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iphoneobjective-ccocoainstruments

iPhone memory leak help

I'm new to iPhone development, and I've just run my iPhone app throught the Intruments Leaks tool for the first time, and discovered a leak with my ListViewController dataArray method.

When I click on the listing it shows the code, and a few lines have percentages next to them. Presumably they're the lines that are leaking memory. I've pasted the code and the percentages below:

- (NSArray*) dataArray {
   MapViewController *map = mainWindow.mainView.mapView;
NSMutableArray *data = [NSMutableArray arrayWithCapacity: 0]; /** REPORTS 25.3% HERE **/

if (selectedIndex == 1 || selectedIndex == 0)
 [data addObjectsFromArray: DataSource.data]; /** REPORTS 7.4% HERE **/

if (selectedIndex == 2 || selectedIndex == 0)
 [data addObjectsFromArray: DataSource.additionalData]; /** REPORTS 67.4% HERE **/

   [data sortUsingSelector:@selector(compareAnnotation:)];

   dataArrayNeedsUpdating = NO;
[data retain];
dataArray = data;

   return data;
}

Is there anything I can change in that code to prevent the leak, or will changes need to be made in the calling code?

Thanks in advance,

Ben

Solution

  • If dataArray is storing a value when this method is called, it will leak, because you're not releasing the old value before you overwrite it. The simple solution is to use a setter (probably one generated by @synthesize) and change the lines

    [data retain];
dataArray = data;

    to the simpler (and more conventional)

    [self setDataArray:data];

    or, if you prefer,

    self.dataArray = data;

    The difference between

    myMemberVariable = somePointerToAnObject;

    and 

    self.myMemberVariable = somePointerToAnObject;

    is one of the subtle gotchas for the new Objective-C coder.