In the following code, I passed the "1.3f" to printFloat, but it was the wrong value (in this case, -2.000000) after was "f" received. And there is a warning that "AppDelegate may not respond to -printFloat:"
Where did I get it wrong?
- (void)applicationDidFinishLaunching:(UIApplication *)application{
// Override point for customization after application launch
[window makeKeyAndVisible];
[self printFloat:1.3f];
}
- (void)printFloat:(float)f {
NSLog(#"%f",f);
}
You can easily resolve both your problems by adding the method prototype into the header file (<sameName>.h):
- (void)printFloat:(float)f;
If you include the correct definition in the class' header file, and you still cannot pass floats by reference, make sure you're not overriding an existing method of a parent class...
For example, I had this problem because my class was derived from NSMutableData (which I did not know then), and I added a method,
- (void) initWithLength:(float)length;
to my class. NSMutableData already defines this method, and it uses an integer.
My method then produced garbage: the float value was passed as 0x0 no matter what I sent it...
Related
This blog offers a nice solution for handling multiple NSURLConnections: make a custom "CustomURLConnection" class that has an additional tag property.
http://blog.emmerinc.be/index.php/2009/03/02/custom-nsurlconnection-class-with-tag/
http://blog.emmerinc.be/index.php/2009/03/15/multiple-async-nsurlconnections-example/
Basically, he has simply added a tag property to the exsisting NSURLConnection:
CustomURLConnection.m
- (id)initWithRequest:(NSURLRequest *)request delegate:(id)delegate startImmediately:(BOOL)startImmediately tag:(NSString*)tag {
self = [super initWithRequest:request delegate:delegate startImmediately:startImmediately];
if (self) {
self.tag = tag;
}
return self;
}
then, later in the normal NSURLConnection loading methods, you can do:
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
//Log the connection’s tag
CustomURLConnection *ttttag = (CustomURLConnection *)connection; // **HERE**
NSLog(#”%#”, ttttag.tag);
NSMutableData *dataForConnection = [self dataForConnection:(CustomURLConnection*)connection];
[connection release];
}
So, that's where I'm having trouble. The way I see it, this is how things go:
I create a "connection+tag"
The first code snippet I posted above creates a regular "connection" (no tag), which will eventually call the the normal NSURLConnection methods like connectionDidFinishLoading. What happens to the tag at this point?
In the connectionDidFinishLoading method I'm able to cast the connection back into a "connection+tag", then find that missing tag information that had been discarded. How?
Maybe I'm just confusing myself, but it seems as if the tag was discarded when it starts down the normal NSURLConnection path. But then by casting it as the subclass, I'm again able to recover the tag property. Where did it live/go in the mean time?
Could someone with a better understanding of inheritance explain this to me?
With this code:
[[CustomURLConnection alloc] initWithRequest:... delegate:... startImmediately:... startImmediately tag:...];
you create an instance of CustomURLConnection. Now here is where your understanding is wrong: this CustomURLConnection object can freely call all methods of its superclasses but it will always remain a CustomURLConnection. The tag is always there.
The methods that are defined in the superclass such as initWithRequest:delegate:startImmediately: don't know about the tag but they don't have to, either. When the delegate method gets called:
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
the connection argument is the very same CustomURLConnection that you created yourself above. The type in the method signature is different but that doesn't matter; because you know that this connection is of the CustomURLConnection type, you can just cast the connection object to the correct type and access the new property. But even if you wouldn't do that, the tag would still be there all the time.
I'm not sure what you mean by:
The first code snippet I posted above creates a regular "connection" (no tag).
What you've done here is create a subclass of NSURLConnection. Anywhere you can use the latter, you can use the former. NSURLConnection* means "a pointer to an NSURLConnection* or a subclass of it." So the original object you created was a CustomURLConnection and it included an extra ivar. That ivar doesn't disappear just because intermediary users refer to it by its superclass.
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;
i've got this method:
-(void)reportAchievementIdentifier: (NSString*) identifier percentComplete: (float) percent
now I want to call this method in another method like:
[self thisMethod];
But how can I do this with a method that has local declarations in it?
thank you
It doesn't matter if a method has local declarations in it, that's completely normal. Have you tried calling [self thisMethod];? Does it crash?
I have this class:
#interface G2Matrix : NSObject
...
- (id) initWithArray:(float *)val;
...
#end
This line below give me a warning saying that the first argument to the method initWithArray has an incompatible pointer type:
float m[16];
...
G2Matrix* matrix = [[[G2Matrix alloc] initWithArray:m] autorelease];
If I change the method name to something like initWithArray1 the warning disappears. I know that some objects in foundation classes have a method with the same name, but I am deriving from NSObject, which doesn't have this method. What gives?
Additional info - I call the same initWithArray method from other init methods in the G2Matrix class, but I don't see the warning there.
At a guess, this is a type problem:
Inside the other init methods, you call [self initWithArray:...]. self is typed as a G2Matrix*. In this context the compiler can fully resolve which imp (C function pointer) will eventually handle the method call, and detect its signature (argument and return types) correctly.
Out in regular code, [G2Matrix alloc] returns an id. In this context the compiler can only tell the method selector, which will be bound to an imp at runtime. It has to guess which initWithArray: you mean, and as you can see from the warning it guesses wrong, since a foundation class has an initWithArray: method with a different signature. Your code does still work, the compiler just can't be certain.
Picking a unique name for the initMethod (initWithFloats: maybe?) is the recommended way to shut the warning up. Other ways are: break it into two lines; or cast the alloc return value to the right class:
G2Matrix *matrix = [G2Matrix alloc];
matrix = [[matrix initWithArray:pointerToFloats] autorelease];
// or
G2Matrix* matrix = [[(G2Matrix *)[G2Matrix alloc] initWithArray:m] autorelease];
Looks a little odd, but allows you to turn the treat-warnings-as-errors compiler flag back on.
#tathagata thats because initWithArray is method defined in NSArray class so you cannot use it unless you subclass NSArray class.
see the documentation on NSArray
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSArray_Class/NSArray.html
PS.
by use the method, i meant Override the existing method for your purpose which is not a good idea you can find the Subclassing Notes in the document.
I came across a strange problem today. I created a subclass of UIView and added only 1 method to the template code provided by xcode.
#interface FloatView : UIView {
}
- (void)floatTest:(CGFloat)x;
#end
- (void)floatTest:(CGFloat)x {
NSLog(#"float was %f", x);
}
Then in my appDelegate I had code like this:
UIView *floatView = [[FloatView alloc] init];
[floatView floatTest:10.0f];
Pretty simple, right? What should this print out? I thought it would something like "10.0000", but no, it prints out "0.000000".
I wrestled with this for hours, trying to figure out what I was doing wrong, and then I changed the code in my appDelegate to
FloatView *floatView = [[FloatView alloc] init];
[floatView floatTest:10.0f];
Only then, did it print out the expected "10.0000". Why is this so? I've declared FloatView as a subclass of UIView, shouldn't I be able to assign a FloatView object to a UIView pointer without problems?
Even though floatView was declared a pointer to a UIView, it's really a floatView and it should be able to handle the floatTest message? Am I totally off base here?
Actually, polymorphism is working as expected. If it didn't work, nothing would have been printed (in your example, 0.0000 is being printed). The thing is, while your instance actually responds to testFloat:10.0f message, since the compiler can't statically see the method declaration (as UIView class doesn't declare such a method), it assumes that your method takes ... as argument and returns id.
When CGFloat is passed to a method that expects variable number of arguments (...), it's promoted to double. Thus, the receiving method is passed a double argument and thinks it's a float and it doesn't get printed correctly.
You can verify this behavior by changing NSLog line to:
NSLog(#"%f", *(double*)&x);
When the compiler sends the message to FloatView* rather than a UIView*, it can find the exact signature of the method. It can see it really expects CGFloat and doesn't promote the argument to double. As a result, it works correctly.
Additionally, if UIView* contained the method declaration that took a CGFloat, the compiler would call the method appropriately. To summarize, this is not a polymorphism issue; it's a missing method signature issue.