Debugging and Profiling

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1 Debugging & Profiling Dr.-Ing. Thomas Springer M.Sc. Martin Weißbach

2 Errors in Swift conditions can occur that require a deviation from the predefined control flow in order to handle e.g. a file does not exist at the given path while it is tried to be opened optionals indicate the absence of values, but cannot specify the reason of errors only non-fatal errors can be handled in the application 2

3 Error protocol enum FileErrors: Error { case FileDoesNotExist case NoReadRights case IncompatibleEncoding case InvalidFilePath(_: String) case UnknownError(errorNumber: Int) } empty protocol used to indicate types that can be used for error handling enums are well suited, because grouping of related error conditions can be easily modeled 3

4 Throwing Errors func method(/** ParameterList **/) throws { } // Method Body func method(/** ParameterList **/) throws -> ReturnType { } // Method Body 4

5 Error Handling resembles exception handling in other languages try, catch, throws keywords does not unwind the call stack of the program similar to a return statement 5

6 Error Handling do { <statements> try <statement that can throw> <statements> } catch <error_pattern_1> { <handle_error_statements> } catch <error_pattern_2> where <error_condition> { <handle_error_statements> } 6

7 Error Handling func throwingfunction() throws -> String { errors can be converted to an Optional Type using try? both approaches are semantically equivalent // } let string_1 = try? throwingfunction() let string_2: String? do { string_2 = try throwingfunction() } catch _ { string_2 = nil } 7

8 ErrorHandling propagation of errors can be disabled let string = try! throwingfunction() should be used cautiously and only when it can be ensured that the throwing function or method never actually throws 8

9 Clean Up when an Error is thrown open resources such as files may not be closed, but remain open do { filehandle = try FileHandle(forReadingFrom: fileurl) } catch _ //... defer { filehandle.closefile() } is always called before the current scope, e.g., method or function, is left position of defer in scope may be arbitrary 9

10 NSError Object representing errors originating from Objective-C days still widely in use NSError Error domain (String) usually a global variabel that uniquely defines the source of the error Error code (Integer) define the error uniquely within the given error domain User info (Dictionary) contains additional info on the error 10

11 NSError with Swift let url = <arbitrary url object> do { let filehandle = try NSFileHandle(forReadingFromURL: url) } catch error as NSError { // NSError properties accessible // e.g. error.code } 11

12 Breakpoints 12

13 Breakpoints General Purpose Breakpoint can be used to inspect variable allocation during runtime Exception Breakpoint halt where Obj-C or C++ exception are thrown or caught Swift Error Breakpoint halts at the line that throws an Swift ErrorType error Symbolic Breakpoint used to halt whenever a specific method or function is going to be executed 13

14 Breakpoint A. Click on the left vertical bar of the editor area of Xcode to create a breakpoint at the specific line B. To edit the breakpoint right click Edit Breakpoint specify a Condition that must be met in order to trigger the code to halt at the breakpoint specify the amount of hits the breakpoint ignores before becoming active trigger an action that will be executed each time the breakpoint is hit e.g. print debug / log message 14

15 Symbolic Breakpoint A. Click the Add button in the bottom left corner of breakpoints navigator in Xcode B. Choose Add Symbolic Breakpoint C. Enter the symbol name in the Symbol field if the symbol is declared in multiple modules, provide the appropriate library in the module field D. Specify a condition in the Condition field, if a condition has to be met to stop at the breakpoint 15

16 Symbols symbols can be specified as: method name e.g. passwordstringwithlength same for methods with and without parameters method of a particular class e.g PasswordCreator.passwordWithLength function name e.g. rand 16

17 Xcode s Breakpoints Navigator List of all currently set breakpoints enabled and disabled Breakpoints can be added via the bottom left button 17

18 Xcode Debug Tools Xcode provides a comprehensive view on CPU utilization Memory consumption I/O operations Network transmissions during runtime Information available via the Debug Navigator 18

19 Xcode Debug Tools stack traces can be grouped via Queue or Thread in the Debug Navigator 19

20 Use Symbolic Breakpoints do Debug AutoLayout layout ambiguities can be difficult to resolve based on the console output provided by default set a symbolic breakpoint: UIViewAlertForUnsatisfiableConstraints enter the following command as Debugger Command of the Breakpoint: expr -l objc++ -O -- [[UIWindow keywindow] _autolayouttrace] the view hierarchy with additional information on the constraints set to layout the view hierarchy is printed on the console 20

21 Instruments Performance-analysis and testing tool Description of all functionalities would far exceed the scope of this lectures includes the underlying system in the analysis processes, so that the interplay of application and system can be better understood as well 21

22 Instruments Instruments enables: performance analysis e.g. determine process time of single methods find memory issues e.g. retain cycles or zombie objects automate UI testing on ios stress-test for part of the application 22

23 Profiling: Instruments Klick and hold the little triangle next to the Run button in Xcode Select Build for Profiling to launch Instruments with your application attached for profiling 23

Xcode & Swift: Introduction

Xcode & Swift: Introduction Dr.-Ing. Thomas Springer M.Sc. Martin Weißbach Concept You need Apple Computer Xcode 8 (ios device) Hands on course to learn how to program ios 1/1/0 means 45min lecture, 45min seminar introducing concepts