视图控制器获取重复的实例化

问题描述

这应该很简单.

当我使用导航控制器从根视图切换到第二视图时，第二视图会很好地加载.第二个视图在"viewDidLoad"中创建一个计时器，以定期调用方法"updateData".

When I use the navigation controller to segue from my root view to my 2nd view, the 2nd view loads fine.The 2nd view creates a timer in "viewDidLoad" to call a method "updateData" periodically.

也许我在这里不了解系统，但是当我回到root并再次转到第二个视图时，我得到了一个第二个视图控制器的全新实例，该实例创建了一个新计时器(updateData是被打两次).

Maybe I'm not understanding the system here, but when I go back to root and forward again to the 2nd view, I'm getting a completely new instance of the 2nd view controller, which makes a new timer (updateData is getting called twice as frequently).

这是不正确的默认行为吗?如何显示第二个视图控制器的第一个实例，而不是创建一个新的实例?

This is not correct default behavior is it? How can I show the first instance of the 2nd view controller instead of creating a new one?

推荐答案

持久对象不应该是视图控制器的属性并不一定是正确的.您可以为第二个控制器(在根视图控制器中)创建一个属性，并且仅在第一次按下它时实例化它.因为您有很强的指向性，所以当您返回第一个控制器时，它不会被释放，并且您的计时器将继续运行.

It's not necessarily true that persistent objects shouldn't be properties of view controller. You can create a property for your second controller (in the root view controller), and only instantiate it the first time you push it. Because you have a strong pointer to it, it won't be deallocated when you go back to the first controller, and your timer will continue to operate.

- (IBAction)goToSecondView {
    if (!self.secondViewController) { // secondViewController is a strong property
        self.secondViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"Second"];
    }
    [self.navigationController pushViewController:self.secondViewController animated:YES];
}

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