support custom animation configuration for elements

Author: Bluelich

BLCollectionViewTagLayout/Classes/BLCollectionViewTagLayout.h

@@ -18,6 +18,23 @@ typedef NS_ENUM (NSUInteger, BLCollectionViewTagLayoutItemRenderPolicy) {
 
 UIKIT_EXTERN NSString *const BLCollectionElementKindSectionDecoration;
 
+typedef NS_ENUM(NSUInteger, BLCollectionViewTagLayoutAnimationState) {
+    BLCollectionViewTagLayoutAnimationStateInitial,
+    BLCollectionViewTagLayoutAnimationStateFinal,
+};
+
+
+/**
+ * Animation configuration for elemets appearing or disappearing
+ *
+ * @param indexPath NSIndexPath
+ * @param kind      kind of the element, or nil if the catrgory is cell
+ * @param catrgory  UICollectionElementCategory
+ */
+typedef
+UICollectionViewLayoutAttributes * _Nullable(^BLCollectionViewTagLayoutAnimation)
+(NSIndexPath *indexPath,NSString * _Nullable kind,UICollectionElementCategory catrgory);
+
 #pragma mark - UICollectionViewTagStyleLayout
 #pragma mark -
 IB_DESIGNABLE NS_CLASS_AVAILABLE_IOS(8_0)
@@ -78,6 +95,14 @@ IB_DESIGNABLE NS_CLASS_AVAILABLE_IOS(8_0)
  * The default value of this property is NO.
  */
 @property (nonatomic) BOOL sectionDecorationVisiable;
+/**
+ * Animation attributes for elements (item|supplementary|decoration) appearing.
+ */
+@property (nonatomic,copy,nullable) BLCollectionViewTagLayoutAnimation elementAppearingAnimationFromValue;
+/**
+ * Animation attributes for elements (item|supplementary|decoration) disappearing.
+ */
+@property (nonatomic,copy,nullable) BLCollectionViewTagLayoutAnimation elementDisappearingAnimationToValue;
 @end
 
 @interface BLCollectionViewTagLayout (UICollectionViewContentInsetAdjustment)

BLCollectionViewTagLayout/Classes/BLCollectionViewTagLayout.m

@@ -831,39 +831,57 @@ - (void)finalizeLayoutTransition
  */
 - (UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingItemAtIndexPath:(NSIndexPath *)itemIndexPath
 {
-    UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:itemIndexPath].copy;
-    attributes.alpha = 0.1;
-    return attributes;
+    if (self.elementAppearingAnimationFromValue) {
+        self.elementAppearingAnimationFromValue(itemIndexPath,
+                                                nil,
+                                                UICollectionElementCategoryCell);
+    }
+    return [super initialLayoutAttributesForAppearingItemAtIndexPath:itemIndexPath];
 }
 - (UICollectionViewLayoutAttributes *)finalLayoutAttributesForDisappearingItemAtIndexPath:(NSIndexPath *)itemIndexPath
 {
-    UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:itemIndexPath].copy;
-    attributes.alpha = 0.1;
-    return attributes;
+    if (self.elementDisappearingAnimationToValue) {
+        self.elementDisappearingAnimationToValue(itemIndexPath,
+                                                 nil,
+                                                 UICollectionElementCategoryCell);
+    }
+    return [super finalLayoutAttributesForDisappearingItemAtIndexPath:itemIndexPath];
 }
 - (UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingSupplementaryElementOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)elementIndexPath
 {
-    UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForSupplementaryViewOfKind:elementKind atIndexPath:elementIndexPath].copy;
-    attributes.alpha = 0.1;
-    return attributes;
+    if (self.elementAppearingAnimationFromValue) {
+        self.elementAppearingAnimationFromValue(elementIndexPath,
+                                                elementKind,
+                                                UICollectionElementCategorySupplementaryView);
+    }
+    return [super initialLayoutAttributesForAppearingSupplementaryElementOfKind:elementKind atIndexPath:elementIndexPath];
 }
 - (nullable UICollectionViewLayoutAttributes *)finalLayoutAttributesForDisappearingSupplementaryElementOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)elementIndexPath
 {
-    UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForSupplementaryViewOfKind:elementKind atIndexPath:elementIndexPath].copy;
-    attributes.alpha = 0.1;
-    return attributes;
+    if (self.elementDisappearingAnimationToValue) {
+        self.elementDisappearingAnimationToValue(elementIndexPath,
+                                                 elementKind,
+                                                 UICollectionElementCategorySupplementaryView);
+    }
+    return [super finalLayoutAttributesForDisappearingSupplementaryElementOfKind:elementKind atIndexPath:elementIndexPath];
 }
 - (nullable UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingDecorationElementOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)decorationIndexPath
 {
-    UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForDecorationViewOfKind:elementKind atIndexPath:decorationIndexPath].copy;
-    attributes.alpha = 0.1;
-    return attributes;
+    if (self.elementAppearingAnimationFromValue) {
+        self.elementAppearingAnimationFromValue(decorationIndexPath,
+                                                elementKind,
+                                                UICollectionElementCategoryDecorationView);
+    }
+    return [super initialLayoutAttributesForAppearingDecorationElementOfKind:elementKind atIndexPath:decorationIndexPath];
 }
 - (nullable UICollectionViewLayoutAttributes *)finalLayoutAttributesForDisappearingDecorationElementOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)decorationIndexPath
 {
-    UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForDecorationViewOfKind:elementKind atIndexPath:decorationIndexPath].copy;
-    attributes.alpha = 0.1;
-    return attributes;
+    if (self.elementDisappearingAnimationToValue) {
+        self.elementDisappearingAnimationToValue(decorationIndexPath,
+                                                 elementKind,
+                                                 UICollectionElementCategoryDecorationView);
+    }
+    return [super finalLayoutAttributesForDisappearingDecorationElementOfKind:elementKind atIndexPath:decorationIndexPath];
 }