给出以下代码示例(iOS 7,Xcode 5):
/**
* SampleProvider Class
*/
typedef void(^RequestCallback)(UIViewController *result);
static NSString * const cControllerRequestNotification = @"controllerRequestNotification";
static NSString * const cRequestClassNameKey = @"className";
static NSString * const cRequestCallbackKey = @"callback";
@interface SampleProvider : NSObject
+ (void)requestControllerForClassName:(NSString *)className completion:(RequestCallback)callback;
@end
@interface SampleProvider ()
- (UIViewController *)controllerForClassName:(NSString *)className;
- (void)didReceiveControllerRequest:(NSNotification *)n;
@end
@implementation SampleProvider
#pragma mark - Overrides
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
- (id)init {
self = [super init];
if( self ) {
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didReceiveControllerRequest:) name:cControllerRequestNotification object:nil];
}
return self;
}
#pragma mark - Public API
+ (void)requestControllerForClassName:(NSString *)className completion:(RequestCallback)callback{
NSDictionary *requestInfo = @{ cRequestClassNameKey : className, cRequestCallbackKey : [callback copy] };
[[NSNotificationCenter defaultCenter] postNotificationName:cControllerRequestNotification object:requestInfo];
}
#pragma mark - Private API
- (UIViewController *)controllerForClassName:(NSString *)className {
UIViewController *result = nil;
Class controllerClass = NSClassFromString(className);
if( (nil != controllerClass) && ([controllerClass isSubclassOfClass:[UIViewController class]]) ) {
result = [[controllerClass alloc] init];
}
return result;
}
- (void)didReceiveControllerRequest:(NSNotification *)n {
NSDictionary *requestInfo = [n object];
NSString *className = requestInfo[cRequestClassNameKey];
RequestCallback callback = requestInfo[cRequestCallbackKey];
UIViewController *result = [self controllerForClassName:className];
if( nil != callback ) {
callback(result);
}
}
@end
/**
* SampleViewController Class
*/
@interface SampleViewController : UIViewController
@end
@implementation SampleViewController
#pragma mark - Overrides
- (void)viewDidAppear:(BOOL)animated{
[super viewDidAppear:animated];
NSString *className = @"ClassName";
[SampleProvider requestControllerForClassName:className completion:^(UIViewController *result) {
if( nil != result ) {
// Result is valid pointer, not a zombie.
[self.navigationController pushViewController:result animated:YES];
// Result is released, not nil.
} else {
NSLog(@"Unable to load controller with class name: %@", className);
}
}];
}
@end
为什么我的UINavigationController无法获得SampleProvider的公共类方法收到的回调控制器的所有权,即使在显示视图后也是如此?
我看到以下行为:
新控制器类已正确分配并通过回调方法返回。进入回调后,result参数指向有效内存。
新控制器被推送到我的UINavigationController导航堆栈。
调用新推送的控制器的“viewDidLoad”方法。
检查UINavigationController的“viewControllers”属性时,数组中会引用新推送的控制器。
新推送控制器已取消分配,而UINavigationController pushViewController:animated:仍在执行。
新控制器现在是一个僵尸。
感谢您的帮助。
答案 0 :(得分:2)
我没有一个明确的答案,因为答案可能是你没有发布的代码 - 你发布的代码看起来有效,除了两个观察结果(这可能会引导你回答):
那个isKindOfClass应该是isSubclassOfClass吗? -isKindOfClass:是一个 NSObject上的实例方法,而不是类方法。
调用pushViewController:在viewDidLoad期间同步调用 危险的。很可能是视图层次结构的状态 那个时候不稳定。应该发生这种推动以应对 我想,其他一些离散的事件。尝试做推(或者 整个requestControllerForClassName :)异步通过 dispatch_async,作为测试,看看是否能解决您的问题。