UIScrollView setContentSize crashes with uncaught

问题:

Call to setContentSize crashes the application after some of the UIScrollView's contents have been removed.

int toolbarHeight = [[[self navigationController] toolbar] frame].size.height;
int navbarHeight = [[[self navigationController] navigationBar] frame].size.height;

int totalHeight = toolbarHeight + navbarHeight;
// contentWidth is 640
CGSize contentSize = CGSizeMake(contentWidth, [scrollView frame].size.height - totalHeight);

[scrollView setContentSize:contentSize]; // Crash happens here, contentSize is perfectly valid

* Terminating app due to uncaught exception 'NSRangeException', reason: '* -[__NSArrayM objectAtIndex:]: index 1 beyond bounds [0 .. 0]'

What could be causing this?

EDIT: Here's the stack trace for those who can make any sense of it:

* thread #1: tid = 0x1c03, 0x34d2e32c libsystem_kernel.dylib`__pthread_kill + 8, stop reason    = signal SIGABRT
frame #0: 0x34d2e32c libsystem_kernel.dylib`__pthread_kill + 8
frame #1: 0x36c2a20e libsystem_c.dylib`pthread_kill + 54
frame #2: 0x36c2329e libsystem_c.dylib`abort + 94
frame #3: 0x308eff6a libc++abi.dylib`abort_message + 46
frame #4: 0x308ed34c libc++abi.dylib`_ZL17default_terminatev + 24
frame #5: 0x36361356 libobjc.A.dylib`_objc_terminate + 146
frame #6: 0x308ed3c4 libc++abi.dylib`_ZL19safe_handler_callerPFvvE + 76
frame #7: 0x308ed450 libc++abi.dylib`std::terminate() + 20
frame #8: 0x308ee824 libc++abi.dylib`__cxa_rethrow + 88
frame #9: 0x363612a8 libobjc.A.dylib`objc_exception_rethrow + 12
frame #10: 0x34e9050c CoreFoundation`CFRunLoopRunSpecific + 404
frame #11: 0x34e9036c CoreFoundation`CFRunLoopRunInMode + 104
frame #12: 0x3618c438 GraphicsServices`GSEventRunModal + 136
frame #13: 0x31f86e7c UIKit`UIApplicationMain + 1080
frame #14: 0x0000cb50 App`main + 152 at main.m:16

回答1:

It seems that the exception is thrown when the content offset is left outside the content size.

I had views side by side in the scroll view and the offset was to the last view.

+------+------+------+
|      |      |offset|
+------+------+------+

Now the last view is removed and the content size changed to a smaller one.

+------+------+
|      |      |offset
+------+------+

The offset is left behind.

I changed the code so that the offset is moved first, then the content size changed.

+------+------+
|      |offset|
+------+------+

No crashes so far.