Xcode的两个选项卡之间的共享变量(Shared variable between two tabs for Xcode)

Xcode的两个选项卡之间的共享变量(Shared variable between two tabs for Xcode)

我有两个我正在处理的视图控制器，它们都从Base视图控制器继承

class A_ViewController：BaseViewController class B_ViewController：BaseViewController

这两个VC都与我的firebase数据库进行了很大的交互。 所以我想要一个变量来跟踪所有下载的项目，这样两个VC就可以访问它而无需再次重新下载文件。

我试图在BaseViewController中放置一个变量名，以便访问两个A，B类

var allPostsDownloaded: [Post]!

因此，在A_VC下载任何数据之前，它会检查此allPostsDownloaded变量，并在数据存在时从中加载。 如果它不存在，我追加到这个变量。 因此，当切换到B_VC时，可以完成相同的操作，并且在不需要时不会重新下载数据。

我不使用segue或protocal来传递数据的原因是两个VC与我的数据库交互得非常重要。 因此，尝试使用可变数据变得更加清晰，以便跟踪事物的位置。

但问题是，我

var allPostsDownloaded: [Post]!

每当我在A和B VC（哪些是标签）之间切换时都会被调用。 这将导致变量为空并取消初始化。

我想我可以使用全局变量，但这不是一个好习惯吗？ 任何人都可以解释为什么在新标签出现时重新调用它？ 对此最好的解决方案。

I have two view controllers that I am working on which both inherits from a Base view controller

class A_ViewController: BaseViewController class B_ViewController: BaseViewController

Both of those VC interacts heavily with my firebase database. So I want a variable to keep track of all the downloaded items so those two VC can access it without the need to re-download the file again.

I tried to put a variable name in BaseViewController for the two A,B class to access

var allPostsDownloaded: [Post]!

So before A_VC downloads any data, it checks for this allPostsDownloaded variable and loads from it if the data exists. If it doesnt exist, I append to this variable. So when switching to B_VC, the same can be done and no data is re-downloaded when not required.

Reason I am not using segue or protocal to pass data around is that the two VC interacts quite heavly with my database. So it was alot cleaner to try and have a mutural data varaible to keep track of where things are.

However, the problem is that i

var allPostsDownloaded: [Post]!

gets called whenever I switch between A and B VC (Which are tabs). This will cause the variable to be empty and de-initialised.

I guess I could use a global variable instead but that is not good practice? Could anyone please explain why it gets re-called when new tab shows up? And the best solution for this.

最满意答案

正如@avi提到的创建新的单例类，那么你可以轻松传递和阅读。 以下是一个例子

class PersistentData { static let sharedInstance = PersistentData() // your global persistent variable var allPostsDownloaded = [Post]() }

因此，在您的控制器中，您可以简单地阅读和设置如下

// read print(PersistentData.sharedInstance.allPostsDownloaded) // set new data. this just example, hence depends on your case PersistentData.sharedInstance.allPostsDownloaded.append(newPost) PersistentData.sharedInstance.allPostsDownloaded = posts

还要记住，如果要在选项卡之间切换时想要读取新值，可以在viewDidAppear或viewWillAppear获取更新

as @avi mentioned create new singleton class, then you can pass and read easily. Below is an example

class PersistentData { static let sharedInstance = PersistentData() // your global persistent variable var allPostsDownloaded = [Post]() }

So in your controllers you can simple read and set as below

// read print(PersistentData.sharedInstance.allPostsDownloaded) // set new data. this just example, hence depends on your case PersistentData.sharedInstance.allPostsDownloaded.append(newPost) PersistentData.sharedInstance.allPostsDownloaded = posts

also keep in mind that if you want to read new value when switching between tabs, you can get the updated in viewDidAppear or viewWillAppear