destination VC as a child
        [container addChildViewController:destination];
        destination.view.frame = container.view.frame;
        [container.view addSubview:destination.view];
        [destination didMoveToParentViewController:container];
    }
    else
    {
        // The containerVC already has an existing child and thus it is necessary to swap it out and replace it with the new child
        UIViewController* currentChild = container.childViewControllers[0];

        currentChild.view.userInteractionEnabled = NO;
        PyngmeAssert([container.childViewControllers count] == 1, @"More than one child controller");

        // First check to make sure the destination type is not the same as the current child
        if([destination isMemberOfClass: [currentChild class]])
        {
            DDLogInfo(@"SEGUE: Trying to swap view controllers of the same type *****");
        }
        else
        {
            // Swap the new VC for the old VC
            destination.view.frame = container.view.frame;
            [currentChild willMoveToParentViewController:nil];
            [container addChildViewController:destination];

            [container transitionFromViewController:currentChild
                                   toViewController:destination
                                           duration:0.35
                                            options:UIViewAnimationOptionTransitionCrossDissolve
                                         animations:^{
                                         }
                                         completion:^(BOOL finished) {
                                             [currentChild removeFromParentViewController];
                                             [destination didMoveToParentViewController:container];
                                             DDLogInfo(@"SEGUE finished swapping seque");
                                         }];
        }
    }
}