diff --git a/FSPageSliderExample-Swift/FSPagerViewExample.xcodeproj/project.pbxproj b/FSPageSliderExample-Swift/FSPagerViewExample.xcodeproj/project.pbxproj
index a14d29d..341d761 100644
--- a/FSPageSliderExample-Swift/FSPagerViewExample.xcodeproj/project.pbxproj
+++ b/FSPageSliderExample-Swift/FSPagerViewExample.xcodeproj/project.pbxproj
@@ -249,7 +249,6 @@
 				TargetAttributes = {
 					F97C96761E1FDE25002D9E7E = {
 						CreatedOnToolsVersion = 8.2.1;
-						DevelopmentTeam = HZF422TY46;
 						ProvisioningStyle = Automatic;
 					};
 					F9C694561E40C720007084B6 = {
@@ -467,7 +466,7 @@
 			isa = XCBuildConfiguration;
 			buildSettings = {
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
-				DEVELOPMENT_TEAM = HZF422TY46;
+				DEVELOPMENT_TEAM = "";
 				INFOPLIST_FILE = "$(SRCROOT)/FSPagerViewExample/Info.plist";
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = com.wenchaod.FSPagerViewExample;
@@ -480,7 +479,7 @@
 			isa = XCBuildConfiguration;
 			buildSettings = {
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
-				DEVELOPMENT_TEAM = HZF422TY46;
+				DEVELOPMENT_TEAM = "";
 				INFOPLIST_FILE = "$(SRCROOT)/FSPagerViewExample/Info.plist";
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = com.wenchaod.FSPagerViewExample;
diff --git a/FSPagerView/FSPageViewLayout.swift b/FSPagerView/FSPageViewLayout.swift
index ad8a434..ad506ee 100644
--- a/FSPagerView/FSPageViewLayout.swift
+++ b/FSPagerView/FSPageViewLayout.swift
@@ -69,8 +69,8 @@ class FSPagerViewLayout: UICollectionViewLayout {
         }()
         
         self.actualInteritemSpacing = {
-            if let transformer = pagerView.transformer {
-                return transformer.proposedInteritemSpacing()
+            if pagerView.transformer != nil {
+                return pagerView.itemSize.width*pagerView.transformer!.proposedInteritemSpacingPercent()
             }
             return pagerView.interitemSpacing
         }()
@@ -239,7 +239,7 @@ class FSPagerViewLayout: UICollectionViewLayout {
         }
         let ruler = collectionView.bounds.midX
         let position = (attributes.center.x-ruler)/self.itemSpan
-        transformer.applyTransform(to: attributes, for: position)
+        transformer.applyTransform(to: attributes, for: position, and: self.itemSpan)
     }
 
 }
diff --git a/FSPagerView/FSPageViewTransformer.swift b/FSPagerView/FSPageViewTransformer.swift
index e52df69..a95ae5c 100644
--- a/FSPagerView/FSPageViewTransformer.swift
+++ b/FSPagerView/FSPageViewTransformer.swift
@@ -21,9 +21,8 @@ public enum FSPagerViewTransformerType: Int {
     case invertedFerrisWheel
 }
 
-open class FSPagerViewTransformer: NSObject {
+open class FSPagerViewTransformer: NSObject, FSPagerViewTransitionAnimatior {
     
-    open internal(set) weak var pagerView: FSPagerView?
     open internal(set) var type: FSPagerViewTransformerType = .none
     
     open var minimumScale: CGFloat = 0.65
@@ -47,11 +46,10 @@ open class FSPagerViewTransformer: NSObject {
     }
     
     // Apply transform to attributes - zIndex: Int, frame: CGRect, alpha: CGFloat, transform: CGAffineTransform or transform3D: CATransform3D.
-    open func applyTransform(to attributes: UICollectionViewLayoutAttributes, for position: CGFloat) {
-        guard let pagerView = self.pagerView else {
-            return
-        }
-        let itemSpan = pagerView.collectionViewLayout.itemSpan
+    open func applyTransform(to attributes: UICollectionViewLayoutAttributes,
+                                  for position: CGFloat,
+                                  and itemSpan: CGFloat) {
+
         switch self.type {
         case .none:
             break
@@ -156,7 +154,7 @@ open class FSPagerViewTransformer: NSObject {
             var transform = CGAffineTransform.identity
             switch position {
             case -5 ... 5:
-                let itemSpacing = attributes.bounds.width+self.proposedInteritemSpacing()
+                let itemSpacing = attributes.bounds.width+attributes.size.width*self.proposedInteritemSpacingPercent()
                 let count: CGFloat = 14
                 let circle: CGFloat = CGFloat(M_PI) * 2.0
                 let radius = itemSpacing * count / circle
@@ -179,24 +177,19 @@ open class FSPagerViewTransformer: NSObject {
     }
     
     // An interitem spacing proposed by transformer class. This will override the default interitemSpacing provided by page slider.
-    open func proposedInteritemSpacing() -> CGFloat {
-        guard let pagerView = self.pagerView else {
-            return 0
-        }
+    open func proposedInteritemSpacingPercent() -> CGFloat {
         switch self.type {
         case .overlap:
-            return pagerView.itemSize.width * -self.minimumScale * 0.6
+            return -self.minimumScale * 0.6
         case .linear:
-            return pagerView.itemSize.width * -self.minimumScale * 0.2
+            return -self.minimumScale * 0.2
         case .coverFlow:
-            return -pagerView.itemSize.width * sin(CGFloat(M_PI_4)/4.0*3.0)
+            return sin(CGFloat(M_PI_4)/4.0*3.0)
         case .ferrisWheel,.invertedFerrisWheel:
-            return -pagerView.itemSize.width * 0.15
+            return 0.15
         default:
-            break
+            return 1
         }
-        return pagerView.interitemSpacing
     }
-    
 }
 
diff --git a/FSPagerView/FSPagerView.swift b/FSPagerView/FSPagerView.swift
index eac3b7f..d29e372 100644
--- a/FSPagerView/FSPagerView.swift
+++ b/FSPagerView/FSPagerView.swift
@@ -8,6 +8,19 @@
 
 import UIKit
 
+@objc
+public protocol FSPagerViewTransitionAnimatior: NSObjectProtocol {
+    /// Customize your switching animation
+    @objc(applyTransformToAttributes:forPosition: itemSpan:)
+    func applyTransform(to attributes: UICollectionViewLayoutAttributes,
+                        for position: CGFloat,
+                        and itemSpan: CGFloat)
+    
+    /// Get proposed interitem spacing percent
+    @objc
+    func proposedInteritemSpacingPercent() -> CGFloat
+}
+
 @objc
 public protocol FSPagerViewDataSource: NSObjectProtocol {
     
@@ -137,9 +150,8 @@ open class FSPagerView: UIView,UICollectionViewDataSource,UICollectionViewDelega
     }
     
     /// The transformer of the pager view
-    open var transformer: FSPagerViewTransformer? {
+    open var transformer: FSPagerViewTransitionAnimatior? {
         didSet {
-            self.transformer?.pagerView = self
             self.collectionViewLayout.forceInvalidate()
         }
     }