[sorry for my weak english]
I have got superclass and it's subclass (subclasses) - subclass is the view with some
sprites - superclass has some helper functions for example function to fire an animation.
I want to call 'fire the animation' in super from subclass but it shows that in superclass.
I need an access the subclass view (to add animated viewsprite to self.view in subclass)
How can I reach the subclass members from superclass ??? :-/
#interface MONBase : NSObject
// example action. required override
- (void)performSomeAction;
// example accessor. required override
- (MONThing *)thing;
#end
#implementation MONBase
- (void)performSomeAction
{
assert(0 && "required override");
}
- (MONThing *)thing
{
assert(0 && "required override");
return nil;
}
- (void)example
{
MONThing * thing = [self thing];
[self configureThing:thing];
[self performSomeAction];
}
#end
#interface MONSubclass : MONBase
#end
#implementation MONSubclass
- (void)performSomeAction
{
[self doStuff];
}
- (MONThing *)thing
{
return self.something;
}
#end
Related
How do I prevent a particular class from being subclassed?
I am not aware of such functionality (say final keyword for example) in the language. However Apple says it has done so for all classes in AddressBookUI.framework (in iOS)
For educational purposes, how can I achieve the same functionality, or how would they have done such thing?
From iOS7 Release Notes(Requires login) :
Here's one way: override allocWithZone: from within your "final" class (substituting MyFinalClassName for your actual class name) like this:
+ (id)allocWithZone:(struct _NSZone *)zone
{
if (self != [MyFinalClassName class]) {
NSAssert(nil, #"Subclassing MyFinalClassName not allowed.");
return nil;
}
return [super allocWithZone:zone];
}
This will prevent a subclass that is not a member of MyFinalClassName from being alloc'ed (and therefore init'ed as well), since NSObject's allocWithZone: must be called eventually, and by refusing to call super from your "final" class, you will prevent this.
There's a simpler way to prevent subclassing in Xcode 6 as a result of Swift interop. To prevent Swift classes from being subclassed in Objective-C the objc_subclassing_restricted is added to all class definitions in the {ProjectName}-Swift.h file.
You can use this in your projects:
#if defined(__has_attribute) && __has_attribute(objc_subclassing_restricted)
# define FOO_FINAL __attribute__((objc_subclassing_restricted))
#else
# define FOO_FINAL
#endif
FOO_FINAL
#interface Foo : NSObject
#end
#interface Bar : Foo
#end
The compiler will halt on the definition of Bar with Cannot subclass a class with objc_subclassing_restricted attribute
Here is possible solution:
#interface FinalClass : NSObject
#end
#implementation FinalClass
- (id)init
{
if (self.class != [FinalClass class]) {
return nil;
}
self = [super init];
if (self) {
// instance initialization
}
return self;
}
#end
#interface InvalidSubclass : FinalClass
#end
#implementation InvalidSubclass
- (id)init
{
self = [super init];
if (self) {
}
return self;
}
#end
I'm not sure this is 100% guaranteed because it's runtime-checking anyway, but it should be enough to block and warn people that they should not subclass this. Subclass might skip superclass's init, but then the instance will not be usable because it's not fully initialised by superclass.
Something like the following will ensure that every time an "impossible subclass" calls +alloc, an object will be allocated that is an instance of FinalClass, and not the subclass. This is essentially what NSObject's +alloc method does, but here we specify an explicit class to create. This is how NSObject allocates instances (in Obj-C 2), but there is no guarantee this will always be the case, so you may want to add an appropriate -dealloc which calls object_dispose. This method also means you don't get a nil object back if you try to instantiate a subclass - you do get an instance of FinalClass.
#interface FinalClass: NSObject
//...
+ (id)alloc; // Optional
#end
// ...
#import <objc/runtime.h>
#implementation FinalClass
+ (id)alloc {
if (![self isMemberOfClass:[FinalClass class]]) {
// Emit warning about invalid subclass being ignored.
}
self = class_createInstance([FinalClass class], 0);
if (self == nil) {
// Error handling
}
return self;
}
#end
#interface InvalidSubclass : FinalClass
// Anything not in FinalClass will not work as +alloc will
// create a FinalClass instance.
#end
Note: I'm not sure I'd use this myself - specifying that a class shouldn't be subclassed is more in the nature of a design-contract with the programmer rather than an enforced rule at compile- or runtime.
I have a view controller which defines a protocol which itself inherits another protocol.
I want any object that implements my protocol to also implement the inherited protocol.
I want to set my class to intercept some of the messages in the inherited protocol in order to configure some things internally but eventually would like to forward all of the messages to the delegate of my class
I could write a lot of boiler plate code to stub all of the protocol and intern call the delegate but I see that it breaks a lot of the time - any time the "super" protocol changes I need to restub this class once again.
I see that this is very predominant in custom UI controls. When reusing existing components - for instance tables or collection views you would like your data source to respond to all of the common protocols but some instances you need to configure the view according to the index or save a particular state.
I've tried using forwardingTargetForSelector in order to forward the messages I do not respond to , but it isn't always forwarding...
Here is a contrived code example:
Class A: (the top most protocol)
#
protocol classAProtocol <NSObject>
-(void)method1;
-(void)method2;
-(void)method3;
#end
My Class
#protocol MyClassProtocol <classAProtocol>
-(void)method4;
#end
#interface MyClass
#property (nonatomic,weak> id <MyClassProtocol> delegate;
#end
#interface MyClass (privateInterface)
#property (nonatomic,strong) ClassA *classAObject;
#end
#implementation MyClass
-(init)
{
self = [super init];
if (self)
{
_classAObject = [[ClassA alloc] init];
_classAObject.delegate = self; // want to answer some of the delegate methods but not all
}
}
-(void)method1
{
// do some internal configuration
// call my delegate with
[self.delegate method1];
}
-(id)forwardingTargetForSelector:(SEL)aSelector
{
if ([self respondsToSelector:aSelector])
{
return self;
}
if ([self.delegate respondsToSelector:aSelector])
{
return self.delegate;
}
return nil;
}
-(void)setDelegate:(id <MyClassProtocol>)delegate
{
self.delegate = delegate; // will forward some of the messages
}
#end
Returning self from forwardingTargetForSelector: makes no sense because it would never be called if self responded to the selector.
You need to implement these three methods:
- (void)forwardInvocation:(NSInvocation *)anInvocation
{
if ([self.delegate respondsToSelector:[anInvocation selector]])
[anInvocation invokeWithTarget:self.delegate];
else
[super forwardInvocation:anInvocation];
}
- (BOOL)respondsToSelector:(SEL)aSelector
{
return [super respondsToSelector:aSelector] || [self.delegate respondsToSelector:aSelector];
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector
{
NSMethodSignature *signature = [super methodSignatureForSelector:selector];
if (!signature) {
signature = [self.delegate methodSignatureForSelector:selector];
}
return signature;
}
You shouldn't ever return self; from forwardingTargetForSelector:. Your check should mean it never is but if you ever did return self it would cause an infinite loop.
You need to be sure that a super class isn't implementing the method as this will prevent forwardingTargetForSelector: from being called. Check if the method is actually called.
forwardingTargetForSelector: is also only called when a method is called on your controller that it doesn't respond to. In your example you aren't calling [self ...];, you're calling [self.delegate ...]; so forwardingTargetForSelector: will not be called.
I'm writting a subclass of UITableView and I want my subclass to handle some of the UITableViewDelegate methods itself before passing them along to the "real" delegate as well as forward all the UITableViewDelegate methods not implemented by my subclass.
In the subclass I have a private property:
#property (nonatomic, assign) id <UITableViewDelegate> trueDelegate;
which holds the "real delegate" that all the unimplemented methods should forward to. In both my init methods I set
self.delegate = self;
and I override - (void)setDelegate:(id) like this
-(void)setDelegate:(id<UITableViewDelegate>)delegate {
if (delegate != self) {
_trueDelegate = delegate;
} else {
[super setDelegate:self];
}
}
Then I override these to handle the message forwarding
-(NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
NSMethodSignature *sig;
sig = [[self.delegate class] instanceMethodSignatureForSelector:aSelector];
if (sig == nil) {
sig = [NSMethodSignature signatureWithObjCTypes:"#^v^c"];
}
return sig;
}
- (void)forwardInvocation:(NSInvocation *)anInvocation {
SEL selector = anInvocation.selector;
if ([self respondsToSelector:selector]) {
[anInvocation invokeWithTarget:self];
} else {
[anInvocation invokeWithTarget:_trueDelegate];
}
}
The problem is that the unimplemented delegate methods never get called on the tableview, therefore they are not given a chance to be forwarded along to the _trueDelegate object.
I tried checking for them here:
- (BOOL)respondsToSelector:(SEL)aSelector {
}
but that method is never called for the UITableViewDelegate methods although it catches other methods just fine.
For performance, UITableView checks and remembers which delegate methods are available as soon as the delegate is set. You set the delegate self first, then the trueDelegate. So at the time the delegate is set on the UITableView, trueDelegate is nil, and so -respondsToSelector: on that one always returns NO.
To fix that, set the delegate after trueDelegate is set. Also, you can simplify the forwarding code. Remove all the code you have above except for the property and replace it with:
- (void)setDelegate:(id <UITableViewDelegate>)delegate
{
if (delegate == self) return;
self.trueDelegate = delegate;
[super setDelegate:self];
}
- (BOOL)respondsToSelector:(SEL)aSelector
{
if ([super respondsToSelector:aSelector]) return YES;
return [self.trueDelegate respondsToSelector:aSelector];
}
- (id)forwardingTargetForSelector:(SEL)aSelector
{
return self.trueDelegate;
}
I have some very small classes that I feel should be "pulled up" but the methods are so small I'm not sure. For example, the only thing that's meaningfully different is the body of the buildFromJSON: selector.
I acknowledge that this is similar to:
Pull-up refactoring, Objective-C
but I feel my question is specific to refactoring very small classes/methods.
Also, not sure it relates to my particular code example, but I'm wondering if a child class says it conforms to a protocol, whether it's enough that it's parent actually supply the implementation of required selector(s)?
#implementation AsyncFoo
-(void)dealloc {
[clientDelegate release];
[super dealloc];
}
- (id)initWithDelegate: (id <ServiceClientProtocol>) delegate {
if((self = [super init])) {
clientDelegate = [delegate retain];
}
return self;
}
- (void)buildFromJSON:(NSString*)jsonResponseString {
[clientDelegate serviceComplete:[RestAdapter buildFooArray: jsonResponseString]];
}
#end
#implementation AsyncBar
-(void)dealloc {
[clientDelegate release];
[super dealloc];
}
- (id)initWithDelegate: (id <ServiceClientProtocol>) delegate {
if((self = [super init])) {
clientDelegate = [delegate retain];
}
return self;
}
- (void)buildFromJSON:(NSString*)jsonResponseString {
[clientDelegate serviceComplete:[RestAdapter buildBarArray:jsonResponseString]];
}
#end
Answers including code example would be great.
EDIT: Post accepted answer I'd like to add that since I was able to subclass, the derived classes did not need to declare that they conformed to protocol:
#interface Async : NSObject <ModelBuilderProtocol> {
id <ServiceClientProtocol> clientDelegate;
}
- (void)buildFromJSON:(NSString*)jsonResponseString;
#end
#interface AsyncArtistById : Async
#end
You don't normally retain your delegates as this can cause a retain cycle.
Knowing what I know from looking at your example I would probably implement like this:
The super class
// Async.h
#interface Async : NSObject
#property (nonatomic, assign) id<ServiceClientProtocol> delegate;
- (void)buildFromJSON:(NSString *)jsonResponseString;
#end
// Async.m
#implementation Async
#synthesize delegate = _delegate;
- (id)initWithDelegate:(id<ServiceClientProtocol>)delegate
{
self = [super init];
if(self) {
_delegate = delegate;
}
return self;
}
- (void)buildFromJSON:(NSString *)jsonResponseString
{
// This will ensure that we over ride this method in a sub class
[NSException raise:NSInternalInconsistencyException
format:#"You must override %# in a subclass", NSStringFromSelector(_cmd)];
}
#end
Concrete subclass AsyncFoo
// AsyncFoo.h
#interface AsyncFoo : Async
#end
// AsyncFoo.m
#implementation AsyncFoo
- (void)buildFromJSON:(NSString *)jsonResponseString
{
[self.delegate serviceComplete:[RestAdapter buildFooArray: jsonResponseString]];
}
#end
Concrete subclass AsyncBar
// AsyncBar.h
#interface AsyncBar : Async
#end
// AsyncBar.m
#implementation AsyncBar
- (void)buildFromJSON:(NSString *)jsonResponseString {
[self.delegate serviceComplete:[RestAdapter buildBarArray:jsonResponseString]];
}
#end
I'm new to objective-c and I'm finding that I don't know how to correctly assert that a text property on some given label is equal to a raw string value. I'm not sure if I just need to cast the label as NSString or if I need to modify my assert statement directly.
#interface MoreTest : SenTestCase {
MagiczzTestingViewController* controller;
}
- (void) testObj;
#end
#implementation MoreTest
- (void) setUp
{
controller = [[MagiczzTestingViewController alloc] init];
}
- (void) tearDown
{
[controller release];
}
- (void) testObj
{
controller.doMagic;
STAssertEquals(#"hehe", controller.label.text, #"should be hehe, was %d instead", valtxt);
}
#end
The implementation of my doMagic method is below
#interface MagiczzTestingViewController : UIViewController {
IBOutlet UILabel *label;
}
#property (nonatomic, retain) UILabel *label;
- (void) doMagic;
#end
#implementation MagiczzTestingViewController
#synthesize label;
- (void) doMagic
{
label.text = #"hehe";
}
- (void)dealloc {
[label release];
[super dealloc];
}
#end
The build is fine when I modify the assert to compare a raw NSString to another but when I try to capture the text value (assuming it's of type NSString) it fails. Any help would be much appreciated!
STAssertEquals() checks for identity of the two values provided, so it's equivalent to doing this:
STAssertTrue(#"hehe" == controller.label.text, ...);
Instead, you want STAssertEqualObjects(), which will actually run an isEqual: check like the following:
STAssertTrue([#"hehe" isEqual:controller.label.text], ...);
You need to load the nib of the view controller. Otherwise there won't be any objects for the label outlet to be hooked up to.
One way to do this is to add an ivar for the view controller's view to your test case:
#interface MoreTest : SenTestCase {
MagiczzTestingViewController *controller;
UIView *view;
}
#end
#implementation MoreTest
- (void)setUp
{
[super setUp];
controller = [[MagiczzTestingViewController alloc] init];
view = controller.view; // owned by controller
}
- (void)tearDown
{
view = nil; // owned by controller
[controller release];
[super tearDown];
}
- (void)testViewExists
{
STAssertNotNil(view,
#"The view controller should have an associated view.");
}
- (void)testObj
{
[controller doMagic];
STAssertEqualObjects(#"hehe", controller.label.text,
#"The label should contain the appropriate text after magic.");
}
#end
Note that you also need to invoke super's -setUp and -tearDown methods appropriately from within yours.
Finally, do not use dot syntax for method invocation, it is not a generic replacement for bracket syntax in message expressions. Use dot syntax only for getting and setting object state.