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Diffstat (limited to 'objective-c.html.markdown')
| -rw-r--r-- | objective-c.html.markdown | 151 |
1 files changed, 136 insertions, 15 deletions
diff --git a/objective-c.html.markdown b/objective-c.html.markdown index 1ed0ed58..406b2e92 100644 --- a/objective-c.html.markdown +++ b/objective-c.html.markdown @@ -50,52 +50,105 @@ int main (int argc, const char * argv[]) // String NSString *worldString = @"World"; - NSLog(@"Hello %@!", worldString); // Print "Hello World!" + NSLog(@"Hello %@!", worldString); // prints => "Hello World!" + // NSMutableString is a mutable version of the NSString object. + NSMutableString *mutableString = [NSMutableString stringWithString:@"Hello"]; + [mutableString appendString:@" World!"]; + NSLog(@"%@", mutableString); // prints => "Hello World!" // Character literals NSNumber *theLetterZNumber = @'Z'; - char theLetterZ = [theLetterZNumber charValue]; + char theLetterZ = [theLetterZNumber charValue]; // or 'Z' NSLog(@"%c", theLetterZ); // Integral literals NSNumber *fortyTwoNumber = @42; - int fortyTwo = [fortyTwoNumber intValue]; + int fortyTwo = [fortyTwoNumber intValue]; // or 42 NSLog(@"%i", fortyTwo); NSNumber *fortyTwoUnsignedNumber = @42U; - unsigned int fortyTwoUnsigned = [fortyTwoUnsignedNumber unsignedIntValue]; + unsigned int fortyTwoUnsigned = [fortyTwoUnsignedNumber unsignedIntValue]; // or 42 NSLog(@"%u", fortyTwoUnsigned); NSNumber *fortyTwoShortNumber = [NSNumber numberWithShort:42]; - short fortyTwoShort = [fortyTwoShortNumber shortValue]; + short fortyTwoShort = [fortyTwoShortNumber shortValue]; // or 42 NSLog(@"%hi", fortyTwoShort); + + NSNumber *fortyTwoShortNumber = [NSNumber numberWithShort:41]; + unsigned short fortyTwoUnsigned = [fortyTwoShortNumber unsignedShortValue]; // or 41 + NSLog(@"%hu", fortyTwoUnsigned); NSNumber *fortyTwoLongNumber = @42L; - long fortyTwoLong = [fortyTwoLongNumber longValue]; + long fortyTwoLong = [fortyTwoLongNumber longValue]; // or 42 NSLog(@"%li", fortyTwoLong); + NSNumber *fortyTwoLongNumber = @53L; + unsigned long fiftyThreeUnsigned = [fortyTwoLongNumber unsignedLongValue]; // or 53 + NSLog(@"%lu", fiftyThreeUnsigned); + // Floating point literals NSNumber *piFloatNumber = @3.141592654F; - float piFloat = [piFloatNumber floatValue]; - NSLog(@"%f", piFloat); + float piFloat = [piFloatNumber floatValue]; // or 3.141592654f + NSLog(@"%f", piFloat); // prints => 3.141592654 + NSLog(@"%5.2f", piFloat); // prints => " 3.14" NSNumber *piDoubleNumber = @3.1415926535; - double piDouble = [piDoubleNumber doubleValue]; + double piDouble = [piDoubleNumber doubleValue]; // or 3.1415926535 NSLog(@"%f", piDouble); + NSLog(@"%4.2f", piDouble); // prints => "3.14" + + // NSDecimalNumber is a fixed-point class that's more precise then float or double + NSDecimalNumber *oneDecNum = [NSDecimalNumber decimalNumberWithString:@"10.99"]; + NSDecimalNumber *twoDecNum = [NSDecimalNumber decimalNumberWithString:@"5.002"]; + // NSDecimalNumber isn't able to use standard +, -, *, / operators so it provides its own: + [oneDecNum decimalNumberByAdding:twoDecNum]; + [oneDecNum decimalNumberBySubtracting:twoDecNum]; + [oneDecNum decimalNumberByMultiplyingBy:twoDecNum]; + [oneDecNum decimalNumberByDividingBy:twoDecNum]; + NSLog(@"%@", oneDecNum); // prints => 10.99 as NSDecimalNumber is immutable. // BOOL literals NSNumber *yesNumber = @YES; NSNumber *noNumber = @NO; + // or + BOOL yesBool = YES; + BOOL noBool = NO; + NSLog(@"%i", yesBool); // prints => 1 // Array object NSArray *anArray = @[@1, @2, @3, @4]; NSNumber *thirdNumber = anArray[2]; NSLog(@"Third number = %@", thirdNumber); // Print "Third number = 3" + // NSMutableArray is mutable version of NSArray allowing to change items in array + // and extend or shrink array object. Convenient, but not as efficient as NSArray. + NSMutableArray *mutableArray = [NSMutableArray arrayWithCapacity:2]; + [mutableArray addObject:@"Hello"]; + [mutableArray addObject:@"World"]; + [mutableArray removeObjectAtIndex:0]; + NSLog(@"%@", [mutableArray objectAtIndex:0]); // prints => "World" // Dictionary object NSDictionary *aDictionary = @{ @"key1" : @"value1", @"key2" : @"value2" }; NSObject *valueObject = aDictionary[@"A Key"]; NSLog(@"Object = %@", valueObject); // Print "Object = (null)" + // NSMutableDictionary also available as a mutable dictionary object. + NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionaryWithCapacity:2]; + [mutableDictionary setObject:@"value1" forKey:@"key1"]; + [mutableDictionary setObject:@"value2" forKey:@"key2"]; + [mutableDictionary removeObjectForKey:@"key1"]; + + // Set object + NSSet *set = [NSSet setWithObjects:@"Hello", @"Hello", @"World", nil]; + NSLog(@"%@", set); // prints => {(Hello, World)} (may be in different order) + // NSMutableSet also available as a mutable set object. + NSMutableSet *mutableSet = [NSMutableSet setWithCapacity:2]; + [mutableSet addObject:@"Hello"]; + [mutableSet addObject:@"Hello"]; + NSLog(@"%@", mutableSet); // prints => {(Hello)} + + // Set object + NSSet *set = [NSSet setWithObjects:@"Hello", @"Hello", @"World", nil]; + NSLog(@"%@", set); // prints => {(Hello, World)} /////////////////////////////////////// // Operators @@ -176,6 +229,14 @@ int main (int argc, const char * argv[]) // "2," // "3," + // Object for loop statement. Can be used with any Objective-C object type. + for (id item in values) { + NSLog(@"%@,", item); + } // => prints "0," + // "1," + // "2," + // "3," + // Try-Catch-Finally statements @try { @@ -225,14 +286,30 @@ int main (int argc, const char * argv[]) // @end @interface MyClass : NSObject <MyProtocol> { - int count; - id data; - NSString *name; + // Instance variable declarations (can exist in either interface or implementation file) + int count; // Protected access by default. + @private id data; // Private access. (More convenient to declare in implementation file) + NSString *name; } -// Convenience notation to auto generate public getter and setter +// Convenient notation to auto generate public access getter and setter @property int count; @property (copy) NSString *name; // Copy the object during assignment. @property (readonly) id data; // Declare only a getter method. +// To access public variable in implementation file, use '_' followed by variable name: +_count = 5; +NSLog(@"%d", _count); // prints => 5 +// To access public variable outside implementation file, @property generates setter method +// automatically. Method name is 'set' followed by @property variable name: +MyClass *myClass = [[MyClass alloc] init]; // create MyClass object instance. +[myClass setCount:10]; +NSLog(@"%@", [myClass count]); // prints => 10 +// You can customize the getter and setter names instead of using default 'set' name: +@property (getter=countGet, setter=countSet:) int count; +[myClass countSet:32]; +NSLog(@"%i", [myClass countGet]); // prints => 32 +// For convenience, you may use dot notation to set object instance variables: +myClass.count = 45; +NSLog(@"%i", myClass.count); // prints => 45 // Methods +/- (return type)methodSignature:(Parameter Type *)parameterName; @@ -247,8 +324,9 @@ int main (int argc, const char * argv[]) @end // Implement the methods in an implementation (MyClass.m) file: - -@implementation MyClass +@implementation MyClass { + long count; // Private access instance variable. +} // Call when the object is releasing - (void)dealloc @@ -299,6 +377,49 @@ int main (int argc, const char * argv[]) @end +/////////////////////////////////////// +// Memory Management +/////////////////////////////////////// +/* +For each object used in an application, memory must be allocated for that object. When the application +is done using that object, memory must be deallocated to ensure application efficiency. +Objective-C does not use garbage collection and instead uses reference counting. As long as +there is at least one reference to an object (also called "owning" an object), then the object +will be available to use (known as "ownership"). + +When an instance owns an object, its reference counter is increments by one. When the +object is released, the reference counter decrements by one. When reference count is zero, +the object is removed from memory. + +With all object interactions, follow the pattern of: +(1) create the object, (2) use the object, (3) then free the object from memory. +*/ + +MyClass *classVar = [MyClass alloc]; // alloc sets classVar's reference count to one. Returns pointer to object. +[classVar release]; // Decrements classVar's reference count. +// retain claims ownership of existing object instance and increments reference count. Returns pointer to object. +MyClass *newVar = [classVar retain]; // If classVar is released, object is still in memory because newVar is owner. +[classVar autorelease]; // Removes ownership of object at end of @autoreleasepool block. Returns pointer to object. + +// @property can use retain or assign as well for small convenient definitions. +@property (retain) MyClass *instance; // Release old value and retain a new one (strong reference). +@property (assign) NSSet *set; // Pointer to new value without retaining/releasing old (weak reference). + +// Because memory management can be a pain, Xcode 4.2 and iOS 4 introduced Automatic Reference Counting (ARC). +// ARC is a compiler feature that inserts retain, release, and autorelease automatically for you, so when using ARC, +// you must not use retain, relase, or autorelease. +MyClass *arcMyClass = [[MyClass alloc] init]; // Without ARC, you will need to call: [arcMyClass release] after +// you're done using arcMyClass. But with ARC, there is no need. It will insert this release statement for you. + +// As for the "assign" and "retain" @property attributes, with ARC you use "weak" and "strong". +@property (weak) MyClass *weakVar; // weak does not take ownership of object. If original instance's reference count +// is set to zero, weakVar will automatically receive value of nil to avoid application crashing. +@property (strong) MyClass *strongVar; // strong takes ownership of object. Ensures object will stay in memory to use. + +// For regular variables (not @property declared variables), use the following: +__strong NSString *strongString; // Default. Variable is retained in memory until it leaves it's scope. +__weak NSSet *weakSet; // Weak reference to existing object. When existing object is released, weakSet is set to nil. +__unsafe_unretained NSArray *unsafeArray; // Like __weak but unsafeArray not set to nil when existing object is released. ``` ## Further Reading |