ios 如何识别导航堆栈中以前的视图控制器

How to identify previous view controller in navigation stack

提问by Zhen

I have 2 seperate navigationcontrollers, one with RootViewControllerA and the other with RootViewControllerB.

我有 2 个单独的navigationcontrollers，一个是RootViewControllerA，另一个是RootViewControllerB。

I am able to push ViewControllerC onto either A or B's navigation stack.

我能够将ViewControllerC推送到 A 或 B 的导航堆栈上。

Question: When I am in ViewControllerC, how can I find out if I am in the stack belonging to A or B?

问题：当我在ViewControllerC 时，如何知道我在堆栈中是属于 A 还是 B？

回答by jburns20

You could use the UINavigationController's viewControllersproperty:

您可以使用UINavigationController的viewControllers属性：

@property(nonatomic, copy) NSArray *viewControllers

Discussion: The root view controller is at index 0 in the array, the back view controller is at index n-2, and the top controller is at index n-1, where n is the number of items in the array.

@property(nonatomic, copy) NSArray *viewControllers

讨论：根视图控制器位于数组中的索引 0，后视图控制器位于索引 n-2，顶部控制器位于索引 n-1，其中 n 是数组中的项数。

https://developer.apple.com/documentation/uikit/uinavigationcontroller

https://developer.apple.com/documentation/uikit/uinavigationcontroller

You could use that to test whether the root view controller (the one at array index 0) is view controller A or B.

您可以使用它来测试根视图控制器（数组索引为 0 的那个）是视图控制器 A 还是 B。

回答by George

Here's the implementation of the accepted answer:

这是已接受答案的实现：

- (UIViewController *)backViewController
{
    NSInteger numberOfViewControllers = self.navigationController.viewControllers.count;

    if (numberOfViewControllers < 2)
        return nil;
    else
        return [self.navigationController.viewControllers objectAtIndex:numberOfViewControllers - 2];
}

回答by Chris

- (UIViewController *)backViewController
{
    NSInteger myIndex = [self.navigationController.viewControllers indexOfObject:self];

    if ( myIndex != 0 && myIndex != NSNotFound ) {
        return [self.navigationController.viewControllers objectAtIndex:myIndex-1];
    } else {
        return nil;
    }
}

回答by tjklemz

A more general implementation of the accepted answer:

已接受答案的更一般实现：

- (UIViewController *)backViewController {
    NSArray * stack = self.navigationController.viewControllers;

    for (int i=stack.count-1; i > 0; --i)
        if (stack[i] == self)
            return stack[i-1];

    return nil;
}

This will return the correct "back view controller" regardless of where the current class is on the navigation stack.

无论当前类在导航堆栈上的哪个位置，这都将返回正确的“后视图控制器”。

回答by grassyburrito

Swift implementation of tjklemzcode as an extension:

作为扩展的tjklemz代码的Swift 实现：

extension UIViewController {

    func backViewController() -> UIViewController? {        
        if let stack = self.navigationController?.viewControllers {
            for(var i=stack.count-1;i>0;--i) {
                if(stack[i] == self) {
                    return stack[i-1]
                }
            }
        }
        return nil
    }
}

回答by Cin316

Here's a modifed version of Prabhu Beeman'sSwift code that adapts it to support Swift 3:

这是Prabhu Beeman 的Swift 代码的修改版本，可对其进行调整以支持 Swift 3：

extension UIViewController {
    func backViewController() -> UIViewController? {
        if let stack = self.navigationController?.viewControllers {
            for i in (1..<stack.count).reverse() {
                if(stack[i] == self) {
                    return stack[i-1]
                }
            }
        }
        return nil
    }
}

回答by Adam Johns

As a UINavigationControllerextension:

作为UINavigationController扩展：

extension UINavigationController {

    func previousViewController() -> UIViewController? {
        guard viewControllers.count > 1 else {
            return nil
        }
        return viewControllers[viewControllers.count - 2]
    }

}

回答by Alex Reynolds

Access the n-2element of the viewControllersproperty to access the parent view controller.

访问属性的n-2元素viewControllers以访问父视图控制器。

Once you have that instance, you can check its type by logging what comes out of the NSStringFromClass()function. Or you could keep some static constidentifier string in controllers A and B, and a getter function that prints out the string.

一旦你有了那个实例，你就可以通过记录NSStringFromClass()函数的结果来检查它的类型。或者您可以static const在控制器 A 和 B 中保留一些标识符字符串，以及一个打印出该字符串的 getter 函数。

回答by cdf1982

Swift implementation of @tjklemz code:

@tjklemz 代码的 Swift 实现：

var backViewController : UIViewController? {

        var stack = self.navigationController!.viewControllers as Array

        for (var i = stack.count-1 ; i > 0; --i) {
            if (stack[i] as UIViewController == self) {
                return stack[i-1] as? UIViewController
            }

        }
        return nil
    }

回答by Perception

Use the navigationControllermethod to retrieve it. See documentation on Apple's site.

使用navigationController方法来检索它。请参阅Apple 网站上的文档。

navigationControllerA parent or ancestor that is a navigation controller. (read-only)

@property(nonatomic, readonly, retain) UINavigationController *navigationController

DiscussionOnly returns a navigation controller if the view controller is in its stack. This property is nil if a navigation controller cannot be found.

AvailabilityAvailable in iOS 2.0 and later.

navigationController作为导航控制器的父级或祖先。（只读）

@property(nonatomic, readonly, retain) UINavigationController *navigationController

讨论如果视图控制器在其堆栈中，则仅返回导航控制器。如果找不到导航控制器，则此属性为零。

可用性在 iOS 2.0 及更高版本中可用。