I read here Learn C Before Objective-C?
Usually I then replace some Obj-C code with pure C code (after all you can mix them as much as you like, the content of an Obj-C method can be entirely, pure C code)
Is this true?
Is it possible to build an iPhone app purely in the C programming language?
Damn, it took me a while but I got it:
main.c:
#include <CoreFoundation/CoreFoundation.h>
#include <objc/runtime.h>
#include <objc/message.h>
// This is a hack. Because we are writing in C, we cannot out and include
// <UIKit/UIKit.h>, as that uses Objective-C constructs.
// however, neither can we give the full function declaration, like this:
// int UIApplicationMain (int argc, char *argv[], NSString *principalClassName, NSString *delegateClassName);
// So, we rely on the fact that for both the i386 & ARM architectures,
// the registers for parameters passed in remain the same whether or not
// you are using VA_ARGS. This is actually the basis of the objective-c
// runtime (objc_msgSend), so we are probably fine here, this would be
// the last thing I would expect to break.
extern int UIApplicationMain(int, ...);
// Entry point of the application. If you don't know what this is by now,
// then you probably shouldn't be reading the rest of this post.
int main(int argc, char *argv[])
{
// Create an #autoreleasepool, using the old-stye API.
// Note that while NSAutoreleasePool IS deprecated, it still exists
// in the APIs for a reason, and we leverage that here. In a perfect
// world we wouldn't have to worry about this, but, remember, this is C.
id autoreleasePool = objc_msgSend(objc_msgSend(objc_getClass("NSAutoreleasePool"), sel_registerName("alloc")), sel_registerName("init"));
// Notice the use of CFSTR here. We cannot use an objective-c string
// literal #"someStr", as that would be using objective-c, obviously.
UIApplicationMain(argc, argv, nil, CFSTR("AppDelegate"));
objc_msgSend(autoreleasePool, sel_registerName("drain"));
}
AppDelegate.c:
#import <objc/runtime.h>
#import <objc/message.h>
// This is equivalent to creating a #class with one public variable named 'window'.
struct AppDel
{
Class isa;
id window;
};
// This is a strong reference to the class of the AppDelegate
// (same as [AppDelegate class])
Class AppDelClass;
// this is the entry point of the application, same as -application:didFinishLaunchingWithOptions:
// note the fact that we use `void *` for the 'application' and 'options' fields, as we need no reference to them for this to work. A generic id would suffice here as well.
BOOL AppDel_didFinishLaunching(struct AppDel *self, SEL _cmd, void *application, void *options)
{
// we +alloc and -initWithFrame: our window here, so that we can have it show on screen (eventually).
// this entire method is the objc-runtime based version of the standard View-Based application's launch code, so nothing here really should surprise you.
// one thing important to note, though is that we use `sel_getUid()` instead of #selector().
// this is because #selector is an objc language construct, and the application would not have been created in C if I used #selector.
self->window = objc_msgSend(objc_getClass("UIWindow"), sel_getUid("alloc"));
self->window = objc_msgSend(self->window, sel_getUid("initWithFrame:"), (struct CGRect) { 0, 0, 320, 480 });
// here, we are creating our view controller, and our view. note the use of objc_getClass, because we cannot reference UIViewController directly in C.
id viewController = objc_msgSend(objc_msgSend(objc_getClass("UIViewController"), sel_getUid("alloc")), sel_getUid("init"));
// creating our custom view class, there really isn't too much
// to say here other than we are hard-coding the screen's bounds,
// because returning a struct from a `objc_msgSend()` (via
// [[UIScreen mainScreen] bounds]) requires a different function call
// and is finicky at best.
id view = objc_msgSend(objc_msgSend(objc_getClass("View"), sel_getUid("alloc")), sel_getUid("initWithFrame:"), (struct CGRect) { 0, 0, 320, 480 });
// here we simply add the view to the view controller, and add the viewController to the window.
objc_msgSend(objc_msgSend(viewController, sel_getUid("view")), sel_getUid("addSubview:"), view);
objc_msgSend(self->window, sel_getUid("setRootViewController:"), viewController);
// finally, we display the window on-screen.
objc_msgSend(self->window, sel_getUid("makeKeyAndVisible"));
return YES;
}
// note the use of the gcc attribute extension (constructor).
// Basically, this lets us run arbitrary code before program startup,
// for more information read here: http://stackoverflow.com/questions/2053029
__attribute__((constructor))
static void initAppDel()
{
// This is objc-runtime gibberish at best. We are creating a class with the
// name "AppDelegate" that is a subclass of "UIResponder". Note we do not need
// to register for the UIApplicationDelegate protocol, that really is simply for
// Xcode's autocomplete, we just need to implement the method and we are golden.
AppDelClass = objc_allocateClassPair(objc_getClass("UIResponder"), "AppDelegate", 0);
// Here, we tell the objc runtime that we have a variable named "window" of type 'id'
class_addIvar(AppDelClass, "window", sizeof(id), 0, "#");
// We tell the objc-runtime that we have an implementation for the method
// -application:didFinishLaunchingWithOptions:, and link that to our custom
// function defined above. Notice the final parameter. This tells the runtime
// the types of arguments received by the function.
class_addMethod(AppDelClass, sel_getUid("application:didFinishLaunchingWithOptions:"), (IMP) AppDel_didFinishLaunching, "i#:##");
// Finally we tell the runtime that we have finished describing the class and
// we can let the rest of the application use it.
objc_registerClassPair(AppDelClass);
}
View.c
#include <objc/runtime.h>
// This is a strong reference to the class of our custom view,
// In case we need it in the future.
Class ViewClass;
// This is a simple -drawRect implementation for our class. We could have
// used a UILabel or something of that sort instead, but I felt that this
// stuck with the C-based mentality of the application.
void View_drawRect(id self, SEL _cmd, struct CGRect rect)
{
// We are simply getting the graphics context of the current view,
// so we can draw to it
CGContextRef context = UIGraphicsGetCurrentContext();
// Then we set it's fill color to white so that we clear the background.
// Note the cast to (CGFloat []). Otherwise, this would give a warning
// saying "invalid cast from type 'int' to 'CGFloat *', or
// 'extra elements in initializer'. Also note the assumption of RGBA.
// If this wasn't a demo application, I would strongly recommend against this,
// but for the most part you can be pretty sure that this is a safe move
// in an iOS application.
CGContextSetFillColor(context, (CGFloat []){ 1, 1, 1, 1 });
// here, we simply add and draw the rect to the screen
CGContextAddRect(context, (struct CGRect) { 0, 0, 320, 480 });
CGContextFillPath(context);
// and we now set the drawing color to red, then add another rectangle
// and draw to the screen
CGContextSetFillColor(context, (CGFloat []) { 1, 0, 0, 1 });
CGContextAddRect(context, (struct CGRect) { 10, 10, 20, 20 });
CGContextFillPath(context);
}
// Once again we use the (constructor) attribute. generally speaking,
// having many of these is a very bad idea, but in a small application
// like this, it really shouldn't be that big of an issue.
__attribute__((constructor))
static void initView()
{
// Once again, just like the app delegate, we tell the runtime to
// create a new class, this time a subclass of 'UIView' and named 'View'.
ViewClass = objc_allocateClassPair(objc_getClass("UIView"), "View", 0);
// and again, we tell the runtime to add a function called -drawRect:
// to our custom view. Note that there is an error in the type-specification
// of this method, as I do not know the #encode sequence of 'CGRect' off
// of the top of my head. As a result, there is a chance that the rect
// parameter of the method may not get passed properly.
class_addMethod(ViewClass, sel_getUid("drawRect:"), (IMP) View_drawRect, "v#:");
// And again, we tell the runtime that this class is now valid to be used.
// At this point, the application should run and display the screenshot shown below.
objc_registerClassPair(ViewClass);
}
It's ugly, but it works.
If you would like to download this, you can get it from my dropbox here
You can get it from my GitHub repository here:
Objective-C is a superset of the C-language, so it is theoretically possible to write a program entirely in C, however, unless you are thoroughly versed in OpenGL ES, You'll need to do at least some objC (Even Rich's sample has a const NSString* in it), else you'll have to write the views yourself.
OK, the above is completely wrong. Let me say, I'm astounded Rich achieved this lofty goal, so I ported it over to the mac (source here). The files below have no headers, do not link to Cocoa, nor does the project have a nib:
AppDelegate.m
#include <objc/runtime.h>
#include <objc/message.h>
extern id NSApp;
struct AppDel
{
Class isa;
//Will be an NSWindow later, for now, it's id, because we cannot use pointers to ObjC classes
id window;
};
// This is a strong reference to the class of the AppDelegate
// (same as [AppDelegate class])
Class AppDelClass;
BOOL AppDel_didFinishLaunching(struct AppDel *self, SEL _cmd, id notification) {
//alloc NSWindow
self->window = objc_msgSend(objc_getClass("NSWindow"),
sel_getUid("alloc"));
//init NSWindow
//Adjust frame. Window would be about 50*50 px without this
//specify window type. We want a resizeable window that we can close.
//use retained backing because this thing is small anyhow
//return no because this is the main window, and should be shown immediately
self->window = objc_msgSend(self->window,
sel_getUid("initWithContentRect:styleMask:backing:defer:"),(NSRect){0,0,1024,460}, (NSTitledWindowMask|NSClosableWindowMask|NSResizableWindowMask|NSMiniaturizableWindowMask),NSBackingStoreRetained,NO);
//send alloc and init to our view class. Love the nested objc_msgSends!
id view = objc_msgSend(objc_msgSend(objc_getClass("View"), sel_getUid("alloc")), sel_getUid("initWithFrame:"), (struct CGRect) { 0, 0, 320, 480 });
// here we simply add the view to the window.
objc_msgSend(self->window, sel_getUid("setContentView:"), view);
objc_msgSend(self->window, sel_getUid("becomeFirstResponder"));
//makeKeyOrderFront: NSWindow to show in bottom left corner of the screen
objc_msgSend(self->window,
sel_getUid("makeKeyAndOrderFront:"),
self);
return YES;
}
static void initAppDel()
{
//Our appDelegate should be NSObject, but if you want to go the hard route, make this a class pair of NSApplication and try initing those awful delegate methods!
AppDelClass = objc_allocateClassPair((Class)
objc_getClass("NSObject"), "AppDelegate", 0);
//Change the implementation of applicationDidFinishLaunching: so we don't have to use ObjC when this is called by the system.
class_addMethod(AppDelClass,
sel_getUid("applicationDidFinishLaunching:"),
(IMP) AppDel_didFinishLaunching, "i#:#");
objc_registerClassPair(AppDelClass);
}
void init_app(void)
{
objc_msgSend(
objc_getClass("NSApplication"),
sel_getUid("sharedApplication"));
if (NSApp == NULL)
{
fprintf(stderr,"Failed to initialized NSApplication... terminating...\n");
return;
}
id appDelObj = objc_msgSend(
objc_getClass("AppDelegate"),
sel_getUid("alloc"));
appDelObj = objc_msgSend(appDelObj, sel_getUid("init"));
objc_msgSend(NSApp, sel_getUid("setDelegate:"), appDelObj);
objc_msgSend(NSApp, sel_getUid("run"));
}
//there doesn't need to be a main.m because of this little beauty here.
int main(int argc, char** argv)
{
//Initialize a valid app delegate object just like [NSApplication sharedApplication];
initAppDel();
//Initialize the run loop, just like [NSApp run]; this function NEVER returns until the app closes successfully.
init_app();
//We should close acceptably.
return EXIT_SUCCESS;
}
View.m
#include <objc/runtime.h>
#include <objc/message.h>
#include <ApplicationServices/ApplicationServices.h>
// This is a strong reference to the class of our custom view,
// In case we need it in the future.
Class ViewClass;
// This is a simple -drawRect implementation for our class. We could have
// used a UILabel or something of that sort instead, but I felt that this
// stuck with the C-based mentality of the application.
void View_drawRect(id self, SEL _cmd, CGRect rect)
{
//make a red NSColor object with its convenience method
id red = objc_msgSend(objc_getClass("NSColor"), sel_getUid("redColor"));
// fill target rect with red, because this is it!
NSRect rect1 = NSMakeRect ( 21,21,210,210 );
objc_msgSend(red, sel_getUid("set"));
NSRectFill ( rect1 );
}
// Once again we use the (constructor) attribute. generally speaking,
// having many of these is a very bad idea, but in a small application
// like this, it really shouldn't be that big of an issue.
__attribute__((constructor))
static void initView()
{
// Once again, just like the app delegate, we tell the runtime to
// create a new class, this time a subclass of 'UIView' and named 'View'.
ViewClass = objc_allocateClassPair((Class) objc_getClass("NSView"), "View", 0);
// and again, we tell the runtime to add a function called -drawRect:
// to our custom view. Note that there is an error in the type-specification
// of this method, as I do not know the #encode sequence of 'CGRect' off
// of the top of my head. As a result, there is a chance that the rect
// parameter of the method may not get passed properly.
class_addMethod(ViewClass, sel_getUid("drawRect:"), (IMP) View_drawRect, "v#:");
// And again, we tell the runtime that this class is now valid to be used.
// At this point, the application should run and display the screenshot shown below.
objc_registerClassPair(ViewClass);
}
prefix.pch
//
// Prefix header for all source files of the 'CBasedMacApp' target in the 'CBasedMacApp' project
//
#ifdef __OBJC__
#import <Foundation/Foundation.h>
#import <AppKit/AppKit.h>
#endif
I read here Learn C Before Objective-C?
Usually I then replace some Obj-C code with pure C code (after all you can mix them as much as you like, the content of an Obj-C method can be entirely, pure C code)
Is this true?
Could I build an iPhone app purely in the C programming language?
The quoted passage is true, but the answer to your question is no.
To illustrate what answerer Mecki on that other question was talking about:
- (void) drawRect:(CGRect)dirtyRect { //Objective-C
CGContextRef context = UIGraphicsGetCurrentContext(); //C
CGContextSetRGBFillColor(context, 1.0, 0.0, 0.0, 1.0); //C
CGContextFillRect(context, dirtyRect); //C
} //Objective-C (balances above “- (void) drawRect:…” line)
There is nothing but pure C code within this method, but the method itself is Objective-C code, as is the class that contains this method.
So it is possible to do what Mecki said, but you can't (practically—as Richard J. Ross III showed, it's technically possible but quite a lot of typing) write a whole Cocoa Touch program in pure C.
Actually, some of the code posted here, while written in C, is still calling objective-C code :). I don't know if that actually fits the scenario from the original poster when he asked
Is it possible to build an iPhone app purely in the C programming
language?
but I would agree with the people saying that, generally speaking and for an app with a GUI, you would need to write your GUI in OpenGL (which is C).
I think that is what most games do, right? Although I'm not sure if there's access to the iPhone's I/O (the touchscreen for example) in C.
Last but not least, the guys that wrote the code above rock! :)
So I am doing this to initialize my selector:
//In .h
SEL selectors[3];
//In .m
selectors[0] = #selector(rotate);
selectors[1] = #selector(discharge);
And here is the problem:
When I call this in my init method in Cocos2d like this:
[self performSelector:selectors[0]];
it works fine, but when I call this line of code in a method called moveThings which is invoked through the schedule ([self schedule:#selector(moveThings:)]) at the end of my init method in Cocos2d it gives EXC_BAD_ACCESS. What is the problem with scheduling things?
UPDATE:
I have found there is a problem with the rotate function (the function being stored in selector[0]). Here it is:
-(void)rotate:(ccTime)delta {
if (((CCSprite *)[creature objectAtIndex:0]).rotation < 360) {
((CCSprite *)[creature objectAtIndex:0]).rotation++;
}
else {
((CCSprite *)[creature objectAtIndex:0]).rotation++;
}
}
If I comment the contents of the method out it works fine when called through moveThings and init.
If I change the methods contents with:
((CCSprite *)[creature objectAtIndex:0]).rotation++;
It fails... But, again, I would like to state that all of these things do work if I call it in my init method, even call it twice in a row, but it will not work (except when I take out the contents of the rotate method) if I call it through the moveThings: method which is being invoke through the schedule method it fails.
Further update:
If I call:
((CCSprite *)[creature objectAtIndex:0]).rotation++;
In moveThings (which is being, as I've said before, invoked by the schedule:(SEL) method) it fails. Where as long as it is not invoked through a method that is the called by schedule it works.
The problem is that when you call performSelector there are only two options:
have your selector take no arguments and leave the ":" off the #selector(foo) definition.
have your selector take either one or two arguments which both must be an NSObject or subclass
it is the latter that is messing you up here I suspect.
Here are the three forms of performSelector:
- (id)performSelector:(SEL)aSelector;
- (id)performSelector:(SEL)aSelector withObject:(id)object;
- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;
You'll note that the withObject arguments are all of type id which is an Objective C object.
The selector you're trying to use takes a ccTime which is a float and not an Objective C object as it's param and that is why things are crashing:
-(void)rotate:(ccTime)delta;
One option is to make a wrapper method that takes a wrapped ccTime and unwraps it and calls the rotate:(ccTime) method:
- (void) wrappedRotate: (NSNumber*) inDelta
{
[self rotate: [inDelta floatValue]];
}
then use
selectors[0] = #selector(wrappedRotate:);
and then call via:
[self schedule: #selector(moveThings:)]); // cocos2d schedule
...
- (void) moveThings: (ccTime) dt
{
[self performSelector: selectors[0] withObject: [NSNumber numberWithFloat: dt]];
...
}
One reason you are getting confused is because Cocos2d is using #selector in somewhat more complicated ways (see CCScheduler.m in the CCTimer::initWithTarget:selector:interval: and CCTimer::update: method in particular).
disclaimer: code typed into SO so not checked with a compiler, but the essence of what you need should be here.
One problem for sure is that you are using a variable declared inside a .h while initializing it inside the relative .m. According to the linking I'm not sure that just one variable selectors will exist (so that different files that include .h will have different versions).
First of all I suggest you to try adding the keyword extern to have
extern SEL selectors[3];
to tell your linker that it is initialized inside the relative .m and to use just that one.
I think your problem stems from your method definition which is - (void)rotate; and not - (void)rotate:(ccTime)dt;
You should adjust your selectors likewise.
If your method does not have any arguments then do not use a colon in your selector call.
// Requires #selector(foo:)
- (void) foo:(id)sender;
// Requires #selector(foo)
- (void) foo;