NSLog (Debugging) Cheat Sheet

#ios #objc #beginners

Purpose of this cheat sheet is to explore debugging tools for logging.

Frequently used format specifiers:

Type	Format specifier
Object (prints description)	`%@`
`NSInteger`	`%ld`
`NSUInteger`	`%lu`
`CGFloat`	`%f`
`pointer`	`%p`

More format specifiers are available on: String Format Specifiers ~ Apple Documentation

Helper method to translate objects/structures into `NSString`:

Function	Description
`NSStringFromClass`	Returns the name of a class as a string.
`NSStringFromCGRect`	Returns a string formatted to contain the data from a rectangle in `{{x, y}, {width, height}}` format.
`NSStringFromCGSize`	Returns a string formatted to contain the data from a size data structure in `{width, height}` format.
`NSStringFromCGPoint`	Returns a string formatted to contain the data from a point in `{x, y}` format.
`NSStringFromRange`	Returns a string representation of a range in `{location, length}` format.

More (less used) methods:

NSStringFromSelector
NSStringFromProtocol
NSStringFromCGVector
NSStringFromMapTable
NSStringFromUIOffset
NSStringFromHashTable
NSStringFromCGAffineTransform
NSStringFromDirectionalEdgeInsets

Debugging wrapper for NSLog

#define Debug(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__)

Log a backtrace of your stack

NSLog(@"%@", [NSThread callStackSymbols]);

2023-04-22 22:37:20.001544+0530 just-objc[5829:186391] (
    0   just-objc                           0x000000010099dda8 -[ViewController viewDidLoad] + 84

<trimmed ...>

    28  UIKitCore                           0x0000000107ebeff0 -[UIApplication _run] + 868
    29  UIKitCore                           0x0000000107ec2f3c UIApplicationMain + 124
    30  just-objc                           0x000000010099e024 main + 120
    31  dyld                                0x0000000100b2d514 start_sim + 20
    32  ???                                 0x0000000100d85f28 0x0 + 4309147432
    33  ???                                 0xdf35000000000000 0x0 + 16083761644223594496
)

Mobile Vitals: A first step to Faster Apps

Slow startup times, UI hangs, and frozen frames frustrate users—but they’re also fixable. Mobile Vitals help you measure and understand these performance issues so you can optimize your app’s speed and responsiveness. Learn how to use them to reduce friction and improve user experience.

Read the guide