UIView removeFromSuperview導致應用程序崩潰

Question

讓我解釋我的問題。我有3 UIView：a LoginView,LibraryView和StoreView。我有此代碼切換從一個UIView的另一：

- (void)showView:(NSInteger)viewTag 
{ 
    if (viewTag == 1) 
    { 
     if (self.loginView) 
     { 
     self.loginView = nil; 
     self.loginView.delegate = nil; 
     } 

     LoginView *loginPage = [[LoginView alloc]initWithFrame:self.view.bounds]; 
     [loginPage setDelegate:self]; 

     self.loginView = loginPage; 

     [loginPage release]; 

     [self.view addSubview:self.loginView]; 
} 
else if(viewTag == 2) 
{ 
    if (self.libraryView) 
    { 
     self.libraryView = nil; 
     self.libraryView.delegate = nil; 
    } 

    LibraryView *libraryPage = [[LibraryView alloc]initWithFrame:self.view.bounds]; 
    [libraryPage setDelegate:self]; 

    self.libraryView = libraryPage; 

    [libraryPage release]; 

    [self.view addSubview:self.libraryView]; 
} 
else 
{ 
    if (self.bookStoreView) 
    { 
     self.bookStoreView = nil; 
     self.bookStoreView.delegate = nil; 
    } 

    BookStoreView *bookStore = [[BookStoreView alloc]initWithFrame:self.view.bounds]; 
    [bookStore setDelegate:self]; 

    self.bookStoreView = bookStore; 

    [bookStore release]; 

    [self.view addSubview:self.bookStoreView]; 
} 

}

基本上，這是我如何初始化UIViews。這裏是用於它們之間進行切換的按鈕：當我調用函數libraryViewToLoginView和storeViewToLoginView

- (void)loginViewToLibraryView 
    { 
    [self.loginView removeFromSuperview]; 
    [self showView:2]; 
    } 

- (void)libraryViewToStoreView 
    { 
    [self.libraryView removeFromSuperview]; 
    [self showView:3]; 
    } 

    //so on... 

，就會出現問題。每當我調用這些函數時，該應用程序都會崩潰，這很奇怪，因爲這兩個函數之前都能正常工作。我查了一下資料，它給了我這個堆棧跟蹤：

# Address  Category Event RefCt Timestamp Size Responsible Library Responsible Caller 
0 0xc4dcac0 CALayer Malloc 1 00:02.233.004 48 UIKit     -[UIView _createLayerWithFrame:] 
1 0xc4dcac0 CALayer Retain 3 00:02.238.317 0 QuartzCore    CA::Layer::insert_sublayer(CA::Transaction*, CALayer*, unsigned long) 
2 0xc4dcac0 CALayer Release 2 00:02.238.324 0 UIKit     -[UIView(Internal) _addSubview:positioned:relativeTo:] 
3 0xc4dcac0 CALayer Retain 3 00:02.238.518 0 QuartzCore   -[CALayerArray copyWithZone:] 
4 0xc4dcac0 CALayer Release 2 00:02.238.602 0 UIKit     -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] 
5 0xc4dcac0 CALayer Retain 3 00:02.238.665 0 QuartzCore   -[CALayerArray copyWithZone:] 
6 0xc4dcac0 CALayer Release 2 00:02.238.796 0 UIKit     -[UIView(Internal) _didMoveFromWindow:toWindow:] 
7 0xc4dcac0 CALayer Retain 3 00:05.107.397 0 QuartzCore   -[CALayerArray copyWithZone:] 
8 0xc4dcac0 CALayer Release 2 00:05.107.539 0 UIKit     -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] 
9 0xc4dcac0 CALayer Retain 3 00:05.107.613 0 QuartzCore   -[CALayerArray copyWithZone:] 
10 0xc4dcac0 CALayer Release 2 00:05.107.700 0 UIKit     -[UIView(Internal) _didMoveFromWindow:toWindow:] 
11 0xc4dcac0 CALayer Retain 2 00:06.105.958 0 QuartzCore   -[CALayerArray copyWithZone:] 
12 0xc4dcac0 CALayer Release 2 00:06.108.134 0 UIKit     -[UIView dealloc] 
13 0xc4dcac0 CALayer Release 1 00:06.108.492 0 UIKit     -[UIView dealloc] 
14 0xc4dcac0 CALayer Zombie -1 00:06.115.332 0 QuartzCore   CA::release_objects(X::List<void const*>*) 

正如你所看到的，它是一堆的CALayer的電話，我真的不明白的。我想明白爲什麼會發生這種情況。誰能解釋一下？

Answer 1

坦白說，我不明白，你想在這裏實現的一切。但是你應該考慮事件的順序。看我的評論：

if (self.loginView) 
    { 
    self.loginView = nil; 
    //self.loginView is nil now. What so you think doese happen on the next line? 
    self.loginView.delegate = nil; 
    // change the sequence of this lines and it will be ok. 
    } 

    LoginView *loginPage = [[LoginView alloc]initWithFrame:self.view.bounds]; 
    [loginPage setDelegate:self]; 

    self.loginView = loginPage; 

    [loginPage release]; //here you release the object. it is gone now. However, there are still references to it. 

    [self.view addSubview:self.loginView]; // here you add the released object. What do you expect to happen? 
    // Switch those two statmetns and you should be fine. 

那麼，它可能甚至工作，因爲這些statmens是彼此相鄰。當你從超級視圖中刪除它時，它會再次被釋放。那裏你的應用程序可能會崩潰。

BTW，而不必它保留你不應該釋放它。還是我在這裏錯了？但是，addSubview應該保留它，removeFromSuperview將會釋放它，所以不需要額外的發佈。 Onece移除它應該消失。 （如果不保留別的地方）