Objective-c UIImage 存储在 MSMutableArray 替代方案中，潜在的内存泄漏？

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.