Does any body know what I have to check if my app freezes? I mean, I can see the app in the iPad screen but no buttons respond. I have tried debugging the code when I click on the button, but I haven't seen anything yet. I was reading about the Instruments tools; specifically how do I use them?
Can anybody help me? I just need an explanation about how use the tools.
It sounds like you've blocked the main thread somehow. To debug, run the app in the debugger and when the app freezes, hit the pause button above the log area at the bottom of Xcode. Then on the left side, you'll be able to see exactly what each thread is doing, and you can see where it's getting stuck.
Probably either a long loop on the main thread or a sync deadlock.
Top answer is correct. You can debug this with "Pause" option. Most common way to block main thread is to call dispatch_sync on the same thread you dispatching. Sometimes you call same code from dispatch_once.
Besides pausing and following the stacktrace I think as an additional thing to do, is to check in the code if there's any loop causing the app freezes.
I recently ran into a similar problem, but stack trace didn't help much, I figured out that I was having an eternal loop when calling a reloadData() inside layoutsubviews method and that was causing a freeze with no errors and no help from instruments.
I have similar case in my project and the reason was another developer who added setNeedsLayout() inside method layoutSubviews() and this make infinite loop and freeze the app.
I suggest checking your sizes especially in collection views if they are not fitted they will freeze your app and also check your constraints
The same Issue Happened to me with ios 13.4 and then I tried the above solution but it doesn't solve it. so I had one element with break constraint on the storyboard. So after resolving the constraint it solve the problem.
Related
So, I haven't been able to figure this out yet, because when I pause execution... Xcode doesn't really show what's going on:
This freeze happens when I scroll a very long UITableView around in the center of its scrollable area constantly, so that it's constantly reusing cells. I think that perhaps there is something not being retained for a dispatch block that might happen there, but I'm not yet sure since no data is displayed using the standard debugger and its a fairly complex view. (reference: https://stackoverflow.com/a/23501382/963901 )
I'm going to attempt some manual diagnosis here, but is there any other way of approaching this with Instruments or something, perhaps?
To investigate this sort of problem I'd suggest the following:
Disable the setting in Xcode's debug navigator pane that hides intermediate stack frames from you. It's one of the buttons at the bottom right of the pane that shows the stack trace.
Look at the newly-revealed portion of the backtrace to see what code is blocking on the semaphore.
Look at the other threads in your program to see which appear to be doing work related to the code discovered in step 2.
So I'm debugging some code I didn't write. It's quite complex, and I'm trying to get a handle on the bug I'm tracking down. But, for some reason, on our login page, none of the lifecycle methods are firing.
I've placed breakpoints on them, put console logs there, and no matter what, everything points to them not firing.
Why would methods such as viewDidLoad: and viewWillAppear: etc. not fire? Are there any times that could happen? Or any times it could skip a breakpoint or console line in those methods?
Sorry if these are dumb questions, I'm just super perplexed as to how a VC on screen doesn't call these methods but still is on screen? I've used chisel to confirm that the code I'm looking at is indeed for the VC on screen, and it is. So I'm at a complete loss. I would be VERY grateful for any help.
Thanks in advance!
I have faced similar issues before and it was due to duplicate copy of container in the simulator.You can try resetting your simulator, clean the build and check once again.
Throughout all the betas of Watchkit I was able to run my watch app seamlessly, but with the recent release this past week (8.2) my willActivate method is hardly ever called. What happens is awakeWithContext gets called and the watch stalls with the spinner spinning forever. Has this issue happened to anyone?
I've found that locking and unlocking the device (simulator) by typing Command-L will cause the willActivate method to be called. I hope you don't have to do that on a real Apple Watch.
Just came into the same problem yesterday.
In my case, I'm using the page navigation, and the initial view controller's awakeWithContext gets called, but willActivate is never called.
After some digging I found out that when using page navigation, ALL of the pages awakeWithContext will be called at launch time and before the initial page's willActivate. If one of the pages awakeWithContext method get stuck, the initial page's willActivate method will never be called.
You may need to check your other view controller's awakeWithContext methods to see if they are stuck.
So, I still don't think I know exactly what is going on or what's causing it, but I'm having the exact same issue, and I have done some investigating and have some results, so I hope this helps us narrow this down. I have identified that it has something to do with the complexity of the layout that is going into my initial controller. If I change to a simpler layout for my initial controller, or if I delete "enough things" from my initial controller, then I no longer get the spinning wheel of death. (Of course that also breaks the logic of my app). My layout is a bit complex, but not that complex; there are groups nested 4 layers deep, and about 20 total UI elements (including the groups themselves), with four buttons and 4 labels. It seemed to work fine in the beta. And there's not a clear rhyme or reason to it; some combinations of layouts seem to cause it, some don't. It is deterministic; if a given layout spins on load it will always spin on load, and if it doesn't, it doesn't. When it spins, I never get willActivate. When it doesn't, I do. It does not seem to have anything to do with the contents of awakeFromContext:. I can delete everything from that method and it does not help. It also has nothing to do with assets, compiler settings, etc., etc. Other than that, I haven't figured it out yet. If anyone has any insight into this, I would love to hear it.
Occasionally, my app will simply not render any frame-relayed animations triggered by +[UIView animateWithDuration:animations:] and friends.
The completion block, when provided, still gets called as I'd expect, but the views simply "snap" into the destination frame, as if I'd simply called -setFrame:.
It is across the whole app, and is completely independent of which view controller is displaying, and whether or not the VC is modally presented. Restarting the app solves the problem temporarily.
Note: This is obviously not enough information to solve the problem, but I'm not even sure where to begin. Comments on where to start debugging are greatly appreciated.
Update: It seems to be reproducible by running a series of animations in succession. If I trigger several animations to run overtop of each other, it would seem animations just turn off, app-wide.
For posterity:
The issues that, direct frame-setting was occurring on a background thread.
To fix the issue, I needed to ensure that that code was getting run on the main thread.
That being said, since I could not post enough code to really substantiate this issue, I'm going to vote to close it as off-topic. Thanks for all your help!
I've been asked to help fix a bug for a client, who is an inexperienced developer. However, I'm absolutely stumped by this one.
The problem is that after a string of opening and closing a view controller, which is being pushed onto a navigation controller, all of the subviews will disappear (including the navigation bar items) and show straight through to the window. After this happens, I can still press the buttons on the navigation bar, but they will immediately disappear on touch-up, and restoring a stable UI state is impossible without a quit & relaunch. Another obscure side effect is that after closing the app, Springboard will flash as I swipe between screens. My initial thoughts were that this was a memory issue (e.g. subviews getting released on memory warning), but I have since cleaned all the leaks & checked all the viewDidLoad/viewDidUnload handling of outlets and the problem is still happening. So now I think that with the Springboard effect, that the code is somehow messing up the state of core animation entirely.
Has anyone seen anything like this before? Or have any idea how it would be possible to make this much of a mess? I would attach some screenshots, but trying to take a screenshot with the phone when the app is in this state causes a system crash.
I've not experienced this, but maybe a memory warning is eating some of your views?
I know that iOS is free to unload view controllers that aren't visible.
I'd stick a breakpoint in viewdidunload or similar and see if that triggers.
As it turned out, this bug was caused by a UIView being deallocated while it had a superview.