Trying to re-write Objective-C code written for the Myo I came across the GLKQuaternion class which is a union and doesn't seem to be supported in Swift (Using GLKMath from GLKit in Swift).
What I am looking for is a workaround to get this to work. Maybe a hybrid application with Math being done in ObjectiveC so I can access those properties. What are my options?
Ended up using a bridge file and creating a small wrapper layer to allow me access to the data I wanted from Swift. I called it a polyfill, similar to what we had on the web to enhance capabilities of old browsers.
The code is available on github. Particularly this commit will be of interest as it shows what needs to be done.
Polyfill.h
#interface OrientationData: NSObject
#property (nonatomic) TLMAngle *pitch;
#property (nonatomic) TLMAngle *yaw;
#property (nonatomic) TLMAngle *roll;
#end
#implementation OrientationData
#end
#interface GLKitPolyfill: NSObject
+ (OrientationData *) getOrientation:(TLMOrientationEvent *)orientationEvent;
#end
Polyfill.m
+ (OrientationData *) getOrientation:(TLMOrientationEvent *)orientationEvent {
TLMEulerAngles *angles = [TLMEulerAngles anglesWithQuaternion:orientationEvent.quaternion];
OrientationData *result = [OrientationData new];
result.pitch = angles.pitch;
result.yaw = angles.yaw;
result.roll = angles.roll;
return result;
}
ViewController.swift
let angles = GLKitPolyfill.getOrientation(orientationEvent)
let pitch = CGFloat(angles.pitch.radians)
let yaw = CGFloat(angles.yaw.radians)
let roll = CGFloat(angles.roll.radians)
Apples Mix & Match guide gives good tips on how to make Obj-C work with Swift and vice-versa.
Related
I have a flow in my app that inserts Response objects into an array, This is the response object:
#interface AppResponse : NSObject
#property (nonatomic, assign) MotSDKState state;
#property (strong, nonatomic) NSError * _Nullable error;
#property (nonatomic, assign) NSInteger errorCode;
#property (strong, nonatomic) NSDictionary * _Nullable response;
#end
I want to check at the end of the flow if the array is correct, so I create a test:
var err = AppResponse()
err.errorCode = 1000
err.state = .failed
let expectedArray = [err]
XCTAssertEqual(self.responsesArray, expectedArray)
I also tried with Nimble:
expect(self.responsesArray).to(equal(expectedArray))
And I get for both of them this unit test failed error:
error: -[****.**** *****] : failed - expected to equal <[<Appesponse: 0x600003288240>]>, got <[<Appesponse: 0x6000032948d0>]>
Any idea what is the problem? how I can compare two arrays of objects?
Caveat
I'm assuming we're seeing most of the AppResponse code, and that you haven't implemented an [AppResponse isEqual:] method. If you have:
this answer doesn't apply
you possibly should include it with the question
Answer
Consider this Swift code (which maybe should have been the first thing you tried):
let a = AppResponse()
let b = AppResponse()
print(a == b) // prints "false"
print(a == a) // prints "true"
Behind the scenes, these last two lines are equivalent to:
print(a.isEqual(b))
print(a.isEqual(a))
which is the Objective-C equality method, [NSObject isEqual:] (see here).
The default implementation of that method just compares the pointers to the objects, not their contents. As we showed above, it will always be false unless you compare literally the same object.
If you want these comparisons to work, you need an [AppResponse isEqual:] method comparing AppResponse objects by their properties. Because you are using these in arrays, I think that also implies needing a compliant [AppResponse hash] method. There are many guides to help you with that, e.g. this one.
I'm trying to use this project which is a synthesizer for Objective-C for an iPhone application I'm building. However, I'm having trouble with the MHAudioBufferPlayer class.
In the MHAudioBufferPlayer.m class, I'm getting a bunch of Use of undeclared identifier errors for _gain, _playing, and _audioFormat. This makes sense, as those identifiers are never declared with an underscore in front of them. However, they are declared in the MHAudioBufferPlayer.h class without the underscores.
I'm sort of confused by this as I'm new to Objective-C. Does an underscore denote a special action to be taken? Is it supposed to be translated into self.gain, self.playing, etc.? How can I fix this? Or is this code just buggy?
- (id)initWithSampleRate:(Float64)sampleRate channels:(UInt32)channels bitsPerChannel:(UInt32)bitsPerChannel packetsPerBuffer:(UInt32)packetsPerBuffer
{
if ((self = [super init]))
{
_playing = NO;
_playQueue = NULL;
_gain = 1.0;
_audioFormat.mFormatID = kAudioFormatLinearPCM;
_audioFormat.mSampleRate = sampleRate;
_audioFormat.mChannelsPerFrame = channels;
_audioFormat.mBitsPerChannel = bitsPerChannel;
_audioFormat.mFramesPerPacket = 1; // uncompressed audio
_audioFormat.mBytesPerFrame = _audioFormat.mChannelsPerFrame * _audioFormat.mBitsPerChannel/8;
_audioFormat.mBytesPerPacket = _audioFormat.mBytesPerFrame * _audioFormat.mFramesPerPacket;
_audioFormat.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
_packetsPerBuffer = packetsPerBuffer;
_bytesPerBuffer = _packetsPerBuffer * _audioFormat.mBytesPerPacket;
[self setUpAudio];
}
return self;
}
If you are using new compiler that comes with Xcode4.4 onwards, then for each of your property it creates an automatic synthesize with _(underscore) as prefix.
Like, if you have created #property.... playing;
then the compiler creates #synthesize playing=_playing;
If you are in older versions of Xcode, this need to be done manually.
#synthesize generated by Xcode => 4.4 as the default. The generated private instance variable, ivar, created for you by Xcode has a leading underscore '' if you don't explicitly create your own #synthesize statement. You MUST include the leading '' when sending messages to this
property (typically UI element as an outlet from your controller.m file).
That is
#property textField;
[_textField setStringValue: #"foo"]; if you DON'T write the '#synthesize'.
The compiler's done this for you, and has made a private instance variable by synthesizing the getter/setters. The convention is to make the private ivar the name of the property prepended by the leading underscore.
OR
#synthesize textField;
#property textField;
[textField setStringValue: #"foo"]; if you DO write your own '#synthesize' or are < Xcode 4.4.
Here, the complier has NOT done it for you, your ivar name/property name are the same and can be used w/o the leading '_'.
Good luck.
Depending on what version of XCode you are using, and compiler there are different ways of doing it. I don't know how familiar you are with OOP, if you are not I suggest you read up a bit on setters and getters and objects as it is the basis of almost everything you will do from now on.
Some examples, Old school style, will create an ivar. In your .h:
#interface TheViewController : UIViewController{
NSString *theString;
}
A bit new style, will create setter and getter In your .h.
#interface TheViewController : UIViewController
#property (nonatomic, weak) NSString *theString;
In your .m file:
#implementation TheViewController
#synthesize theString = _theString;
Can be accessed by _theString or self.theString
The new way of doing it. In your .h file:
#property (nonatomic, weak) NSString *theString;
The compiler Will create everything the above way did.
Hope that helps you a bit.
Ever since starting to work on iOS apps and objective C I've been really puzzled by the different locations where one could be declaring and defining variables. On one hand we have the traditional C approach, on the other we have the new ObjectiveC directives that add OO on top of that. Could you folks helps me understand the best practice and situations where I'd want to use these locations for my variables and perhaps correct my present understanding?
Here's a sample class (.h and .m):
#import <Foundation/Foundation.h>
// 1) What do I declare here?
#interface SampleClass : NSObject
{
// 2) ivar declarations
// Pretty much never used?
}
// 3) class-specific method / property declarations
#end
and
#import "SampleClass.h"
// 4) what goes here?
#interface SampleClass()
// 5) private interface, can define private methods and properties here
#end
#implementation SampleClass
{
// 6) define ivars
}
// 7) define methods and synthesize properties from both public and private
// interfaces
#end
My understanding of 1 and 4 is that those are C-style file-based declarations and definitions that have no understanding whatsoever of the concept of class, and thus have to be used exactly how they would be used in C. I've seen them used for implementing static variable-based singletons before. Are there other convenient uses I'm missing?
My take from working with iOS is that ivars have been alost completely phased out outside of the #synthesize directive and thus can be mostly ignored. Is that the case?
Regarding 5: why would I ever want to declare methods in private interfaces? My private class methods seem to compile just fine without a declaration in the interface. Is it mostly for readability?
Thanks a bunch, folks!
I can understand your confusion. Especially since recent updates to Xcode and the new LLVM compiler changed the way ivars and properties can be declared.
Before "modern" Objective-C (in "old" Obj-C 2.0) you didn't have a lot of choices. Instance variables used to be declared in the header between the curly brackets { }:
// MyClass.h
#interface MyClass : NSObject {
int myVar;
}
#end
You were able to access these variables only in your implementation, but not from other classes. To do that, you had to declare accessor methods, that look something like this:
// MyClass.h
#interface MyClass : NSObject {
int myVar;
}
- (int)myVar;
- (void)setMyVar:(int)newVar;
#end
// MyClass.m
#implementation MyClass
- (int)myVar {
return myVar;
}
- (void)setMyVar:(int)newVar {
if (newVar != myVar) {
myVar = newVar;
}
}
#end
This way you were able to get and set this instance variable from other classes too, using the usual square bracket syntax to send messages (call methods):
// OtherClass.m
int v = [myClass myVar]; // assuming myClass is an object of type MyClass.
[myClass setMyVar:v+1];
Because manually declaring and implementing every accessor method was quite annoying, #property and #synthesize were introduced to automatically generate the accessor methods:
// MyClass.h
#interface MyClass : NSObject {
int myVar;
}
#property (nonatomic) int myVar;
#end
// MyClass.m
#implementation MyClass
#synthesize myVar;
#end
The result is much clearer and shorter code. The accessor methods will be implemented for you and you can still use the bracket syntax as before. But in addition, you can also use the dot syntax to access properties:
// OtherClass.m
int v = myClass.myVar; // assuming myClass is an object of type MyClass.
myClass.myVar = v+1;
Since Xcode 4.4 you don't have to declare an instance variable yourself anymore and you can skip #synthesize too. If you don't declare an ivar, the compiler will add it for you and it will also generate the accessor methods without you having to use #synthesize.
The default name for the automatically generated ivar is the name or your property starting with an underscore. You can change the generated ivar's name by using #synthesize myVar = iVarName;
// MyClass.h
#interface MyClass : NSObject
#property (nonatomic) int myVar;
#end
// MyClass.m
#implementation MyClass
#end
This will work exactly as the code above. For compatibility reasons you can still declare ivars in the header. But because the only reason why you would want to do that (and not declare a property) is to create a private variable, you can now do that in the implementation file as well and this is the preferred way.
An #interface block in the implementation file is actually an Extension and can be used to forward declare methods (not needed anymore) and to (re)declare properties. You could for instance declare a readonly property in your header.
#property (nonatomic, readonly) myReadOnlyVar;
and redeclare it in your implementation file as readwrite to be able to set it using the property syntax and not only via direct access to the ivar.
As for declaring variables completely outside of any #interface or #implementation block, yes those are plain C variables and work exactly the same.
First, read #DrummerB's answer. It a good overview of the whys and what you should generally do. With that in mind, to your specific questions:
#import <Foundation/Foundation.h>
// 1) What do I declare here?
No actual variable definitions go here (it's technically legal to do so if you know exactly what you're doing, but never do this). You may define several other kinds of things:
typdefs
enums
externs
Externs look like variable declarations, but they're just a promise to actually declare it somewhere else. In ObjC, they should only be used to declare constants, and generally only string constants. For instance:
extern NSString * const MYSomethingHappenedNotification;
You would then in your .m file declare the actual constant:
NSString * const MYSomethingHappenedNotification = #"MYSomethingHappenedNotification";
#interface SampleClass : NSObject
{
// 2) ivar declarations
// Pretty much never used?
}
As noted by DrummerB, this is legacy. Don't put anything here.
// 3) class-specific method / property declarations
#end
Yep.
#import "SampleClass.h"
// 4) what goes here?
External constants, as described above. Also file static variables can go here. These are the equivalent of class variables in other languages.
#interface SampleClass()
// 5) private interface, can define private methods and properties here
#end
Yep
#implementation SampleClass
{
// 6) define ivars
}
But very rarely. Almost always you should allow clang (Xcode) to create the variables for you. The exceptions are usually around non-ObjC ivars (like Core Foundation objects, and especially C++ objects if this is an ObjC++ class), or ivars that have weird storage semantics (like ivars that don't match with a property for some reason).
// 7) define methods and synthesize properties from both public and private
// interfaces
Generally you shouldn't #synthesize anymore. Clang (Xcode) will do it for you, and you should let it.
Over the last few years, things have gotten dramatically simpler. The side-effect is that there are now three different eras (Fragile ABI, Non-fragile ABI, Non-fragile ABI + auto-syntheisze). So when you see the older code, it can be a little confusing. Thus confusion arising from simplicity :D
I'm also pretty new, so hopefully I don't screw anything up.
1 & 4: C-style global variables: they have file wide scope. The difference between the two is that, since they're file wide, the first will be available to anyone importing the header while the second is not.
2: instance variables. Most instance variables are synthesized and retrieved/set through accessors using properties because it makes memory management nice and simple, as well as gives you easy-to-understand dot notation.
6: Implementation ivars are somewhat new. It's a good place to put private ivars, since you want to only expose what's needed in the public header, but subclasses don't inherit them AFAIK.
3 & 7: Public method and property declarations, then implementations.
5: Private interface. I always use private interfaces whenever I can to keep things clean and create a kind of black box effect. If they don't need to know about it, put it there. I also do it for readability, don't know if there are any other reasons.
This is an example of all kinds of variables declared in Objective-C. The variable name indicate its access.
File: Animal.h
#interface Animal : NSObject
{
NSObject *iProtected;
#package
NSObject *iPackage;
#private
NSObject *iPrivate;
#protected
NSObject *iProtected2; // default access. Only visible to subclasses.
#public
NSObject *iPublic;
}
#property (nonatomic,strong) NSObject *iPublic2;
#end
File: Animal.m
#import "Animal.h"
// Same behaviour for categories (x) than for class extensions ().
#interface Animal(){
#public
NSString *iNotVisible;
}
#property (nonatomic,strong) NSObject *iNotVisible2;
#end
#implementation Animal {
#public
NSString *iNotVisible3;
}
-(id) init {
self = [super init];
if (self){
iProtected = #"iProtected";
iPackage = #"iPackage";
iPrivate = #"iPrivate";
iProtected2 = #"iProtected2";
iPublic = #"iPublic";
_iPublic2 = #"iPublic2";
iNotVisible = #"iNotVisible";
_iNotVisible2 = #"iNotVisible2";
iNotVisible3 = #"iNotVisible3";
}
return self;
}
#end
Note that the iNotVisible variables are not visible from any other class. This is a visibility issue, so declaring them with #property or #public doesn't change it.
Inside a constructor it's good practice to access variables declared with #property using underscore instead self to avoid side effects.
Let's try to access the variables.
File: Cow.h
#import "Animal.h"
#interface Cow : Animal
#end
File: Cow.m
#import "Cow.h"
#include <objc/runtime.h>
#implementation Cow
-(id)init {
self=[super init];
if (self){
iProtected = #"iProtected";
iPackage = #"iPackage";
//iPrivate = #"iPrivate"; // compiler error: variable is private
iProtected2 = #"iProtected2";
iPublic = #"iPublic";
self.iPublic2 = #"iPublic2"; // using self because the backing ivar is private
//iNotVisible = #"iNotVisible"; // compiler error: undeclared identifier
//_iNotVisible2 = #"iNotVisible2"; // compiler error: undeclared identifier
//iNotVisible3 = #"iNotVisible3"; // compiler error: undeclared identifier
}
return self;
}
#end
We can still access the not visible variables using the runtime.
File: Cow.m (part 2)
#implementation Cow(blindAcess)
- (void) setIvar:(NSString*)name value:(id)value {
Ivar ivar = class_getInstanceVariable([self class], [name UTF8String]);
object_setIvar(self, ivar, value);
}
- (id) getIvar:(NSString*)name {
Ivar ivar = class_getInstanceVariable([self class], [name UTF8String]);
id thing = object_getIvar(self, ivar);
return thing;
}
-(void) blindAccess {
[self setIvar:#"iNotVisible" value:#"iMadeVisible"];
[self setIvar:#"_iNotVisible2" value:#"iMadeVisible2"];
[self setIvar:#"iNotVisible3" value:#"iMadeVisible3"];
NSLog(#"\n%# \n%# \n%#",
[self getIvar:#"iNotVisible"],
[self getIvar:#"_iNotVisible2"],
[self getIvar:#"iNotVisible3"]);
}
#end
Let's try to access the not visible variables.
File: main.m
#import "Cow.h"
#import <Foundation/Foundation.h>
int main(int argc, char *argv[]) {
#autoreleasepool {
Cow *cow = [Cow new];
[cow performSelector:#selector(blindAccess)];
}
}
This prints
iMadeVisible
iMadeVisible2
iMadeVisible3
Note that I was able to access the backing ivar _iNotVisible2 which is private to the subclass. In Objective-C all variables can be read or set, even those that are marked #private, no exceptions.
I didn't include associated objects or C variables as they are different birds. As for C variables, any variable defined outside #interface X{} or #implementation X{} is a C variable with file scope and static storage.
I didn't discuss memory management attributes, or readonly/readwrite, getter/setter attributes.
I'm slightly confused as to the proper conventions when dealing with properties. I'll illustrate my question through an example. So from the example below I know that functionally "self.loan = self.loan + 250.00;" is the same as "_loan = _loan + 250.00;" or is it not? I see numerous tutorials all over the web that may or may not use both methods to access a property. So what exactly is the difference between using _loan and self.loan (I know that self.loan is the same as [self setLoan:])
//ClassA.h
#interface ClassA: UIViewController
#property double loan;
#end
//ClassA.m
#implementation ClassA
#synthesize loan = _loan;
-(void)doSomething{
self.loan = self.loan + 250.00; //Exhibit A
_loan = _loan + 250.00; // Exhibit B
}
_loan is a variable and assigning a value to it has no particular side effect.
self.loan = self.loan + 250.00 is essentially the same as writing [self setLoan:[self loan] + 250.00] in that methods are called that may do other things than simply set or get the value of a variable. The extra things those methods do depend on whether you write custom versions of them (the setters and the getters) or use #synthesize to create them and, if you use #synthesize, what attributes you apply in the #property declaration.
When you write out #synthesize loan = _loan; it is basically shorthand to say that what you are synthesizing is = to a private member it would be similar to the verbose way of coding it below:
//ClassA.h
#interface ClassA: UIViewController {
double _loan;
}
#property double loan;
#end
//ClassA.m
#implementation ClassA
#synthesize loan = _loan;
It is good practice to write it out this way so you can clearly have a '_' to signify your private members within your class code but when exposing this as a property to other classes that shouldn't be shown.
You should never use direct reference to a variable when accessing a property. Always go for self.property in your code.
If you use _property you are not making use for your getters and setters. In this case you are just wasting #synthesize use.
self.loan = self.loan + 250.00; //Exhibit A
This should be right approach.
So, I thought consulting you guys about my design, cause I sense there might be a better way of doing it.
I need to implement game bonuses mechanism in my app.
Currently there are 9 bonuses available, each one is based of different param of the MainGame Object.
What I had in mind was at app startup to initialize 9 objects of GameBonus while each one will have different SEL (shouldBonus) which will be responsible for checking if the bonus is valid.
So, every end of game I will just run over the bonuses array and call the isBonusValid() function with the MainGame object(which is different after every game).
How's that sound ?
The only issue I have currently, is that I need to make sure that if some bonuses are accepted some other won't (inner stuff)... any advice how to do that and still maintain generic implementation ?
#interface GameBonus : NSObject {
int bonusId;
NSString* name;
NSString* description;
UIImage* img;
SEL shouldBonus;
}
#implementation GameBonus
-(BOOL) isBonusValid(MainGame*)mainGame
{
[self shouldBonus:mainGame];
}
#end
Sounds ok, the only change I would consider is perhaps removing a bonus from the array should it be acepted. That way it is not checked in the future. This would also work for bonus that for other reason should no longer be available.
Whether or not the player can obtain a particular bonus according to the rules of your game isn't something the individual bonuses would know about. This is something the game itself would know. For example, you may have one game that allows bonuses A and B together, but another game that wouldn't.
So the logic to grant or deny a bonus should be in the MainGame object. I would organize it so that GameBonus is a plain bit bucket class and the logic is all in the MainGame. MainGame would be a superclass of any other custom games that might want to override the bonus logic.
A starting point:
typedef enum {
BonusTypeA, BonusTypeB, BonusTypeC
} BonusId;
#interface GameBonus : NSObject {
BonusId bonusId;
NSString *name;
NSString *description;
UIImage *img;
}
#property (nonatomic,assign) BonusId bonusId;
#property (nonatomic,retain) NSString *name;
#property (nonatomic,retain) NSString *description;
#property (nonatomic,retain) NSString *img;
#end
#interface MainGame : NSObject {
NSMutableSet *activeBonuses;
}
-(BOOL) tryToSetBonus:(BonusId)bonus; // tries to set, returns YES if successful.
-(BOOL) isBonusValid:(BonusId)bonus; // has no side effect, just check validity.
#end