Tech Talk: Advanced Debugging with Xcode

An internal presentation on advanced debugging, tips, and techniques for getting the most out of Xcode.

Transcript

1. Tech Talk: Advanced Debugging with Xcode Craig Pearlman, iOS Developer Fjord ATX © 2018 Fjord/Accenture Interactive
2. Agenda » Why? » Gettin' Around » What's This Do? » Fun with Breakpoints » LLDB Is Your Friend » When Good Layouts Go Bad » Don't Forget Instruments! » Question Time Advanced Debugging with Xcode 2/53
3. Why? » iOS 7 Tech Talks: Hidden iOS 7 Development Gems » https://developer.apple.com/videos/play/techtalks-ios-7/8/ » CocoaConf Boston 2014: Effective Xcode: Tips & Techniques by Laura Savino » Notes from Xcode Walkabout: https://gist.github.com/ lsavino/860a5bfa47c6834e890b » Leveling Up: Walk away having learned at least one thing Advanced Debugging with Xcode 3/53
4. Gettin' Around Advanced Debugging with Xcode 4/53
5. Open Quickly… » File ▸ Open Quickly… (⌘⇧O) » Append ":##" to jump to a specific line (ViewCon:12) » All symbols—classes, structs, enums, functions, etc. » Matches across symbol names in sequence: UINC will find UINavigationController Advanced Debugging with Xcode 5/53
6. Useful Shortcuts Command Shortcut Navigate ▸ Reveal in Project Navigator ⌘⇧J Navigate ▸ Jump to Definition ⌃⌘J Navigate ▸ Jump to Next/Previous Issue ⌘'/⌘" Navigate ▸ Go Back/Forward ⌃⌘⇠/⌃⌘⇢ View ▸ Debug Area ▸ Activate Console ⌘⇧C View ▸ Debug Area ▸ Hide/Show Debug Area ⌘⇧Y View ▸ Standard Editor ▸ Show Document Items ⌃6 Debug ▸ Activate/Deactivate Breakpoints ⌘Y Advanced Debugging with Xcode 6/53
7. Related Files (⌃1) » Callers and Callees submenus are particularly helpful Advanced Debugging with Xcode 7/53
8. Filters » Need to find a specific file? Use filters! » Great way to find all matching files in a complex hierarchy Advanced Debugging with Xcode 8/53
9. Searching » Search can do much more than look for text » Search by type, limit match scope, and limit where to search » Limiting project scope useful to ignore Pods Advanced Debugging with Xcode 9/53
10. Behaviors » Xcode ▸ Preferences… (⌘,) » Xcode ▸ Behaviors ▸ Edit Behaviors… Advanced Debugging with Xcode 10/53
11. What's This Do? Advanced Debugging with Xcode 11/53
12. Arguments » Change app runtime behavior: » Launch arguments » Environment variables » NSHipster: Launch Arguments & Environment Variables » http://nshipster.com/launch- arguments-and- environment-variables/ Advanced Debugging with Xcode 12/53
13. Diagnostic Options » Many arguments are available in the Edit Scheme sheet » Product ▸ Scheme ▸ Edit Scheme… (⌘<) » Set and Run: Option (⌥) + Product ▸ Run… (⌥⌘R) » Memory Allocator: Enabling the Malloc Debugging Features » https://developer.apple.com/library/ content/documentation/Performance/ Conceptual/ManagingMemory/ Articles/MallocDebug.html Advanced Debugging with Xcode 13/53
14.  Code Diagnostics » Thread Sanitizer » https://developer.apple.com/documentation/code_diagnostics/thread_sanitizer » Address Sanitizer » https://developer.apple.com/documentation/code_diagnostics/address_sanitizer » Main Thread Checker » https://developer.apple.com/documentation/code_diagnostics/ main_thread_checker » Undefined Behavior Sanitizer » https://developer.apple.com/documentation/code_diagnostics/ undefined_behavior_sanitizer Advanced Debugging with Xcode 14/53
15. Visual Memory Debugger » Shows a visual graph of allocated memory » Use Your Loaf: Xcode Visual Memory Debugger (source of the screen shots) » https://useyourloaf.com/blog/xcode-visual-memory-debugger/ » Pete the Developer: iOS — Identifying Memory Leaks using the Xcode Memory Graph Debugger » http://petethedeveloper.com/post/identityingmemoryleaksgraphdebugger/ Advanced Debugging with Xcode 15/53
16. ! Zombies ! Advanced Debugging with Xcode 16/53
17. Localized Strings » -NSDoubleLocalizedStrings » Doubles the text to simulate languages with long words without breakable space » "cut" in German is ausschneiden (for example) » -NSShowNonLocalizedStrings YES » Shows text from non-localized strings IN ALL CAPS » Both are also available from the Options tab in Edit Scheme… Advanced Debugging with Xcode 17/53
18. Set Language/Locale at Runtime » Run your app in Canadian French: » -AppleLanguages (fr) » -AppleLocale fr_CA » Use Your Loaf: Using Launch Arguments To Test Localizations » https://useyourloaf.com/blog/using-launch-arguments- to-test-localizations/ » Both are also available from the Options tab in Edit Scheme… Advanced Debugging with Xcode 18/53
19. Overriding UserDefaults » https://twitter.com/johnsundell/status/973273054699773953 Advanced Debugging with Xcode 19/53
20. ⚠ WARNING Turn off these features when you no longer need them! Many have a significant performance impact! Advanced Debugging with Xcode 20/53
21. Fun with Breakpoints Advanced Debugging with Xcode 21/53
22. Not These Breakpoints Try it anyway; it's music by geeks, for geeks (available on iTunes) Advanced Debugging with Xcode 22/53
23. Conditional Breakpoints » No more print(), NSLog(), or os_log() just to debug » Set a conditional breakpoint with an action of "Log Message" » Check "Automatically continue after evaluating actions" » No need to recompile and re-run Advanced Debugging with Xcode 23/53
24. Breakpoints in User Space » User breakpoints live across all your projects » Drag and drop a breakpoint to move it between groups Advanced Debugging with Xcode 24/53
25. Breakpoint Types » There are also different types of breakpoints » Save an All Exceptions breakpoint in user space » In LLDB, po $arg1 to print the exception » Symbolic breakpoints can break inside Apple's frameworks Advanced Debugging with Xcode 25/53
26. Watchpoints » Pause execution whenever a value is changed » On pause, use the call stack to find where the change occurred » Watchpoints can be managed from LLDB Watchpoint 1 hit: old value: true new value: false Advanced Debugging with Xcode 26/53
27. LLDB is Your Friend Advanced Debugging with Xcode 27/53
28. The Debugger » LLDB lives in the same pane as the console log » Look for the (lldb) prompt » Enter help for a full list of commands » Awesome way to test a specific line of code in context » Examine contents of complex data structures » Test and tweak an expression to get the correct syntax » See if an expression is returning what you expect » http://lldb.llvm.org Advanced Debugging with Xcode 28/53
29. p <expr> » Evaluate an expression on the current thread » Displays any returned value with LLDB's default formatting (lldb) p anInt (Int) $R0 = 10 (lldb) p anObject (UIView) $R1 = 0x00007fa331606770 { UIKit.UIResponder = { baseNSObject@0 = { isa = UIView } } } Advanced Debugging with Xcode 29/53
30. po <expr> » Evaluate an expression on the current thread » Displays any returned value with formatting controlled by the type's author (debugDescription) (lldb) po anInt 10 (lldb) po anObject <UIView: 0x7fa331606770; frame = (0 0; 0 0); layer = <CALayer: 0x604000030b00>> Advanced Debugging with Xcode 30/53
31. fr v <expr> » Show variables for the current stack frame » Defaults to all arguments and local variables in scope » Names of argument, local, file static and file global variables can be specified » Children of aggregate variables can be specified such as var->child.x (lldb) fr v anInt (Int) anInt = 10 (lldb) fr v anObject (UIView) anObject = 0x00007fa331606770 { UIKit.UIResponder = { baseNSObject@0 = { isa = UIView } } } Advanced Debugging with Xcode 31/53
32. expr <expr> » Evaluate an expression on the current thread » Displays any returned value with LLDB's default formatting » Can affect the current context and change variable values (lldb) p varInt (Int) $R0 = 12 (lldb) expr varInt = 15 (lldb) p varInt (Int) $R2 = 15 Advanced Debugging with Xcode 32/53
33. Quick Look » Useful to view data not easily expressible as (short) text » Much more reliable from the variables pane than hovering over a symbol in code » You can Quick Look a view and see a preview of it, too! Advanced Debugging with Xcode 33/53
34. When Good Layouts Go Bad Advanced Debugging with Xcode 34/53
35. Visual Debugger » View your view hierarchy visually at runtime » Bottom toolbar: » View 2D/3D (can rotate in 3D) » Zoom » Show constraints » Show hidden/obscured views » Right-hand slider to modify shown scope Advanced Debugging with Xcode 35/53
36. Visual Debugger, continued » Filter the outline view using the filter bar » Use the "Focus on" option to show a specific view and its hierarchy Advanced Debugging with Xcode 36/53
37. Recursive Descriptions » po view.value(forKey: "recursiveDescription")! (lldb) po view.value(forKey: "recursiveDescription")! <UIView: 0x7fcf646166f0; frame = (0 0; 375 812); autoresize = W+H; layer = <CALayer: 0x60c00022e1a0>> | <UILabel: 0x7fcf64615210; frame = (166 323; 42 21); text = 'Label'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x60c000286770>> Advanced Debugging with Xcode 37/53
38. Constraint Identifiers let height = label.heightAnchor.constraint(equalToConstant: 20.0) height.identifier = "LabelHeight" height.active = true 2018-03-27 11:44:50.061399-0400 Example[44373:13943052] [LayoutConstraints] Unable to simultaneously satisfy constraints. Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. ( "<NSLayoutConstraint:0x604000280aa0 UILabel:0x7f9098405820'Label'.centerY == UIView:0x7f9098405520.centerY (active)>", "<NSLayoutConstraint:0x604000280b40 UILabel:0x7f9098405820'Label'.top == UILayoutGuide:0x6040007ac5c0'UIViewSafeAreaLayoutGuide'.top + 200 (active)>", "<NSLayoutConstraint:0x604000280050 'LabelHeight' UILabel:0x7f9098405820'Label'.height == 20 (active)>", "<NSLayoutConstraint:0x608000286680 'UIView-Encapsulated-Layout-Height' UIView:0x7f9098405520.height == 812 (active)>", "<NSLayoutConstraint:0x604000280b90 'UIViewSafeAreaLayoutGuide-top' V:|-(44)-[UILayoutGuide:0x6040007ac5c0'UIViewSafeAreaLayoutGuide'] (active, names: '|':UIView:0x7f9098405520 )>" ) Will attempt to recover by breaking constraint <NSLayoutConstraint:0x604000280050 'LabelHeight' UILabel:0x7f9098405820'Label'.height == 20 (active)> Advanced Debugging with Xcode 38/53
39. Et tu, Auto Layout? » http://www.wtfautolayout.com » Paste in the constraint issue(s) from the console » Returns a human-readable interpretation Advanced Debugging with Xcode 39/53
40. Feedback Loop Debugger » Disabled by default » When enabled, runs layout x times before throwing an error » -UIViewLayoutFeedbackLoopDebuggingThreshold x » Replace UI with NS for macOS » Provides layout detail for each pass // don't actually do this override func viewDidLayoutSubviews() { view.setNeedsLayout() } Advanced Debugging with Xcode 40/53
41. Don't Forget Instruments! Advanced Debugging with Xcode 41/53
42. Where art thou, Instruments.app? Advanced Debugging with Xcode 42/53
43. Profiling Options Advanced Debugging with Xcode 43/53
44. Allocations » Samples an app's memory usage and shows class-level retain/release for objects » Once opened, click the red record icon on the top left to start capturing results » Switch to your app and use it to capture activity » Pause when you no longer need to capture Advanced Debugging with Xcode 44/53
45. Allocations, continued » To get the most out of the outline: » Switch the display to Call Trees » Select "Invert Call Tree" and "Hide System Libraries" Advanced Debugging with Xcode 45/53
46. Allocations, continued Advanced Debugging with Xcode 46/53
47. Question Time Advanced Debugging with Xcode 47/53
48. Thanks Gracias Danke  Merci Mahalo ת ו ד ה Спасибо Asante Tack Diolch
    
    Kiitos ευχαριστώ Grazie Gratias ago
     Obrigado א ד א נ ק Advanced Debugging with Xcode 48/53
49. Resources (1/5) » iOS 7 Tech Talks: Hidden iOS 7 Development Gems » https://developer.apple.com/videos/play/techtalks-ios-7/8/ » CocoaConf Boston 2014: Effective Xcode: Tips & Techniques by Laura Savino » Notes from Xcode Walkabout: https://gist.github.com/lsavino/860a5bfa47c6834e890b » Appdevcon 2018: Learn to Debug Like a Pro by Paul Hudson (@twostraws) » https://speakerdeck.com/twostraws/learn-to-debug-like-a-pro » NSHipster: Launch Arguments & Environment Variables » http://nshipster.com/launch-arguments-and-environment-variables/ » Use Your Loaf: Using Launch Arguments To Test Localizations » https://useyourloaf.com/blog/using-launch-arguments-to-test-localizations/ Advanced Debugging with Xcode 49/53
50. Resources (2/5) » Memory Allocator: Enabling the Malloc Debugging Features » https://developer.apple.com/library/content/documentation/Performance/Conceptual/ ManagingMemory/Articles/MallocDebug.html » @johnsundell: https://twitter.com/johnsundell/status/973273054699773953 » James Dempsey and the Breakpoints: Backtrace » https://itunes.apple.com/us/album/backtrace/id926558924?uo=4&at=11lpkp&ct=09 » The LLDB Debugger » http://lldb.llvm.org » Why The Failure, Auto Layout » http://www.wtfautolayout.com Advanced Debugging with Xcode 50/53
51. Resources (3/5) » Documentation > Code Diagnostics > Thread Sanitizer: » https://developer.apple.com/documentation/code_diagnostics/thread_sanitizer » Documentation > Code Diagnostics > Address Sanitizer » https://developer.apple.com/documentation/code_diagnostics/address_sanitizer » Documentation > Code Diagnostics > Main Thread Checker » https://developer.apple.com/documentation/code_diagnostics/ main_thread_checker » Documentation > Code Diagnostics > Undefined Behavior Sanitizer » https://developer.apple.com/documentation/code_diagnostics/ undefined_behavior_sanitizer Advanced Debugging with Xcode 51/53
52. Resources (4/5) » Technical Note TN2239: iOS Debugging Magic » https://developer.apple.com/library/content/technotes/tn2239/_index.html » Technical Note TN2124: Mac OS X Debugging Magic » https://developer.apple.com/library/content/technotes/tn2124/_index.html » Debugging with Xcode: Specialized Debugging Workflows » https://developer.apple.com/library/content/documentation/DeveloperTools/Conceptual/ debugging_with_xcode/chapters/special_debugging_workflows.html » Use Your Loaf: Xcode Visual Memory Debugger » https://useyourloaf.com/blog/xcode-visual-memory-debugger/ » Pete the Developer: iOS — Identifying Memory Leaks using the Xcode Memory Graph Debugger » http://petethedeveloper.com/post/identityingmemoryleaksgraphdebugger/ Advanced Debugging with Xcode 52/53
53. Resources (5/5) » WWDC 2016: Visual Debugging with Xcode [Session 410] » https://developer.apple.com/videos/play/wwdc2016/410/ » WWDC 2017: App Startup Time: Past, Present, and Future [Session 413] » https://developer.apple.com/videos/play/wwdc2017/413/ » WWDC 2017: Debugging with Xcode 9 [Session 404] » https://developer.apple.com/videos/play/wwdc2017/404/ » Also recommend similar WWDC sessions for Xcode 6, 7, and 8 » WWDC 2017: Finding Bugs Using Xcode Runtime Tools [Session 406] » https://developer.apple.com/videos/play/wwdc2017/406/ Advanced Debugging with Xcode 53/53