multiple identical pointers, can't figure out why - objective-c

I'm new to Objective-C, I feel like I'm probably just making a dumb mistake, but I have tried googling this with no luck (maybe I'm just not searching the right things)
Essentially, I tried to write my own object class, and then make several instances of it, but the data seems locked together; Changing the data for any one reference changes it for all of them.
here's where I make the objects and use them.
#implementation Drawing
//leaving many functions out as they are not part of the problem
Ball * balls[10];
int numPoints;
//this gets called first
- (id) initWithCoder: (NSCoder *)aDecoder
{
//leaving out loading of images.....
numPoints=10;
for(int i=0; i<10; i++){
balls[i]=[[Ball alloc] init];
printf("bmem: %p\n",%balls[i]);
float tpx=arc4random()%1024;
float tpy=arc4random()%768;
printf("randX: %f\n",tpx);
printf("randY: %f\n",tpy);
CGPoint tempPt = CGPointMake(tpx,tpy);
printf("mem: %p\n",%tempPt);
[balls[i] setLocation:tempPt];
}
//code to start a timer on the drawRect function....
}
//called regularly, every 30 seconds
- (void) drawRect:(CGRect)rect
{
CGContextRef c=UIGraphicsGetCurrentContext();
CGContextClearRect(c, rect);
for(int i=0; i<numPoints; i++)
{
int ptX=[balls[i] getX];
int ptY=[balls[i] getY];
printf("index: %d\n",i);
printf("x: %d\n",ptX);
printf("y: %d\n",ptY);
CGContextDrawImage(c, CGRectMake((int)ptX-WIDTH/2, (int)ptY-WIDTH/2, WIDTH, HEIGHT), image);
}
}
This program outputs a series of numbers which I thought would be useful.
- "bmem", or the point in memory where the ball is, increments by regular intervals, as expected.
- "randX" and "randY" are completely random, as they should be.
- "mem", or the point in memory with the CGPoint, doesn't change
and this is the ball object:
#implementation Ball
int x;
int y;
-(void)setLocation:(CGPoint)loc{
x=loc.x;
y=loc.y;
}
-(int)getX{
return x;
}
-(int)getY{
return y;
}
#end
At first I just though I had static attributes in the Ball class, but on googling I found out that objective-c does not have static attributes. I've blindly tried about a dozen different things with no success. I really just need this to work.

You are using the global variables:
Ball * balls[10];
int numPoints;
When you probably want instance variables:
#interface Balls : NSObject
{
Ball * balls[10];
int numPoints;
}
...
#end

Related

Objective-C source code debug: Thread Error

I cannot seem to solve this problem, im not sure what it is at this point but the tread error wont go away. I cant seem to find what im doing wrong.
This code may be a handful to read (sorry) but its very simple. I'am basically invoking a function from main and passing an array of function values, from there im passing two fractions at a time to a method so it find the LCM(least common multiple) using the denominators and return the value. But a thread error seems to be occurring at the call to the findLCM method from function at the point of where the method is declared.
#interface Fraction: NSObject
#property int numerator, denominator;
-(Fraction *)findLCM:(Fraction *)fraction withXFractions:(int)Xfraction;
#implementation Fraction
-(Fraction *)findLCM:(Fraction *)fraction withXFractions:(int)Xfraction{
int lcmOfFraction = 0;
int a, b;
a = fraction.denominator;
b = self.denominator;
int max =(a>b) ? a : b; // get max value out of the two denominators.
for (int i = 0; i < Xfraction; i++) {
while(1) /* Always true. */
{
if(max%a==0 && max%b==0)
{ lcmOfFraction = max;
break; /* while loop terminates. */
}
++max;
}
}
Fraction *lcmDenominator = [Fraction new];
[lcmDenominator setTo:0 over:max]; //passing just LCM (denominator of 2 fractions)
return lcmDenominator;
}
Fraction *addFraction(Fraction **arrayOfFractions, int arraySize) {
Fraction *LCM = [[Fraction alloc] init];
int lcmOfFractions = 0;
[LCM setTo:0 over:1];
for (int i = 0; i <= arraySize; i++) {
LCM = [LCM findLCM:arrayOfFractions[i] withXFractions:4];
//^gets the LCM (the common denominator)
}
return LCM;
}
int main () {
#autoreleasepool {
[frac1 setTo:2 over:12]; [frac2 setTo:2 over:4];
[frac3 setTo:6 over:8]; [frac4 setTo:8 over:3];
Fraction __autoreleasing *arrayOfFractions[4] = {frac1, frac2, frac3, frac4 };
Fraction *LCMFraction = addFraction(arrayOfFractions, 4);
//common LCM return
}
}
You create no threads in this code. When asking a question like this you should clearly explain what the error is, and what you have tried to find its source. People may then be able to help you.
Some hints/suggestions:
use breakpoints to stop your code during execution to allow you to examine the values of your variables
pay close attention to indexing operations, you are using a C array and those do not do bounds checking
ask whether using a C array here, rather than an NSArray is your best choice. Note there is nothing wrong with using C arrays when appropriate.
__autoreleasing probably doesn't mean what you think it does, it is rare to see this used explicitly in user code.
If you have a specific question when you've got further ask a new question on SO, somebody will probably be able to help you out.
HTH

Store an array of NSObject Pointers in C array

I'd like to create an NSObject subclass that contains a few member vars:
#interface PointMass : NSObject
{
CGPoint mCurPosition;
CGPoint mLastPosition;
CGPoint mAcceleration;
}
-(id) initWithPosition:(CGPoint*) pos;
#import "PointMass.h"
#implementation PointMass
-(id) initWithPosition:(CGPoint*)pos
{
mCurPosition = *pos;
mLastPosition = *pos;
mAcceleration = ccp(0,0);
return self;
}
#end
And I would like to create a C-style array to hold a bunch of them within a cocos2d class:
// mNumPoint declared in interface, I've set it to 100
PointMass *pointMassList;
pointMassList = malloc(sizeof(PointMass*) * mNumPointMass);
for (int = 0; i < mNumPointMass; i++)
{
CGPoint point = ccp(100,100);
PointMass *p = [[PointMass alloc] initWithPosition: &point];
pointMassList[i] = p;
}
But I get an error
Expected method to write array element not found on object of type 'PointMass *'
Do I need to tell the compiler more about my PointMass Object if I want to store pointers to it in a C array?
I'm basically trying to have a play around with some particle math on iPhone without needing to unpack points from an NSArray constantly if it isn't clear what I'm trying to achieve here.
If I've gone about this in a backwards way I'd love to be corrected - it has been a while since I wrote vanilla C and I'm a little rusty!
it has been a while since I wrote vanilla C
You should still be able to make the distinction between a pointer-to-T and a pointer-to-pointer-to-T (T being PointMass in this case). You want to store an array of PointMass *, and not an array of PointMass (which you couldn't do anyway). So change the declaration of pointMassList to
PointMass **pointMassList;
and it will work. However, if you're using Objective-C anyway, why don't you simply store the instances into an NSArray?

Objective-c: Adding a custom object to a NSMutableArray

I usually program in java or c++ and I recently started with objective-c. Looking for vectors in objective-c, I found NSMutableArray which seems to be the best option. I'm working on an opengl game and I'm trying to create an NSMutableArray of textured quads for my sprites. Here is the relevant code:
I define textured quads:
typedef struct {
CGPoint geometryVertex;
CGPoint textureVertex;
} TexturedVertex;
typedef struct {
TexturedVertex bl;
TexturedVertex br;
TexturedVertex tl;
TexturedVertex tr;
} TexturedQuad;
I create an array in the interface:
#interface Sprite() {
NSMutableArray *quads;
}
I initiate the array and I create the texturedQuads based on "width" and "height", which are the dimensions of a single sprite, and "self.textureInfo.width" and "self.textureInfo.height", which are the dimensions of the entire sprite sheet:
quads = [NSMutableArray arrayWithCapacity:1];
for(int x = 0; x < self.textureInfo.width/width; x++) {
for(int y = 0; y < self.textureInfo.height/height; y++) {
TexturedQuad q;
q.bl.geometryVertex = CGPointMake(0, 0);
q.br.geometryVertex = CGPointMake(width, 0);
q.tl.geometryVertex = CGPointMake(0, height);
q.tr.geometryVertex = CGPointMake(width, height);
int x0 = (x*width)/self.textureInfo.width;
int x1 = (x*width + width)/self.textureInfo.width;
int y0 = (y*height)/self.textureInfo.height;
int y1 = (y*height + height)/self.textureInfo.height;
q.bl.textureVertex = CGPointMake(x0, y0);
q.br.textureVertex = CGPointMake(x1, y0);
q.tl.textureVertex = CGPointMake(x0, y1);
q.tr.textureVertex = CGPointMake(x1, y1);
//add q to quads
}
}
The problem is I don't know how to add the quad "q" to the array "quads". Simple writing [quads addObject:q] doesn't work because the parameter should be an id not a TexturedQuad. I've seen examples of how to make an id from an int etc, but I don't know how to do it with an object like my TexturedQuad.
The essence of it is that you wrap your C struct in an Obj-C class. The Obj-C class to use is NSValue.
// assume ImaginaryNumber defined:
typedef struct {
float real;
float imaginary;
} ImaginaryNumber;
ImaginaryNumber miNumber;
miNumber.real = 1.1;
miNumber.imaginary = 1.41;
// encode using the type name
NSValue *miValue = [NSValue value: &miNumber withObjCType:#encode(ImaginaryNumber)];
ImaginaryNumber miNumber2;
[miValue getValue:&miNumber2];
See here for more information.
As #Bersaelor pointed out, if you need better performance use pure C or switch to Obj-C++ and use vectors instead of Obj-C objects.
An NSMutableArray takes any NSObject* but not just structs.
If you're serious about programming in Objective-C, take a look at some tutorials.
Furthermore, NSMutableArrays are meant for convenience, if your adding/deleting a lot of objects to that Array, use plain C-stacks.
Especially for your use-case that more low-level approach will get better performance.
Keep in mind, Objective-C(++) is just a superset of C(++), so you can use any C(++) code you are already familiar with.
When I wrote my game tactica for iOS, I switched to C-Code whenever I had to do heavy lifting (i.e. recursive AI-functions that get called hundreds of times per second).

Create an global array containing floating numbers

I wanted to create 2 global arrays which can be updated during the run of the programme.In each update i add one element to zeroth position and deleted the last number
I created the arrays as....
In the .h file..........
//////////////
#interface Shared : NSObject{
NSMutableArray *x;
NSMutableArray *y;
}
#property (nonatomic,retain) NSMutableArray *x;
#property (nonatomic,retain) NSMutableArray *y;
+(Shared*)sharedInstance;
#end
In .m file
staticShared* sharedInstance;
#implementation Shared
#synthesize x;
#synthesize y;
+(Shared*)sharedInstance
{
if (!sharedInstance) {
sharedInstance=[[Sharedalloc]init];
}
returnsharedInstance;
}
-(Shared*)init
{
self = [superinit];
if(self)
{
x=[[NSMutableArrayalloc] init];
x=[NSMutableArrayarrayWithObjects:#"0",#"0",#"0",#"0",#"0",#"0",#"0",nil];
y=[[NSMutableArrayalloc] init];
y=[NSMutableArrayarrayWithObjects:#"0",#"0",#"0",#"0",#"0",#"0",nil];
}
returnself;
}
#end
Then i used to call them and re,ove and added elements using the following code....
[[shared sharedInstance].y removeLastObject];
[[shared sharedInstance].y insertObject:new_element atIndex:0];
[[shared sharedInstance].x removeLastObject];
[[shared sharedInstance].x insertObject:new_element atIndex:0];
In the mean time i call these values and calculate an arithmetic value using an expression.
This seems to work well. But it seems to be an inefficient way to handle floating point numbers which i store in it. As these arrays creates objects. Is there any easy method that i can create a global array containing specified amount of floating point numbers and update it during the run of the programm(array size is fixed) by deleting the last object, and call them back to do calculation?
Please help me!
EDIT 1
To sir deanWombourne
.................................
I implement as you instructed! Can you please go through this and help me to correct 2 errors i get.
IN the .h file
#interface Shared : NSObject{
#private
float input[7];
float output[6];
}
+(Shared*)sharedInstance;
-(void)addNewInput:(float)input1;
-(float *)input;
-(void)addNewOutput:(float)output1;
-(float *)output;
#end
in .m file............
#implementation Shared
-(id)init{
if((self =[superinit])){
for(int n=0; n<7 ;++n)
input[n]=0.00f;
for(int n=0; n<6 ;++n)
output[n]=0.00f;
}
returnself;
}
-(void)addNewInput:(float)input1{
input[0]=input[1];
input[1]=input[2];
input[2]=input[3];
input[3]=input[4];
input[4]=input[5];
input[5]=input[6];
input[6]=input1;
}
-(float *)input {
returninput;
}
-(void)addNewOutput:(float)output1{
output[0]=output[1];
output[1]=output[2];
output[2]=output[3];
output[3]=output[4];
output[4]=output[5];
input[5]=output1;
}
-(float *)output {
returnoutput;
}
#end
When calling it
float reading= (accel_reading)/(1.165969038*1e5f);
[[SharedsharedInstance] addNewInput:reading];
Problems i get
1. In the implementation, it says incomplete implementation (it's a warning not an error)
2. How can i used a for loop to fill array values or is this way ok?
Major problem i get,
When i call it as shown above, program stops running telling
Terminating application due to uncaught exception 'NSInvalidArgumentException', reason '+[SharedsharedInstance]: unrecognized selector sent to class 0x5780'
Please help me through this...............
Your code Smells (and I mean that in the nicest possible way!)
Using two parallel arrays and keeping in sync is a bad design pattern (and a performance hit in quite a few ways!). Especially as there is already a struct that handles storing an x and y at the same time - CGPoint).
You're solving the 'only objects go in arrays' problem by converting your float' primitives toNSString` objects, which is horrendously inefficient - take a look instead at the NSValue class, it's designed to put native C primitives into an object without expensive parsing operations :)
You might also want to look into malloc (and free etc) and deal with the whole problem at the C level - this will mean no objects at all and would be blindingly fast (at the cost of more complicated code).
Hope this helps, if you have any questions just add a comment to this answer :)
EDIT
If all you want to do is store 4 x and y values, then this is probably the easiest way to do it :
#interface Shared : NSObject {
#private
CGPoint points[4];
}
+(Shared *)sharedInstance;
- (void)addNewPoint:(CGPoint)point;
- (CGPoint *)points;
#end
#implementation
- (id)init {
if ((self = [super init])) {
// Start with 0,0 for all your points
for (int n = 0; n < 4; ++n)
points[n] = CGPointZero;
}
return self;
}
- (void)addNewPoint:(CGPoint)point {
// Just move all the points along one and add the new one to the end
// (yes, this could be done in a loop but there's not that much point for 4 points!)
points[0] = points[1];
points[1] = points[2];
points[2] = points[3];
points[3] = point;
}
- (CGPoint *)points {
return points;
}
#end
This gives you a method addNewPoint that removes the first point and adds the new point to the end of your array.
You also get the method points that returns the 4 points. Use it something like :
// To add a point
CGPoint newPoint = CGPointMake(100, 100);
[[Shared sharedInstance] addNewPoint:newPoint];
// To do something with the points (in this case, NSLog them)
CGPoint *points = [[Shared sharedInstance] points];
for (int n = 0; n < 4; ++n)
NSLog(#" Point %i : %#", n, NSStringFromCGPoint(points[n]));
EDIT #2
From your comments, you need two arrays, one with input data and one with output data. Try something like this :
#interface Shared : NSObject {
float inputs[4];
float outputs[5];
}
...
This will give you two arrays to read/write to - one called inputs and the other called outputs. Access them in pretty much the same way you did the ones in my first edit :
float *inputs = [[Shared sharedInstance] inputs];
for (int n = 0; n < 4; ++n)
NSLog(#" Input %i : %f", n, inputs[n]);
float *outputs = [[Shared sharedInstance] outputs];
for (int n = 0; n < 5; ++n)
NSLog(#" Output %i : %f", n, output[n]);
Would a linked list be overkill for what you're trying to achieve? It's not quite as simple as a static array of floats, but makes the removal of the last object and insertion of the zeroth object reasonably simple and fast.
If you want an array containing a specific number of Objects, you can use NSArray, which is static, opposed to NSMutableArray.
As for the array being Global, just implement a singleton class that contains the 2 arrays and provides the associated methods.
in Globals.h:
#interface Globals : NSObject
+ (Globals *) sharedGlobals;
#end
in Globals.m:
#implementation Globals
static Globals *sharedGlobals = nil;
+ (Globals *) sharedGlobals{
#synchronized(self){
if (sharedGlobals == nil){
sharedGlobals = [[self alloc] init];
}
}
return sharedGlobals;
}
you then can access the arrays (after you implemented them) with the following line:
[[Globals sharedGlobals] getArrayX];
Here is a sketch to get you going.
Your array size is fixed and only contains floating point numbers, start with a C array:
double x[] = {0, 0, 0, 0, 0, 0, 0};
double y[] = {0, 0, 0, 0, 0, 0};
The number of elements in these arrays can be calculated rather than hard-coded:
int xCount = sizeof(x)/sizeof(double);
int yCount = sizeof(y)/sizeof(double);
Now use these arrays as a circular buffer, declare a cursor and initialise:
int xCursor = 0;
The item at the front of the queue is at the cursor:
valueAtFrontOfQueue = x[xCursor]; // get the current front item
To remove the value at front and add a new one to the rear replace the value at the cursor with the new value and increment the cursor:
x[xCursor] = newValueForBackOfQueue; // replace it with new item for back of queue
xCursor = (xCursor + 1) % xCount; // and advance cursor using mod arithmetic to it cycles around
No wrapping doubles as objects, no dynamic allocation at all.
Wrap the above up as you see fit, maybe as a class, and you're done.

Method in Objective-C that points to an object

I have created a few sprites using a spriteclass and I have loaded them into an array. In my app, I loop over the array checking for particular conditions (position, etc.). I want to create an explosion method that I can pass one of these objects to and then using the pointer pull the position of the object on the screen and show an explosion there. I don't know how to pass the pointer/object that is in my array to the method to be used.
Here is essentially what I had in mind:
for (int i=1; i<4; i++) {
EnemySprite *currentenemy = [enemies objectAtIndex:i-1];
//Blow this guy up
[self explosion:currentenemy]
}
-(void)explosion someobject {
explosion.position = someobject.position
someobject.setHidden=YES;
}
You would write it like this for one param
// definition
-(void) explosion:(EnemySprite*) someObject
{
}
// usage
[self explosion: object];
For two params things are a bit more involved. Consider;
// definition
-(void) explosion:(EnemySprite*) someObject radius:(float)explosionRadius
{
...
if (pos < explosionRadius)
...
}
// usage
[self explosion: object radius:10.0f];
Everything before the : is used for the external name, everything after is the name internal to the function.
This is why you will often see Objective-C functions written with function names that end with the name of the first type:
-(void) explodeSprite:(EnemySprite*) sprite radius:(float)radius;
Both the sprite and radius params then appear to be "named" when the function is written;
[self explodeSprite:sprite radius:10.0f];
Why not make your object the receiver of the explosion?
for (id currentenemy in enemies)
{
[currentenemy explode];
}