On an iOS single view app, when is the earliest ti

问题:

I am trying to add a UITableView object that covers up the whole screen, by

  UITableView *tabelView = [[UITableView alloc] initWithFrame:self.view.bounds];
  [self.view addSubview:tabelView];

but I realized that even if a physical iPad 2 is rotated to Landscape mode, self.view.bounds is {{0, 0}, {768, 1004}} in viewDidLoad and viewWillAppear. Only in viewDidAppear is it finally {{0, 0}, {1024, 748}}

What is the earliest time that self.view.bounds is set correctly to {{0, 0}, {1024, 748}}? If viewDidAppear is the one, then I have to create the UITableView there, and if the "Launch image" is a static Landscape blank table, then the screen will flash a white screen when viewDidAppear is called, and then the table is added and seen, so a flash of white screen is seen.

So when is the earliest time that self.view.bounds is set correctly to {{0, 0}, {1024, 748}}? It seems like it needs to be slightly before viewDidAppear, so that the blank table is drawn (with the grey lines), and show it and seamlessly get displayed to cover up the Launch image. If the table is created in viewDidLoad or viewWillAppear using self.view.bounds, then the table ends up being 768 points wide and is meant for the Portrait mode.

Update: I just tried to add the Launch image and for some reason, even if the UITableView is added in viewDidAppear, the "flash of white screen" didn't happen... I don't know why, but previously if I use CALayer and bitmap to show content, and didn't use any view or drawRect, then the flash occurred... by the way, the earliest one I found was viewWillLayoutSubviews, and then later in viewDidLayoutSubviews, both of which happened before viewDidAppear, and both showed self.view.bounds as {{0, 0}, {1024, 748}}

Update 2: What if the view is complicated and time consuming to make? To test, I added a usleep(100000); in the tableView:cellForRowAtIndexPath to sleep 0.1 second for each cell, and the "flash" did occur... but cell and table supposedly should be light weight and fast to make, but what if there are other type of views that are more time consuming to make? If I move UITableView creation to viewWillLayoutSubviews, then it is still slow to show something, but at least there is no "flash". However, later on when I rotate the device, it actually call viewWillLayoutSubviews again and add another table to the main view (with correct screen size), so viewWillLayoutSubviews will need to remove any old table view first, if any, or just resize the old one and not add a new one.

回答1:

The simplest way to avoid the flash is to create the table view in viewDidLoad and set the table view's autoresizing mask properly, so that the system automatically makes the table view fill its superview:

- (void)viewDidLoad {
    [super viewDidLoad];
    UITableView *tableView = [[UITableView alloc] initWithFrame:self.view.bounds];
    tableView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    [self.view addSubview:tableView];
}

Otherwise, the earliest time that you can see the final view bounds are in the view controller's viewWillLayoutSubviews method. You would add your table view once in viewDidLoad, and then adjust its frame in viewWillLayoutSubviews or a method called after that. See my answer to UIViewController returns invalid frame? for more details.

回答2:

I was trying to solve a similar problem - I wanted to load some UI elements programmatically based on the size of a UIView added in Interface Builder.

Inside viewDidLoad and viewWillAppear, the UIView still hadn't had its frame/bounds set. Placing my code inside viewDidAppear worked, however it meant that the UI would "flash" with an update rather than appearing already loaded when the UIViewController was pushed onto the navigation stack.

I found that overriding viewDidLayoutSubviews solved the problem - at that point, the view had its bounds and frame set - I could add in my own subviews relative to its size, all before viewDidAppear.

The end result is that the UI loaded properly before it appeared, and hence didn't "flash" in for the user.