I have a struct Position, like this:
typedef struct Position { int x, y; } Position;
How may I pass it in NSObject performSelector:withObject:afterDelay:? Like this:
Position pos;
pos.x = pos.y = 1;
[self performSelector:#selector(foo:)
withObject:pos // ERROR
afterDelay:5.0f];
EDIT: changed code to fix typo
Uhm.. use a CGPoint and something like
[self performSelector:#selector(foo:)
withObject:[NSValue valueWithCGPoint:CGPointMake(pos.x, pos.y)]
afterDelay:5.0f];
And read it again as
NSValue v;
CGPoint point = [v CGPointValue];
or leave the Position class away completely, CGPoint does the same
You could wrap your custom type using NSValue class. The error is that you didn't provide an object reference to the method.
Try using NSValue's +(NSValue *)valueWithBytes:(const void *)value objCType:(const char *)type; class method. On the other side you can retrieve the value using -(void)getValue:(void *)buffer;.
preformSelector:withObject: accepts only objects as parameters, hence you'll have to implement your foo: method to accept an object. There are two ways to pass the struct as an object:
create a struct-like object or
wrap it into NSValue and unwrap it in the method.
Full answer, based on user756245's (which doesn't tell you how to use it, not a great deal of help). Also, Apple suggests you use a slightly different method these days, IIRC:
typedef myStruct { int a; } myStruct;
myStruct aLocalPointer = ... assign to it
[self performSelector:#selector(myOtherMethod:) withObject:[NSValue value:&aLocalPointer withObjCType:#encode(myStruct)] afterDelay:0.25];
This is most likely asking for trouble, but you can pass CGPoint as id by bridging it in this way:
withObject:(__bridge id)((void *)(&point))
This will lead to a crash if point goes out of scope and your selector tries to read it, though.
Related
Let's say I have an NSArray called myArray of NSStrings (#"a0",#"a1",#"a2")
Then in a fast enumeration I loop into my array to build properties according to that NSStrings. I've got a problem accessing that properties.
I'm trying something like that :
#property (nonatomic) float a0propertyLow;
#property (nonatomic) float a0propertyHigh;
#property (nonatomic) float a1propertyLow;
#property (nonatomic) float a1propertyHigh;
..
.. etc.
for (NSString *aPos in myArray) {
NSString *low = [NSString stringWithFormat:#"%#propertyLow",aPos];
NSString *high = [NSString stringWithFormat:#"%#propertyHigh",aPos];
SEL lowSel = NSSelectorFromString(low);
SEL highSel = NSSelectorFromString(high);
if ([self respondsToSelector:lowSel]&&[self respondsToSelector:highSel]) {
id sumPartOne = [self performSelector:lowSel];
id sumPartTwo = [self performSelector:highSel];
float bla = (float)sumPartOne + (float)sumPartTwo;
}
}
I know my code is wrong but I don't know how to make it work.
My problem is that lowSel and highSel are getters which returns float but the perform selector method returns id which is ok for an object but not for floats.
So, how can I access my float getters with variable names ? I'm sure answer must be simple but it seems that my mind is looking for something complicated (and which obviously doesn't work) so I'm asking for help :)
Thank you very much for your help
You can't use performSelector: to call a method that returns a scalar value. The documentation for performSelector: clearly says what you have to do:
For methods that return anything other than an object, use NSInvocation.
An NSInvocation is a little more complex to set up but more flexible regarding arguments and return types.
In your case, it is probably easier to use Key-Value Coding instead:
[self valueForKey:low];
takes the return type into account and will automatically wrap the float in an NSNumber.
If you really need to use these getter methods, you can change your properties to double and use objc_msgSend_fpret():
#include <objc/runtime.h>
#include <objc/message.h>
double arg0 = objc_msgSend_fpret(self, lowSel);
If you can avoid getters (I know, that's not good practice, but anyway, it works for sure with the following method), and use the instance variables directly:
void *object_getIvarPtr(id obj, const char *name)
{
if (!obj || !name)
{
return NULL;
}
Ivar ivar = object_getInstanceVariable(obj, name, NULL);
if (!ivar)
{
return NULL;
}
return ((char *)obj + ivar_getOffset(ivar));
}
float arg0 = *(float *)object_getIvarPtr(self, [lowSel UTF8String]);
Hope this helps.
One way you can do is convert your floats into objects at runtime such as:-
NSString *str=[NSSTring stringWithFormat:#"%f",yourFloatValue];
and then u can retrive it using
[str floatValue];
I would like to initially set a CGPoint property to a particular point (middle of screen). Other methods may subsequently wish to change this property. My thoughts were to initialise it if empty in the getter, but I get the message invalid argument type 'struct CGPoint' to unary expression. I also tried using if property == nil or 0 but no joy.
Any thoughts?
-(CGPoint)graphOrigin
{
// initialise to centre of screen if has not been set
if(!_graphOrigin) // this expression is causing the problem
{
CGPoint origin = CGPointMake(self.bounds.origin.x + self.bounds.size.width / 2, self.bounds.origin.y + self.bounds.size.height / 2);
_graphOrigin = origin;
}
return _graphOrigin;
}
A CGPoint is a struct, so you can't set it to nil or NULL (it's not a pointer). In a sense, there's really no "uninitialized" state. Perhaps you could use {0.0, 0.0} to designate an unset CGPoint, but that's also a valid coordinate. Or you could use negative x and y values to flag an "uninitialized" point, since negative values can't be valid drawing points, but that's a bit of a hack, too.
Probably your best bet is to do one of two things:
Store the property as a pointer to a CGPoint. This value can be set to NULL when uninitialized. Of course, you have to worry about mallocing and freeing the value.
Store the CGPoint alongside a BOOL called pointInitialized or somesuch, initially set to NO, but set to YES once the point has been initialized. You can even wrap that up in a struct:
struct {
CGPoint point;
BOOL initialized;
} pointData;
An easier way would be to initialize _graphOrigin to CGRectZero and change your if statement for this:
if (!CGPointEqualToPoint(_graphOrigin, CGPointZero)) {
}
CGPoint does not have an uninitialized state. However, if you consider the point (0, 0) as uninitialized, you could use
if (_graphOrigin.x == 0 && _graphOrigin.y == 0)
{
...
This works because when an Objective-C instance is initialized, all its ivar are cleared to bits of zero, which in the CGFloat representation is 0.0.
(Note: The == is fine here even if the operands are CGFloat because we want to compare with the an exact bit pattern (ignoring the issue of -0))
Since CGPointZero (0,0) and any other value you give a point may exist in your context
you may want to initialize an NSValue with your point using:
NSValue *pointVal = [NSValue valueWithCGPoint:point];
You could do this based on some condition and then later test the NSValue for nil.
NSValue can also be added to an array which would allow you to have an array of points should you need.
To get the point later simply use:
CGPoint point = [pointVal CGPointValue];
static CGPoint kInvalidPoint = {.x = NSIntegerMax, .y = NSIntegerMax};
#implementation MyClass
- init()
{
self = [super init];
if (self) {
_oldPoint = kInvalidPoint;
}
return self;
}
- (void)foo
{
if (CGPointEqualToPoint(self.oldPoint, kInvalidPoint)) {
// Invalid point.
return;
}
}
#end
Create two CGPoint properties, that way they are both "uninitialized". Set one of them and use the second one to check whether or not they are equal.
#interface ClassName ()
#property (nonatomic) CGPoint point1;
#property (nonatomic) CGPoint point2;
#end
#implementation ClassName
self.point1 = CGPointMake(69.0f, 180.0f); //arbitrary numbers
//if not equal, then if statement proceeds
if (!CGPointEqualToPoint(self.point1, self.point2) {
//your code here
}
#end
Idk if you'd consider this way hackish though. And I know your question was already answered, but I had kinda the same dilemma till I thought of this.
Hello stackoverflow fellow members?
Struct Declaration in class A
struct PointSprite
{
GLfloat x;
GLfloat y;
GLfloat size;
Color4f color;
} ParticleSystems[MAXIMUM_PARTICLES_ON_SCREEN];
// I generally put some stuffs in ParticleSystem array.
// for ex) struct PointSprite *ps = &ParticleSystems[index];
// and it works well on the class A, but I want to get class B to access this array.
My question is, how am I suppose be return the array of 'ParticlelSystems' array so that other class can access to it? I have tried below code to return the pointer, but compiler gives me a warning.
- (struct ParticleSystems *) commitParticles
{
struct ParticleSystems *ptr = &ParticleSystems; // it said, assigning incompatible pointer type
return ptr;
}
Or should I need to allocate the 'ParticleSystems' array? Please help ! Thanks
If you are creating the array inside the function then you should dynamically allocate it using new and then return a pointer to it.
You cannot return arrays from a function, you will have to return a pointer to it.
Sample Code:
ParticleSystems* doSomethingInteresting()
{
ParticleSystems *ptr = new ParticleSystems[MAXIMUM_PARTICLES_ON_SCREEN];
//do the processing
return ptr;
}
The caller takes the ownership of the returned dynamically allocated array and needs to deallocate it to avoid memory leaks:
delete []ptr;
You can either return it, after allocating one, or you can fill one passed to you by the user. The latter leaves the responsibility to the user to provide a ParticleSystem to the method which receives the data. It can be a local array, or a malloced one.
- (void) commitParticles: (ParticleSystems *) sprites
{
// set members of the structs here
}
I prefer this kind of passing to returning a malloced array. Your mileage may vary.
You're getting the assigning incompatible pointer type compiler warning because your ptr declaration should be of type PointSprite *, not ParticleSystems *
I have got a Matrix-Class from which a Vector-Class is derived from and for extra functionality and better usage I've got a Vector3-Class which is derived from the Vector class. My problem is now that the Vector-class implements a function for instance +normalizeVector: which returns a new allocated Vector-instance. The subclass Vector3 should inherit these two functions but an inheritance leads to the function-prototypes that return a Vector-instance and not a Vector3-instance. This is just how inheritance works but is there a good practice how to solve that problem? A naive solution is to create Vector3 als a new class which subclasses NSObject but I want that Vector- and Vector3-instances can interact easily.
Here an code-example:
#interface Vector : NSObject {
....
}
+(Vector*) normalizeVector:(Vector*)v; //returns a new allocated Vector-instance
-(Vector*) normalize; //normalizes itself and returns itself
-(Vector*) otherFunction;
#end
#interface Vector3 : Vector {
}
-(Vector3*) specialFunction;
#end
usage of that code:
Vector3 *v3 = ...;
[[v3 normalize] specialFunction]; //Compiler gives me a warning because Vector has no specialFunction. Cast would help
[[Vector3 normalizeVector:v3] specialFunction]; //Compiler gives me a warning and during runtime it will crash because a `Vector` doesn't implement specialFunction
a cast to Vector3 would help but is not nice to work with and that also fails with the static function +normalizeVector: because in that static function a Vector-instance is allocated and a pointer-cast doesn't help.
any ideas? or other approaches / other modeling ?
edit: Code for my static function normalizeVector which gets inherited by Vector3:
#implementation Vector
...
+(Vector*) normalizeVector:(Vector *)v
{
unsigned int dim = vector_max(v.cols, v.rows);
Vector *res = [[[Vector alloc]initAsColumnVectorWithDim:dim] autorelease];
[Vector normalizeVector:v destination:res]; // this does only the logic: calc length and divide each component by the len and store at the vector passed to destination
return res;
}
#end
You will notice that -init methods always return type id -(id)init {..} exactly becauase of this.
Also, instead of [Vector alloc] - as you have noticed you don't actually know what Class you are in at runtime (it could be a subclass), so instead just use [self alloc] where self is the current Class because you are in a Class method. So, if you do [Vector3 normalizeVector:v] self is Vector3 and if you do [Vector normalizeVector:v] self is Vector.
Try adjusting your +normailzeVector: method to
+ (id)normalizeVector:(Vector *)v {
unsigned int dim = vector_max(v.cols, v.rows);
id res = [[[self alloc] initAsColumnVectorWithDim:dim] autorelease];
[self normalizeVector:v destination:res];
return res;
}
Just a note, + (id)normalizeVector: is not a function and definitely not a static function. It is a class method, it just helps to get the terms right.
In this case I would make normaliseVector an instance method. So instead of
Vector *newV = [Vector normalizeVector:v];
call
Vector *newV = [v normalizeVector];
Then you can produce a different normalizeVector for Vector and Vector3
EDIT:
For [[v3 normalize] specialFunction]; there is a problem in that normalize can sometimes return an object that specialFunction does not work on - ie it only works if v3 is a Vector3. So in this case there is extra information you have so a cast would be needed or that Vector3 normailze differs from Vector's. In this case I would produce a cover method on Vector3 to call normalize] specialFunction] so that the cast is in Vector3 specific code.
I've got object_getInstanceVariable to work as here however it seems to only work for floats, bools and ints not doubles. I do suspect I'm doing something wrong but I've been going in circles with this.
float myFloatValue;
float someFloat = 2.123f;
object_getInstanceVariable(self, "someFloat", (void*)&myFloatValue);
works, and myFloatValue = 2.123
but when I try
double myDoubleValue;
double someDouble = 2.123f;
object_getInstanceVariable(self, "someDouble", (void*)&myDoubleValue);
I get myDoubleValue = 0. If I try to set myDoubleValue before the function eg. double myDoubleValue = 1.2f, the value is unchanged when I read it after the object_getInstanceVariable call. Setting myIntValue to some other value before the getinstancevar function above returns 2 as it should, ie. it has been changed.
then I tried
Ivar tmpIvar = object_getInstanceVariable(self, "someDouble", (void*)&myDoubleValue);
If I do ivar_getName(tmpIvar) I get "someDouble", but myDoubuleValue = 0 still! Then I try ivar_getTypeEncoding(tmpIvar) and I get "d" as it should be.
So to summarize, if typeEncoding = float, it works, if it is a double, the result is not set but it correctly reads the variable and the return value (Ivar) is also correct.
I must be doing something basic wrong that I cant see so I'd appreciate if someone could point it out.
object_getInstanceVariable is a confused little function. It is documented that the last parameter is a void ** parameter—that is, you pass the address of a void * variable and get a pointer to the instance variable—but it is implemented as if it was a void * parameter—that is, you pass the address of the variable that you want to hold a copy of the instance variable. The problem is that the implementation ignores the size of the instance variable and just does a pointer copy. So anything that's the same size as a pointer will work perfectly. If you're running on a 32-bit architecture, only the high 32 bits will be copied. (You should witness the same behavior with a long long instance variable as well.)
The solution is to use the primary API, key-value coding, using -valueForKey:.
The other solution: If you wanted to write a fixed version, say as a category for NSObject, it would look something like this:
#implementation NSObject (InstanceVariableForKey)
- (void *)instanceVariableForKey:(NSString *)aKey {
if (aKey) {
Ivar ivar = object_getInstanceVariable(self, [aKey UTF8String], NULL);
if (ivar) {
return (void *)((char *)self + ivar_getOffset(ivar));
}
}
return NULL;
}
#end
Then your code would look like this:
double myDoubleValue = *(double *)[self instanceVariableForKey:#"someDouble"];
What about using valueForKey:?
NSNumber * value = [self valueForKey:[NSString stringWithUTF8String:ivar_getName(tmpIvar)]];
NSLog(#"Double value: %f", [value doubleValue];
Note: this requires you to have a "someFloat" method. If you want to use setValue:forKey:, you'll also need the "setSomeFloat:" method. This is easily implemented by declaring the ivar as an #property and synthesizing it.