iOS应用状态保存和恢复

当应用被后台Kill掉的时候希望从后台返回的时候显示进入后台之前的内容

在Appdelegate中设置

- (BOOL)application:(UIApplication *)application shouldSaveApplicationState:(NSCoder *)coder{
    return YES;
}
- (BOOL)application:(UIApplication *)application shouldRestoreApplicationState:(NSCoder *)coder{
    return YES;
}

 为每个ViewController设置：restorationIdentifier（可以直接在sb中设置），restorationClass

     如果设置了restorationClas则必须遵守UIViewControllerRestoration协议返回恢复时的控制器

+ (UIViewController *)viewControllerWithRestorationIdentifierPath:(NSArray<NSString *> *)identifierComponents coder:(NSCoder *)coder{
    UIStoryboard *storybord = [UIStoryboard storyboardWithName:@"Main" bundle:[NSBundle mainBundle]];
    UIViewController *controller = [storybord instantiateViewControllerWithIdentifier:@"mywebcontroller"];
     controller.restorationIdentifier = [identifierComponents lastObject];
    controller.restorationClass = [MyWebViewController class];
    return controller;
}

如果未指定代理方法则从Appdelgate中的代理中返回

If a view controller has an associated restoration class, the viewControllerWithRestorationIdentifierPath:coder: method of that class is called during state restoration. That method is responsible for returning the view controller object that matches the indicated view controller. If you do not specify a restoration class for your view controller, the state restoration engine asks your app delegate to provide the view controller object instead.

在控制器中保存和恢复状态

//只保存状态，如果是数据的话保存在文件中如NSUserdefault等
- (void)encodeRestorableStateWithCoder:(NSCoder *)coder{
    //保存开关状态
    [coder encodeBool:_switchBtn.isOn forKey:@"ison"];
    
    [super encodeRestorableStateWithCoder:coder];
}
- (void)decodeRestorableStateWithCoder:(NSCoder *)coder{
    [super decodeRestorableStateWithCoder:coder];
    //获取开关状态
    _switchBtn.on = [coder decodeBoolForKey:@"ison"];
    
}