iOS中的轉場研究(3)

kid143發表於2014-11-11
iOS

實現自定義的Container View Controller

上一篇文章中提到了如何定製Segue。我們知道Unwind Segue的正常工作需要Container View Controller的支援。我們可以實現：

  • canPerformUnwindSegueAction:fromViewController:withSender:
  • viewControllerForUnwindSegueAction:fromViewController:withSender:
  • segueForUnwindingToViewController:fromViewController:identifier:

三個方法來定製自己的Container View Controller（以下簡稱“容器”）。

我們一般會在子Controller中通過實現canPerformUnwindSegueAction:fromViewController:withSender:來決定要不要執行相應的Unwind Segue。
在自定義的容器中，我們必須實現viewControllerForUnwindSegueAction:fromViewController:withSender:和segueForUnwindingToViewController:fromViewController:identifier:方法。前一個方法用來決定那個View Controller來處理Unwind Segue action，後一個方法用來返回自定義的Unwind Segue例項。

使用Modal presentation時需要注意的情況

當我們使用UIViewController的presentViewController:animated:completion:方法以Modal presentation的方式來跳轉場景的時候，情況與在Navigation View Controller有很大不同。首先，使用這種方式跳轉場景的時候，跳轉到的View Controller為Source View Controller的子Controller，而在Navigation View Controller中，所有的流程Controller基本上都是Navgation View Controller的子Controller，所以二者在View Controller的層次管理上有很多不同。因此實現Modal presentation風格的Segue的時候，動畫的view不能搞錯，必須對View Controller中的頂層View操作。一個參考實現如下（略掉動畫效果程式碼，僅提供轉場方法呼叫程式碼）1:

Segue部分：

- (UIView *)findTopMostViewForViewController:(UIViewController *)viewController
{
    UIView *theView = viewController.view;
    UIViewController *parentViewController = viewController.parentViewController;
    while (parentViewController != nil)
    {
        theView = parentViewController.view;
        parentViewController = parentViewController.parentViewController;
    }
    return theView;
}

- (void)perform
{
    UIViewController *source = self.sourceViewController;
    UIViewController *destination = self.destinationViewController;

    // Find the views that we will be animating. If the source or destination
    // view controller sits inside a container view controller, then the view
    // to animate will actually be that parent controller`s view.
    UIView *sourceView = [self findTopMostViewForViewController:source];
    UIView *destinationView = [self findTopMostViewForViewController:destination];

    [source presentViewController:destination animated:NO completion:^{
        // completion code here
    }];
}

Unwind Segue部分：

- (UIView *)findTopMostViewForViewController:(UIViewController *)viewController
{
    UIView *theView = viewController.view;
    UIViewController *parentViewController = viewController.parentViewController;
    while (parentViewController != nil)
    {
        theView = parentViewController.view;
        parentViewController = parentViewController.parentViewController;
    }
    return theView;
}

- (void)perform
{
    UIViewController *source = self.sourceViewController;
    UIViewController *destination = self.destinationViewController;

    // Find the views that we will be animating. If the source or destination
    // view controller sits inside a container view controller, then the view
    // to animate will actually be that parent controller`s view.
    UIView *sourceView = [self findTopMostViewForViewController:source];
    UIView *destinationView = [self findTopMostViewForViewController:destination];

    [source dismissViewControllerAnimated:NO completion:^{
        // completion code here
    }];
}

注意：Modal Presentation的Unwind Segue很難實現無Bug的任意跳轉，因為UIViewController中，跟Container View Controller相關的方法的預設實現並不能很好的定位Container View Controller。而以正確的方式重寫這些方法並不容易。所以如果有任意跳轉的需求，我們可以嘗試自己實現一個簡單的Container View Controller。

使用AddChildViewController API實現自己的Container View Controller

我們偶爾會希望有一個跟Navigation View Controller差不多的容器，但是又不希望像Navigation View Controller那麼笨重，且限制多多。我們知道Navigation View Controller在Interface Builder中，其Navigation Bar能容納的元素樣式並不豐富，儘管大多數時候，我們能夠通過UIAppearance來定製一些樣式，但我們希望定製能容納更加豐富的元素的Navigation Bar，或者其他定製的導航介面的時候，希望能夠實現一個類似的容器。我們當然可以模仿Navigation View Controller的公開API實現一個差不多的東西，如果我們要很方便的使用自定義Segue和任意跳轉的Unwind Segue的話，還需要以特定的方式實現上面提到的一些方法。UIViewController的addChildViewController:方法同樣可以做出類似的功能，而且相比Modal presentation，這種方式程式碼更加直觀。因為使用這個API實現的容器，對子Controller的管理方式與Navigation View Controller類似。

容器的部分程式碼如下：

- (UIViewController *)viewControllerForUnwindSegueAction:(SEL)action fromViewController:(UIViewController *)fromViewController withSender:(id)sender
{
    for (UIViewController *childController in self.childViewControllers) {
        if ([childController canPerformUnwindSegueAction:action fromViewController:fromViewController withSender:sender]) {
            return childController;
        }
    }
    return nil;
}

- (UIStoryboardSegue *)segueForUnwindingToViewController:(UIViewController *)toViewController fromViewController:(UIViewController *)fromViewController identifier:(NSString *)identifier
{
    UIStoryboardSegue *unwindSegue = [[MyLeftToRightUnwindSegue alloc] initWithIdentifier:identifier source:fromViewController destination:toViewController];
    return unwindSegue;
}

Segue程式碼:

- (BOOL)controllerInStack:(UIViewController *)controller
{
    UIViewController *fromController = self.sourceViewController;
    UIViewController *containerController = fromController.parentViewController;

    for (UIViewController *childController in containerController.childViewControllers) {
        if (childController == controller) {
            return YES;
        }
    }
    return NO;
}

- (void)perform
{
    // A simple transition.
    // New scene slides in from right and old scene slides out to left.
    UIViewController *fromController = self.sourceViewController;
    UIViewController *toController = self.destinationViewController;

    UIViewController *parentController = fromController.parentViewController;

    UIView *containerView = parentController.view;

    [containerView addSubview:toController.view];

    CGRect initialFromRect = fromController.view.frame;
    CGRect initialToRect = CGRectOffset(initialFromRect, initialFromRect.size.width, 0);
    CGRect finalFromRect = CGRectOffset(initialFromRect, -initialFromRect.size.width, 0);
    CGRect finalToRect = initialFromRect;

    toController.view.frame = initialToRect;
    if (![self controllerInStack:toController]) {
        // notify containment event.
        [toController willMoveToParentViewController:parentController];
    }

    [UIView animateWithDuration:0.4f animations:^{
        fromController.view.frame = finalFromRect;
        toController.view.frame = finalToRect;
    } completion:^(BOOL finished) {
        if (![self controllerInStack:toController]) {
            // Add new controller as a child controller to the container view controller
            [parentController addChildViewController:toController];
            // notify containment event.
            [toController didMoveToParentViewController:toController];
        }
        [fromController.view removeFromSuperview];
    }];
}

Unwind Segue程式碼：

- (void)perform
{
    // A simple transition.
    // New scene slides in from left and old scene slides out to right.
    UIViewController *fromController = self.sourceViewController;
    UIViewController *toController = self.destinationViewController;

    UIViewController *parentController = fromController.parentViewController;

    UIView *containerView = parentController.view;

    [containerView addSubview:toController.view];

    CGRect initialFromRect = fromController.view.frame;
    CGRect initialToRect = CGRectOffset(initialFromRect, -initialFromRect.size.width, 0);
    CGRect finalFromRect = CGRectOffset(initialFromRect, initialFromRect.size.width, 0);
    CGRect finalToRect = initialFromRect;

    toController.view.frame = initialToRect;

    [UIView animateWithDuration:0.4f animations:^{
        fromController.view.frame = finalFromRect;
        toController.view.frame = finalToRect;
    } completion:^(BOOL finished) {
        [fromController.view removeFromSuperview];
    }];
}

當我們定義的Container View中有需要置頂的元素（比如定製的導航條）時，可以將addSubView:方法換成insertSubView:atIndex:方法來調整子檢視的層次。

  1. 下面的程式碼修改自iOS6 by Tutorial中的示例程式碼。 ↩

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