Create README.md

Author: seedante

README.md

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+# SDECollectionViewAlbumTransition
+UICollectionViewController Transition like open and close an album.
+
+![AlbumTransition](https://raw.githubusercontent.com/seedante/SDECollectionViewAlbumTransition/PinchPopTransition/AlbumTransition.gif)
+
+
+## Installtion
+
+Drag files in "Classes" folder into your project.
+
+## Usage
+
+- In your storyboard, drag a object to your navigation controller, and set its custom class to "SDENavigationControllerDelegate"
+
+![drag an Object and set the custom class](https://raw.githubusercontent.com/seedante/SDECollectionViewAlbumTransition/PinchPopTransition/Config1.png)
+
+- Set this object to be your navigation controller's delegate.
+
+![set the delegate](https://raw.githubusercontent.com/seedante/SDECollectionViewAlbumTransition/PinchPopTransition/Config2.png)
+
+Or, you want to set it in the code.
+- At the last, add a line code in your UICollectionView's delegate:
+
+        override func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
+            self.selectedIndexPath = indexPath
+            ...
+        }
+        
+**Now your project supports to pinch to pop.**
+
+
+## Requirements
+
+- iOS 7.0+
+
+Thanks for [@CezaryKopacz](https://github.com/CezaryKopacz/CKWaveCollectionViewTransition), [@ColinEberhardt](https://github.com/ColinEberhardt/VCTransitionsLibrary). I learn a lot from their repo.
+And thanks for [ Vincent Ngo](http://www.raywenderlich.com/94565/how-to-create-an-ios-book-open-animation-part-1) very much, I find the key to resolve the problem of pinching to push.
+There is a little problem with time delta algorithm, I will update if I find the way to improvement. 
+
+## Pinch to push?
+
+Pinching to push is a little complex. 
+
+If you want to support pinch to push, switch to the branch "Pinch-Push-Pop-Transition", drag files in "Classes" folder in this branch into your project, 
+there is a little difference between "Pinch-Push-Pop-Transition" branch with other branches.
+
+Add the below properties to your UICollectionViewController child class:
+
+    var transitionDelegate: SDENavigationControllerDelegate?
+    var pinchGestureRecognizer: UIPinchGestureRecognizer?{
+        didSet(newValue){
+            collectionView?.addGestureRecognizer(pinchGestureRecognizer!)
+        }
+    }
+
+    override viewDidLoad(){
+        ...
+        pinchGestureRecognizer = UIPinchGestureRecognizer(target: self, action: "handlePinch:")
+    }
+    
+    deinit{
+        if pinchGestureRecognizer != nil{
+            collectionView?.removeGestureRecognizer(pinchGestureRecognizer!)
+        }
+    }
+
+    //MARK: Pinch Push and Pop
+    func getIndexPathForGesture(gesture: UIPinchGestureRecognizer) -> NSIndexPath?{
+        let location0 = gesture.locationOfTouch(0, inView: gesture.view)
+        let location1 = gesture.locationOfTouch(1, inView: gesture.view)
+        let middleLocation = CGPointMake((location0.x + location1.x)/2, (location0.y + location1.y)/2)
+        let indexPath = collectionView?.indexPathForItemAtPoint(middleLocation)
+        return indexPath
+    }
+
+    func handlePinch(gesture: UIPinchGestureRecognizer){
+        switch gesture.state{
+        case .Began:
+            if gesture.scale >= 1.0{
+                guard let indexPath = getIndexPathForGesture(gesture) else{
+                    return
+                }
+
+                self.selectedIndexPath = indexPath
+                let layoutAttributes = collectionView!.layoutAttributesForItemAtIndexPath(indexPath)
+                let areaRect = collectionView!.convertRect(layoutAttributes!.frame, toView: collectionView?.superview)
+
+                if let toVC = ...{
+                    toVC.coverRectInSuperview = areaRect
+
+                    transitionDelegate = navigationController?.delegate as? SDENavigationControllerDelegate
+                    transitionDelegate?.interactive = true
+                    navigationController?.pushViewController(toVC, animated: true)
+                }
+
+            }else{
+                //after view controller is poped, UIViewController.navigationController is nil. So you need to keep it somewhere before pop
+                transitionDelegate = self.navigationController?.delegate as? SDENavigationControllerDelegate
+                transitionDelegate?.interactive = true
+                self.navigationController?.popViewControllerAnimated(true)
+            }
+
+        case .Changed:
+            guard transitionDelegate != nil else{
+                return
+            }
+            guard let interactionController = transitionDelegate?.interactionController else{
+                return
+            }
+
+            var progress = gesture.scale
+            if transitionDelegate!.isPush{
+                progress = gesture.scale - 1.0 >= 0.9 ? 0.9 : gesture.scale - 1.0
+            }else{
+                progress = 1.0 - gesture.scale
+            }
+
+            interactionController.updateInteractiveTransition(progress)
+        case .Ended, .Cancelled:
+            guard transitionDelegate != nil else{
+                return
+            }
+            guard let interactionController = transitionDelegate?.interactionController else{
+                return
+            }
+
+            var progress = gesture.scale
+            if transitionDelegate!.isPush{
+                progress = gesture.scale - 1.0 >= 0.9 ? 0.9 : gesture.scale - 1.0
+            }else{
+                progress = 1.0 - gesture.scale
+            }
+
+            if progress >= 0.4{
+                interactionController.finishInteractiveTransition()
+            }else{
+                interactionController.cancelInteractiveTransition()
+            }
+            transitionDelegate?.interactive = false
+        default:
+            guard transitionDelegate != nil else{
+                return
+            }
+            transitionDelegate?.interactive = false
+        }
+    }