在Apples MultipleDetailViews示例中加载已经初始化的DetailViewControllers

如何解决在Apples MultipleDetailViews示例中加载已经初始化的DetailViewControllers

|| Apple在其iOS开发站点上提供了一个示例，说明如何将splitview与不同的detailviews一起使用（请参见MultipleDetailViews示例）。在选择RootViewController的时间内，将初始化一个新的DetailViewController：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

/*
 Create and configure a new detail view controller appropriate for the selection.
 */
NSUInteger row = indexPath.row;

UIViewController <SubstitutableDetailViewController> *detailViewController = nil;

if (row == 0) {
    FirstDetailViewController *newDetailViewController = [[FirstDetailViewController alloc] initWithNibName:@\"FirstDetailView\" bundle:nil];
    detailViewController = newDetailViewController;
}

if (row == 1) {
    SecondDetailViewController *newDetailViewController = [[SecondDetailViewController alloc] initWithNibName:@\"SecondDetailView\" bundle:nil];
    detailViewController = newDetailViewController;
}

// Update the split view controller\'s view controllers array.
NSArray *viewControllers = [[NSArray alloc] initWithObjects:self.navigationController,detailViewController,nil];
splitViewController.viewControllers = viewControllers;
[viewControllers release];

// dismiss the popover if it\'s present.
if (popoverController != nil) {
    [popoverController dismisspopoverAnimated:YES];
}

// Configure the new view controller\'s popover button (after the view has been displayed and its toolbar/navigation bar has been created).
if (rootPopoverButtonItem != nil) {
    [detailViewController showRootPopoverButtonItem:self.rootPopoverButtonItem];
}

[detailViewController release];
}

现在，我的想法不是每次都初始化视图控制器，只需在viewDidLoad（以及标头）中初始化控制器，并在选择单元格时传递它们的引用： rootviewcontroller中的viewDidLoad的一部分：

firstDetailViewController = [[FirstDetailViewController alloc] initWithNibName:@\"FirstDetailView\" bundle:nil];
secondDetailViewController = [[FirstDetailViewController alloc] initWithNibName:@\"FirstDetailView\" bundle:nil];

现在，tableView didselectrow方法看起来像这样：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

/*
 Create and configure a new detail view controller appropriate for the selection.
 */
NSUInteger row = indexPath.row;

UIViewController <SubstitutableDetailViewController> *detailViewController = nil;

if (row == 0) {
    detailViewController = firstDetailViewController;
}

if (row == 1) {
    detailViewController = secondDetailViewController;
}

// Update the split view controller\'s view controllers array.
NSArray *viewControllers = [[NSArray alloc] initWithObjects:self.navigationController,nil];
splitViewController.viewControllers = viewControllers;
[viewControllers release];

// dismiss the popover if it\'s present.
if (popoverController != nil) {
    [popoverController dismisspopoverAnimated:YES];
}

// Configure the new view controller\'s popover button (after the view has been displayed and its toolbar/navigation bar has been created).
if (rootPopoverButtonItem != nil) {
    [detailViewController showRootPopoverButtonItem:self.rootPopoverButtonItem];
}

//[detailViewController release];
}

在横向模式下，一切正常，但是在纵向模式下，从第一个详细视图控制器切换到第二个，然后切换到第一个，然后又想切换到第二个时出现错误。出现以下消息：由于未捕获的异常'NSinvalidargumentexception \'，终止了应用程序，原因：\'无法从没有窗口的视图中显示Popovers。\' 从昨天晚上开始，我试图找出答案，但是我没有找到解决方案。有人有主意吗？ 干杯，多米尼克     

解决方法

        我有一个类似的问题，但是我发现这篇文章证明了您必须在设置splitView的视图控制器之前从以前的detailView中删除leftBarButtonItem的想法。这段代码为我解决了这个问题。 这是TPoschel编写的代码。

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

// Retrieve the new detail view controller
UIViewController *detailViewController = [[self.allData objectAtIndex:indexPath.section] objectAtIndex:indexPath.row];

// Add the detail view controller to a navigation controller and set the bar style
UINavigationController *detailNavigationController = [[UINavigationController alloc] initWithRootViewController:detailViewController];
detailNavigationController.navigationBar.barStyle = [[NSUserDefaults standardUserDefaults] integerForKey:@\"UIBarStyle\"];

// Retrieve previous detail view controller and remove the leftBarButtonItem
UINavigationController *previousDetailNavigationController = [splitViewController.viewControllers objectAtIndex:1];
UIViewController *previousDetailViewController = [[previousDetailNavigationController viewControllers] lastObject];
previousDetailViewController.navigationItem.leftBarButtonItem = nil;

// Update the split view controller\'s view controllers array.
NSArray *viewControllers = [[NSArray alloc] initWithObjects:self.navigationController,detailNavigationController,nil];
splitViewController.viewControllers = viewControllers;

[detailNavigationController release];
[viewControllers release];

// Dismiss the popover if it\'s present.
if (popoverController != nil) {
    [popoverController dismissPopoverAnimated:YES];
}

// This sets the left bar to nil when in landscape and equal to \"Menu\" when in portrait.
// We need to remove rootPopoverButtonItem from the previous viewController...
detailViewController.navigationItem.leftBarButtonItem = rootPopoverButtonItem;

}