问题
I'm trying so create a collection view that behaves like the iOS springboard screen. That means that I want to have a collection view, with all of my items, and to have a page controller underneath the grid (just like the springboard screen). I also want to implement the same edit mode, meaning that one my icons are in edit mode, I can drag them from one page to another, in such a way that a page doesn't have to be full. I've tried to set a single collection view to scroll horizontally, but it doesn't act as I want. first of all, the icons are added one below the other, instead of one beside the other. secondly, I don't have the page dots this way, and the user can't put icons on different pages I also tried to set a page controller, and put in every page the collection view. In this case, I get that while in edit mode, I can't go between screens. I guess that is because I have more that one collection view, and they don't interact with each other. I though of another way, of using a scroll view, and try to put a collection view inside that scroll view. But it sounds to me like a very not elegant solution.
Does anyone have an idea about how to create such a scene?
Edit: I think the answer for my problem is hiding in this question. It describes the same situation I want to have: a collection view, that is scrolled horizontally, with paging, and that the order of the icons is not flowing vertically, but also flowing horizontally. There is a partially good answer there. I say it's partially good since the answer describes a subclass of UICollectionViewFlowLayout, but in the sample project uploaded the subclass is of UICollectionViewLayout, and I think the whole point was to maintain the functions that the UICollectionViewFlowLayout has. This question was asked a year ago, so I believe someone has an answer, or at least, I hope.
回答1:
I have partial solution to my question. I did use the answer (of Bogdan) to the linked question above. Here's the code:
layout.h:
#import <UIKit/UIKit.h>
@interface V9Layout : UICollectionViewLayout
@property (nonatomic, assign) NSInteger itemsInOneRow;
@property (nonatomic, assign) NSInteger itemsInOneCol;
@property (nonatomic, assign) CGSize itemSize;
@end
layout.m:
#import "V9Layout.h"
@interface V9Layout()
-(void)calculateLayoutProperties;
-(int)pagesInSection:(NSInteger)section;
@property (nonatomic, strong) NSMutableArray *frames;
@property (nonatomic, assign) CGFloat lineSpacing;
@property (nonatomic, assign) CGFloat interitemSpacing;
@property (nonatomic, assign) CGSize pageSize;
@end
@implementation V9Layout
@synthesize itemsInOneRow = _itemsInOneRow, itemsInOneCol = _itemsInOneCol, itemSize = _itemSize;
@synthesize lineSpacing = _lineSpacing, interitemSpacing = _interitemSpacing;
@synthesize frames = _frames;
- (id)init
{
self = [super init];
if (self) {
[self setup];
}
return self;
}
- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super init];
if (self) {
[self setup];
}
return self;
}
- (void)setup
{
self.itemsInOneRow = 3;
self.itemsInOneCol = 4;
self.frames = [NSMutableArray array];
}
-(void)calculateLayoutProperties {
self.pageSize = self.collectionView.bounds.size;
// The width of all line spacings is equal to width of ONE item. The same for interitem spacing
CGFloat itemWidth = self.pageSize.width / (self.itemsInOneRow + 1); // +1 because we all spaces make width of one additional item
CGFloat itemHeight = self.pageSize.height / (self.itemsInOneCol + 1); // the same
NSLog(@"calculateLayoutProperties item width: %f, item height: %f", itemWidth, itemHeight);
self.itemSize = CGSizeMake(itemWidth, itemHeight);
// this part is only to make a global parameter, because I'm using this data to create the size of the UICollectionViewCell. I think I need to use a delegate method for the UICollectionViewCell to ask the UICollectionViewLayout for the calculated size of cell.
NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
if (standardUserDefaults) {
[standardUserDefaults setObject:[NSNumber numberWithFloat:itemWidth] forKey:@"cellWidth"];
[standardUserDefaults setObject:[NSNumber numberWithFloat:itemHeight] forKey:@"cellHeight"];
[standardUserDefaults synchronize];
}
// spacing for x
self.lineSpacing = (self.pageSize.width - (self.itemsInOneRow * self.itemSize.width)) / (self.itemsInOneRow + 1);
// spacing for y
self.interitemSpacing = (self.pageSize.height - (self.itemsInOneCol * self.itemSize.height)) / (self.itemsInOneCol + 1);
}
-(int)pagesInSection:(NSInteger)section {
NSLog(@"v9layout: numberOfItemsInSection is %ld", (long)[self.collectionView numberOfItemsInSection:section]);
return ([self.collectionView numberOfItemsInSection:section] - 1) / (self.itemsInOneRow * self.itemsInOneCol) + 1;
}
-(CGSize)collectionViewContentSize {
// contentSize.width is equal to pages * pageSize.width
NSInteger sections = 1;
if ([self.collectionView respondsToSelector:@selector(numberOfSections)]) {
sections = [self.collectionView numberOfSections];
}
int pages = 0;
for (int section = 0; section < sections; section++) {
pages = pages + [self pagesInSection:section];
}
return CGSizeMake(pages * self.pageSize.width, self.pageSize.height);
}
-(void)prepareLayout {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
[self calculateLayoutProperties];
});
[self.frames removeAllObjects];
NSInteger sections = 1;
if ([self.collectionView respondsToSelector:@selector(numberOfSections)]) {
sections = [self.collectionView numberOfSections];
}
int pagesOffset = 0; // Pages that are used by prevoius sections
int itemsInPage = self.itemsInOneRow * self.itemsInOneCol;
for (int section = 0; section < sections; section++) {
NSMutableArray *framesInSection = [NSMutableArray array];
int pagesInSection = [self pagesInSection:section];
int itemsInSection = [self.collectionView numberOfItemsInSection:section];
for (int page = 0; page < pagesInSection; page++) {
int itemsToAddToArray = itemsInSection - framesInSection.count;
int itemsInCurrentPage = itemsInPage;
if (itemsToAddToArray < itemsInPage) { // If there are less cells than expected (typically last page of section), we go only through existing cells.
itemsInCurrentPage = itemsToAddToArray;
}
for (int itemInPage = 0; itemInPage < itemsInCurrentPage; itemInPage++) {
CGFloat originX = (pagesOffset + page) * self.pageSize.width + self.lineSpacing + (itemInPage % self.itemsInOneRow) * (self.itemSize.width + self.lineSpacing);
CGFloat originY = self.interitemSpacing + (itemInPage / self.itemsInOneRow) * (self.itemSize.height + self.interitemSpacing);
CGRect itemFrame = CGRectMake(originX, originY, self.itemSize.width, self.itemSize.height);
[framesInSection addObject:NSStringFromCGRect(itemFrame)];
}
}
[self.frames addObject:framesInSection];
pagesOffset += pagesInSection;
}
}
-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
NSMutableArray *attributes = [NSMutableArray array];
NSInteger sections = 1;
if ([self.collectionView respondsToSelector:@selector(numberOfSections)]) {
sections = [self.collectionView numberOfSections];
}
int pagesOffset = 0;
int itemsInPage = self.itemsInOneRow * self.itemsInOneCol;
for (int section = 0; section < sections; section++) {
int pagesInSection = [self pagesInSection:section];
int itemsInSection = [self.collectionView numberOfItemsInSection:section];
for (int page = 0; page < pagesInSection; page++) {
CGRect pageFrame = CGRectMake((pagesOffset + page) * self.pageSize.width, 0, self.pageSize.width, self.pageSize.height);
if (CGRectIntersectsRect(rect, pageFrame)) {
int startItemIndex = page * itemsInPage;
int itemsInCurrentPage = itemsInPage;
if (itemsInSection - startItemIndex < itemsInPage) {
itemsInCurrentPage = itemsInSection - startItemIndex;
}
for (int itemInPage = 0; itemInPage < itemsInCurrentPage; itemInPage++) {
UICollectionViewLayoutAttributes *itemAttributes = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:startItemIndex + itemInPage inSection:section]];
if (CGRectIntersectsRect(itemAttributes.frame, rect)) {
[attributes addObject:itemAttributes];
}
}
}
}
pagesOffset += pagesInSection;
}
return attributes;
}
-(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
attributes.frame = CGRectFromString(self.frames[indexPath.section][indexPath.item]);
return attributes;
}
@end
This implement the horizontal paging with order of cells one beside each other and not one underneath each other. I still want to add a drag and drop ability so that the user can change the order of cells. I poset this question about it. Hopefully, I'll find answer to this and update this answer.
来源：https://stackoverflow.com/questions/23914579/ios-creating-a-springboard-screen