App does not work on real device - iphone

Question

Here is the situation.
Device: ipod Touch 3rd generation. iOS 4.1
OS X: Lion
This is a very simple App, a ViewController, there is a UIImageView and a UIButton on it. When clicking the button, it would do some computing, generate a image and load it to the UIImageView. Generally speaking, when you click the button, it would do some image processing working in the click event.
This App works well on the simulator. It would display a picture on the UIImageView correctly when you click the button. It costs about 1~2 seconds, not so long.
I connect my ipod touch to my MBP, and load it from Xcode. I set some break points in one for loop in my code (in click event). There is some strange things.
This for loop is the main loop which do the most of the computing. It would stop at the break point at first, the i is 0 i=0; When I continue the app, the app seems stop, you need wait for a while, then the i becomes 4 or 8 or 9, not the correct number which is 1.
I suspect, if I put the computing work in another thread, not in the UI thread. Does it help? Actually, there is nothing strange code in the click event, however, I can't get the correct images, only a black one. Does anyone meet it before, or please provide your suggestion.
UPDATE
Here is what the button click event doing.
int width=320;
int height=480;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
void *imageData = malloc( height * width * 4 );
CGContextRef contextRef = CGBitmapContextCreate( imageData, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big );
//CGColorSpaceRelease( colorSpace );
CGContextClearRect( contextRef, CGRectMake( 0, 0, width, height ) );
CGContextTranslateCTM( contextRef, 0, height - height );
for(int i=0;i<height;i++)
{
for (int j=0; j<width; j++) {
*((char *)(imageData+i*width*4+j*4))=0;
*((char *)(imageData+i*width*4+j*4+1))=0;
*((char *)(imageData+i*width*4+j*4+2))=0;
*((char *)(imageData+i*width*4+j*4+3))=255;
}
}
int xmin=-2;
int xmax=2;
int ymin=-2;
int ymax=2;
int fre[320 * 480]={0};
CGPoint p=CGPointZero;
float x=arc4random()*1.0/ARC4RANDOM_MAX;
float y=arc4random()*1.0/ARC4RANDOM_MAX;
p.x=x*(xmax-xmin)+xmin;
p.y=y*(ymax-ymin)+ymin;
int MIN_ITERATE=10;
int ite_from_start=0;
DataPoint point;
point.p=p;
point.red=0.0;
point.green=0.0;
point.blue=0.0;
IFSFunctions *ifsfunction=[[IFSFunctions alloc] init];
for (int i=0; i<1000000; i++) {
if(p.x<=160 && p.x >=-160 && p.y <= 240 && p.y >= -240)
{
//fre[((int)p.y+240)*320+(int)p.x+160]++;
point=[ifsfunction caculate:point];
int data_x=(int)(320*(point.p.x-xmin)/(xmax-xmin));
int data_y=(int)(480*(point.p.y-ymin)/(ymax-ymin));
if(data_x >=0 && data_x<320 && data_y >=0 && data_y < 480 && ite_from_start < 20000)
{
ite_from_start++;
if(ite_from_start > MIN_ITERATE)
{
*((char *)(imageData+data_y*width*4+data_x*4))=(int)point.red;
*((char *)(imageData+data_y*width*4+data_x*4+1))=(int)point.green;
*((char *)(imageData+data_y*width*4+data_x*4+2))=(int)point.blue;;
}
fre[data_y*width+data_x]++;
}
else
{
ite_from_start=0;
point=[ifsfunction caculate:point];
}
}
}
int max_int=0;
for (int i=0; i<320*480; i++) {
if (fre[i]>max_int) {
max_int=fre[i];
}
}
//NSLog([NSString stringWithFormat:#"The max interation %f",logf(max_int+1)]);
for (int i=0; i<height; i++) {
for(int j=0;j<width;j++){
float intensity=logf(fre[i*width+j]+1.0)/logf(max_int/300+1);
//NSLog([NSString stringWithFormat:#"The %f",intensity]);
float gamma=powf(intensity, 0.25);
*((char *)(imageData+i*width*4+j*4))=(int)(gamma*(*((char *)(imageData+i*width*4+j*4))));
*((char *)(imageData+i*width*4+j*4+1))=(int)(gamma*(*((char *)(imageData+i*width*4+j*4+1))));
*((char *)(imageData+i*width*4+j*4+2))=(int)(gamma*(*((char *)(imageData+i*width*4+j*4+2))));
}
}
CGDataProviderRef dataProvider=CGDataProviderCreateWithData(NULL, imageData, height * width * 4, NULL);
CGImageRef imageRef=CGImageCreate(width, height, 8, 32, 4*width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big, dataProvider, NULL, NO, kCGRenderingIntentDefault);
CGColorSpaceRelease(colorSpace);
CGDataProviderRelease(dataProvider);
CGContextDrawImage(contextRef, CGRectMake( 0, 0, width, height ), imageRef);
imgView.image=[UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
CGContextRelease(contextRef);
free(imageData);
Best Regards,

Answer 1

If it takes 1~2 seconds on the simulator, it will take a lot more on a device. In fact, the simulator is just the iOS APIs on the Mac. I'd create an NSOperation and execute it on a separated thread. And make sure your for loop looks like this:
for(int i = 0; i < YOURNUMBERHERE; i++)