UIView removeFromSuperview 导致应用程序崩溃

Question

让我解释一下我的问题。我有 3 个UIView：一个 LoginView、LibraryView 和一个 StoreView。我有这段代码可以从一个 UIView 切换到另一个：

- (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，这就是我初始化 UIView 的方式。以下是用于在它们之间切换的按钮：

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

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

  //so on...

当我调用函数libraryViewToLoginView 和storeViewToLoginView 时出现问题。每当我调用这些函数时，应用程序就会崩溃，这很奇怪，因为这两个函数之前都可以正常工作。我检查了个人资料，它给了我这个堆栈跟踪：

#   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*>*)

如您所见，这是我不太了解的 CALayer 上的一堆调用。我想了解为什么会这样。谁能解释一下？

Answer 1

坦率地说，我还没有理解您想要在这里实现的所有目标。但是你应该考虑事件的顺序。查看我的 cmets：

  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. 

嗯，它甚至可以工作，因为这些 statmen 彼此相邻。当你从它的超级视图中删除它时，它会再次被释放。你的应用程序可能会崩溃。

顺便说一句，如果不保留它，您根本不应该释放它。还是我在这里错了？但是， addSubview 应该保留它，而 removeFromSuperview 将释放它，因此不需要额外的释放。一次删除它应该消失了。 （如果没有保留在其他地方）