Question

In my iOS app I have a view that moves a UIImageView using the accelerometer. When I exit the view back to the main screen, the app crashes. I cannot figure out why. In the viewDidUnload method I have this:

[ball removeFromSuperview];

In the .h file:

@interface PlayShotguniPad : UIViewController  <UIAccelerometerDelegate> {

// Declare IBOutlets for the moving fly
IBOutlet UIImageView *ball;

// Floats for the movement data
float valueX;
float valueY;

}

In the .m, I have this code to move the fly:

-(void)awakeFromNib {
[[UIAccelerometer sharedAccelerometer] setUpdateInterval:1.0/100.0];
[[UIAccelerometer sharedAccelerometer] setDelegate:self];
}

// Get accelerometer movement data, move fly with device tilt
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {
valueX = acceleration.x*60.0;
valueY = acceleration.y*60.0;

int newX = (int)(ball.center.x +valueY);
if (newX > 1000-BALL_RADIUS)
    newX = 1000-BALL_RADIUS;
if (newX < 0+BALL_RADIUS)
    newX = 0+BALL_RADIUS;

int newY = (int)(ball.center.y +valueX);
if (newY > 740-BALL_RADIUS)
    newY = 740-BALL_RADIUS;
if (newY < 0+BALL_RADIUS)
    newY = 0+BALL_RADIUS;

CGPoint newCenter = CGPointMake(newX, newY);

ball.center = newCenter ;

}

viewDidLoad method:

[self awakeFromNib];

IS there anything I have to do, like releasing anything when leaving the view, to prevent the crashing?

Answer 1

You have to set the accelerometer delegate to nil in your dealloc, otherwise a selector of a view controller that no longer exists will be called.

- (void)dealloc {
[[UIAccelerometer sharedAccelerometer] setDelegate:nil];
}