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POIn trouble with NSMutableArray retention
 

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    <p>I've had this problem for a couple of days now, I've googled a lot but found out nothing useful so I thought to ask here. I've got a retention problem with an NSMutableArray, however I can't understand where the trouble is and how to fix it. I am drawing a a line chart using Quartz 2D, and in order to do so I have subclassed UIView with GraphView. The header looks like this:</p> <pre><code>@interface GraphView : UIView { NSMutableArray *data; } - (void)drawBar:(CGRect)rect context:(CGContextRef)ctx; - (void)drawLineGraphWithContext:(CGContextRef)ctx; - (void)addValue:(float)value; @property(nonatomic, retain) NSMutableArray *data; @end </code></pre> <p>I use the "data" array to store data points to draw, within the drawLineGraphWithContext: method. The addValue: method, on the other hand, is used in the main controller to fill in the data array. In the viewDidLoad of the controller I do, to fill in the data array:</p> <pre><code>graphView = [[GraphView alloc] init]; float data[] = {0.7, 0.4, 0.9, 1.0, 0.2, 0.85, 0.11, 0.75, 0.53, 0.44, 0.88, 0.77, 0.99, 0.55}; for(int i = 0; i &lt; 14; i++) { [graphView addValue:data[i]]; } </code></pre> <p>Everything is good at this point, and in debug I can see the array is populated with all elements. The problem is when the drawLineGraphWithContext: method is invoked; for some reason, the array suddenly gets empty and its retain count is 0. I have tried changing the way I access the object, using dot notation or omitting the self, however the behaviour looks the same. Strangely enough, I have tried identifying zombies (with both GDB and Instruments), however none seems to be found. As a matter of fact, then the main loop within the drawLineGraphWithContext: below is started the data array has zero elements, and nothing is drawn. Below complete files (I am omitting irrelevant parts).</p> <p>I am using Xcode 4.2 with Automatic Reference Counting.</p> <p>Thanks in advance to anyone helping!</p> <p>GraphView.h:</p> <pre><code>@interface GraphView : UIView { NSMutableArray *data; } - (void)drawBar:(CGRect)rect context:(CGContextRef)ctx; - (void)drawLineGraphWithContext:(CGContextRef)ctx; - (void)addValue:(float)value; @property(nonatomic, retain) NSMutableArray *data; @end </code></pre> <p>GraphView.m:</p> <pre><code>#import "GraphView.h" @implementation GraphView @synthesize data; - (id) init { self = [super init]; if(self) { data = [NSMutableArray array]; NSLog(@"%s", __FUNCTION__); } return self; } - (void)addValue:(float)value { NSMutableArray *tempArr = [self data]; NSNumber *val = [NSNumber numberWithFloat:value]; [tempArr addObject:val]; [self setData:tempArr]; } - (void)drawLineGraphWithContext:(CGContextRef)ctx { CGContextSetLineWidth(ctx, 2.0); CGContextSetStrokeColorWithColor(ctx, [[UIColor colorWithRed:1.0 green:0.5 blue:0 alpha:1] CGColor]); int maxGraphHeight = kGraphHeight - kOffsetY; CGContextBeginPath(ctx); CGContextMoveToPoint(ctx, kOffsetX, kGraphHeight - maxGraphHeight * [[[self data] objectAtIndex:0] floatValue]); int i = 0; NSMutableArray *arr = [self data]; for(NSNumber *elem in arr) { float val = [elem floatValue]; CGContextAddLineToPoint(ctx, kOffsetX + i * kStepX, kGraphHeight - maxGraphHeight * val); i++; } CGContextDrawPath(ctx, kCGPathStroke); } - (void)drawRect:(CGRect)rect { CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetLineWidth(context, 0.6); CGContextSetStrokeColorWithColor(context, [[UIColor lightGrayColor] CGColor]); CGFloat dash[] = {2.0, 2.0}; CGContextSetLineDash(context, 0.0, dash, 2); int lines = (kDefaultGraphWidth - kOffsetX)/kStepX; for(int i = 0; i &lt; lines; i++) { CGContextMoveToPoint(context, kOffsetX + i * kStepX, kGraphTop); CGContextAddLineToPoint(context, kOffsetX + i * kStepX, kGraphBottom); } int horizontalLines = (kDefaultGraphWidth-kOffsetY)/kStepY; for(int i = 0; i &lt; horizontalLines; i++) { CGContextMoveToPoint(context, kOffsetX, kGraphBottom - kOffsetY - i * kStepY); CGContextAddLineToPoint(context, kDefaultGraphWidth, kGraphBottom - kOffsetY -i * kStepY); } CGContextStrokePath(context); CGContextSetLineDash(context, 0, NULL, 0); [self drawLineGraphWithContext:context]; } @end </code></pre> <p>GRViewController.m:</p> <pre><code>#import "GRViewController.h" @implementation GRViewController @synthesize scroller; @synthesize graphView; #pragma mark - View lifecycle - (void)viewDidLoad { [super viewDidLoad]; scroller.contentSize = CGSizeMake(kDefaultGraphWidth, kGraphHeight); graphView = [[GraphView alloc] init]; float data[] = {0.7, 0.4, 0.9, 1.0, 0.2, 0.85, 0.11, 0.75, 0.53, 0.44, 0.88, 0.77, 0.99, 0.55}; for(int i = 0; i &lt; 14; i++) { [graphView addValue:data[i]]; } } </code></pre> <p>@end</p> <p>GRViewController.h:</p> <pre><code>#import &lt;UIKit/UIKit.h&gt; #import "GraphView.h" @interface GRViewController : UIViewController @property (retain, nonatomic) IBOutlet UIScrollView *scroller; @property (retain, nonatomic) IBOutlet GraphView *graphView; @end </code></pre>
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