我一直在忙于国家恢复.在下面的代码中,UITableViewController的滚动位置被恢复,但是,如果我要进入细节视图(将MyViewController的一个实例推送到导航堆栈),当应用程序重新启动时,它总是返回到第一个视图控制器在导航堆栈(即MyTableViewController)中.有人能够帮助我恢复正确的视图控制器(即MyOtherViewController)吗？
AppDelegate.m
- (BOOL)launchWithOptions:(NSDictionary *)launchOptions
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken,^{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
MyTableViewController *table = [[MyTableViewController alloc] initWithStyle:UITableViewStylePlain];
table.depth = 0;
UINavigationController *navCon = [[UINavigationController alloc] initWithRootViewController:table];
navCon.restorationIdentifier = @"navigationController";
self.window.rootViewController = navCon;
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
});
return YES;
}
- (BOOL)application:(UIApplication *)application willFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
return [self launchWithOptions:launchOptions];
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
return [self launchWithOptions:launchOptions];
}
MyTableViewController.m
- (id)initWithStyle:(UITableViewStyle)style
{
self = [super initWithStyle:style];
if(self)
{
self.restorationIdentifier = @"master";
}
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
self.title = @"Master";
self.tableView.restorationIdentifier = @"masterView";
}
#pragma mark - Table view data source
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 5;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return 10;
}
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
return [NSString stringWithFormat:@"Section %d",section];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if(!cell)
{
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
cell.textLabel.text = [NSString stringWithFormat:@"%d",indexPath.row];
return cell;
}
#pragma mark - Table view delegate
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
MyOtherViewController *vc = [[MyOtherViewController alloc] initWithNibName:nil bundle:nil];
[self.navigationController pushViewController:vc animated:YES];
}
MyOtherViewController.m
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
self.restorationIdentifier = @"detail";
}
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
self.title = @"Detail";
self.view.backgroundColor = [UIColor redColor];
self.view.restorationIdentifier = @"detailView";
}
解决方法
因为您正在代码中创建您的详细视图控制器,并且不将其从故事板实例化,您需要实现一个还原类,因此系统还原过程知道如何创建详细视图控制器.
恢复类实际上只是一个工厂,它知道如何从恢复路径创建一个特定的视图控制器.你实际上不必为此创建一个单独的类,我们可以在MyOtherViewController中处理它：
在MyOtherViewController.h中,实现协议：UIViewControllerRestoration
然后在MyOtherViewController.m中设置recoverID时,还要设置还原类：
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
self.restorationIdentifier = @"detail";
self.restorationClass = [self class]; //SET THE RESTORATION CLASS
}
return self;
}
然后,您需要在恢复类(MyOtherViewController.m)中实现此方法
+(UIViewController *) viewControllerWithRestorationIdentifierPath:(NSArray *)identifierComponents coder:(NSCoder *)coder
{
//At a minimum,just create an instance of the correct class.
return [[MyOtherViewController alloc] initWithNibName:nil bundle:nil];
}
这可以让您恢复子系统能够创建并将Detail View控制器推送到导航堆栈上. (你最初问的是什么)
扩展示例来处理状态：
在一个真实的应用程序中,您需要同时保存状态并处理恢复它…我将以下属性定义添加到MyOtherViewController以模拟此：
@property (nonatomic,strong) NSString *selectedRecordId;
而且我还修改了MyOtherViewContoller的viewDidLoad方法,将Detail标题设置为用户选择的任何记录ID：
- (void)viewDidLoad
{
[super viewDidLoad];
// self.title = @"Detail";
self.title = self.selectedRecordId;
self.view.backgroundColor = [UIColor redColor];
self.view.restorationIdentifier = @"detailView";
}
为了使该示例工作,在最初从MyTableViewController中推送Detail View时,设置selectedRecordId：
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
MyOtherViewController *vc = [[MyOtherViewController alloc] initWithNibName:nil bundle:nil];
vc.selectedRecordId = [NSString stringWithFormat:@"Section:%d,Row:%d",indexPath.section,indexPath.row];
[self.navigationController pushViewController:vc animated:YES];
}
另一个缺失的部分是MyOtherViewController中的方法,您的详细信息视图,用于保存Detail控制器的状态.
-(void)encodeRestorableStateWithCoder:(NSCoder *)coder
{
[coder encodeObject:self.selectedRecordId forKey:@"selectedRecordId"];
[super encodeRestorableStateWithCoder:coder];
}
-(void)decodeRestorableStateWithCoder:(NSCoder *)coder
{
self.selectedRecordId = [coder decodeObjectForKey:@"selectedRecordId"];
[super decodeRestorableStateWithCoder:coder];
}
现在这实际上还不行.这是因为在DecoreRestorablStateWithCoder方法之前的“ViewDidLoad”方法在恢复时被调用.因此,在显示视图之前,标题不会设置.要解决这个问题,我们处理在viewWillAppear中设置Detail视图控制器的标题：或者我们可以修改viewControllerWithRestorationIdentifierPath方法来恢复创建类的状态：
+(UIViewController *) viewControllerWithRestorationIdentifierPath:(NSArray *)identifierComponents coder:(NSCoder *)coder
{
MyOtherViewController *controller = [[self alloc] initWithNibName:nil bundle:nil];
controller.selectedRecordId = [coder decodeObjectForKey:@"selectedRecordId"];
return controller;
}
而已.
一些其他注意事项…
我假设你在App代表中做了以下,即使我没有看到代码？
-(BOOL) application:(UIApplication *)application shouldSaveApplicationState:(NSCoder *)coder
{
return YES;
}
- (BOOL) application:(UIApplication *)application shouldRestoreApplicationState:(NSCoder *)coder
{
return YES;
}
在模拟器中运行演示代码时,我正确地保留了滚动偏移量,我看到有点薄弱.这似乎偶尔为我工作,但并不是所有的时间.我怀疑这可能是因为MyTableViewController的真正恢复也应该使用一个restoreClass方法,因为它是在代码中实例化的.但是我还没有尝试过.
我的测试方法是将应用程序置于后台,返回跳板(需要保存应用程序状态),然后从XCode中重新启动应用程序以模拟干净的开始.
