Drag Down UIView in iOS 5

Question

I saw in my iPhone app that there is a gesture on the status bar which can access Notification Center. How can I implement that kind of transition in my app?. I think this is done with the swipe gesture recognizer, but how do I include a swipe gesture from top to bottom (how you can drag the Notification Center through its full transition)? Is there any sample code or something that can help me do this? Thaks in advance

Answer 1

Should be easy to do. Let's say you have a UIView (mainView) from which you want to trigger the pull down thing.

1. Put a subview (pulldownView) on mainView top-outside of visible area.
2. Implement touchesBegan on mainView and check if the touch is in the top 30 pixels (or points).
3. Implement touchesMoved where you check, if move direction is down and pulldownView not visible and if so drag the pulldownView down into visible area of main view or check if move direction is up and pulldownView visible and if so push upwards out of visible area.
4. Implement touchesEnd where you end the drag or push movement by checking in which direction the pulldownView was moved.

EDIT:

Here's some sample code. Untested, may contain typos, maybe won't compile, but should contain the essential part needed.

//... inside mainView impl:
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
  UITouch *touch = (UITouch *)[touches anyObject];
  start = [touch locationInView:self.superview].y;
  if(start > 30 && pulldownView.center.y < 0)//touch was not in upper area of view AND pulldownView not visible
  {
    start = -1; //start is a CGFloat member of this view
  }
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
  if(start < 0)
  {
    return;
  }
  UITouch *touch = (UITouch *)[touches anyObject];
  CGFloat now = [touch locationInView:self.superview].y;
  CGFloat diff = now - start;
  directionUp = diff < 0;//directionUp is a BOOL member of this view
  float nuCenterY = pulldownView.center.y + diff;
  pulldownView.center = CGPointMake(pulldownView.center.x, nuCenterY);
  start = now;
}


-(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
  if (directionUp)
  {
    //animate pulldownView out of visibel area
    [UIView animateWithDuration:.3 animations:^{pulldownView.center = CGPointMake(pulldownView.center.x, -roundf(pulldownView.bounds.size.height/2.));}];
  }
  else if(start>=0)
  {
    //animate pulldownView with top to mainviews top
    [UIView animateWithDuration:.3 animations:^{pulldownView.center = CGPointMake(pulldownView.center.x, roundf(pulldownView.bounds.size.height/2.));}];
  }
}

Answer 2

You can implement UISwipeGestureRecognizer to handle swipe gestures in your app, and specify the direction of the swipe to detect as UISwipeGestureRecognizerDirectionDown.

There's an Apple sample here. There are also some WWDC10 sessions that are worth a look. I'd suggest "Simplifying Touch Event Handling with Gesture Recognizers" and "Advanced Gesture Recognition" from that page.