Objective-c UIImage storage in MSMutableArray alternative, potential memory-leaks? - iphone

Question

I am building an app for iOS 5 using ARC and I seem to be having some memory issues. Basically its taking screen-shots of a portion of the display, placing the UIImage in an MSMutableArray and then piecing the screen-shots together for one big image. Now the problem is that after doing this a couple of times the OS closes the application due to high memory usage.
Here is the snippet that pieces the UIImage's together:
UIImage* finalImage = nil;
//join the screenshot images together
UIGraphicsBeginImageContext(CGSizeMake(collage.width, collage.height));
{
int hc = 0;
for(UIImage *img in imageArr)
{
NSLog(#"drawing image at:: %i", hc);
[img drawAtPoint:CGPointMake(0, hc)];
hc+=img.size.height;
img = nil;
}
//NSLog(#"creating finalImage");
finalImage = UIGraphicsGetImageFromCurrentImageContext();
}
UIGraphicsEndImageContext();
//do something with the combined image
//remove all the objects
[imageArr removeAllObjects];
//reset class instance
[self setImageArr: [[NSMutableArray alloc] init]];
Are they any other alternatives that I could use so there isn't so much memory being used? Maybe storing a CGImageRef in the array? Are there any potential memory leaks with the above code?
Any tips, pointers would be greatly appreciated.
Thanks.

Answer 1

[imageArr removeAllObjects]; will remove the objects from array. No need to reset the array again with
[self setImageArr: [[NSMutableArray alloc] init]];
By doing this you are allocating a NSMutableArray object and not releasing it.
Try by removing the line [self setImageArr: [[NSMutableArray alloc] init]];

Answer 2

make sure you alloc and init setImageArr
if (setImageArr == nil){
setImageArr = [[NSMutableArray alloc]init];
}
else
{
[setImageArr removeAllObjects];
}
or use (if you want to init from an existing Array):
NSMutableArray *setImageArr = [[NSMtableArray]initWithArray:arrayOfImages];

Answer 3

Because you say it will have memory issue after doing this a couple of times. Then how about you use NSAutoreleasePool to force system release objects after your method, example below:
#autoreleasepool {
UIImage* finalImage = nil;
//join the screenshot images together
UIGraphicsBeginImageContext(CGSizeMake(collage.width, collage.height));
{
int hc = 0;
for(UIImage *img in imageArr)
{
NSLog(#"drawing image at:: %i", hc);
[img drawAtPoint:CGPointMake(0, hc)];
hc+=img.size.height;
img = nil;
}
finalImage = UIGraphicsGetImageFromCurrentImageContext();
}
UIGraphicsEndImageContext();
//do something with the combined image
//remove all the objects
[imageArr removeAllObjects];
//reset class instance
[self setImageArr: [[NSMutableArray alloc] init]];
}
And I also doubt there is any memory leak problem in your other codes.
Using ARC doesn't meaning without memory leak problem, maybe you store many useless objects in a global variable etc.
Maybe you should use Instruments to monitor the memory to figure out where does the memory go.

Answer 4

Turns out the imageArr is being cleared properly. There appears to be a memory issue somewhere else in the program.