问如何设置UICollectionView底部填充和滚动尺寸

EN

self.automaticallyAdjustsScrollViewInsets = false
self.collectionView.contentInset =  UIEdgeInsetsMake(20, 20, 120, 100);

import UIKit

public var CELL_HEIGHT = CGFloat(22)

protocol CustomCollectionViewDelegateLayout: NSObjectProtocol {

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, widthForItemAtIndexPath indexPath: NSIndexPath) -> CGFloat
}

class CustomCollectionViewLayout: UICollectionViewLayout {

    // Used for calculating each cells CGRect on screen.
    // CGRect will define the Origin and Size of the cell.

    let STATUS_BAR = UIApplication.sharedApplication().statusBarFrame.height

    // Dictionary to hold the UICollectionViewLayoutAttributes for
    // each cell. The layout attribtues will define the cell's size
    // and position (x, y, and z index). I have found this process
    // to be one of the heavier parts of the layout. I recommend
    // holding onto this data after it has been calculated in either
    // a dictionary or data store of some kind for a smooth performance.
    var cellAttrsDictionary = Dictionary<NSIndexPath, UICollectionViewLayoutAttributes>()

    // Defines the size of the area the user can move around in
    // within the collection view.
    var contentSize = CGSize.zero

    // Used to determine if a data source update has occured.
    // Note: The data source would be responsible for updating
    // this value if an update was performed.
    var dataSourceDidUpdate = true

    weak var delegate: CustomCollectionViewDelegateLayout?

    override func collectionViewContentSize() -> CGSize {
        return self.contentSize
    }

    override func prepareLayout() {

        // Only update header cells.
        if !dataSourceDidUpdate {

            // Determine current content offsets.
            let xOffset = collectionView!.contentOffset.x
            let yOffset = collectionView!.contentOffset.y

            if collectionView?.numberOfSections() > 0 {
                for section in 0...collectionView!.numberOfSections()-1 {

                    // Confirm the section has items.
                    if collectionView?.numberOfItemsInSection(section) > 0 {

                        // Update all items in the first row.
                        if section == 0 {
                            for item in 0...collectionView!.numberOfItemsInSection(section)-1 {

                                // Build indexPath to get attributes from dictionary.
                                let indexPath = NSIndexPath(forItem: item, inSection: section)

                                // Update y-position to follow user.
                                if let attrs = cellAttrsDictionary[indexPath] {
                                    var frame = attrs.frame

                                    // Also update x-position for corner cell.
                                    if item == 0 {
                                        frame.origin.x = xOffset
                                    }

                                    frame.origin.y = yOffset
                                    attrs.frame = frame
                                }

                            }

                            // For all other sections, we only need to update
                            // the x-position for the fist item.
                        } else {

                            // Build indexPath to get attributes from dictionary.
                            let indexPath = NSIndexPath(forItem: 0, inSection: section)

                            // Update y-position to follow user.
                            if let attrs = cellAttrsDictionary[indexPath] {
                                var frame = attrs.frame
                                frame.origin.x = xOffset
                                attrs.frame = frame
                            }

                        }
                    }
                }
            }


            // Do not run attribute generation code
            // unless data source has been updated.
            return
        }

        // Acknowledge data source change, and disable for next time.
        dataSourceDidUpdate = false

        var maxWidthInASection = CGFloat(0)

        // Cycle through each section of the data source.
        if collectionView?.numberOfSections() > 0 {
            for section in 0...collectionView!.numberOfSections()-1 {

                // Cycle through each item in the section.
                if collectionView?.numberOfItemsInSection(section) > 0 {

                    var prevCellAttributes: UICollectionViewLayoutAttributes?

                    for item in 0...collectionView!.numberOfItemsInSection(section)-1 {

                        let cellIndex = NSIndexPath(forItem: item, inSection: section)

                        guard let width = delegate?.collectionView(collectionView!, layout: self, widthForItemAtIndexPath: cellIndex) else {
                            print("Please comform to CustomCollectionViewDelegateLayout protocol")
                            return
                        }

                        // Build the UICollectionVieLayoutAttributes for the cell.

                        var xPos = CGFloat(0)
                        let yPos = CGFloat(section) * CELL_HEIGHT

                        if let prevCellAttributes = prevCellAttributes {
                            xPos = CGRectGetMaxX(prevCellAttributes.frame)
                        }

                        let cellAttributes = UICollectionViewLayoutAttributes(forCellWithIndexPath: cellIndex)
                        cellAttributes.frame = CGRect(x: xPos, y: yPos, width: width, height: CELL_HEIGHT)

                        // Determine zIndex based on cell type.
                        if section == 0 && item == 0 {
                            cellAttributes.zIndex = 4
                        } else if section == 0 {
                            cellAttributes.zIndex = 3
                        } else if item == 0 {
                            cellAttributes.zIndex = 2
                        } else {
                            cellAttributes.zIndex = 1
                        }

                        // Save the attributes.
                        cellAttrsDictionary[cellIndex] = cellAttributes
                        prevCellAttributes = cellAttributes

                        let maxX = CGRectGetMaxX(cellAttributes.frame)

                        if maxWidthInASection < maxX {
                            maxWidthInASection = maxX
                        }
                    }
                }

            }
        }

        // Update content size.
        let contentWidth = maxWidthInASection
        let contentHeight = Double(collectionView!.numberOfSections())
        self.contentSize = CGSize(width: Double(contentWidth), height: contentHeight)
        self.contentSize.height = CGFloat(Double(collectionView!.numberOfSections()))


    }

    override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {

        // Create an array to hold all elements found in our current view.
        var attributesInRect = [UICollectionViewLayoutAttributes]()

        // Check each element to see if it should be returned.
        for cellAttributes in cellAttrsDictionary.values.elements {
            if CGRectIntersectsRect(rect, cellAttributes.frame) {
                attributesInRect.append(cellAttributes)
            }
        }

        // Return list of elements.
        return attributesInRect
    }

    override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
        return cellAttrsDictionary[indexPath]!
    }

    override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
        return true
    }

}