Xcode debugging cheatsheet

#xcode #ios #objc #swift

This is a cheatsheet - starting point to look for things that you can do.
Avoided complex / 3rd party things as they require some additional setup that may not be allowed in certain projects.

Breakpoints

Breakpoint is user enabled point in code where the application pauses
Line and column breakpoints
- Pauses the program before the statement on line/column is executed
Conditions
- Execute walk method just for LadyBug: self.bugType == 1
Actions: Sound, Log message, Debug command
Symbolic breakpoints: Add breakpoint on a method without source file [UIImage systemImageNamed:]
- po $arg1 -> Receiver object
- po $arg2 -> po (SEL)$arg2 -> Method name
- po $arg3 -> First argument, and goes
Watch points: Pauses when the value changes

LLDB commands

help: Information about commands
v: Does not compile the expression instead it just dumps value from the stack
p: Evaluates and prints the output
po: Evaluates the print debug output
- description method
- Use [] syntax if . is failing due to typecasting
expression: Evaluates and prints, also stores the output in a variable
- Expressions in other languages: expression -l swift/objc -O -- <code>
alias: Creates a shortcut for complex commands
- command alias greet p @"Hello World"

Techniques

Inject code without building it: expression <sample fix/feature>
- expr [bugs addObjectsFromArray:[[self makeAntViews:20] mutableCopy]]
Short circuit / skip code execution:
- Move the debugger handle
- thread jump --by 1
Early return through a method: thread return <return value>
- NOTE: This does not always work and can be dangerous
Print the view hierarchy: po [self.view recursiveDescription]
Highlight a view:
- (UIColor *)[bug setBackgroundColor:UIColor]
- (void)[CATransition flush]: Refreshes UI
Add delay in code: expr [NSThread sleepForTimeInterval:2]
Auto layout debugging: po [self.view _autolayoutTrace]