iOS中的轉場研究(3)

實現自定義的Container View Controller

上一篇文章中提到了如何定製Segue。咱們知道Unwind Segue的正常工做須要Container View Controller的支持。咱們能夠實現：

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

三個方法來定製本身的Container View Controller（如下簡稱「容器」）。

咱們通常會在子Controller中經過實現canPerformUnwindSegueAction:fromViewController:withSender:來決定要不要執行相應的Unwind Segue。
在自定義的容器中，咱們必須實現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實例。

使用Modal presentation時須要注意的狀況

當咱們使用UIViewController的presentViewController:animated:completion:方法以Modal presentation的方式來跳轉場景的時候，狀況與在Navigation View Controller有很大不一樣。首先，使用這種方式跳轉場景的時候，跳轉到的View Controller爲Source View Controller的子Controller，而在Navigation View Controller中，全部的流程Controller基本上都是Navgation View Controller的子Controller，因此兩者在View Controller的層次管理上有不少不一樣。所以實現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操做。一個參考實現以下（略掉動畫效果代碼，僅提供轉場方法調用代碼）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，由於UIViewController中，跟Container View Controller相關的方法的默認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。因此若是有任意跳轉的需求，咱們能夠嘗試本身實現一個簡單的Container View Controller。

使用AddChildViewController API實現本身的Container View Controller

咱們偶爾會但願有一個跟Navigation View Controller差很少的容器，可是又不但願像Navigation View Controller那麼笨重，且限制多多。咱們知道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，咱們可以經過UIAppearance來定製一些樣式，但咱們但願定製能容納更加豐富的元素的Navigation Bar，或者其餘定製的導航界面的時候，但願可以實現一個相似的容器。咱們固然能夠模仿Navigation View Controller的公開API實現一個差很少的東西，若是咱們要很方便的使用自定義Segue和任意跳轉的Unwind Segue的話，還須要以特定的方式實現上面提到的一些方法。UIViewController的addChildViewController:方法一樣能夠作出相似的功能，並且相比Modal presentation，這種方式代碼更加直觀。由於使用這個API實現的容器，對子Controller的管理方式與Navigation View Controller相似。

容器的部分代碼以下：

- (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代碼:

- (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代碼：

- (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];
    }];
}

當咱們定義的Container View中有須要置頂的元素（好比定製的導航條）時，能夠將addSubView:方法換成insertSubView:atIndex:方法來調整子視圖的層次。

---

1. 下面的代碼修改自iOS6 by Tutorial中的示例代碼。 ↩