保存和恢复选项卡栏控制器的状态

Question

我有一个应用程序，它有一个带有两个选项卡的 UITabBarController，每个选项卡都有自己的导航控制器。现在我想在用户关闭应用程序时存储应用程序的状态，以便当用户重新启动应用程序时将显示与上次关闭前相同的位置。
所以，在 applicationWillTerminate: 我有

[NSKeyedArchiver archiveRootObject:tabBarController toFile:@"lastVisitedTab"];

然后，在 applicationDidFinishLaunching: 我有

UITabBarController *last= (UITabBarController *)[NSKeyedUnarchiver unarchiveObjectWithFile:@"lastVisitedTab"];
if (last)
    tabBarController = [last retain];

我还有 UIImage 的扩展，以使其符合 NSCoding。然而，这不起作用，因为状态没有被保留。第一个选项卡始终被选中，并且也不保留导航。
有人可以告诉我出了什么问题，或者告诉我如何正确地做吗？

Answer 1

我认为保留实际对象是多余的。相反，只需保存 selectedIndex 属性（使用 [NSNumber numberWithInt: tabBar.selectedIndex]），然后读回并在启动时设置该属性。也许这不能正确回答您的问题，但它可能足以满足您想要实现的目标。

Answer 2

感谢 Felixyz 的想法，我终于弄清楚了如何做到这一点。以下是我必须执行的操作来存储选项卡，无论其数据如何。如果视图加载了从 URL 下载的数据，则存储 URL 而不是整个视图。您必须

- (void)encodeWithCoder:(NSCoder *)encoder
- (id)initWithCoder:(NSCoder *)decoder

在 UIViewController 子类中进行重写，以告诉视图控制器在应用程序停止之前保存适当的数据。
现在，在您的应用程序委托中，在退出之前保存数据

- (void)applicationWillTerminate:(UIApplication *)application
    // data buffer for archiving
    NSMutableData *data = [NSMutableData data];
    NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
    // the index of selected tab
    [archiver encodeInt:tabBarController.selectedIndex forKey:@"TAB_INDEX"];
    // array of keys for each navigation controller, here I have 3 navigation controllers
    NSArray *keys = [NSArray arrayWithObjects:
                     @"NAVIGATION_CONTROLLER_1",
                     @"NAVIGATION_CONTROLLER_2",
                     @"NAVIGATION_CONTROLLER_3", nil];
    for (int i = 0; i < keys.count; i++) {
        UINavigationController *controller = [tabBarController.viewControllers objectAtIndex:i];
        NSMutableArray *subControllers = [NSMutableArray arrayWithArray:controller.viewControllers];
        // the first view controller would already be on the view controller stack and should be removed
        [subControllers removeObjectAtIndex:0];
        // for each of the navigation controllers save its view controllers, except for the first one (root)
        [archiver encodeObject:subControllers forKey:[keys objectAtIndex:i]];
    }
    [archiver finishEncoding];
    // write that out to file
    NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    [data writeToFile:[documentsDirectory stringByAppendingPathComponent:@"ARCHIVE_PATH"] atomically:YES];
}

，然后在重新启动时

- (void)applicationDidFinishLaunching:(UIApplication *)application {
    // set up the tabs
    tabBarController = [[UITabBarController alloc] init];
    tabBarController.viewControllers = [NSArray arrayWithObjects:
                                        [[[UINavigationController alloc] initWithRootViewController:rootViewController1] autorelease],
                                        [[[UINavigationController alloc] initWithRootViewController:rootViewController2] autorelease],
                                        [[[UINavigationController alloc] initWithRootViewController:rootViewController3] autorelease], nil];
    // look for saved data, if any
    NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    NSData *archive = [NSData dataWithContentsOfFile:[documentsDirectory stringByAppendingPathComponent:@"ARCHIVE_PATH"]];
    // if no data found, skip this step
    if (archive) {
        NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:archive];
        // set the tab
        tabBarController.selectedIndex = [unarchiver decodeIntForKey:@"TAB_INDEX"];
        NSArray *keys = [NSArray arrayWithObjects:
                         @"NAVIGATION_CONTROLLER_1",
                         @"NAVIGATION_CONTROLLER_2",
                         @"NAVIGATION_CONTROLLER_3", nil];
        // push view controllers up the stack
        for (int i = 0; i < keys.count; i++) {
            NSArray *controllers = [unarchiver decodeObjectForKey:[keys objectAtIndex:i]];
            for (UIViewController *controller in controllers) {
                [((UINavigationController *)[tabBarController.viewControllers objectAtIndex:i]) pushViewController:controller animated:NO];
            }
        }
    }
    // Add the tab bar controller's current view as a subview of the window
    [window addSubview:tabBarController.view];
}