pragmatically scroll UIScrollView upon shake gesture - iphone

Question

HI,
I have a view that has three UIScrollViews on the screen. I want to randomly scroll the UIScrollViews to different positions whenever a user shakes the iPhone, but I am unable to get it done.
I have implemented the following in my ViewController class to detect and handle the shake gesture, the 3 UIScrollViews also belong to the same class. The shake gesture is detected, but the UIScrollViews do not change. What am I doing Wrong??
i have tried both motionBegan and motionEnded.
-(BOOL)canBecomeFirstResponder {
return YES;
}
-(void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
[self becomeFirstResponder];
}
- (void)viewWillDisappear:(BOOL)animated {
[self resignFirstResponder];
[super viewWillDisappear:animated];
}
- (void)motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event
{
if (motion == UIEventSubtypeMotionShake)
{
int randomTag = arc4random() % [dirContents count];
CGRect nextImageView = [[scrollView1 viewWithTag:2] frame];
[scrollView1 scrollRectToVisible:nextImageView animated:YES];
randomTag = arc4random() % [dirContents count];
nextImageView = [[scrollView2 viewWithTag:4] frame];
[scrollView2 scrollRectToVisible:nextImageView animated:YES];
randomTag = arc4random() % [dirContents count];
nextImageView = [[scrollView3 viewWithTag:4] frame];
[scrollView3 scrollRectToVisible:nextImageView animated:YES];
NSLog(#"Shake Detected End");
}
}
Thank You

Answer 1

Have you tried using SetContentOffset instead of scrollRectToVisible yet?
if the images in your tableView are of equal height the offset per "Element" is always the same.
[scrollView3 setContentOffset:yourRandomOffsetInPixels animated:YES];
maybe this works.
also consider, that The Problem might be that your shake-detection Method runs on a separate Thread this would mean that you have to call your motionEnded Method on the mainthread like so:
[self performSelectorOnMainThread:#selector(motionEnded) withObject:nil waitUntilDone:NO];

Answer 2

Did you check your nextImageView variable to see if it was correct ?
Further more if you are trying will have the motion of a slot machine, I would recommend you to use UITableView instead of doing it by yourself with scrollView

Answer 3

Just one quick question. In your example code, you generate a random tag:
randomTag = arc4random() % [dirContents count];
but then you use a specific tag value (4 in this case)? I assume it still doesn't work when you use the randomTag value? and that you were just doing some testing?
nextImageView = [[scrollView2 viewWithTag:4] frame];