我不知道为什么这个表视图代码崩溃了

Question

hello i'm studying iOS programming

i created a project, which is an empty application

and i created table view controller without xib file.

and i inserted follow code in didFinishLaunchingWithOptions

TableViewController *tvc = [[TableViewController alloc] init];
[self.window addSubView:tvc.view];
[tvc release];

this code was crashed when i scrolled down. why is that?

when i comment this code

[tvc release];

program doesn't crash.

i didn't write dealloc in AppDelegate file.

why is that??

i think i created table view controller with alloc

so retain count is 1.

and add sub view to window and table view controller retain count is 2.

so i release table view controller

but it crash when i scrolled down.

i don't know why..

help me please

Answer 1

Simple, adding tvc.view as a subview of the window causes tvc.view to be retained but does not retain tvc itself. In essence, your TableViewController instance becomes invalid as soon as you call release on it. The app crashes when you scroll presumably because the TableViewController instance is configured as a delegate or datasource for a UITableView or UIScrollView or any other thing associated with tvc.view .

Also note that the way you are displaying the view is not the recommended way to go about it. Really you should be calling presentModalViewController: or pushViewController: and passing the TableViewController instance. This will cause the TableViewController to be retained until it is dismissed/popped, making it safe for you to call release as in your example code.

Or, since you are doing this setup manually as part of didFinishLaunchingWithOptions , you can also set window.rootViewController directly, though again that's not really recommended. XCode allows you to specify the app's default/root view controller and will automatically set it up for you when the app launches.

Answer 2

Actually you have just added the view alone. So the view alone will be retained. The viewcontroller will be released. But the viewcontroller needs to be the datasource and delegate for the tableview. Since it has been deallocated, that datasource will not have any valid reference and so it crashes.