Autoscroll UIScrollView when subview is out of the visible area - objective-c

Question

EDIT:
I uploaded my implementation to github. Maybe it is better to understand what I want and what my problem is.
I changed the code in the github project a little bit than the posted code here. I think the implementation in the github project is better, but not perfect.
What I want to do:
Have a UIScrollView with movable UIViews (e.g. Images). The user can pan this subviews and zoom in and out. When the user zooms in and moves a subview over the current visible area the scrollView should automatically scroll. As lang as the subview is over the edge the scrollview should scroll. When the subview isn't over the visible area anymore the scrollview should stop moving.
I try to explain my problem as good as possible.
What I have managed to do:
Zoom the scrollview, move the subviews with the UIPanGestureRecognizer, recognize when the subview is over the visible area and start moving (changing the contentOffset) the scrollview. Here I using a NSTimer to move the scrollview as long as the subview is over the visible area.
My problem:
When the subview is over the visible area a NSTimer is started, to change the contentOffset of the subview and the frame (position) of the subview.
After that I can't pan the subview anymore.
I can't figure out how to implement the pan gesture with changing the subview frame in a correct way.
My implementation:
I am using three views:
UIScrollView
MyImageContainerView (UIView, added as a subview to the scrollview)
MyImageView (UIView, added as a subview to MyImageContainerView)
Currently MyImageContainerView manages the workflow. A MyImageView has a UIPanGestureRecognizer attached. The method for this recognizer is implemented in MyImageContainerView:
- (void)handlePanGesture:(UIPanGestureRecognizer *)gestureRecognizer
{
//UIView which is moved by the user
MyImageView *currentView = gestureRecognizer.view;
switch (gestureRecognizer.state)
{
case UIGestureRecognizerStatePossible:
{
break;
}
case UIGestureRecognizerStateBegan:
{
//save both values in global instance variables
currentFrameOriginX = currentView.frame.origin.x;
currentFrameOriginY = currentView.frame.origin.y;
//global BOOL variable, to check if scrollView movement is performed
scrolling = NO;
break;
}
case UIGestureRecognizerStateChanged:
{
CGRect rect = CGRectMake(currentFrameOriginX + [gestureRecognizer translationInView:currentView.superview].x, currentFrameOriginY + [gestureRecognizer translationInView:currentView.superview].y, currentView.frame.size.width, currentView.frame.size.height);
if (CGRectContainsRect(currentView.superview.frame, rect)) {
/*PROBLEM: Here is a problem. I need this change of the frame here, to move the UIView along the movement from the user. In my autoScroll-method I have to set the frame of currentView, too. But I can't set the frame of currentView here and in the autoScroll. But as long as the NSTimer runs and is calling autoScroll: this if-statement isn't called, so I can't move the UIView with my finger anymore. */
if (!scrolling) {
//currently the NSTimer method for the automatically scrolling isn't performed, so:
//change the frame according to the pan gesture
currentView.frame = rect;
}
UIScrollView *scrollView = self.myScrollView; //reference to the "root" UIScrollView
CGRect visibleRect;
visibleRect.origin = scrollView.contentOffset;
visibleRect.size = scrollView.bounds.size;
CGRect frame = currentView.frame;
CGFloat scale = 1.0 / scrollView.zoomScale;
visibleRect.origin.x *= scale;
visibleRect.origin.y *= scale;
visibleRect.size.width *= scale;
visibleRect.size.height *= scale;
CGSize scrollZone = CGSizeMake(10.0f, 10.0f);
float scrollStep = 3.0f;
CGPoint scrollAmount = CGPointZero;
//determine the change of x and y
if (frame.origin.x+scrollZone.width < visibleRect.origin.x) {
scrollAmount.x = -scrollStep;
}
else if((frame.origin.x+frame.size.width)-scrollZone.width > visibleRect.origin.x + visibleRect.size.width) {
scrollAmount.x = scrollStep;
}
else if (frame.origin.y+scrollZone.height < visibleRect.origin.y) {
scrollAmount.y = -scrollStep;
}
else if((frame.origin.y+frame.size.height)-scrollZone.height > visibleRect.origin.y + visibleRect.size.height) {
scrollAmount.y = scrollStep;
}
if ((scrollAmount.x != 0) | (scrollAmount.y != 0)) {
if (![scrollTimer isValid]) {
//scrollTimer is a global NSTimer instance variable
[scrollTimer invalidate];
scrollTimer = nil;
NSString *scrollString = NSStringFromCGPoint(scrollAmount);
NSDictionary *info = [NSDictionary dictionaryWithObjectsAndKeys:scrollString, #"scrollString", currentView, #"currentView", nil];
scrollTimer = [[NSTimer alloc]initWithFireDate:[NSDate date] interval:0.03f target:self selector:#selector(autoScroll:) userInfo:info repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:scrollTimer forMode:NSRunLoopCommonModes];
}
}
else {
[scrollTimer invalidate];
scrollTimer = nil;
scrolling = NO;
}
}
break;
}
case UIGestureRecognizerStateEnded:
{
//quite know the scrolling should stop, maybe it would be better when the scrollView scrolls even if the user does nothing when the subview is over the visible area
[scrollTimer invalidate];
scrollTimer = nil;
scrolling = NO;
break;
}
default:
{
[scrollTimer invalidate];
scrollTimer = nil;
scrolling = NO;
break;
}
}
}
-(void)autoScroll:(NSTimer*)timer {
scrolling = YES; //the scroll method is executed quite know
NSDictionary *info = [timer userInfo];
UIScrollView *scrollView = self.myScrollView;
CGRect visibleRect;
visibleRect.origin = scrollView.contentOffset;
visibleRect.size = scrollView.bounds.size;
CGPoint scrollAmount = CGPointFromString([info objectForKey:#"scrollString"]);
MyImageView *currentView = [info objectForKey:#"currentView"];
//stop scrolling when the UIView is at the edge of the containerView (referenced over 'self')
if ((currentView.frame.origin.x <= 0 | currentView.frame.origin.y <= 0) ||
((currentView.frame.origin.x+currentView.frame.size.width) > self.frame.size.width | (currentView.frame.origin.y+currentView.frame.size.height) > self.frame.size.height)
) {
scrolling = NO;
return;
}
//move the UIView
CGFloat scale = 1.0 / scrollView.zoomScale;
if (scrollAmount.x != 0) {
scrollAmount.x *= scale;
}
if (scrollAmount.y != 0) {
scrollAmount.y *= scale;
}
CGRect frame = currentView.frame;
frame.origin.x += scrollAmount.x;
frame.origin.y += scrollAmount.y;
currentView.frame = frame;
currentFrameOriginX = currentView.frame.origin.x;
currentFrameOriginY = currentView.frame.origin.y;
//move the scrollView
CGPoint contentOffset = scrollView.contentOffset;
contentOffset.x += scrollAmount.x;
contentOffset.y += scrollAmount.y;
[scrollView setContentOffset:contentOffset animated:NO];
}