I can't seem to find any solution to following bug. I'm using collection view in usual UIViewController, and using new ios9 feature for interactive reordering. Also I define where i can move picked cell using targetIndexPathForMoveFromItemAtIndexPath:.
The bug is when the targetIndex is not visible in collectionView, moving cell leaves duplicate of itself in place, where touch ended.
Please see bug scrren shot here. The gray cell are not allowed to be placed between pink cells and it should be placed after last gray cell which is not visible cause it's in the beginning of view.
I also use wiggle animation for reordering taken from this article.
https://littlebitesofcocoa.com/104-interactive-collection-view-re-ordering
If you need code where i define my gesture recognizer, here it is
if (gesture.state==UIGestureRecognizerStateBegan){
NSIndexPath *selectedIndexPath = [self.collectionView indexPathForItemAtPoint:[gesture locationInView:self.collectionView]];
if(!selectedIndexPath)
return;
movingIndexPath=selectedIndexPath;
[self setEditing:YES];
[self.collectionView beginInteractiveMovementForItemAtIndexPath:selectedIndexPath];
TLTimelineCollectionCell *pickedCell=[self pickedUpCell];
movingCollectionCell=pickedCell;
[pickedCell stopWiggling];
[self animatePickingUpCell:pickedCell];
UICollectionViewLayoutAttributes *attributes = [self.collectionView layoutAttributesForItemAtIndexPath:selectedIndexPath];
CGRect cellRect = attributes.frame;
CGRect rect=[self.collectionView convertRect:cellRect toView:self.collectionView];
} else if (gesture.state==UIGestureRecognizerStateChanged) {
[self.collectionView updateInteractiveMovementTargetPosition:CGPointMake([gesture locationInView:gesture.view].x,39)];
} else {
if (gesture.state==UIGestureRecognizerStateEnded) {
[self.collectionView endInteractiveMovement];
} else {
[self.collectionView cancelInteractiveMovement];
}
[self animatePuttingDownCell:movingCollectionCell];
movingIndexPath=nil;
movingCollectionCell=nil;
[self setEditing:NO];
}
Appreciate any help, thank you!
UPDATE
Found out that this bug also happens without any "wiggle animations" in clear project with just one collection view controller
Turned out that it's iOS 9 bug. On iOS 10 works fine.
Related
This is my first time working with UICollectionView.
I've got everything set up and laid out as it should be (as far as I know). I've had a little bit of difficulty with the way the dequeue function works for the UICollectionView, but I think I've gotten past that. It was tricky setting up my custom cell classes when I didn't know if initWithFrame would be called or prepareForReuse.
I'm pretty sure the problem lies within the prepareForReuse function, but where is the question.
What happens is, the cells will apparently randomly draw at the top-left of the collection view and some cells will not be where they belong in the grid. (see image attached)
When bouncing, scrolling, and zooming (so as to cause reuse to occur), the problem happens. Randomly a slide will appear in the top left, and other slides will randomly disappear from the grid.
( I need more rep to post an image. Ugh. :| If you can help me, I'll email you the image. bmantzey#mac.com )
-(UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
Slide* thisSlide = [_presentation.slidesInEffect objectAtIndex:indexPath.row];
[BuilderSlide prepareWithSlide:thisSlide];
BuilderSlide* cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"PlainSlide" forIndexPath:indexPath];
return cell;}
I'm using a static method to set the Slide object, which contains the data necessary to either prepare the asynchronous download or retrieve the image from disk cache.
It's simply:
+(void)prepareWithSlide:(Slide*)slide{
if(s_slide)
[s_slide release];
s_slide = [slide retain];}
I'm not sure if it's a big no-no to do this but in my custom Cell class, I'm calling prepareForReuse in the initWithFrame block because I need that setup code to be the same:
-(id)initWithFrame:(CGRect)frame{
self = [super initWithFrame:frame];
if(self)
{
[self prepareForReuse];
}
return self;}
Here's the prepareForReuse function:
-(void)prepareForReuse{
CGSize size = [SpringboardLayout currentSlideSize];
[self setFrame:CGRectMake(0, 0, size.width, size.height)];
self.size = size;
// First remove any previous view, so as not to stack them.
if(_builderSlideView)
{
if(_builderSlideView.slide.slideID == s_slide.slideID)
return;
[_builderSlideView release];
}
for(UIView* aView in self.contentView.subviews)
{
if([aView isKindOfClass:[BuilderSlideView class]])
{
[aView removeFromSuperview];
break;
}
}
// Then setup the new view.
_builderSlideView = [[BuilderSlideView alloc] initWithSlide:s_slide];
self.builderCellView = _builderSlideView;
[s_slide release];
s_slide = nil;
[self.contentView addSubview:_builderSlideView];
if([SlideCache isImageCached:_builderSlideView.slide.slideID forPresentation:_builderSlideView.slide.presentationID asThumbnail:YES])
{
[_builderSlideView loadImageFromCache];
}
else
{
[_builderSlideView loadView];
}}
Finally, when the slide image has been downloaded, a Notification is posted (I plan on changing this to a delegate call). The notification simply reloads the cell that has received an update. Here's the notification code:
-(void)didLoadBuilderCellView:(NSNotification*)note{
BuilderCellView* cellView = [[note userInfo] objectForKey:#"cell"];
BuilderSlideView* slideView = (BuilderSlideView*)cellView;
NSIndexPath* indexPath = [self indexPathForSlide:slideView.slide];
if(indexPath)
[self.collectionView reloadItemsAtIndexPaths:[NSArray arrayWithObject:indexPath]];}
Note that the slide objects exist in the model.
Any ideas as to what may be causing this problem? Thanks in advance!
The problem that was causing the cells to draw top left and/or disappear was caused by infinite recursion on a background thread. Plain and simply, I wasn't implementing the lazy loading correctly and safely. To solve this problem, I went back to the drawing board and tried again. Proper implementation of a lazy loading algorithm did the trick.
I'm developing an app that has a UICollectionView - the collection view's job is to display data from a web service.
One feature of the app I am trying to implement is enabling the user to change the layout of this UICollectionView from a grid view to a table view.
I spent a lot of time trying to perfect this and I managed to get it to work. However there are some issues. The transition between the two layout doesn't look good and sometimes it breaks between switching views and my app is left with a view in an unexpected state. That only happens if the user switches between grid and table view very quickly (pressing the changeLayoutButton) continuously.
So, obviously there are some problems and I feel the code is a little fragile. I also need to fix the above mentioned issues.
I'll start off with how I implemented this view.
Implementation
Since I needed the two different cells (grideCell and tableViewCell) to show different things - I decided it would be better to subclass UICollectionViewFlowLayout since it does everything I need - all I need to do is change the cell sizes.
With that in mind I created two classes that subclassed UICollectionViewFlowLayout
This is how those two classes look:
BBTradeFeedTableViewLayout.m
#import "BBTradeFeedTableViewLayout.h"
#implementation BBTradeFeedTableViewLayout
-(id)init
{
self = [super init];
if (self){
self.itemSize = CGSizeMake(320, 80);
self.minimumLineSpacing = 0.1f;
}
return self;
}
#end
BBTradeFeedGridViewLayout.m
#import "BBTradeFeedGridViewLayout.h"
#implementation BBTradeFeedGridViewLayout
-(id)init
{
self = [super init];
if (self){
self.itemSize = CGSizeMake(159, 200);
self.minimumInteritemSpacing = 2;
self.minimumLineSpacing = 3;
}
return self;
}
#end
Very simple and as you can see - just changing the cell sizes.
Then in my viewControllerA class I implemented the UICollectionView like so:
Created the properties:
#property (strong, nonatomic) BBTradeFeedTableViewLayout *tableViewLayout;
#property (strong, nonatomic) BBTradeFeedGridViewLayout *grideLayout;
in viewDidLoad
/* Register the cells that need to be loaded for the layouts used */
[self.tradeFeedCollectionView registerNib:[UINib nibWithNibName:#"BBItemTableViewCell" bundle:nil] forCellWithReuseIdentifier:#"TableItemCell"];
[self.tradeFeedCollectionView registerNib:[UINib nibWithNibName:#"BBItemGridViewCell" bundle:nil] forCellWithReuseIdentifier:#"GridItemCell"];
The user taps a button to change between layouts:
-(void)changeViewLayoutButtonPressed
I use a BOOL to determine which layout is currently active and based on that I make the switch with this code:
[self.collectionView performBatchUpdates:^{
[self.collectionView.collectionViewLayout invalidateLayout];
[self.collectionView setCollectionViewLayout:self.grideLayout animated:YES];
} completion:^(BOOL finished) {
}];
In cellForItemAtIndexPath
I determine which cells I should use (grid or tableView) and the load the data - that code looks like this:
if (self.gridLayoutActive == NO){
self.switchToTableLayout = NO;
BBItemTableViewCell *tableItemCell = [collectionView dequeueReusableCellWithReuseIdentifier:tableCellIdentifier forIndexPath:indexPath];
if ([self.searchArray count] > 0){
self.switchToTableLayout = NO;
tableItemCell.gridView = NO;
tableItemCell.backgroundColor = [UIColor whiteColor];
tableItemCell.item = self.searchArray[indexPath.row];
}
return tableItemCell;
}else
{
BBItemTableViewCell *gridItemCell= [collectionView dequeueReusableCellWithReuseIdentifier:gridCellIdentifier forIndexPath:indexPath];
if ([self.searchArray count] > 0){
self.switchToTableLayout = YES;
gridItemCell.gridView = YES;
gridItemCell.backgroundColor = [UIColor whiteColor];
gridItemCell.item = self.searchArray[indexPath.row];
}
return gridItemCell;
}
Lastly in the two cell classes - I just use the data to set the image / text as I need.
Also in grid cell - the image is bigger and I remove text I don't want - which was the primary reason for uses two cells.
I'd be interested in how to make this view look a little more fluid and less buggy in the UI. The look I am going for is just like eBays iOS app - they switch between three different views. I just need to switch between two different views.
#jrturton's answer is helpful, however unless I'm missing something it is really overcomplicating something very simple. I'll start with the points we agree on...
Prevent interaction while changing layouts
First off, I agree with the approach of disabling user interaction at the start of the layout transition & reenabling at the end (in the completion block) using [[UIApplication sharedApplication] begin/endIgnoringInteractionEvents] - this is much better than trying cancel an in-progress transition animation & immediately begin the reverse transition from the current state.
Simplify the layout transition by using a single cell class
Also, I very much agree with the suggestion to use the same cell class for each layout. Register a single cell class in viewDidLoad, and simplify your collectionView:cellForItemAtIndexPath: method to just dequeue a cell and set its data:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
BBItemCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellID forIndexPath:indexPath];
if ([self.searchArray count] > 0) {
cell.backgroundColor = [UIColor whiteColor];
cell.item = self.searchArray[indexPath.row];
}
return cell;
}
(Notice that the cell itself shouldn't (in all but exceptional cases) need to be aware of anything to do with what layout is currently in use, whether layouts are transitioning, or what the current transition progress is)
Then when you call setCollectionViewLayout:animated:completion: the collection view doesn't need to reload any new cells, it just sets up an animation block to change each cell's layout attributes (you don't need to call this method from inside an performBatchUpdates: block, nor do you need to invalidate the layout manually).
Animating the cell subviews
However as pointed out, you will notice that subviews of the cell jump immediately to their new layout's frames. The solution is to simply force immediate layout of the cells subviews when the layout attributes are updated:
- (void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)layoutAttributes
{
[super applyLayoutAttributes:layoutAttributes];
[self layoutIfNeeded];
}
(No need to create special layout attributes just for the transition)
Why does this work? When the collection view changes layouts, applyLayoutAttributes: is called for each cell as the collection view is setting up the animation block for that transition. But the layout of the cell's subviews is not done immediately - it is deferred to a later run loop - resulting in the actual subview layout changes not being incorporated into the animation block, so the subviews jump to their final positions immediately. Calling layoutIfNeeded means that we are telling the cell that we want the subview layout to happen immediately, so the layout is done within the animation block, and the subviews' frames are animated along with the cell itself.
It is true that using the standard setCollectionViewLayout:... API does restrict control of the animation timing. If you want to apply a custom easing animation curve then solutions like TLLayoutTransitioning demonstrate a handy way of taking advantage of interactive UICollectionViewTransitionLayout objects to take control of the animation timing. However, as long as only a linear animation of subviews is required I think most people will be satisfied with the default animation, especially given the one-line simplicity of implementing it.
For the record, I'm not keen on the lack of control of this animation myself, so implemented something similar to TLLayoutTransitioning. If this applies to you too, then please ignore my harsh reproval of #jrturton's otherwise great answer, and look into TLLayoutTransitioning or UICollectionViewTransitionLayouts implemented with timers :)
Grid / table transitions aren't as easy as a trivial demo would have you believe. They work fine when you've got a single label in the middle of the cell and a solid background, but once you have any real content in there, it falls over. This is why:
You have no control over the timing and nature of the animation.
While the frames of the cells in the layout are animated from one value to the next, the cells themselves (particularly if you are using two separate cells) don't seem to perform internal layout for each step of the animation so it seems to "flick" from one layout to the next inside each cell - your grid cell looks wrong in table size, or vice versa.
There are many different solutions. It's hard to recommend anything specific without seeing your cell's contents, but I've had success with the following:
take control of the animation using techniques like those shown here. You could also check out Facebook Pop to get better control over the transition but I haven't looked into that in any detail.
use the same cell for both layouts. Within layoutSubviews, calculate a transition distance from one layout to the other and use this to fade out or in unused elements, and to calculate nice transitional frames for your other elements. This prevents a jarring switch from one cell class to the other.
That's the approach I used here to fairly good effect.
It's harder work that relying on resizing masks or Autolayout but it's the extra work that makes things look good.
As for the issue when the user can toggle between the layouts too quickly - just disable the button when the transition starts, and re- enable it when you're done.
As a more practical example, here's a sample of the layout change (some of it is omitted) from the app linked above. Note that interaction is disabled while the transition occurs, I am using the transition layout from the project linked above, and there is a completion handler:
-(void)toggleLayout:(UIButton*)sender
{
[[UIApplication sharedApplication] beginIgnoringInteractionEvents];
HMNNewsLayout newLayoutType = self.layoutType == HMNNewsLayoutTable ? HMNNewsLayoutGrid : HMNNewsLayoutTable;
UICollectionViewLayout *newLayout = [HMNNewsCollectionViewController collectionViewLayoutForType:newLayoutType];
HMNTransitionLayout *transitionLayout = (HMNTransitionLayout *)[self.collectionView transitionToCollectionViewLayout:newLayout duration:0.5 easing:QuarticEaseInOut completion:^(BOOL completed, BOOL finish)
{
[[NSUserDefaults standardUserDefaults] setInteger:newLayoutType forKey:HMNNewsLayoutTypeKey];
self.layoutType = newLayoutType;
sender.selected = !sender.selected;
for (HMNNewsCell *cell in self.collectionView.visibleCells)
{
cell.layoutType = newLayoutType;
}
[[UIApplication sharedApplication] endIgnoringInteractionEvents];
}];
[transitionLayout setUpdateLayoutAttributes:^UICollectionViewLayoutAttributes *(UICollectionViewLayoutAttributes *layoutAttributes, UICollectionViewLayoutAttributes *fromAttributes, UICollectionViewLayoutAttributes *toAttributes, CGFloat progress)
{
HMNTransitionLayoutAttributes *attributes = (HMNTransitionLayoutAttributes *)layoutAttributes;
attributes.progress = progress;
attributes.destinationLayoutType = newLayoutType;
return attributes;
}];
}
Inside the cell, which is the same cell for either layout, I have an image view and a label container. The label container holds all the labels and lays them out internally using auto layout. There are constant frame variables for the image view and the label container in each layout.
The layout attributes from the transition layout are a custom subclass which include a transition progress property, set in the update layout attributes block above. This is passed into the cell using the applyLayoutAttributes method (some other code omitted):
-(void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)layoutAttributes
{
self.transitionProgress = 0;
if ([layoutAttributes isKindOfClass:[HMNTransitionLayoutAttributes class]])
{
HMNTransitionLayoutAttributes *attributes = (HMNTransitionLayoutAttributes *)layoutAttributes;
self.transitionProgress = attributes.progress;
}
[super applyLayoutAttributes:layoutAttributes];
}
layoutSubviews in the cell subclass does the hard work of interpolating between the two frames for the images and labels, if a transition is in progress:
-(void)layoutSubviews
{
[super layoutSubviews];
if (!self.transitionProgress)
{
switch (self.layoutType)
{
case HMNNewsLayoutTable:
self.imageView.frame = imageViewTableFrame;
self.labelContainer.frame = labelContainerTableFrame;
break;
case HMNNewsLayoutGrid:
self.imageView.frame = imageViewGridFrame;
self.labelContainer.frame = self.originalGridLabelFrame;
break;
}
}
else
{
CGRect fromImageFrame,toImageFrame,fromLabelFrame,toLabelFrame;
if (self.layoutType == HMNNewsLayoutTable)
{
fromImageFrame = imageViewTableFrame;
toImageFrame = imageViewGridFrame;
fromLabelFrame = labelContainerTableFrame;
toLabelFrame = self.originalGridLabelFrame;
}
else
{
fromImageFrame = imageViewGridFrame;
toImageFrame = imageViewTableFrame;
fromLabelFrame = self.originalGridLabelFrame;
toLabelFrame = labelContainerTableFrame;
}
CGFloat from = 1.0 - self.transitionProgress;
CGFloat to = self.transitionProgress;
self.imageView.frame = (CGRect)
{
.origin.x = from * fromImageFrame.origin.x + to * toImageFrame.origin.x,
.origin.y = from * fromImageFrame.origin.y + to * toImageFrame.origin.y,
.size.width = from * fromImageFrame.size.width + to * toImageFrame.size.width,
.size.height = from * fromImageFrame.size.height + to * toImageFrame.size.height
};
self.labelContainer.frame = (CGRect)
{
.origin.x = from * fromLabelFrame.origin.x + to * toLabelFrame.origin.x,
.origin.y = from * fromLabelFrame.origin.y + to * toLabelFrame.origin.y,
.size.width = from * fromLabelFrame.size.width + to * toLabelFrame.size.width,
.size.height = from * fromLabelFrame.size.height + to * toLabelFrame.size.height
};
}
self.headlineLabel.preferredMaxLayoutWidth = self.labelContainer.frame.size.width;
}
And that's about it. Basically you need a way of telling the cell how far through the transition it is, which you need the layout transitioning library (or, as I say, Facebook pop might do this) for, and then you need to make sure you get nice values for layout when transitioning between the two.
I am trying to create custom tiled layout using UICollectionView.
It renders perfectly as desired in simulator once I run my app.
But the moment I scroll the view and bring it back all the cell's frame changes and the cells get overlapped, leaving spaces, randomly.
I am not able to solve this issue past 2 days.
Here goes the code from my custom layout class.
-(void)prepareLayout{
[self createCellSizeArray];//cellSizeArray holds cell sizes for all the cells(calculated statically)
[self createAttributeArrayOfAll];//attributeArrayOfAll holds attributes for all the cells and also calculates their frames using cellSizeArray
}
-(CGSize)collectionViewContentSize{
return CGSizeMake(768, 1500);//The size is static to check for scrolling, is this creating problems?
}
-(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{
UICollectionViewLayoutAttributes * layoutAttributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
return layoutAttributes;
}
-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{
NSMutableArray *attArray =[NSMutableArray array];
for (NSInteger i =0; i< attributeArrayOfAll.count; i++) {
UICollectionViewLayoutAttributes * attribute = (UICollectionViewLayoutAttributes*)[attributeArrayOfAll objectAtIndex:i];
if(CGRectIntersectsRect(rect, attribute.frame)){
[attArray addObject:attribute];
}
}
return attArray;
}
-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{
return YES;
}
Please help, Thanks in advance.
Edit:
In my [self createAttributeArrayOfAll]; I have these lines of code
CGRect frame = CGRectMake(_startNewRowPoint.x, _startNewRowPoint.y, cellSize.width, cellSize.height);
UICollectionViewLayoutAttributes * attribute = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:[NSIndexPath indexPathForItem:i inSection:0]];
attribute.alpha = 1.0;
attribute.frame = frame;
[attributeArrayOfAll addObject:attribute];
While I modified layoutAttributesForItemAtIndexPath:, to look something like this
-(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{
UICollectionViewLayoutAttributes * layoutAttributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
layoutAttributes.frame = ((UICollectionViewLayoutAttributes*)[attributeArrayOfAll objectAtIndex:indexPath.item]).frame;
return layoutAttributes;
}
Moreover, the method layoutAttributesForItemAtIndexPath: never gets called implicitly. I even tried this:
-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{
NSMutableArray *attArray =[NSMutableArray arrayWithCapacity:attributeArrayOfAll.count];
for (NSInteger i =0; i< attributeArrayOfAll.count; i++) {
UICollectionViewLayoutAttributes * attribute = (UICollectionViewLayoutAttributes*)[attributeArrayOfAll objectAtIndex:i];
if(CGRectIntersectsRect(rect, attribute.frame)){
[attArray insertObject:[self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:i inSection:0]] atIndex:i];
}
}
return attArray;
}
But still the result is the same distorted set of cells on scrolling.
I worked with 5 cells, first time it renders correctly, on scrolling away and then bringing it back in visible rect it gets distorted, if i scroll away again and bring it back in visible rect it renders correctly. However, when I do this with around 400 cells, once i scroll it never renders correctly. Even on reloading collection view, The cells gets distort. Please help.
Your layoutAttributesForItemAtIndexPath: method is not setting any properties of the layoutAttributes object before returning it. It needs to set frame (or center and size).
So finally managed a workaround!!! dequeue each cell with an unique Cell Identifier in cellForRow:
[self.summaryView registerClass:[BFSSummaryViewCell class] forCellWithReuseIdentifier:[NSString stringWithFormat:#"%#%d",CellIdentifier,indexPath.row]];
UICollectionViewCell *collectionCell = [collectionView dequeueReusableCellWithReuseIdentifier:[NSString stringWithFormat:#"%#%d",CellIdentifier,indexPath.row] forIndexPath:indexPath];
These two lines inside cellForRow worked for me, however with my collection view having around 1000 cells it increases the size of my application considerably. Lets hope apple fixes this bug asap.
Disclaimer: I've been working too late. But, I'm determined to get through this one tonight.
I have an app where I support different color themes. The dark cell backgrounds have been problematic.
I've been poking around trying to find a formidable way to draw the accessory disclosure icon in uitableviewcells with black backgrounds.
I decided to try overriding setAccessoryType to inherit the functionality for my 50+ views:
-(void) addWhiteDisclosureImage {
UIImageView *disclosureView = (UIImageView*) [self.contentView viewWithTag:kDisclosureReplacementImageTag];
if(!disclosureView) {
[super setAccessoryType:UITableViewCellAccessoryNone];
disclosureView = [[UIImageView alloc] initWithImage:self.whiteDisclosureImage];
disclosureView.tag = kDisclosureReplacementImageTag;
disclosureView.autoresizingMask = UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleLeftMargin;
DebugLog(#"%f, %f", self.frame.size.width, self.frame.size.height);
[self.contentView addSubview:disclosureView];
[self.contentView bringSubviewToFront:disclosureView];
[disclosureView release];
}
}
- (void)setAccessoryType:(UITableViewCellAccessoryType)accessoryType {
if(accessoryType == UITableViewCellAccessoryDisclosureIndicator) {
if ([self.viewController isKindOfClass:[ViewControllerBase class]]) {
ViewControllerBase *view = (ViewControllerBase*) self.viewController;
if(view.colorTheme && view.colorTheme.controlBackgroundColor) {
if([ViewColors colorAverage:view.colorTheme.controlBackgroundColor] < 0.2) { //substitute white disclosure indicator
[self addWhiteDisclosureImage];
return;
} else { //not dark enough
[self removeWhiteDisclosureImage];
[super setAccessoryType:accessoryType];
return;
}
} else { //no colorTheme.backgroundColor
[self removeWhiteDisclosureImage];
[super setAccessoryType:accessoryType];
return;
}
} else { //viewController is not type ViewControllerBase
[self removeWhiteDisclosureImage];
[super setAccessoryType:accessoryType];
return;
}
}
UIView *disclosureView = [self.contentView viewWithTag:kDisclosureReplacementImageTag];
if(disclosureView)
[disclosureView removeFromSuperview];
[super setAccessoryType:accessoryType];
}
This override is typically called in cellForRowAtIndexPath.
It seemed like a good option until I drill down and come back. For some cells, the cell frame will be a great deal larger than the first time through. This consistently happens to the same cell in a list of 6 that I've been testing against. There's clearly something unique about this cell: it's frame.size.
Here is the size of the cell that I log for the first tableview load (in some cases every load/reload):
320.000000, 44.000000
This is the difference in what I get for some (not all) of the cells after call to reloadData:
759.000000, 44.000000
Does anyone know why this might happen?
Update: the suspect cell's custom accessory disclosure view almost acts like it's autoresizing flag is set to none. I confirmed this by setting all to none. I say almost because I see it line up where it should be after reloadData. A split second later it moves clear over to the left (where they all end up when I opt for no autoresizing).
Don't mess around with subviews and calculating frames.
Just replace the accessoryView with the new imageView. Let iOS do the work.
I would like to implement an app using a UIScrollView with paging, similar to the apple weather app.
But I am a little concerned about performance. The example implementation I have been using loads all of the views then the application launches. After a certain point, once this prove slow?
I wonder how Apple's camera roll is dealing with this, where a user may have 100+ photos that can be scrolled through. Should I try to figure out a way to build the view only when it is needed? Or maybe there is a way to replicate the dequeue reusable cell technique from a UITableView, only for horizontal view loading, since each view will have the same layout.
By far the most efficient solution (and this is used in many photo-browsing apps such as Facebook, and probably the native Photos app too) is going to be to load the content on-demand, just as UITableView does. Apple's StreetScroller sample project should get you on the right track.
A very efficient solution, is to make sure to reuse any views whenever possible. If you are going to be simply displaying images, you could use a subclass of UIScrollView, and layout these reusable views within layoutSubviews. Here you could detect what views are visible and not visible and create the subviews as needed.
An example dequeuing function may look like:
- (UIImageView *)dequeueReusableTileWithFrame:(CGRect) frame andImage:(UIImage *) image
{
UIImageView *tile = [reusableTiles anyObject];
if (tile) {
[reusableTiles removeObject:tile];
tile.frame = frame;
}
else {
tile = [[UIImageView alloc] initWithFrame:frame];
}
tile.image = image;
return tile;
}
Where reusableTiles is just an iVar of NSMutableSet type. You could then use this to load fetch any currently offscreen image views and quickly and easily bring them back into view.
Your layoutSubviews may look something like:
- (void)layoutSubviews {
[super layoutSubviews];
CGRect visibleBounds = [self bounds];
CGPoint contentArea = [self contentOffset];
//recycle all tiles that are not visible
for (GSVLineTileView *tile in [self subviews]) {
if (! CGRectIntersectsRect([tile frame], visibleBounds)) {
[reusableTiles addObject:tile];
[tile removeFromSuperview];
}
}
int col = firstVisibleColumn = floorf(CGRectGetMinX(visibleBounds)/tileSize.width);
lastVisibleColumn = floorf(CGRectGetMaxX(visibleBounds)/tileSize.width) ;
int row = firstVisibleRow = floorf(CGRectGetMinY(visibleBounds)/tileSize.height);
lastVisibleRow = floorf(CGRectGetMaxY(visibleBounds)/tileSize.height);
while(row <= lastVisibleRow)
{
col = firstVisibleColumn;
while (col <= lastVisibleColumn)
{
if(row < firstDisplayedRow || row > lastDisplayedRow || col < firstDisplayedColumn || col >lastDisplayedColumn)
{
UImageView* tile = [self dequeueReusableTileWithFrame:CGRectMake(tileSize.width*col, tileSize.height*row, tileSize.width, tileSize.height) andImage:YourImage];
[self addSubview:tile];
}
++col;
}
++row;
}
firstDisplayedColumn = firstVisibleColumn;
lastDisplayedColumn = lastVisibleColumn;
firstDisplayedRow = firstVisibleRow;
lastDisplayedRow = lastVisibleRow;
}
I used something similar to this to tile in areas of a line when I was working with an exceptionally large area of a scroll view and it seemed to work quite well. Sorry for any typos that I may have created when updating this for an image view instead of my custom tileView class.