Introductory ios Development

Transcription

1 Introductory ios Development Unit 2 - Basic Objective-C Syntax Quick Links & Text References Console Application Pages Running Console App Pages Basic Syntax Pages Variables & Types Pages Sequential Processing Pages Decision Processing Pages Debugging Pages Repetition Processing Pages String Processing Pages Arrays Pages Free Resources Learning Objective-C: A Primer Programming with Objective-C Creating a Console Application Console applications allow you to practice your Objective-C (ObjC) programming skills without having to worry about creating a GUI and interfacing with it. Create Unit 2 Inclass Start Xcode Create new project (from Welcome Screen) or FileNewProject from menu Click OS X, Application, Command Line Tool Enter Product Name (project name) Organization: your name Company Identifier: edu.mstc or your domain name (reversed) Type: Foundation (includes more tools) Store in your ios development folder Click on main.m in navigation pane Replace lines with your code Page 1 of 10

2 Running a Console Application.m is the extension used for ObjC programs Note the NSLog command. Used for debugging and logging in ObjC Can be used for output in console apps Click the (Build and run) button. Xcode compiles your program After compiling, Xcode runs your program All Output window appears at bottom of screen with program results Make some room Close Utilities pane Click Hide the Variables View Run the default code Make some room: Basics ObjC is a curly-bracket language Statements end with semi-colons Blocks of statements are surrounded by {curly brackets} Comments // or /* */ Tip: Command-/ toggle entire line comment Variables and Types ObjC is a strongly-typed language all variables must be assigned a type Integer types short int long Decimal types float double char (single character) pointer (actually a long) string (see below) Page 2 of 10

3 Next Step (NS) Types (late 80s) Apple compiler has added additional types NSInteger These types change size depending on the operating system. Typically use primitives NSArrays require objects NSUInteger NSNumber NSDate Your string here Scope Variables declared inside a function are local Variables declared outside a function are global Variables declared static are available to current file only Generally a better idea than global static int age; Sequential Processing Order of precedence [ ] (message) ( ) (unary) - (unary)! (not) * (pointer) & (address of) * / % (mod) + - < <= > >= ==!= assignment = += -= *= /= %= Division of two integers results in an integer Use type casting to get a float or double average = total / (float)count; Page 3 of 10

4 Input GUI only Output NSLog (formatstring, text); printf("the loop ran %d times", count); %d is an integer placeholder Value of count replaces placeholder %f %.2f for strings (NSString) (actually any object) %ld for long integer Debugging Ensure the Debug area is visible Show the Variables View (optional) Click a line number to set a breakpoint A blue arrow will appear Run the program (no special debug mode) See variable values by hovering over the variable or looking in Variables View Debug buttons appear in Variables View Continue to next breakpoint Step Over (F6) Step Into (F7) Step Out (F8) Demo Page 4 of 10

5 Decision Processing Relational operators ==!= < <= > >= No string relational operators Use NSString methods (see below) Logical operators &&! Boolean variables Need to #include <objc/objc.h> BOOL ismarried; if(condition) { } else if(condition) { } else { }//end if Inline if (ternary conditional operator) minutesperpound = isboneless? 15 : 20; switch(expression) { case value1: break; case value2: case value3: break; default: break; }//end switch Page 5 of 10

6 Repetition Processing for(i=0; i<max; i++) { }//end for i for(onevalue in somearray) { //do something with onevalue } while(condition) { }//end while do { }while(condition); break and continue available break exists the loop immediately continue immediately starts the next iteration of loop String Processing NSString class used to process strings Though NSString is a class, it actually built in to the ObjC language Since NSString is a class all string variables are pointers More on pointers and classes in the next unit Declaring a string NSString *mystring; //Initialized to null NSString *mystring name here"; Once the string is declared, you no longer need to use the * to reference it NSLog(@"%@", mystring); designates that this is an ObjC string literal Since ObjC strings will be the only strings we use, from now on, I ll simply refer to them as strings Note NSLog uses a string to designate how the string should be output %@ is the formatting code for an ObjC string Page 6 of 10

7 There is no concatenation operator in in ObjC. To concatenate strings, you use an NSString method: stringwithformat NSString *CSZ; //null NSString *city Point"; NSString *state NSString *zip CSZ = [NSString stringwithformat:@"%@, %@ %@", city, state, zip]; NSLog(@"%@", CSZ); Note each string is declared with a * (pointer to an object) Note after CSZ, a new string is declared (NSString) stringwithformat first includes a formatting string In this example, the formatting string includes placeholders for 3 strings (%@). Commas and spaces are included in the formatting string Following the formatting string come the variables that are to be concatenated. There must be one variable for each placeholder The new, formatted string is then assigned to the CSZ variable Finally, the CSZ variable is sent to NSLog to display it Note the formatting string. Note after declaration, the variables don t include * Don t worry about the [ ] or : syntax. We ll cover that in the next unit. String methods length long stringlength = [CSZ length]; = CSZ.length; isequal (only way to compare strings) if([city isequal:@"plover"]) Watch the square brackets and parenthesis uppercase (also lowercase) state = [state uppercasestring]; Index of (search) Indexes are 0-based long index = [CSZ rangeofstring:@"wisconsin"].location; if(index!= NSNotFound) Page 7 of 10

8 Substrings Note all indexes are 0-based [CSZ substringfromindex:15]); (Characters from position 15 to end of string) [CSZ substringtoindex:13]); (Characters from beginning to position 13) Arrays [CSZ substringwithrange:nsmakerange(15,9)]); (9 characters from position 15) Good resource for additional string functions Array indexes are 0-based Most arrays in ObjC are implemented using classes Each element of the array is a pointer to a class The examples below implement the latest updates to arrays that started in Xcode 4.4. You may see other syntax when searching online C Arrays ObjC still supports plain old C arrays. These are best for immutable arrays of numbers NSArray (below) must store number objects which are much more difficult to change/access Declare int count[10]; //11 element array 0-10 int samples[] = {1, 2, 3}; Access count[0] = 15; NSLog(@"Fifth count is %d", count[4]); Create an array of student test scores and initialize to dummy values NSArray Immutable (size can t be changed and elements can t be changed) Very fast NSArray @"Third"]; Page 8 of 10

9 In designates an ObjC object (as opposed to a C object). This command demonstrates the new ObjC way to declare an array. Accessing an element NSString *element = myarray[1]; //Second Make element is declared with correct type Determine number of elements int objectcount = [myarray count]; //3 Define a corresponding NSArray of student names and initialize NSMutableArray Like a collection in other languages: elements can be added/removed NSMutableArray *myarray = [NSMutableArray array]; [myarray addobject:@"first"]; [myarray addobject:@"second"]; [myarray addobject:@"third"]; [myarray removeobjectatindex:1]; myarray[1] //Removes Second //Changes Third to Second NSLog(@"%@", myarray); Declares a mutable array and instantiates it to an empty array Adds three (string) objects to the array Removes the object with index 1 (2 nd object) Accessing elements and count are the same as NSArray Can change contents of existing element using square brackets (must assign an object) Can display an array using NSLog with %@. Displayed in a reasonably attractive manner Looping through arrays. Regardless of the type of array, the for-in loop makes visiting elements easy for(nsstring *element in myarray) { NSLog(@"%@", element); } Using number objects and NS arrays You cannot store integer or double primitive types in NSArrays or NSMutable arrays You must use the NSInteger or NSNumber object types Page 9 of 10

10 NSInteger anumber = 15; [mymutablearray addobject:anumber]; NSNumber *dblnumber = [NSNumber numberwithdouble:25.6]; NSArray @30]; To extract the primitive number from a number class, you have to call a method. NSLog(@"Your number is %d", [anumber intvalue]); NSLog(@"Your number [dblnumber doublevalue]); NSLog(@"Your number is %d", [numbers[0] intvalue]); int another = anumber; //Legal for NSInteger only double dbl = [dblnumber doublevalue]; Page 10 of 10