Dynamically loading cells for UICollectionView - ios

Hi I am very new for Ios and in my project I am using UICollectionView ok that's fine.
But here my main requirement is that I want to load the UICollectionView cells dynamically when we are scrolling the collectionView.
I mean when we launch the app then first "5" records need to load and when we are scrolling for the first time next "5" records need to load and when we scrolling for the second time the next "5" records need to be displayed and in that way all records need to load.
Please help me.
How can I do this?
my code:-
#import "ViewController.h"
#interface ViewController ()
{
UICollectionView * _collectionView;
}
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
UICollectionViewFlowLayout *layout=[[UICollectionViewFlowLayout alloc] init];
_collectionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, 320, 480) collectionViewLayout:layout];
[_collectionView setDataSource:self];
[_collectionView setDelegate:self];
[_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:#"cellIdentifier"];
[_collectionView setBackgroundColor:[UIColor clearColor]];
[self.view addSubview:_collectionView];
UIView *refreshView = [[UIView alloc] initWithFrame:CGRectMake(0, _collectionView.frame.size.height - 50, 0, 0)];
[_collectionView addSubview:refreshView];
UIRefreshControl *refreshControl = [UIRefreshControl new];
refreshControl.tintColor = [UIColor redColor];
[refreshControl addTarget:self action:#selector(viewDidBeginRefreshing:) forControlEvents:UIControlEventValueChanged];
[refreshView addSubview:refreshControl];
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
return 5;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:#"cellIdentifier" forIndexPath:indexPath];
for (id subview in cell.contentView.subviews) {
if ([subview isKindOfClass:[UIImageView class]]) {
[subview removeFromSuperview];
} else if ([subview isKindOfClass:[UILabel class]]) {
[subview removeFromSuperview];
}
}
cell.backgroundColor = [UIColor lightGrayColor];
return cell;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath{
return CGSizeMake(70, 70);
}
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section{
UIEdgeInsets insets=UIEdgeInsetsMake(10, 10, 10, 10);
return insets;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
return 30.0;
}

Solution: You can add infinite scrolling to your existing UICollectionView use the following open source library to archive your requirement.
UIScrollView-InfiniteScroll

Solution 1: If you want to do infinite scrolling in a manner more like a desktop web app, you should implement the UIScrollViewDelegate protocol (or UICollectionViewDelegate, which is a superset) and listen for the scrollViewDidScroll: callback.
Within that callback, iterate through the UICollectionView's indexPathsForVisibleItems and check to see if any of the index paths map to the 'last' item in your collection, which indicates the user has scrolled to the end.
At that point, call your logic to load more stuff.
Solution 2:
In table view, you should load more data in willDisplayCell() method. With collections, there is no such a counterpart. But, you can do like this. Hope, it helps.
(void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath
{
// Other code here ...
if (indexPath.item == [self.data count] - 1) {
[self loadMoreData];
}
}
May be it will help you.

Related

uicollectionview scrolling change cell indexpath

I'm trying to create a week calendar by using uiclloectionview. here is what it would look like when the view come to focus:
original view
when I scroll to bottom and scroll back to top. those cells that were disappeared because of scrolling change text.
scrolled view
Here is my code:
#interface ViewController ()
#end
#implementation ViewController
#synthesize calendar;
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
//[self.calendar setCollectionViewLayout:[[CalendarFlowLayout alloc]init]];
timeline = [NSArray arrayWithObjects:#"8:00", #"9:00",#"10:00",#"11:00",#"12:00",#"13:00",#"14:00",#"15:00",#"16:00",#"17:00",#"18:00",#"19:00",#"20:00",#"21:00",#"22:00",nil];
weekline=[NSArray arrayWithObjects:#"Mon", #"Tue",#"Wen",#"Thr",#"Fri",#"Sat",#"Sun",nil];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(NSInteger) numberOfSectionsInCollectionView:(UICollectionView *)collectionView{
return 1;
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
return 128;
}
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
UICollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"cell" forIndexPath:indexPath];
if (![cell.contentView viewWithTag:2]) {
UILabel * title;
UIView *message;
title =[[UILabel alloc]initWithFrame:CGRectMake(0, 0, cell.frame.size.width, cell.frame.size.height)];
title.font=[UIFont systemFontOfSize:14.0];
title.textAlignment=NSTextAlignmentCenter;
//title.backgroundColor=[UIColor redColor];
if (indexPath.row%8==0) {
int time =indexPath.row/8;
if (time<[timeline count]) {
title.text =[NSString stringWithFormat:#"%#",[timeline objectAtIndex:time]];
}
}else if(indexPath.row>0&&indexPath.row<8){
if (indexPath.row<[weekline count]+1) {
title.text =[NSString stringWithFormat:#"%#",[weekline objectAtIndex:indexPath.row-1]];
}
[cell.layer setBorderColor:[UIColor blackColor].CGColor];
[cell.layer setBorderWidth:1.0f];
}else{
[cell.layer setBorderColor:[UIColor blackColor].CGColor];
[cell.layer setBorderWidth:1.0f];
}
title.textColor=[UIColor blackColor];
message = [[UIView alloc] initWithFrame:CGRectMake(0.0, 0.0, cell.frame.size.width, cell.frame.size.height)];
message.tag = 2;
message.backgroundColor =[UIColor clearColor];
[message addSubview:title];
[cell.contentView addSubview:message];
}
return cell;
}
-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath{
CGFloat width =[[UIScreen mainScreen]bounds].size.width/8;
return CGSizeMake(width, width);
}
-(UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section{
return UIEdgeInsetsMake(0, 0, 0, 0);
}
-(CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section{
return 0.0;
}
-(CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section{
return 0.0;
}
#end
I just wonder why indexpath keep changing and how to fix this issue? thank you.
You only configure the cell if it doesn't have the message UIView (tag 2) - so when cells are reused you are simply returning them as they were configured previously - however there is no guarantee that the cell be reused in the same indexPath as it was previously - in fact you can pretty much guarantee that it won't.
You need to correctly configure your cell every time. This will be much easier if you configure your prototype cell in the storyboard, or if you don't want to do that create a UICollectionViewCell subclass that adds the title and message controls in its init method.

UICollectionView doesn't scroll full 320 points with paging enabled

Alright so lets say I have UICollection with 20 cells That scrolls horizontally with paging enabled and can fit 9 cells on each page, when I make it 10 cells instead of creating a second page it moves just enough to fit the 10th cell on the page. I want it to display the 10th cell on its own page when I scroll over.
Also i have tried changing the collectionview.contentsize but for some reason it stays the same no matter what i do.
Here is my code -
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
return CGSizeMake(82, 119);
}
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
return UIEdgeInsetsMake(20, 10, 50, 10);
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
customCell *cell= (customCell*)[collectionView dequeueReusableCellWithReuseIdentifier:#"cellIdentifier" forIndexPath:indexPath];
return (UICollectionViewCell*)cell;
}
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{
return 1;
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
return 20;
}
- (void)viewDidLoad {
UICollectionViewFlowLayout *layout=[[UICollectionViewFlowLayout alloc] init];
_collectionView=[[UICollectionView alloc] initWithFrame:self.view.frame collectionViewLayout:layout];
[_collectionView setDataSource:self];
[_collectionView setDelegate:self];
[_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:#"cellIdentifier"];
[_collectionView setBackgroundColor:[UIColor lightGrayColor]];
[layout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
_collectionView.pagingEnabled = YES;
layout.minimumInteritemSpacing = 15;
layout.minimumLineSpacing = 25;
[_collectionView setContentInset:UIEdgeInsetsMake(65, 0, 0, 0)];
_collectionView.allowsMultipleSelection = YES;
[self.view addSubview:_collectionView];
[super viewDidLoad];
// Do any additional setup after loading the view.
}
You can't force the collection view to completely scroll to a new page like that unfortunately.
Instead, just calculate the number of cells required to fill out the page and add empty ones to the end of your dataset.
For example, if you've got 19 items in your NSArray of data, add another 8 to bring the total up to 27.
In your collectionView:numberOfItemsInSection: delegate, do something like:
return (dataArray.count % 9 == 0) ? dataArray.count : ((dataArray.count/9|0)+1)*9;
// 17 returns 18
// 19 returns 27
Just make sure you perform a contingency operation in cellForItemAtIndexPath to display a blank cell (since your dataset won't actually contain data for that item).

Customizing UICollectionViewCell depending on indexPath

Hi i'm trying to customize my collectionviewcell depending on its indexPath but also if I set
if (indexPath.row == 0)
{
[cell addSubView: view];
}
the view appear random in some cells.
This is the code I'm using
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
return 15;
}
// The cell that is returned must be retrieved from a call to -dequeueReusableCellWithReuseIdentifier:forIndexPath:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:#"cellIdentifier" forIndexPath:indexPath];
NSInteger row = indexPath.row;
UIView *contentCell = [[UIView alloc] initWithFrame:cell.frame];
if (row == 0)
{
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(1.0f, 1.0f, 50.0f, 50.0f)];
label.text = #"Test";
[contentCell addSubview:label];
}
[cell addSubview:contentCell];
cell.backgroundColor=[UIColor colorWithPatternImage:[UIImage imageNamed:#"container"]];
return cell;
}
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(#"%d", indexPath.row);
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
return CGSizeMake(414, 228);
}
You have to read about reusable cells.
you can avoid the problem for now by doing this.
if (row == 0)
{
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(1.0f, 1.0f, 50.0f, 50.0f)];
label.text = #"Test";
label.tag = 200;
[contentCell addSubview:label];
}else{
UIView* lbl = [contentCell viewWithTag:200];
if(lbl)
[lbl removeFromSuperView];
}
but this will affect the scrolling and memory performance, you can put the label in the cell by default && show/hide it in the if/else blocks
You are adding view several times as a subview. Cells are reused due to "dequeueReusableCellWithReuseIdentifier", so after you scroll up and down, you get back existing view, which already has subview added.
You should read more about reusing cells.
One way to avoid that behavior is to create all views when you create a cell and just show / hide them.
Otherwise create cells with different identifier for different rows - in your case for row 0.

UICollectionView insertItemAtIndexPath not working

I am using a UICollectionView to produce a grid of cells say total of 10 i.e. 0-9.
Now, I want to insert a new cell in the grid on click of one of the cells.
so I have added the following line of code [_collectionView insertItemsAtIndexPaths:#[[NSIndexPath indexPathForItem:10 inSection:0]]]; inside the function didSelectItemAtIndexPath.
So now, if I set indexPathForItem: as 10 (i.e. insert at last) then I get 'Assertion failure' error on this line. If I set `indexPathForItem:' anything between 0-9 then I get 'EXC_BAD_ACCESS...' error on this line.
This is my complete code implementing UICollectionView:
- (void)loadView
{
self.view = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
UICollectionViewFlowLayout *layout=[[UICollectionViewFlowLayout alloc] init];
_collectionView=[[UICollectionView alloc] initWithFrame:CGRectMake(0, 97.5, self.view.frame.size.width, self.view.frame.size.height-67.5) collectionViewLayout:layout];
[_collectionView setDataSource:self];
[_collectionView setDelegate:self];
[_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:#"cellIdentifier"];
[_collectionView setBackgroundColor:[UIColor whiteColor]];
[self.view addSubview:_collectionView];
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection: (NSInteger)section
{
return 35;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:#"cellIdentifier" forIndexPath:indexPath];
cell.layer.borderWidth=.5f;
cell.layer.borderColor=[UIColor blackColor].CGColor;
if(indexPath.item<31)
{
_dayNumber = [[UILabel alloc] initWithFrame:CGRectMake(30, 30, 15, 15)];
_dayNumber.font = [UIFont systemFontOfSize:12];
_dayNumber.text = [NSString stringWithFormat:#"%ld",(indexPath.item + 1)];
[cell addSubview:_dayNumber];
}
return cell;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout: (UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
return CGSizeMake(self.view.frame.size.width/7, self.view.frame.size.width/7);
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout: (UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex: (NSInteger)section
{
return 0.0;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
{
return 0.0;
}
// Layout: Set Edges
- (UIEdgeInsets)collectionView:
(UICollectionView *)collectionView layout: (UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
return UIEdgeInsetsMake(0,0,0,0); // top, left, bottom, right
}
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath: (NSIndexPath *)indexPath
{
[_collectionView insertItemsAtIndexPaths:#[[NSIndexPath indexPathForItem:0 inSection:0]]];
}
Any help?
Well,
first let's consider this method,
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection: (NSInteger)section
{
return 35; // returning constant value means that you can't add or remove cells later
}
so let me change this to
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection: (NSInteger)section
{
return self.itemsCount;
}
declare itemsCount property in your class interface, like this
#interface YourClass ()
#property (nonatomic) NSInteger itemsCount;
#end
initialize it in loadView or init method,
_itemsCount = 35; // or whatever you want, initial count
now we can insert/delete items, right ? when we call insertItemAtIndexPaths all we have to do is updating actual data before that call, (for example self.itemsCount++, [self.myItems addObject:newItem] )
here is changes in your code
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
self.itemsCount++; // updating data
[_collectionView insertItemsAtIndexPaths:#[[NSIndexPath indexPathForItem:0 inSection:0]]];
}
One last important thing, in cellForItemAtIndexPath don't alloc init any kind of view and add as subview on cell, this code every time creates UILabels on cell, if you want custom view on cell (like an imageview, button, etc ..) you should subclass UICollectionViewCell and create this stuff in it's init method, here is how it will look like
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
YourCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:#"cellIdentifier" forIndexPath:indexPath];
cell.layer.borderWidth = 0.5;
cell.layer.borderColor = [UIColor blackColor].CGColor;
cell.dayNumber.font = [UIFont systemFontOfSize:12];
cell.dayNumber.text = [NSString stringWithFormat:#"%d",(indexPath.row + 1)];
return cell;
}
assuming you also changed this line,
[_collectionView registerClass:[YourCell class] forCellWithReuseIdentifier:#"cellIdentifier"];
note that YourCell is a subclass of UICollectionViewCell and has property dayNumber
Apple has a great guide about collection views. I recommend to read it.
Good luck.

UICollectionView not calling didSelectItemAtIndexPath

I have a Collection View and has custom cells with images and labels in there. I have set my collection view as follows -
UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
flowLayout.minimumLineSpacing = 150.0f;
flowLayout.minimumInteritemSpacing = 104.0f;
flowLayout.sectionInset = UIEdgeInsetsMake(20, 20, 100, 120);
_archiveCollectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:flowLayout];
_archiveCollectionView.frame = CGRectMake(30, 218, _archiveCollectionView.frame.size.width - 60, _archiveCollectionView.frame.size.height - 350);
_archiveCollectionView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
_archiveCollectionView.backgroundColor = [UIColor clearColor];
_archiveCollectionView.delegate = self;
_archiveCollectionView.dataSource = self;
[self.archiveCollectionView registerNib:[UINib nibWithNibName:#"FullArchiveEditionCell" bundle:nil] forCellWithReuseIdentifier:#"MyCell"];
[_archiveCollectionView reloadData];
[self.view addSubview:_archiveCollectionView];
I have also set the following methods:
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return _chosenCategoryArray.count;
}
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
return 1;
}
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
[self addEditionsChildView];
}
-(BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath {
return YES;
}
However, my didSelectItemAtIndexPath never gets called when I select a cell. Any help please?
I had a similar problem and it turned out I was using the same cell reuse identifier in two different collection views
In your header file have you implemented UICollectionViewDelegate as like below,
#interface HAViewController : UIViewController <UICollectionViewDataSource, UICollectionViewDelegate>
I have the same problem. And I solved by using storyboard to locate the collection cell in the collection view controller. Then tick User InterAction Enabled. I think using code to set in the UICollectionViewCell would also work. Hope it would help.
Try with changing sequence as given below
[_archiveCollectionView reloadData];
[self.view addSubview:_archiveCollectionView];
to
[self.view addSubview:_archiveCollectionView];
[_archiveCollectionView reloadData];
Implement the below delegate method.
- (BOOL)collectionView:(UICollectionView *)collectionView shouldDeselectItemAtIndexPath:(NSIndexPath *)indexPath{
return YES;
}
And implement your
- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath {
//your selection management code
}
and
- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath{
//deselection handling code
}

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