Following problem: I receive an Object from a framework (which is not instantiable) and I want to extend it. When I make a category, the problem is, that it doesn't have an effect on the existing object.
I thought of isa swizzling. So let the isa field point to the extended "list of selectors". But that doesn't seem to be possible? (Syntax for it?)
Does anyone know a better approach to do it ?
That is the code:
- (void)peripheralManager:(CBPeripheralManager *)peripheral didReceiveWriteRequests:(NSArray<CBATTRequest *> *)requests {
//want to do something that uses the extension
}
And I want to extend CBATTRequest. I think the problem lies in CoreBluetooth?
This is how I make my category:
BLERequestable.h
#protocol BLERequestable <NSObject>
- (nonnull NSString *)getCentralUUID;
- (nonnull NSString *)getCharacteristicUUID;
- (nullable NSData*)getData;
- (void)setData:(nullable NSData *) data;
#end
CBATTRequest+Requestable.h
#import <CoreBluetooth/CoreBluetooth.h>
#import "BLERequestable.h"
#interface CBATTRequest (Requestable) <BLERequestable>
#end
CBATTRequest+Requestable.m
#import "CBATTRequest+Requestable.h"
#implementation CBATTRequest (Requestable)
- (NSString *)getCentralUUID {
return self.central.identifier.UUIDString;
}
- (NSString *)getCharacteristicUUID {
return self.characteristic.UUID.UUIDString;
}
- (NSData*)getData {
return self.value;
}
- (void)setData:(NSData *) data {
self.value = data;
}
#end
And I import the Category everywhere I want to use it.
After long researching and testing (thanks to Rob Napier), I found the source of error.
My project consists of a library and and executable target. In the library I defined my category and used it inside. The problem is, that when it comes to linking due to the executable, the o-file with my category isn't linked. See this stack post for further details on problems with categories in static libraries.
One possible solution would be setting the linker flag from the exe target to -Objc.
But I don't like this solution, because the library's ability to work properly would depend on the exe.
So I included the implementation of the category in the m-file where I use it.
If somebody has another (better) solution, I would be glad to see it. Otherwise I would close this question.
Related
I'm a beginner with Objective-C, and am trying to use a global variable. I know that this question has been asked a hundred times, but none of the answers have worked for me. I'm trying to declare a BOOL variable in one class, and check its value in another. This is what I'm working with:
SController.h:
#interface SController : UIViewController {
BOOL leftSide;
BOOL rightSide;
}
SController.m:
- (void)viewDidLoad {
leftSide = YES;
rightSide = YES;
}
Now, for the class I'm trying to access the value of the BOOLs in:
#import "SController.h"
#interface VViewController : UIViewController
{
}
And VViewController's .m:
- (void)viewDidLoad {
// See what the BOOL values from SController are.
}
What I've tried:
Going off of the previous related questions on here, I've tried putting "extern" in front of the BOOLs declaration in SController.h, but that did not work. I tried simply importing the SControllers header file into VViewController, and that did not work either. I'm very new to Objective-C and programming in general, so I'm having a tough time wrapping my head around basic concepts like this. I understand the potential issues surrounding using a global variable, but this program is very small and for personal use. If anyone can show me what to change to make this happen, that would be great.
Like the others said, don't use a global variable for that (and most other) purpose.
You created iVars and in order to access them, you need to expose them to other objects.
You generally do that by defining #properties in your SControllers header file. When doing that, you don't need to create iVars yourself, they are created implicitly. And methods to access the iVars are also automagically created (getters and setters).
Your SControllers header could look something like this:
#interface SController: UIViewController
//no need to declare the iVars here, they are created by the #property definitions
#property (nonatomic, assign) BOOL leftSide;
#property (nonatomic, assign) BOOL rightSide;
#end
In your other viewController you need a reference to the instance of SController you previously created and want to "talk" to (it is important you understand this), then you could access the instance variable through the generated getter/setter methods like so:
//this is "dot notation", the first line would be equivalent
//to writing: [sControllerInstance setLeftSide: YES]
sControllerInstance.leftSide = YES;
BOOL valueRightSide = sControllerInstance.rightSide;
Please read up on: objective-c properties, getters/setters and dot notation.
You will find plenty of information on google and SO
I know this is not the answer you're looking for, but try rethinking your app. Global variables is not the best way to go for Object oriented programming.
Create GlobalVariable.h header class file and defined following externs as follows
extern NSString * googleURL;
And then in your implementation GlobalVariable.m file
#import "GlobalVariable.h"
NSString * googleURL = #"www.google.co.uk";
And then import the class wherever you want to use it across.
By default the variables (as defined in your code) are protected. You can add the #public keyword before the 2 variables to make them public but it's not recommended. Generally you want to expose those as properties using the #property keyword
Example:
#interface SController : UIViewController {
#public
BOOL leftSide;
BOOL rightSide;
#protected
//other protected variables here
}
I want to use Protocol Buffers in an iOS project. I'm trying to avoid making the whole project into an Objective-C++ fiasco, so I want to wrap the C++ protobuf classes into Objective-C ones. I have several dozen protobuf messages, and while I have done this successfully one class at a time, ideally I would like to use inheritance to minimize the repeated code. I'm new to Objective-C and I haven't used what little I knew of C++ in 10 years, so this has mostly been an exercise in frustration. Below is an example of how I have wrapped a single message.
Code
.proto:
message MessageA {
optional string value = 1;
}
MessageAWrapper.h:
#import <Foundation/Foundation.h>
#interface MessageAWrapper : NSObject
#property (nonatomic) NSString *value;
+ (id)fromString:(NSString *)string;
- (NSString *)serialize;
#end
MessageAWrapper.mm:
#import "MessageA.h"
#import "message.pb.h"
#interface MessageAWrapper ()
#property (nonatomic) MessageA *message;
#end
#implementation MessageAWrapper
- (id)init
{
self = [super init];
if (self) {
self.message = new MessageA();
}
return self;
}
- (void)dealloc {
delete self.message;
self.message = NULL;
}
- (NSString *)value {
return [NSString stringWithUTF8String:self.message->value().c_str()];
}
- (void)setValue:(NSString *)value {
self.message->set_value([value UTF8String]);
}
- (NSString *)serialize {
std::string output;
self.message->SerializeToString(&output);
return [NSString stringWithUTF8String:output.c_str()];
}
+ (id)fromString:(NSString *)string {
MessageA *message = new MessageA();
message->ParseFromString([string UTF8String]);
MessageAWrapper *wrapper = [[MessageAWrapper alloc] init];
wrapper.message = message;
return wrapper;
}
#end
Goal
There is a lot of code here that will be repeated dozens of times in which the only variation is the wrapped class type (init, dealloc, serialize, fromString), so ideally I would like to put it on a parent ProtobufMesssage class instead. Unfortunately I've had no success in making this work because I can't find a way for the parent class to know the class its children are using, which is required for example in init and fromString.
Things I've attempted
struct
template class
void*
Obstacles I've encountered
can't find a way to store a reference to a class/type
can't have any C++ headers or code in the .h file (as this requires the whole project to be Objective-C++)
difficulty keeping references to the protobuf message parents (Message or MessageLite) because they are abstract
As I said I have very little understanding of C++ or Objective-C; most of my experience is with much higher level languages like Python and Java (though I do mostly understand basic C things like pointers).
Is this perhaps not even possible? Am I approaching it wrong or missing something obvious? Any help would be much appreciated. Thanks.
I don't know much about C++ at all, but can't you declare the Objective-C property to be a Message *?
You've already separated the C++ code from the header by declaring the property in the .mm file, the problem you will have is with instance methods named by the compiler (value() and set_value()) and only being valid methods for the subclass. It might help to use the Reflection class to get and set fields by their name. Here is an excerpt from Google's message.h showing this:
Message* foo = new Foo;
const Descriptor* descriptor = foo->GetDescriptor();
const FieldDescriptor* text_field = descriptor->FindFieldByName("text");
assert(text_field != NULL);
assert(text_field->type() == FieldDescriptor::TYPE_STRING);
assert(text_field->label() == FieldDescriptor::LABEL_OPTIONAL);
const Reflection* reflection = foo->GetReflection();
assert(reflection->GetString(foo, text_field) == "Hello World!");
You could create Objective-C -objectForKey: and -setObject:forKey: instance methods that typecheck and get or set the value (confusingly, the key in the case of MessageAWrapper would be #"value"). Your subclasses would not even need to be aware of the C++ code.
You can also separate the creator function in -init and +fromString: method into something like, +_createNewInstance;
+(Message*)_createNewInstance{ return new MessageA(); }
allowing your subclasses of MessageWrapper to reuse all code except for creating the C++ object.
While Objective C has very powerful instrospection capabilities, C++ is more limited. You do have RTTI (Run time type information), but it's not even as powerful as the Objective C counterpart.
However, it might be enough for you. Within your Objective C++ class, you might find the type of you message object with the typeid operator:
if( (typeid(self.message) == typed(foo)){
//doSomething
else if( (typeid(self.message) == typed(bar)){
// doSomething else
}
Maybe the best option is to add another indirection level. Make an Objective C class hierarchy that wraps all your protocol buffer C++ classes and then create another Objective C that uses those classes (as delegates maybe). I believe this might be a better option. Use C++ only for those unavoidable cases.
Good luck!
My iPhone game has a lot of recurring code (move pictures, add score), that makes it too big when repeating the same code on each button click.
this is ViewController.m
interface and implementation between Viewcontroller.h and ViewController.m is correct - workes well
- (IBAction)button_xx_pressed:(id)sender
{
//trying to call the outsourced code
[self this_is_a_test];
}
so I tried to make outsourced recurring code. I don't need method or functions that gives a result back or something. Just do some action like NSLog output...(just a test). Or in the original version - move pictures, add score and other stuff.
this is Outsourcing.h
#import "Outsourcing.m"
#end
this is Outsourcing.m
#import "Outsourcing.h"
- (void)this_is_a_test {
int test_variable = 999;
NSLog(#"Give me a test output: = %i", test_variable);
}
#end
this would shrink the size of my game more than 80% (very important). I have thousands of recurring programming lines and at the moment, I don't know how to handle it.
actual error messages:
Outsourcing.h => missing context for method declaration
Outsourcing.m => missing context for method declaration
=> #end must appear in Objective-C context
Anyone any hints for me? Thank you very much... The rest of my game is ok... everything would run without issues. I'm very glad that I got it running (but the game size is a problem).
1 or 2 months ago, I never used xcode before. I just had some experience in VBA. And what I want is similar to.
=> Call this_is_a_test
=> Private Sub this_is_a_test()
But it seems I'm too stupid :-(
thanks
#interface Outsourcing : NSObject
- (void)this_is_a_test;
#end
#import "Outsourcing.h"
#implementation
- (void)this_is_a_test {
int test_variable = 999;
NSLog(#"Give me a test output: = %d", test_variable);
}
#end
and you call it like this in your ViewController:
#import "Outsourcing.h"
...
- (IBAction)button_xx_pressed:(id)sender
{
Outsourcing *outsourcing = [[[Outsourcing alloc] init] autorelease];
//trying to call the outsourced code
[outsourcing this_is_a_test];
}
You are missing
#interface Outsourcing : NSObject
in your header file (Outsourcing.h). Remove:
#import "Outsourcing.m"
You import header files, not source files....You are also missing:
#implementation Outsourcing
In your .m file, just after the import declaration.
I have a class (MyClass) with a lot of methods. Consequently, the .m file has become quite difficult to read. I'm relatively new to Objective-C (having come from REALbasic) and I was wondering if it's possible to put some of the methods in MyClass into different files and then include them in the class. How would I go about this in Xcode?
Yes it is possible and fortunately this can be done easily in Objective-C with Categories.
Say you have your base class MyClass.
#interface MyClass : NSObject
-(void) methodA;
#end
And the according implementation file (not relevant here).
Then you can create a category by defining a new interface in a new header file:
// the category name is in parenthesis, can be anything but must be unique
#interface MyClass (extended)
-(void) methodB;
#end
and the implementation file:
#implementation MyClass (extended)
-(void) methodB {
}
#end
Common convention to name these files is ClassToAddMethodsTo+CatgoryName, i.e.:
MyClass+extended.h
MyClass+extended.m
Group related functionality into categories and give it a meaningful name.
In Objective-c you can break a class into 'categories' - a class spread across many files. The normal Object-Oriented way is to use SuperClasses and SubClasses.
This is almost certainly a code smell telling you that you have a design problem. See this antipattern
There is one thing you could do..........
But be warned, some might consider this pure blasphemy. :)
Say you have a class with two methods you want to have in separate files.
You'll have three files:
• Class.h
• Class.m
• Class_otherMethod.m
Your Class.h should look just like any other. I think it's better to keep the header file complete, but this 'trick' can work on separating .h files just as well.
#interface Class : NSObject
- (void) method;
- (void) otherMethod;
#end
In your Class.m file you will #include the Class_otherMethod.m inside the Class #implementation like this:
#import "Class.h"
#implementation Class
- (void) method {
// do something.
}
#include "Class_otherMethod.m"
#end
And your Class_otherMethod.m file will have only the bare otherMethod implementation:
- (void) otherMethod {
// do something different.
}
Why this works
It's quite simple actually. The preprocessor simply "pastes" the content of Class_otherMethod.m inside the Class.m file and the compiler treats it as one big long file. :P
Here's an odd one. I have a class named TileMap with the following interface:
#interface TileMap : NSObject
{
int *data;
int tilesWide;
int tilesHigh;
NSString *imageName;
}
+ (id)mapNamed:(NSString *)filename;
- (id)initWithFile:(NSString *)filename;
#end
The implementation looks like this:
#implementation TileMap
+ (id)mapNamed:(NSString *)filename
{
return [[self alloc] initWithFile:filename];
}
- (id)initWithFile:(NSString *)filename
{
if (self = [super init])
{
// ...
}
return self;
}
#end
But when I add a call to [TileMap mapNamed:#"map.plist"]; to my application Xcode warns:
'TileMap' may not respond to '+mapNamed:'
The application compiles fine and calls to NSLog within TileMap-initWithFile: are logged. I noticed that Xcode's syntax coloring was off for this class and method so I tried renaming both the class and the method separately. The only combination that eliminated the warning and syntax coloring issues was to rename both the class and the method.
Am I colliding with some undocumented framework class or method? Find in Documentation doesn't reveal anything. Find in Project only reveals the call, interface definition and the implementation. I'm stumped (not that it takes much). Is there a way around this without munging my existing naming conventions?
Did you #import the TileMap.h header? Did you save your TileMap.h header?
Turns out my project directory ended up with two TileMap.h and TileMap.m files—visible from the Finder but not in Xcode. One, a complete interface and implementation, in my root project directory. The other just a bare NSObject subclass in my framework subdirectory. Not sure how that happened. Deleting the latter resolved the problem. Thanks for the help just the same Dave.
Shaun,
besides the problem you asked about, you also have a memory leak in +mapNamed:. The following line returns a non-autoreleased object with a retain count of +1, which basically gives ownership to the caller:
return [[self alloc] initWithFile:filename];
According to the Memory Management Programming Guide for Cocoa, you should return autoreleased objects from convenience methods, such as this:
return [[[self alloc] initWithFile:filename] autorelease];
If you have Snow Leopard and Xcode 3.2, you might want to try running the static analyzer to find mistakes such as this one by pressing Cmd+Shift+A.