最近在iOS的项目中出现了Can't add self as subview 的crash，日志信息如下
从日志上来看崩溃是在main函数，定位不到具体的地方。
像这种crash，一般最简单地情况是：
[self.view addSubview:self.view];
这种确实会直接导致崩溃，但不是引起原因。
另一种错误原因是说一次push了两次，动画被打断后引起的crash。
对push的UIViewController来进行进行控制。
另一种方法：
创建一个分类，拦截控制器入栈\出栈的方法调用，通过安全的方式，确保当有控制器正在进行入栈\出栈操作时，没有其他入栈\出栈操作。
此分类用到运行时 (Runtime) 的方法交换Method Swizzling，因此只需要复制下面的代码到自己的项目中，此 bug 就不复存在了。
#import "UINavigationController+Consistent.h"
#import <objc/runtime.h>
/// This char is used to add storage for the is PushingViewController property.
static char const *const ObjectTagKey ="ObjectTag";
@interfaceUINavigationController ()
@property(readwrite, getter= isViewTransitionInProgress) BOOL viewTransitionInProgress;
@end
@implementation UINavigationController (Consistent)
- (void)setViewTransitionInProgress:(BOOL)property {
NSNumber *number = [NSNumber numberWithBool:property];
objc_setAssociatedObject(self, ObjectTagKey, number , OBJC_ASSOCIATION_RETAIN);
}
- (BOOL)isViewTransitionInProgress {
NSNumber *number = objc_getAssociatedObject(self, ObjectTagKey);
return [number boolValue];
}
#pragma mark - Intercept Pop, Push, PopToRootVC
/// @name Intercept Pop, Push, PopToRootVC
- (NSArray *)safePopToRootViewControllerAnimated:(BOOL)animated {
if(self.viewTransitionInProgress) return nil;
if(animated) {
self.viewTransitionInProgress =YES;
}
//-- This is not a recursion, due to method swizzling the call below calls the originalmethod.
return [self safePopToRootViewControllerAnimated:animated];
}
- (NSArray *)safePopToViewController:(UIViewController *)viewController animated:(BOOL)animated {
if(self.viewTransitionInProgress) return nil;
if(animated) {
self.viewTransitionInProgress = YES;
}
//-- This is not a recursion, due to method swizzling the call below calls the originalmethod.
return [self safePopToViewController:viewController animated:animated];
}
- (UIViewController *)safePopViewControllerAnimated:(BOOL)animated {
if(self.viewTransitionInProgress) return nil;
if(animated) {
self.viewTransitionInProgress =YES;
}
//-- This is not a recursion, due to method swizzling the call below calls the originalmethod.
return [self safePopViewControllerAnimated:animated];
}
- (void)safePushViewController:(UIViewController *)viewController animated:(BOOL)animated {
self.delegate =self;
//-- If we are already pushing a view controller, we dont push another one.
if(self.isViewTransitionInProgress ==NO) {
//-- This is not a recursion, due to method swizzling the call below calls the originalmethod.
[self safePushViewController:viewController animated:animated];
if(animated) {
self.viewTransitionInProgress =YES;
}
}
}
// This is confirmed to be App Store safe.
// If you feel uncomfortable to use Private API, you could also use the delegate method navigationController:didShowViewController:animated:.
- (void)safeDidShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
//-- This is not a recursion. Due to method swizzling this is calling the original method.
[self safeDidShowViewController:viewController animated:animated];
self.viewTransitionInProgress =NO;
}
// If the user doesnt complete the swipe-to-go-back gesture, we need to intercept it and set the flag to NO again.
- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
id tc = navigationController.topViewController.transitionCoordinator;
[tc notifyWhenInteractionEndsUsingBlock:^(id context) {
self.viewTransitionInProgress =NO;
//--Reenable swipe back gesture.
self.interactivePopGestureRecognizer.delegate = (id)viewController;
[self.interactivePopGestureRecognizer setEnabled:YES];
}];
//-- Method swizzling wont work in the case of a delegate so:
//-- forward this method to the original delegate if there is one different than ourselves.
if(navigationController.delegate !=self) {
[navigationController.delegate navigationController:navigationController
willShowViewController:viewController
animated:animated];
}
}
+ (void)load {
//-- Exchange the original implementation with our custom one.
method_exchangeImplementations(class_getInstanceMethod(self,@selector(pushViewController:animated:)),class_getInstanceMethod(self,@selector(safePushViewController:animated:)));
method_exchangeImplementations(class_getInstanceMethod(self,@selector(didShowViewController:animated:)),class_getInstanceMethod(self,@selector(safeDidShowViewController:animated:)));
method_exchangeImplementations(class_getInstanceMethod(self,@selector(popViewControllerAnimated:)),class_getInstanceMethod(self,@selector(safePopViewControllerAnimated:)));
method_exchangeImplementations(class_getInstanceMethod(self,@selector(popToRootViewControllerAnimated:)),class_getInstanceMethod(self,@selector(safePopToRootViewControllerAnimated:)));
method_exchangeImplementations(class_getInstanceMethod(self,@selector(popToViewController:animated:)),class_getInstanceMethod(self,@selector(safePopToViewController:animated:)));
}
@end
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