swanhella swanhella - 4 months ago 53
iOS Question

how to make a sliding up panel like the Google Maps app?

I'm looking for something like AndroidSlidingUpPanel for iOS. I found MBPullDownController, but it requires two ViewControllers to use, and requires a big change to the architecture of the app I'm working on to implement.

I just want something that adds a subview in an existing view controller. How would I go about doing that?

Answer

I use sliding up panels in my iOS apps quite a lot and I've found that the trick is to add a custom view to a view controller in the storyboard (or xib file) but to set its frame so that it is off the screen. You can ensure that the view stays off screen on any device using layout constraints.

Then it's just a case of animating the view on screen when appropriate. e.g.:

- (IBAction)showPanel:(id)sender
{
    // panelShown is an iVar to track the panel state...
    if (!panelShown) {
        // myConstraint is an IBOutlet to the appropriate constraint...
        // Use this method for iOS 8+ otherwise use a frame based animation...
        myConstraint.constant -= customView.frame.size.height;
        [UIView animateWithDuration:0.5 animations:^{
            [self.view setNeedsLayout];
        }];
    }  
    else { 
        myConstraint.constant += customView.frame.size.height;
        [UIView animateWithDuration:0.5 animations:^{
            [self.view setNeedsLayout];
        }];
    }
}

If you want to have just a swipe up/down and that will reveal the panel you can use UISwipeGestureRecognizer like so:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // iVar
    swipeUp = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(didSwipe:)];
    swipeUp.direction = UISwipeGestureRecognizerDirectionUp;
    [self.view addGestureRecognizer:swipeUp];

    // Do the same again with swipeDown using UISwipeGestureRecognizerDirectionDown...
}

- (void)didSwipe:(UIGestureRecognizer *)swipe
{
    if (swipe == swipeUp) {
        // Show panel (see above)...
    } else {
        // Hide panel (see above)...
    }
}

If you want the panel to track your finger like when you show the iOS panel (to turn wifi on an off e.t.c). then you can use UIPanGestureRecognizer and get the translationInView: and velocityInView: and adjust the panel accordingly. Here is a snippet of code that tracks finger movement but using the touchesBegan:withEvent: - (void)touchesMoved:withEvent: and - (void)touchesEnded:withEvent: methods in a UIViewController to give you a taste:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    // Don't worry too much about buttonView this is another view that I animate upwards to get out the way of the panel as it slides in from the left...
    [super touchesBegan:touches withEvent:event];
    CGPoint loc = [[touches anyObject] locationInView:self.view];
    // Save last touch for reference...
    lastTouch = loc;
    // leftBeginRect is an area where the user can start to drag the panel...
    // trackFinger defines whether the panel should move with the users gestures or not...
    if (CGRectContainsPoint(leftBeginRect, loc) && canTrack) {
        trackFinger = YES;
    }
    // Left view is a reference to the panel...
    else if (leftView.frame.size.width >= 300) {
        // This means that the panel is shown and therefore should track the user's finger back towards the edge of the screen...
        CGRect frame = CGRectMake(250, 0, 100, self.view.frame.size.height);
        if (CGRectContainsPoint(frame, loc) && canTrack) {
            trackFinger = YES;
        }
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    [super touchesMoved:touches withEvent:event];
    CGPoint loc = [[touches anyObject] locationInView:self.view];
    // Need to work out the direction in which the user is panning...
    if (lastTouch.x > loc.x) {
        currentFingerDirection = RHFingerDirectionLeft;
    }
    else {
        currentFingerDirection = RHFingerDirectionRight;
    }
    lastTouch = loc;
    if (trackFinger) {
        if (loc.x <= 300) {
            // This means that the panel is somewhere between fully exposed and closed...
            // This is where the frame for the left view (and the constraints) are adjusted according to the user's current finger position...
            CGRect frame = leftView.frame;
            frame.size.width = loc.x;
            [leftView setFrame:frame];
            leftViewConstraint.constant = loc.x;
            if (loc.x <= 80) {
                float percentage = loc.x / 80;
                int amount = 100 * percentage;
                CGRect otherFrame = buttonView.frame;
                otherFrame.origin.y = -amount;
                [buttonView setFrame:otherFrame];
                constraint.constant = constraintConstant + amount;
            }
        }
        else {
            CGRect frame = leftView.frame;
            frame.size.width = 300;
            [leftView setFrame:frame];
            leftViewConstraint.constant = 300;
            frame = buttonView.frame;
            frame.origin.y = -100;
            [buttonView setFrame:frame];
            constraint.constant = constraintConstant + 100;
            trackFinger = NO;
        }
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    // This method works out if the panel should pop open or spring closed when the user ends the gesture...
    [super touchesEnded:touches withEvent:event];
    if (trackFinger) {
        CGPoint loc = [[touches anyObject] locationInView:self.view];
        if (loc.x >= 50 && currentFingerDirection == RHFingerDirectionRight) {
            CGRect frame = leftView.frame;
            frame.size.width = 300;
            leftViewConstraint.constant = 300;
            CGRect otherFrame = buttonView.frame;
            otherFrame.origin.y = -100;
            constraint.constant = constraintConstant + 100;
            [UIView animateWithDuration:0.2 animations:^{
                [leftView setFrame:frame];
                [buttonView setFrame:otherFrame];
            }];
        }
        else if (loc.x <= 250 && currentFingerDirection == RHFingerDirectionLeft) {
            CGRect frame = leftView.frame;
            frame.size.width = 0;
            leftViewConstraint.constant = 0;
            CGRect otherFrame = buttonView.frame;
            otherFrame.origin.y = 0;
            constraint.constant = constraintConstant;
            [UIView animateWithDuration:0.2 animations:^{
                [leftView setFrame:frame];
                [buttonView setFrame:otherFrame];
            }];
        }
        else if (loc.x <= 150) {
            CGRect frame = leftView.frame;
            frame.size.width = 0;
            leftViewConstraint.constant = 0;
            CGRect otherFrame = buttonView.frame;
            otherFrame.origin.y = 0;
            constraint.constant = constraintConstant;
            [UIView animateWithDuration:0.2 animations:^{
                [leftView setFrame:frame];
                [buttonView setFrame:otherFrame];
            }];
        }
        else {
            CGRect frame = leftView.frame;
            frame.size.width = 300;
            leftViewConstraint.constant = 300;
            CGRect otherFrame = buttonView.frame;
            otherFrame.origin.y = -100;
            constraint.constant = constraintConstant + 100;
            [UIView animateWithDuration:0.2 animations:^{
                [leftView setFrame:frame];
                [buttonView setFrame:otherFrame];
            }];
        }
        trackFinger = NO;
    }
    currentFingerDirection = RHFingerDirectionNone;
}

The code is quite involved but it results in a nice panel animation that follows your finger very like the iOS panel.

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