blocks|key|4004498|text|如果您的window+rootViewController是UITabbarController(在大多数情况下都是UITabbarController)，那么您可以在AppDelegate文件中访问didFinishLaunchingWithOptions中的tabbar。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4004499|func+application(application:+UIApplication!,+didFinishLaunchingWithOptions+launchOptions:+NSDictionary!)+->+Bool+{
++++//+Override+point+for+customization+after+application+launch.

++++if+let+tabBarController+=+self.window!.rootViewController+as?+UITabBarController+{
++++++++tabBarController.selectedIndex+=+1
++++}

++++return+true
}|code-block|syntax|javascript|4004500|这将使用index+(1)在selectedIndex中打开选项卡。|4004501|如果您在viewDidLoad+of您的firstViewController中这样做，您需要通过标志来管理，或者用另一种方法来跟踪所选的选项卡。在您的didFinishLaunchingWithOptions文件或rootViewController自定义类viewDidLoad中执行此操作的最佳位置。|4004502|entityMap^0|4|6|B|I|U|I|1M|I|2C|B|2S|T|3N|6|0|0|4|5|E|D|0|4|B|K|J|24|T|30|I|3M|B|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1B|8|@$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]]|P|$]]

If your <code>window</code> <code>rootViewController</code> is <code>UITabbarController</code>(which is in most cases) then you can access <code>tabbar</code> in <code>didFinishLaunchingWithOptions</code> in the <code>AppDelegate</code> file.

<pre><code>func application(application: UIApplication!, didFinishLaunchingWithOptions launchOptions: NSDictionary!) -&gt; Bool {
 // Override point for customization after application launch.

 if let tabBarController = self.window!.rootViewController as? UITabBarController {
 tabBarController.selectedIndex = 1
 }

 return true
}
</code></pre>

This will open the tab with the <code>index</code> given (1) in <code>selectedIndex</code>.

If you do this in <code>viewDidLoad</code> of your <code>firstViewController</code>, you need to manage by flag or another way to keep track of the selected tab. The best place to do this in <code>didFinishLaunchingWithOptions</code> of your <code>AppDelegate</code> file or <code>rootViewController</code> custom class <code>viewDidLoad</code>.

blocks|key|4695853|text|要扩展@codester的答案，您不需要检查然后分配，只需一步即可：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4695854|func+application(application:+UIApplication!,+didFinishLaunchingWithOptions+launchOptions:+NSDictionary!)+->+Bool+{
++++//+Override+point+for+customization+after+application+launch.

++++if+let+tabBarController+=+self.window!.rootViewController+as?+UITabBarController+{
++++++++tabBarController.selectedIndex+=+1
++++}

++++return+true
}|code-block|syntax|javascript|4695855|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

To expand on @codester's answer, you don't need to check and then assign, you can do it in one step:

<pre><code>func application(application: UIApplication!, didFinishLaunchingWithOptions launchOptions: NSDictionary!) -&gt; Bool {
 // Override point for customization after application launch.

 if let tabBarController = self.window!.rootViewController as? UITabBarController {
 tabBarController.selectedIndex = 1
 }

 return true
}
</code></pre>

blocks|key|4004578|text|1.创建一个超UITabBarController的新类。例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4004579|class+xxx:+UITabBarController+{
override+func+viewDidLoad()+{
++++++++super.viewDidLoad()
}|code-block|syntax|javascript|4004580|2.向函数viewDidLoad()添加以下代码：|4004581|self.selectedIndex+=+1;+//set+the+tab+index+you+want+to+show+here,+start+from+0|4004582|3.转到故事板，并将Tab+Bar控制器的自定义类设置为这个新类。(图中以MyVotes1为例)|4004583|​|4004584|📷|atomic|offset|length|4004585|4004586|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://developer.qcloudimg.com/http-save/yehe-900000/dae562b27e32da578bf3d8d1562592c1.png|imageAlt^0|0|0|0|0|0|0|0|1|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|15|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|17|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|18|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|19|8|@]|9|@$R|1A|S|1B|1|1C]]|A|$]]|$1|T|3|N|5|6|7|1D|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11|12|-4]]]]

1.Create a new class which supers UITabBarController.
E.g:

<pre><code>class xxx: UITabBarController {
override func viewDidLoad() {
 super.viewDidLoad()
}
</code></pre>

2.Add the following code to the function viewDidLoad():

<pre><code>self.selectedIndex = 1; //set the tab index you want to show here, start from 0
</code></pre>

3.Go to storyboard, and set the Custom Class of your Tab Bar Controller to this new class.
(MyVotes1 as the example in the pic)

<img src="https://i.stack.imgur.com/793Lf.png" alt="enter image description here">

blocks|key|4004603|text|Swift+3|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|4004604|可以将此代码添加到index+0中的默认视图控制器(TabBarController)中：|CODE|4004605|++++override+func+viewWillAppear(_+animated:+Bool)+{
++++++++_+=+self.tabBarController?.selectedIndex+=+1
++++}|code-block|syntax|javascript|4004606|加载后，这将自动将选项卡移动到列表中的第二项，但也允许用户在任何时候手动返回该视图。|4004607|entityMap^0|0|7|0|9|7|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@$9|V|A|W|B|H]]|D|@]|E|$]]|$1|I|3|J|5|K|7|X|8|@]|D|@]|E|$L|M]]|$1|N|3|O|5|6|7|Y|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|Q|$]]

Swift 3

You can add this code to the default view controller (<code>index 0</code>) in your tabBarController:

<pre><code> override func viewWillAppear(_ animated: Bool) {
 _ = self.tabBarController?.selectedIndex = 1
 }
</code></pre>

Upon load, this would automatically move the tab to the second item in the list, but also allow the user to manually go back to that view at any time.

blocks|key|4695958|text|UITabBarControllerDelegate.必须是viewController的孩子因此，您只需在SWIFT+3上添加以下代码|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|4695959|self.tabBarController?.selectedIndex+=+1|code-block|syntax|javascript|4695960|entityMap^0|0|Q|1I|7|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

The viewController has to be a child of UITabBarControllerDelegate. So you just need to add the following code on SWIFT 3 

<pre><code>self.tabBarController?.selectedIndex = 1
</code></pre>

blocks|key|4300909|text|在一个典型的应用程序中，有一个UITabBarController，它将3个或更多个UIViewController作为它的选项卡。在这种情况下，如果将UITabBarController子类为YourTabBarController，则可以通过以下方式设置所选索引：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4300910|selectedIndex+=+1+//+Displays+2nd+tab.+The+index+starts+from+0.|code-block|syntax|javascript|4300911|如果您从任何其他视图导航到YourTabBarController，那么在该视图控制器的准备(for：)方法中，可以这样做：|4300912|override+func+prepare(for+segue:+UIStoryboardSegue,+sender:+Any?)+{
++++++++//+Get+the+new+view+controller+using+segue.destination.
++++++++//+Pass+the+selected+object+to+the+new+view+controller.
++++++++if+segue.identifier+==+"SegueToYourTabBarController"+{
++++++++++++if+let+destVC+=+segue.destination+as?+YourTabBarController+{
++++++++++++++++destVC.selectedIndex+=+0
++++++++++++}
++++++++}|4300913|我使用这种方式使用Xcode+10和Swift+4.2设置选项卡。|4300914|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

In a typical application there is a UITabBarController and it embeds 3 or more UIViewController as its tabs. In such a case if you subclassed a UITabBarController as YourTabBarController then you can set the selected index simply by:

<pre><code>selectedIndex = 1 // Displays 2nd tab. The index starts from 0.
</code></pre>

In case you are navigating to YourTabBarController from any other view, then in that view controller's prepare(for segue:) method you can do:

<pre><code>override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
 // Get the new view controller using segue.destination.
 // Pass the selected object to the new view controller.
 if segue.identifier == "SegueToYourTabBarController" {
 if let destVC = segue.destination as? YourTabBarController {
 destVC.selectedIndex = 0
 }
 }
</code></pre>

I am using this way of setting tab with Xcode 10 and Swift 4.2.

blocks|key|4004678|text|为了更新，在iOS+13之后，我们现在有了SceneDelegates。因此，可以选择将所需的选项卡选择在SceneDelegate.swift中，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4004679|class+SceneDelegate:+UIResponder,+UIWindowSceneDelegate+{

++++var+window:+UIWindow?

++++func+scene(_+scene:+UIScene,+
+++++++++++++++willConnectTo+session:+UISceneSession,+
+++++++++++++++options+connectionOptions:+UIScene.ConnectionOptions)+{

++++++++guard+let+_+=+(scene+as?+UIWindowScene)+else+{+return+}

++++++++if+let+tabBarController+=+self.window!.rootViewController+as?+UITabBarController+{
++++++++++++tabBarController.selectedIndex+=+1
++++++++}

++++}|code-block|syntax|javascript|4004680|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Just to update, following iOS 13, we now have SceneDelegates. So one might choose to put the desired tab selection in SceneDelegate.swift as follows:

<pre><code>class SceneDelegate: UIResponder, UIWindowSceneDelegate {

 var window: UIWindow?

 func scene(_ scene: UIScene, 
 willConnectTo session: UISceneSession, 
 options connectionOptions: UIScene.ConnectionOptions) {

 guard let _ = (scene as? UIWindowScene) else { return }

 if let tabBarController = self.window!.rootViewController as? UITabBarController {
 tabBarController.selectedIndex = 1
 }

 }
</code></pre>

blocks|key|4004701|text|Swift+5|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4004702|//MARK:-+if+you+are+in+UITabBarController+
self.selectedIndex+=+1|code-block|syntax|javascript|4004703|或|4004704|tabBarController?.selectedIndex+=+1|4004705|如果您使用的是UITabBarController|4004706|//+UITabBarDelegate
override+func+tabBar(_+tabBar:+UITabBar,+didSelect+item:+UITabBarItem)+{
++++print("Selected+item")
++++if+kAppDelegate.isLoggedIn+==+false+{
++++++++switch+tabBar.selectedItem?.title+{
++++++++case+"Favorite":
++++++++++++DispatchQueue.main.async+{
++++++++++++++++self.selectedIndex+=+0
++++++++++++++++DispatchQueue.main.async+{
++++++++++++++++++++Timer.scheduledTimer(withTimeInterval:+1,+repeats:+false)+{+timer+in
++++++++++++++++++++++++self.showAlert(Constants.GlobalConstants.APP_NAME,+message:+"You+are+not+login.")
++++++++++++++++++++}
++++++++++++++++}
++++++++++++}
++++++++++++++++break
++++++++case+"Track+Order":
++++++++++++
++++++++++++DispatchQueue.main.async+{
++++++++++++++++self.selectedIndex+=+0
++++++++++++++++DispatchQueue.main.async+{
++++++++++++++++++++Timer.scheduledTimer(withTimeInterval:+1,+repeats:+false)+{+timer+in
++++++++++++++++++++++++self.showAlert(Constants.GlobalConstants.APP_NAME,+message:+"You+are+not+login.")
++++++++++++++++++++}
++++++++++++++++}
++++++++++++}
++++++++++++break
++++++++default:
++++++++++++break
++++++++}
++++}
}|4004707|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Swift 5
<pre><code>//MARK:- if you are in UITabBarController 
self.selectedIndex = 1
</code></pre>
or
<pre><code>tabBarController?.selectedIndex = 1
</code></pre>
if you are using UITabBarController
<pre><code>// UITabBarDelegate
override func tabBar(_ tabBar: UITabBar, didSelect item: UITabBarItem) {
 print(&quot;Selected item&quot;)
 if kAppDelegate.isLoggedIn == false {
 switch tabBar.selectedItem?.title {
 case &quot;Favorite&quot;:
 DispatchQueue.main.async {
 self.selectedIndex = 0
 DispatchQueue.main.async {
 Timer.scheduledTimer(withTimeInterval: 1, repeats: false) { timer in
 self.showAlert(Constants.GlobalConstants.APP_NAME, message: &quot;You are not login.&quot;)
 }
 }
 }
 break
 case &quot;Track Order&quot;:
 
 DispatchQueue.main.async {
 self.selectedIndex = 0
 DispatchQueue.main.async {
 Timer.scheduledTimer(withTimeInterval: 1, repeats: false) { timer in
 self.showAlert(Constants.GlobalConstants.APP_NAME, message: &quot;You are not login.&quot;)
 }
 }
 }
 break
 default:
 break
 }
 }
}
</code></pre>

blocks|key|4300956|text|如果您想从作为特定视图控制器的一部分编写的代码中执行此操作，例如响应按下按钮或其他操作，您可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4300957|@IBAction+func+pushSearchButton(_+sender:+UIButton?)+{
++++if+let+tabBarController+=+self.navigationController?.tabBarController++{
++++++++tabBarController.selectedIndex+=+1
++++}
}|code-block|syntax|javascript|4300958|您还可以添加代码来使用UITabBarControllerDelegate方法处理选项卡切换。使用每个选项卡的基本视图控制器上的标记，您可以看到您所在的位置并采取相应的行动:例如|4300959|func+tabBarController(_+tabBarController:+UITabBarController,+shouldSelect+viewController:+UIViewController)+->+Bool+{
++++
++++//+if+we+didn't+change+tabs,+don't+do+anything
++++if+tabBarController.selectedViewController?.tabBarItem.tag+==++viewController.tabBarItem.tag+{
++++++++return+false
++++}
++++
++++if+viewController.tabBarItem.tag+==+4096+{+//+some+particular+tab
++++++++//+do+stuff+appropriate+for+a+transition+to+this+particular+tab
++++}
++++else+if+viewController.tabBarItem.tag+==+2048+{+//+some+other+tab
++++++++//+do+stuff+appropriate+for+a+transition+to+this+other+tab
++++}
}|4300960|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If you want to do this from code that you are writing as part of a particular view controller, like in response to a button press or something, you can do this:
<pre><code>@IBAction func pushSearchButton(_ sender: UIButton?) {
 if let tabBarController = self.navigationController?.tabBarController {
 tabBarController.selectedIndex = 1
 }
}
</code></pre>
And you can also add code to handle tab switching using the UITabBarControllerDelegate methods. Using tags on the base view controllers of each tab, you can see where you are and act accordingly: For example
<pre><code>func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -&gt; Bool {
 
 // if we didn't change tabs, don't do anything
 if tabBarController.selectedViewController?.tabBarItem.tag == viewController.tabBarItem.tag {
 return false
 }
 
 if viewController.tabBarItem.tag == 4096 { // some particular tab
 // do stuff appropriate for a transition to this particular tab
 }
 else if viewController.tabBarItem.tag == 2048 { // some other tab
 // do stuff appropriate for a transition to this other tab
 }
}
</code></pre>

blocks|key|4300986|text|Swift+5|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|4300987|如果您的类是UITabBarController的子类，则只需执行以下操作：|CODE|4300988|selectedViewController+=+viewControllers![yourIndex]|code-block|syntax|javascript|4300989|entityMap^0|0|7|0|6|I|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@$9|T|A|U|B|H]]|D|@]|E|$]]|$1|I|3|J|5|K|7|V|8|@]|D|@]|E|$L|M]]|$1|N|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|O|$]]

Swift 5
If your class is a subclass of <code>UITabBarController</code>, you can just do:
<pre><code>selectedViewController = viewControllers![yourIndex]
</code></pre>

blocks|key|4004741|text|试一试|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4004742|DispatchQueue.main.async+{
+++self.tabBarController?.selectedIndex+=+1
}|code-block|syntax|javascript|4004743|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try
<pre><code>DispatchQueue.main.async {
 self.tabBarController?.selectedIndex = 1
}
</code></pre>

blocks|key|4004768|text|从任何地方的应用程序中，你可以切换之间的选项卡。
|type|blockquote|depth|inlineStyleRanges|entityRanges|data|4004769|unstyled|4004770|struct+Constants{
static+var+tabbarVC+:+TabbarViewController!|code-block|syntax|javascript|4004771|}|4004772|在选项卡条的初始化过程中，视图控制器存储对Constants.tabbarVC的引用
|4004773|4004774|+++++let+sb+=+UIStoryboard(name:+"Main",+bundle:+nil)
++++let+vc+=+sb.instantiateViewController(withIdentifier:+"TabbarViewController")+as!+TabbarViewController
++++Constants.tabbarVC+=+vc|4004775|最后，通过使用此引用，您可以切换选项卡。
|4004776|4004777|Constants.tabbarVC.selectedIndex+=+2|4004778|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|-4|5|C|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|C|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|-4|5|C|7|11|8|@]|9|@]|A|$]]|$1|N|3|O|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|P|3|Q|5|6|7|13|8|@]|9|@]|A|$]]|$1|R|3|-4|5|C|7|14|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|15|8|@]|9|@]|A|$G|H]]|$1|U|3|-4|5|C|7|16|8|@]|9|@]|A|$]]]|V|$]]

<blockquote>
From any where in-app you can switch between tabs
</blockquote>
<pre><code>struct Constants{
static var tabbarVC : TabbarViewController!
</code></pre>
}
<blockquote>
During initialization of tab bar view controller store its reference to Constants.tabbarVC
</blockquote>
<pre><code> let sb = UIStoryboard(name: &quot;Main&quot;, bundle: nil)
 let vc = sb.instantiateViewController(withIdentifier: &quot;TabbarViewController&quot;) as! TabbarViewController
 Constants.tabbarVC = vc
</code></pre>
<blockquote>
Finally by using this reference you can switch tabs
</blockquote>
<pre><code>Constants.tabbarVC.selectedIndex = 2
</code></pre>

I need write some code to switch the view to another tab when the iOS app starts (so, for example, the second tab is shown by default rather than the first).

I'm new to Swift, and have worked out the following:

<ul>
<li>The code should probably go in the override func viewDidLoad() function of the ViewController of the first tab.</li>
<li>The following code shows the second ViewController, but not with the tab bar at the bottom (vcOptions is the second ViewController tab item:</li>
</ul>

<pre class="lang-Objective-C prettyprint-override"><code>let vc : AnyObject! = self.storyboard.instantiateViewControllerWithIdentifier("vcOptions")
self.showViewController(vc as UIViewController, sender: vc)
</code></pre>

I think the answer may lie in using the UITabbarController.selectedIndex = 1, but not quite sure how to implement this.

Programmatically switching between tabs within Swift

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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