Merge pull request #5 from foursquare/section-headers

Adds support for pinned section headers

Author: Brian Dorfman

FSQAlignedLayoutExample/FSQAlignedLayoutExample/FSQAlignedIndentExampleViewController.m

@@ -12,6 +12,7 @@
 
 @interface FSQExampleSectionData : NSObject
 @property (nonatomic) FSQCollectionViewHorizontalAlignment hAlignment;
+@property (nonatomic) NSString *headerString;
 @property (nonatomic) NSArray *cellData;
 @end
 
@@ -27,6 +28,28 @@ @interface FSQExampleCellData : NSObject
 @implementation FSQExampleCellData
 @end
 
+@interface FSQExampleHeaderView : UICollectionReusableView
+@property (nonatomic) UILabel *label;
+@end
+
+@implementation FSQExampleHeaderView
+
+- (instancetype)initWithFrame:(CGRect)frame {
+    if ((self = [super initWithFrame:frame])) {
+        self.backgroundColor = [UIColor colorWithWhite:0.96f alpha:1.0f];
+        UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(15.0f, 0, frame.size.width - 30.0f, frame.size.height)];
+        label.autoresizingMask = (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);
+        label.backgroundColor = [UIColor clearColor];
+        label.font = kMainFont;
+        label.numberOfLines = 1;
+        [self addSubview:label];
+        self.label = label;
+    }
+    return self;
+}
+
+@end
+
 @interface FSQExampleCell : UICollectionViewCell
 @property (nonatomic) UILabel *label;
 @end
@@ -72,7 +95,9 @@ - (void)viewDidLoad {
     [super viewDidLoad];
     self.view.backgroundColor = [UIColor whiteColor];
     self.collectionView.backgroundColor = [UIColor whiteColor];
+    self.collectionView.alwaysBounceVertical = YES;
     [self.collectionView registerClass:[FSQExampleCell class] forCellWithReuseIdentifier:@"cell"];
+    [self.collectionView registerClass:[FSQExampleHeaderView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"header"];
 
     CGRect frame = self.collectionView.frame;
     frame.origin.y += 20;
@@ -136,6 +161,22 @@ - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView
     return cell;
 }
 
+- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceHeightForHeaderInSection:(NSInteger)section {
+    FSQExampleSectionData *sectionData = self.sectionData[section];
+    return (sectionData.headerString.length > 0) ? 30.0f : 0.0f;
+}
+
+- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
+    UICollectionReusableView *view = nil;
+    if (kind == UICollectionElementKindSectionHeader) {
+        FSQExampleSectionData *sectionData = self.sectionData[indexPath.section];
+        FSQExampleHeaderView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:@"header" forIndexPath:indexPath];
+        headerView.label.text = sectionData.headerString;
+        view = headerView;
+    }
+    return view;
+}
+
 - (NSArray *)generateExampleData {
     // First section
     FSQExampleSectionData *sectionOne = [FSQExampleSectionData new];
@@ -148,6 +189,7 @@ - (NSArray *)generateExampleData {
     // Second section
     FSQExampleSectionData *sectionTwo = [FSQExampleSectionData new];
     sectionTwo.hAlignment = FSQCollectionViewHorizontalAlignmentLeft;
+    sectionTwo.headerString = @"Paul";
 
     FSQExampleCellData *sectionTwoAvatarCell = [FSQExampleCellData new];
     sectionTwoAvatarCell.backgroundColor = [UIColor redColor];
@@ -170,6 +212,7 @@ - (NSArray *)generateExampleData {
     // Third Section
     FSQExampleSectionData *sectionThree = [FSQExampleSectionData new];
     sectionThree.hAlignment = FSQCollectionViewHorizontalAlignmentLeft;
+    sectionThree.headerString = @"Jessica";
 
     FSQExampleCellData *sectionThreeAvatarCell = [FSQExampleCellData new];
     sectionThreeAvatarCell.backgroundColor = [UIColor blueColor];

FSQCollectionViewAlignedLayout.h

@@ -8,11 +8,11 @@
  Overview:
  
  FSQCollectionViewAlignedLayout lays out collection view cells sort of like how a type setter would draw out a string,
- but with collection cells instead of font glyphs. Each section can have both a vertical and horizontal alignment 
- (horizontal aligns each line relative to the whole section, vertical aligns the items within each line if they are 
+ but with collection cells instead of font glyphs. Each section can have both a vertical and horizontal alignment
+ (horizontal aligns each line relative to the whole section, vertical aligns the items within each line if they are
  different heights). It also allows you to specify distance between items in each section and between lines.
  
- Each cell can have not only a size, but insets. You can also tell it to insert "line breaks" before or 
+ Each cell can have not only a size, but insets. You can also tell it to insert "line breaks" before or
  after each cell to get things to wrap how you want.
  
  You can set defaults for section and cell styles just like you can in Flow Layout. Or you can implement delegate methods:
@@ -23,7 +23,7 @@
  
  - (FSQCollectionViewAlignedLayoutCellAttributes*)collectionView:layout:attributesForCellAtIndexPath:
  
- To return cell layout information for the specified indexPath. 
+ To return cell layout information for the specified indexPath.
  
  - (CGSize)collectionView:layout:sizeForItemAtIndexPath:remainingLineSpace:
  
@@ -39,6 +39,12 @@
 
 @class FSQCollectionViewAlignedLayoutSectionAttributes, FSQCollectionViewAlignedLayoutCellAttributes;
 
+@interface FSQCollectionViewAlignedLayoutInvalidationContext : UICollectionViewLayoutInvalidationContext
+
+@property (nonatomic) BOOL invalidateAlignedLayoutAttributes; // if set to NO, aligned layout will keep all layout information, effectively not invalidating - useful for a subclass which invalidates only a piece of itself
+
+@end
+
 @interface FSQCollectionViewAlignedLayout : UICollectionViewLayout <NSFastEnumeration>
 
 /**
@@ -48,11 +54,11 @@
  */
 @property (nonatomic) IBInspectable CGSize defaultCellSize;
 
-/** 
+/**
  Used if attributesForSectionAtIndex delegate method is not implemented
  
  Defaults to [FSQCollectionViewAlignedLayoutSectionAttributes topLeftAlignment] if not set.
- */ 
+ */
 @property (nonatomic) FSQCollectionViewAlignedLayoutSectionAttributes *defaultSectionAttributes;
 
 /**
@@ -62,14 +68,14 @@
  */
 @property (nonatomic) FSQCollectionViewAlignedLayoutCellAttributes *defaultCellAttributes;
 
-/** 
+/**
  Space in points between the bottom most part of a section and the top most part of the next one.
  
  Defaults to 10 if not set.
  */
 @property (nonatomic) IBInspectable CGFloat sectionSpacing;
 
-/** 
+/**
  Insets in points around the entire contents of the collection. Defaults to (5, 5, 5, 5) if not set
  */
 @property (nonatomic) UIEdgeInsets contentInsets;
@@ -88,7 +94,7 @@
  @param indexPath            The index path of the item.
  @param remainingLineSpace   The amount of space in pts remaining on the line the layout is currently laying out.
  
- @return The size the cell should be. If you return a size whose width is less than or equal to @c remainingLineSpace 
+ @return The size the cell should be. If you return a size whose width is less than or equal to @c remainingLineSpace
  it will be laid out on the same lane.
  
  @note remainingLineSpace takes into account any insets that may exist for the current cell, subtracting the
@@ -99,6 +105,18 @@
   sizeForItemAtIndexPath:(NSIndexPath *)indexPath
       remainingLineSpace:(CGFloat)remainingLineSpace;
 
+/**
+ *  Asks the delegate for the height of the header view in the specified section.
+ *  If you do not implement this method, or the height returned is 0, no header is added.
+ *
+ *  @param collectionView       The collection view object displaying the layout.
+ *  @param collectionViewLayout The layout object requesting the information.
+ *  @param section              The index of the section whose header size is being requested.
+ *
+ *  @return The height of the header. If you return a value of 0, no header is added.
+ */
+- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceHeightForHeaderInSection:(NSInteger)section;
+
 /**
  Used instead of defaultSectionAttributes if implemented.
  
@@ -223,16 +241,16 @@ typedef NS_ENUM(NSInteger, FSQCollectionViewVerticalAlignment) {
  */
 @interface FSQCollectionViewAlignedLayoutCellAttributes : NSObject
 
-/** 
- Insets will be added to size for layout purposes, but the collection cell will end up actually being the size reported 
+/**
+ Insets will be added to size for layout purposes, but the collection cell will end up actually being the size reported
  in either the sizeForItemAtIndexPath or the layout's defaultCellSize property.
  
- You can add more padding around cells with positive insets, 
+ You can add more padding around cells with positive insets,
  or effectively shrink cell/line spacing or make cells overlap by using negative insets.
  */
 @property (nonatomic, readonly) UIEdgeInsets insets;
 
-/** 
+/**
  If YES, ensures this cell is the first thing on the line by inserting a line break before if necessary
  
  If there was going to be a line break before anyway, this has no effect (does not insert an EXTRA newline)
@@ -249,20 +267,20 @@ typedef NS_ENUM(NSInteger, FSQCollectionViewVerticalAlignment) {
 /**
  If YES and section alignment is Left or Right, future lines will start from this cell's left or right edge respectively.
  
- The available width of all future lines will be lowered and padding will be added to the appropriate side to inset 
+ The available width of all future lines will be lowered and padding will be added to the appropriate side to inset
  future lines
  
- @note There is no way to stop indenting once you start it without creating a new section, although you can start a new 
+ @note There is no way to stop indenting once you start it without creating a new section, although you can start a new
  indentation from a different cell.
  
- @note The alignment is from the actual position of the cell, not including its insets. Therefore you can fake an 
+ @note The alignment is from the actual position of the cell, not including its insets. Therefore you can fake an
  "unindentation" by using negative insets and then starting a new indentation.
  */
 @property (nonatomic, readonly) BOOL startLineIndentation;
 
-/** 
- Reusable shared pointer to a simple cell attribute object. 
- Zero insets, no line breaks, no indentation. 
+/**
+ Reusable shared pointer to a simple cell attribute object.
+ Zero insets, no line breaks, no indentation.
  */
 + (FSQCollectionViewAlignedLayoutCellAttributes *)defaultCellAttributes;
 
@@ -281,4 +299,4 @@ typedef NS_ENUM(NSInteger, FSQCollectionViewVerticalAlignment) {
              shouldEndLine:(BOOL)shouldEndLine
       startLineIndentation:(BOOL)startLineIndentation;
 
-@end
+@end