Call method hierarchy in Objective-C - ios

I declare a class method:
+(int)widthScaled:(UIImage *)image maximumHeight:(int)max{
int width = 0;
width = (image.size.width - (((image.size.height - max)*100)/image.size.height)*image.size.width)/100;
return width;
}
In the same class, I declare an instance method like these:
- (void)generarVistas{
if(...){
...
}else{
for(...){
...
//I need to put the class method here but if I call the class method like this, don't recognize
int variable = [[self class] widthScaled:image maximumHeight:max];
...
}
}
I try to put the class method in instance method but doesn't work.
What context should I indicate to recognize the class method?

The problem you are facing is that [self class] is a runtime call who's return result is not known until runtime. The compiler doesn't know what class it is. The code you're writing must always be invoked from a fixed class, so don't do that. If the class is FooClass, then use this form:
int variable = [FooClass widthScaled:image maximumHeight:max];
(replace [self class] with your class name, e.g. FooClass.)

Related

Use of undeclared identifier error in my case

My code invokes a C library function:
#implementation Store
...
-(void) doWork {
// this is a C function from a library
int data = getData();
...
}
end
I am unit testing the above function, I want to mock the C function getData() in my test, here is my test case:
#interface StoreTests : XCTestCase {
int mData;
Store *store;
}
#end
#implementation StoreTests
-(void) setUp {
[super setUp];
mData = 0;
store = [[Store alloc] init];
}
-(void) testDoWork {
// this call will use the mocked getData(), no problem here.
[store doWork];
}
// mocked getData()
int getData() {
mData = 10; // Use of undeclared identifier 'mData', why?
return mData;
}
...
#end
Why I get complier error:
Use of undeclared identifier 'mData' inside mocked getData() function?
You are misunderstanding how instance methods and variables work.
Every instance method has a variable self which references the current instance (or "current object") and a use of an instance variable, such as mData, is shorthand for accessing that variable using self, e.g self->mData, where -> is the (Objective-)C operator for field access. So your setup method written "long hand" is:
-(void) setUp {
[super setUp];
self->mData = 0;
self->store = [[Store alloc] init];
}
But where does self, the reference to the instance, itself come from? Well it's not magical, just hidden, it is passed to an instance method automatically as a hidden extra argument. At this point which switch to pseudo-code to show this. Your setup method is effectively compiled as:
-(void) setUp withSelf:(StoreTest *)self {
[super setUp];
self->mData = 0;
self->store = [[Store alloc] init];
}
and a call such as:
StoreTests *myStoreTests = ...
[myStoreTests setup];
is effectively compiled as something like:
[myStoreTests setup withSelf:myStoreTests];
automatically adding the extra self argument.
Now all the above only applies to methods, and enables them to access instance variables and methods, it does not apply to plain C functions - they have no hidden self argument and cannot access instance variables.
The solution you mention in the answer you added of declaring mData outside of the interface:
int mData;
#interface StoreTests : XCTestCase {
Store *store;
}
#end
changes mData into a global variable, instead of being an instance variable. C functions can access global variables. However this does mean that every instance of the class shares the same mData, there is only one mData in this case rather than one for every instance.
Making an instance variable into a global is therefore not a general solution to to issues like this, however as it is unlikely that you will have more than one instance of your StoreTests class it is a suitable solution in this case.
You should however make one change: you can only have one global variable with a given name with a program, so your mData must be unique and is accessible by any code within your program, not just the code of StoreTests. You can mitigate this my declaring the variable as static:
static int mData;
this keeps the variable as global but only makes it visible to code within the same file as the declaration, which is probably just the code of StoreTests.
HTH
I found one solution for my question, that is declare mData above #interface StoreTests : XCTestCase, something like this:
int mData;
#interface StoreTests : XCTestCase {
Store *store;
}
#end
...

Unit test a very simple method, but failed

I have a simple School class which defines a init method:
#implementation School
- (id) init {
self = [super init];
if (self) {
// call class method of MyHelper class
if ([MyHelper isWeekend]) {
[MyHelper doSomething];
}
}
}
#end
(MyHelper is a class contains only class methods, the isWeekend is a class method returns a boolean value)
I use OCMock to unit test this simple init method:
- (void)testInit {
// mock a school instance
id schoolMock = [OCMockObject partialMockForObject:[[School alloc] init]];
// mock class MyHelper
id MyHelperMock = OCMStrictClassMock([MyHelper class]);
// stub class method 'isWeekend()' to return true
OCMExpect([MyHelperMock isWeekend]).andReturn(true);
// run init method
[schoolMock init];
// verify
OCMVerify([MyHelperMock isWeekend]);
}
But when run it, I get error:
OCMockObject(MyHelper): Method isWeekend was not invoked. why?
You've created a mock for the MyHelper class, but this isn't going to be used within the implementation of your School object. You'd only get the mocked response if you wrote [MyHelperMock isWeekend], which you can't do inside the initialiser without rewriting it for tests.
To make your School class more testable you should be passing in any dependencies on initialisation. For example, you could pass in the isWeekend value as part of the initialiser, instead of obtaining it inside the method, or pass in the class object (MyHelper or MyHelperMock).
It's worth noting that finding certain classes or methods difficult to test because of things like this is often a good indicator that your code isn't structured very well.

how to declare method which returns base Class

I would like to add a method which returns Class like below:
-(Class) validatorClass{
return [AddItemValidator class]; }
and use it like this:
self.validator = [[self validatorClass] alloc] initWithParentDirectory:self.parentDirectory];
How should I declare the return type -(Class) of this method to allow returning only classes which extend from defined class?
I would like to return something like -(Class<'NameValidator'>) where AddItemValidator extends from NameValidator.
How should I declare it?
As SomeGuy mentioned, you can't achieve compile-time safety in this case. Instead, you can use an assertion to have it checked at the runtime (better than nothing):
-(Class) validatorClass{
Class theClass = [AddItemValidator class];
NSAssert([theClass isSubclassOfClass:[NameValidator class]], #"Has to return subclass of %#", [NameValidator class]);
return theClass;
}
You can even go further and apply Factory pattern here to decouple validator class from the class being validated:
#implementation NameValidatorFactory
+(NameValidator*)validatorForObject:(YourObjectType*)validatedObject {
//choose proper validator depending on your object's type or anything you want
if([validatedObject isKindOfClass:[YourObjectTypeSuperclass class]]) {
return [AddItemValidator alloc];
}
else {
// handle other cases
}
}
And then create your validator like that:
self.validator = [[NameValidatorFactory validatorForObject:self] initWithParentDirectory:self.parentDirectory];

iOS jailbreak get object based on class name

I have a dylib which has a object of class "mConWifi". I have the main app which loads this dylib and executes following code
Class klass = objc_getClass("mConWifi");
SEL sel = sel_getUid("ListAllWifi:");
if ( [klass respondsToSelector:sel] )
objc_msgSend(klass, sel);
When above code is called, object of class mConWifi is already created in Memory.
My objective is to get object based on class name and then invoke a method. With above code I am not able to as respondsToSelector fails. I have already tried "ListAllWifi" and "ListAllWifi:"
Any ideas how to get object of a class based on class name?
Thanks in advance.
I think your problem is that you are trying to test a method of class (which are declared with +), but in fact you have an instance method, declared with -.
Try this:
Class klass = objc_getClass("mConWifi");
SEL sel = sel_getUid("ListAllWifi:");
if ( [klass instancesRespondToSelector:sel] ) {
id object = [[klass alloc] init];
objc_msgSend(object, sel);
}

Getters and setters for constants?

Is is possible to create getters and setters for constants? I want to refer to a constant directly, and have it instantiate itself if it's value is nil. A constant declared like this:
// Prefs.h
extern MyClass * const kThing;
// Prefs.m
MyClass * const kThing = nil;
and the getter/setter would look like:
// getter
+ (MyClass *)kThing
{
_kThing = _kThing ? : [MyClass new];
return _kThing;
}
// setter
+ (void)setKThing:(MyClass *)myClass
{
_kThing = myClass
}
And then I could use it like:
[kThing doSomething];
Is this possible?
edit edited the methods to class methods
What you describe are not constants, they are global variables. You cannot define getters and setters for them, but you can use their values to back class methods, which is precisely what you have done.
However, when you send message like this
[kThing doSomething];
the global variable is used directly, bypassing your getter. If you want to go through a getter, you can write
[[MyClass kThing] doSomething];
or inside methods of MyClass you can write
[[[self class] kThing] doSomething];
Another note is that when yo implement accessor methods like that, you should make the backing variables static, rather than extern. This will ensure that other modules cannot access these variables bypassing your getters.
Global variable declaration in other file is very dangerous in objective C. Ideally we use sharedInstance. Try like this:
In MyGame.h
#interface MyGame : NSObject
{
int mScore;
}
#property(nonatomic,assign) int score;
+(MyGame*)sharedObject;
-(void)someFunction;
#end
In MyGame.m
static MyGame *gGame = nil;
#implementation MyGame
#synthesize score = mScore;
+(MyGame*)sharedObject
{
if(!gGame)
{
gGame = [[MyGame alloc] init];
}
return gGame;
}
-(void)someFunction
{
}
#end
To access anywhere in project:
#import "MyGame.h"
[MyGame sharedObject].score;
[MyGame sharedObject] someFunction];
The short answer is that this is not possible.
MyClass * const kThing = nil;
means that kThing is a constant pointer, which means that the address in memory that it points to cannot be changed. So once it's set to nil, it can't later be set to a new object.

Resources