如何记住 UITabBarController 中最后选择的选项卡？

Question

我试图让我的应用程序记住应用程序退出之前最后一次查看的选项卡，以便应用程序在下次启动时打开相同的选项卡。这就是iPhone电话功能的功能：我该如何做到这一点？

Answer 1

更新

In the UITabBarControllerDelegate's Delegate, overwrite

目标 C

- (BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController
{
NSLog(@"%lu",self.tabBarController.selectedIndex);
return YES;
}

In this delegate method you will get last selected index.

Swift 3.2

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool
{
    print("%i",tabBarController.selectedIndex)
    return true
}

Answer 2

在 UITabBar 的 Delegate 中，覆盖

- (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item

item 的索引并将其存储在 NSUserDefaults 中。下次您的应用程序启动时，从那里读取它，并将其设置回选中状态。像这样的事情：

-首先，您将为 UITabBar 设置一个委托，如下所示：

tabBarController.delegate = anObject;

-在 anObject 中，覆盖 didSelectItem：

       - (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item
        {
          NSUserDefaults *def = [NSUserDefaults standardUserDefaults];

          [def setInteger: [NSNumber numberWithInt: tabBarController.selectedIndex]
 forKey:@"activeTab"];

          [def synchronize];
        }

请注意，您保存了一个 NSNumber，如 int 值不能直接序列化。
当您再次启动应用程序时，它将读取并设置默认值中的 selectedIndex 值：

- (void)applicationDidFinishLaunchingUIApplication *)application {  
   NSUserDefaults *def = [NSUserDefaults standardUserDefaults];

   int activeTab = [(NSNumber*)[def objectForKey:@"activeTab"] intValue];

   tabBarController.selectedIndex = activeTab;
} 

Answer 3

我对 TabBarController 进行了子类化并：

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    self.selectedIndex = [[NSUserDefaults standardUserDefaults] integerForKey:@"activeTab"];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];

    [[NSUserDefaults standardUserDefaults] setInteger: self.selectedIndex
             forKey:@"activeTab"];
}

Answer 4

我是这样做的。
这两个方法都在 appDelegate 中，tabBarController 是一个实例变量。

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    /*
     Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
     If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
     */

    //Remember the users last tab selection
    NSInteger tabIndex = self.tabBarController.selectedIndex;
    NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
    [userDefaults setInteger: tabIndex forKey:@"activeTab"];

    if (![userDefaults synchronize]) 
    {
        NSLog(@"Error Synchronizing NSUserDefaults");
    }

}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    /*
     Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
     */

    //Set the tabBarController to the last visted tab
    NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
    int activeTab = [(NSNumber*)[userDefaults objectForKey:@"activeTab"] intValue];
    self.tabBarController.selectedIndex = activeTab;
}

Answer 5

这是 Swift 3 的解决方案。只需在情节提要中将 TabBarController 的类设置为 RememberingTabBarController

import Foundation
import UIKit

class RememberingTabBarController: UITabBarController, UITabBarControllerDelegate {
    let selectedTabIndexKey = "selectedTabIndex"

    override func viewDidLoad() {
        super.viewDidLoad()
        self.delegate = self

        // Load the last selected tab if the key exists in the UserDefaults
        if UserDefaults.standard.object(forKey: self.selectedTabIndexKey) != nil {
            self.selectedIndex = UserDefaults.standard.integer(forKey: self.selectedTabIndexKey)
        }
    }

    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        // Save the selected index to the UserDefaults
        UserDefaults.standard.set(self.selectedIndex, forKey: self.selectedTabIndexKey)
        UserDefaults.standard.synchronize()
    }
}

Answer 6

每次用户选择新选项卡时，将所选选项卡索引存储在 NSUserDefaults 首选项中。然后，当应用程序重新启动时，从首选项加载该值并手动选择该选项卡。