Presentacion de la charla acerca de consejos y trucos para debuguear en Xcode

1. Brian Kernighan

2. Debugging tips and tricks

3. Everyone knows that debugging is twice as hard
as writing a program in the first place. So if you're
as clever as you can be when you write it, how
will you ever debug it?
Brian Kerninghan

4. Basic notions
○Breakpoint
○Watchpoint
○Continue to Here (gutter)
○Debug bar
○Show debug area (cmd + shift + y)
○variable view
○watch
○console
○Frame

5. Basic notions
○ Debug bar
○ (de)activate breakpoints
○ Continue execution
○ Step over
○ Execute current line and go to the next
○ Step in
○ “enter” the called method/function
○ Step out
○ “exit” the called method/function

6. Basic notions
○ Debug bar
○ Debug view hierarchy
○ Simulate location
○ Choose stack frame

7. Basic notions
○ watchpoint
○ Behaviors like a breakpoint
○ Stop at value change
○ Variable or memory address
○ Command line
○ Click
○ view memory
○ breakpoint navigator
○ edit
○ condition
○ action

8. lldb - low level debugger
○ Have you done that?:
print("log just for debug: (self.object)")
○ Or that?
let n = 0 // self.someMethodThatReturnInteger()
○ Or that?
if true !|| self.someMethodThatReturnBool() {
○ Or that?
func someMethodThatReturnBool() !-> Bool {
return true !//TODO: implement
}

9. lldb - breakpoints
○ Breakpoint stop execution of a instruction
○ Allow add command just for debug
○ May have stop condition
○ Via command
breakpoint set —file ViewController.swift —line 7
○ One shot - code execute just once, automatically removed
breakpoint set —oneshot true —name MyType.myMethod()
○ Via Xcode - just click gutter

10. lldb - stop conditions

11. lldb - condições de parada
○ - NSManagedObject.setValue(Any?, forKey: String)

12. lldb - low level debugger
○ Exception Breakpoint
○ Symbolic Breakpoint
UIKit symbols in Objective-C
○ Method signature
○ Symbols

13. lldb - exception breakpoint - stopping on crash
- Exception Breakpoint

14. lldb - commands and expressions
○ Expression (expression)
○ Print - p / expression — : - lldb internal formatters
○ parray
○ Print Object - po / expression -O — - use implementation of debugDescription
○ poarray
○ Frame variable (only Xcode 10.2) - v
Print variables of current stack frame. Can be way faster
○ Watchpoint (watchpoint)

15. Moving breakpoint position

16. Skipping line and returning value

17. Expressions
○ Evaluated as code
○ Result is shown and storage in convenience variable ($1, $2, etc)
○ Can do a lot
○ Arithmetic
○ function/method calling
○ type casting
○ Attributions
○ Variable declaration (let variable: Type = value)

18. lldb - mais expressões
(lldb) e let user.name = “John Doe”
(lldb) e let $count = 42
(lldb) po $count
42
(lldb) e let $dict: Dictionary<String, Int> = ["answer": 42]
(lldb) po $dict
▿ 1 element
▿ 0 : 2 elements
- key : "answer"
- value : 42

19. lldb - low level debugger
○ Watchpoint
○ Monitor state/value of a variable
○ Variable inspector

20. lldb - low level debugger
○ Watchpoint
○ Monitor state/value of a variable
○ Since Xcode 10 shown in breakpoint navigator

21. lldb - low level debugger
○ Rule of Thumb - keep it fast
○ “Automatically continue after evaluating”
○ po $arg1
○ Audible breakpoints
○ breakpoint with shell command
○ Command: say
○ Arguments: -v, Zarvox, “Your breakpoint %B has been hit %H times”

22. Referências
○ http://www.slideshare.net/talesp/debugging-fast-track
○ https://github.com/facebook/chisel
○ https://www.objc.io/issues/19-debugging/lldb-debugging/#let-s-
dance
○ http://lldb.llvm.org/tutorial.html
○ https://www.bignerdranch.com/blog/xcode-breakpoint-wizardry/
○ https://developer.apple.com/videos/play/wwdc2018/412/

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