我正在研究BNR的iOS编程书的第7章，但遇到了一个问题。在本章的开头，我设置了一个UIViewController(HypnosisViewController)和一个UIView(HypnosisView)，以响应上一章中的运动事件。
我在AppDelegate.m文件中创建UIViewController:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
...
HypnosisViewController *hvc = [[HypnosisViewController alloc] init];
[[self window] setRootViewController:hvc];
...
}
在HypnosisViewController中，我将HypnosisView设置为第一响应者:
- (void)loadView
{
// Create a view
CGRect frame = [[UIScreen mainScreen] bounds];
HypnosisView *view = [[HypnosisView alloc] initWithFrame:frame];
[self setView:view];
[view becomeFirstResponder];
}
并且在HypnosisView中，确保将canBecomeFirstResponder返回YES。不幸的是，HypnosisView没有像以前那样对运动事件做出响应。当我最终继续前进时，我做了一个有趣的发现。如果将HypnosisViewController移到UITabBarController，则HypnosisView将开始响应运动事件。代码看起来像这样:
HypnosisViewController *hvc = [[HypnosisViewController alloc] init];
UITabBarController *tabBarController = [[UITabBarController alloc] init];
NSArray *viewControllers = [NSArray arrayWithObjects:hvc, <insert more objs here>, nil];
[tabBarController setViewControllers:viewControllers];
[[self window] setRootViewController:tabBarController];
将HypnosisViewController设置为RootViewController时，为什么HypnosisView没有成为第一响应者？将HypnosisViewController放置在另一个控制器中后，为什么它开始工作？我对RootViewController缺少什么？
谢谢!
最佳答案
您的问题很贴切。我也在学习同一本书，并且在同一章上。问题是，在使用UITabBarController之前，我们将使用HypnosisViewController或TimeViewController。然后，我们将在AppDelegate.m文件中执行[self.window setRootViewController:hvc]或[self.window setRootViewController:tvc]。在这种情况下，setRootViewController方法在内部调用loadView方法。因此，如果应该调用loadView，则应该触发beginFirstResponder(作为方法调用驻留在其内部)。所以在内部canBecomeFirstResponder应该被调用
现在，当我们使用UITabBarController时，事情往往会破裂。发生的是不是通过[[[self window] setRootViewController:tabBarController];”调用loadView。的代码行，通过“[tabBarController setViewControllers:viewControllers];”来调用。因此，最重要的是rootViewController属性(当设置为tabBarController时)不会调用loadView方法，因此不会调用'becomeFirstResponder'。您可能会争辩说loadView确实是通过'[tabBarController setViewControllers:viewControllers];'调用的但是setViewControllers不用于设置根viewController。
遇到此问题时，我明确调用了成为FirstResponder的电话。这是如何做:-
@implementation HypnoTimeAppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions //method of UIApplicationDelegate protocol
{
NSLog(@"lets begin");
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
HypnosisViewController *viewController= [[HypnosisViewController alloc] init];
TimeViewController *viewController2= [[TimeViewController alloc] init];
NSLog(@"view controllers are done initializing!");
UITabBarController *tabBarController= [[UITabBarController alloc] init];
NSArray *viewControllers= [NSArray arrayWithObjects:viewController,viewController2, nil];
[tabBarController setViewControllers:viewControllers];//loadView of HypnosisViewController gets called internally since the 'app view' isn't going to load from a XIB file but from 'HypnosisView.m'.loadView method of TimeViewController loads its own view from the XIB file.
[self.window setRootViewController:tabBarController];
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
return YES;
}
@implementation HypnosisViewController
-(void)loadView{
NSLog(@"HypnosisView loading...");
HypnosisView *myView= [[HypnosisView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
self.view= myView;
[self configureFirstResponder];//configuring first responder
}
-(void) configureFirstResponder{
BOOL viewDidBecomeFirstResponder= [self.view becomeFirstResponder];
NSLog(@"Is First Responder set as HypnosisView? %i",viewDidBecomeFirstResponder);
}