How to gently drag panel from offscreen like JetBlue iPhone app

Question

I'm looking for a way to slide a partially concealed tool panel from off screen like the JetBlue iPhone app does. I know how to do this with regular swipe gesture recognizers, but that app has a certain threshold, after which the panel "snaps" to the on-screen position, otherwise it hides back offscreen.

How can I implement this kind of swipe-to show, but with a threshold kind of gesture recognizer? Are there any open source projects that do this kind of UI manipulation?

Answer 1

If you can already implement the basics with gestures, then you're almost there!

To be honest, while I've done exactly this in my application, I use the old fashioned touchesBegan, touchesMoved, etc.

In terms of gestures, you'll have to use UIPanGestureRecognizer so you can have full control of the drag. UISwipeGestureRecognizer only recognizes swipes.

Anyway, after a certain point, you simply translate the panel only a fraction of the distance the person dragged.

CGRect newPanelFrame = panel.frame;
if (newPanelFrame.origin.y + dragOffset > 275) {
   newPanelFrame.origin.y += dragOffset / 2.0;
}
panel.frame = newPanelFrame;

In touchesEnded:withEvent: or if (gestureRecognizer.state == UIGestureRecognizerStateEnded)

CGRect newPanelFrame = panel.frame;
if (newPanelFrame.origin.y > 275) {
   newPanelFrame.origin.y = 275;
}
panel.frame = newPanelFrame;

The reason why I've never bothered with the UIPanGestureRecognizer is because I could never figure out how to get the non-cumulative translation (translationForView: is cumulative), which is necessary if you want to essentially slow down the drag after the threshold.

Answer 2

I have a similar interface element in an app I've written. My interface element is a UIViewController for the entire tool panel. I put a UIButton over the gripper illustration, change the button's type to custom so it visually disappears. I connect Touch Drag Inside and Touch Drag Outside to an IBAction that adjusts the position of the panel according to where the drag moves. I connect Touch Up Inside and Touch Up Outside to an IBAction that finalizes the positioning of the view. If the touch up event happens too close to the bottom, I just close the panel. If it happens anywhere higher than that threshold I open the panel. I use UIView's animation methods to smooth out these transitions. The over extension element seen in the JetBlue app can be accomplished in the drag event handler. As the panel gets closer and closer to the limit, open the view a smaller and smaller amount with each move of the touch higher. Then in the finalization, just animate the panel back down into it's preferred ending position.

The JetBlue app differs from my app in that I have a small gripper area, but JetBlue's app allows you to swipe the whole panel to adjust position. To match that functionality, I would adjust my implementation to totally cover the panel with buttons. Each would respond to my drag events with the addition that dragging would set a flag. Then my touch up event handler would check if the flag was set. If so, finalize the dragging of the panel. Otherwise, perform the appropriate action associated with each button.

Answer 3

I was just doing some research into achieving a similar effect, stumbled across this post, and as a result decided to give JetBlue a try.

After playing with the sliding panel for a bit, I'm actually thinking the JetBlue guys actually went about this in a slightly more different manner.

The motions of the slider in the JetBlue app seem to handle much nicer than what you could do with a collection of UIGestureRecognizers; it's capable of animating at different velocities depending how quickly the user swipes it, and the rubber-banding compensates for this properly too.

So on that note, I actually think that they're not using UIGestureRecognizers, but that panel is actually just a standard UIScrollView aligned to the bottom of the app window, and with a bit of extra logic (probably applied via the delegate) that just makes sure it isn't possible for the scroll view to stop animating between the 'open' and 'shut' state.