In a UITableViewController I am instantiating UITableViewCells where some cells are highlighted by an accessoryView. For me, this works:
// works for me
UIImageView *favoriteImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"icon"]];
[cell setAccessoryView:favoriteImageView];
It seems wasteful to me to instantiate the same view repeatedly for multiple cells; however when I attempt to re-use the same view as the accessoryView of multiple cells my app fails in a miserable way (completely black screen, no views presented) I haven't been able to debug. Whether I declare favoriteImageView as a static inside the method such as
// doesn't work for me
static UIImageView *favoriteImageView = nil;
if (!favoriteImageView)
favoriteImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"icon"]];
[cell setAccessoryView:favoriteImageView];
Or declare it as an ivar and define it in init such that I wind up with:
// doesn't work for me
[cell setAccessoryView:[self favoriteImageView]];
In these two not-working cases, when one cell has its accessoryView set, it displays properly. As soon as I mark a second row such that the accessoryView would be set to reference the same view, the whole thing hangs up.
What are the requirements for constructing a UIView and/or configuring a UITableViewCell in such a way that the same UIView may be referenced as the accessoryView of multiple UITableViewCells?
UIImageView extends from UIView. And a UIView can't be in two or more places at the same time.
Therefor, if you try to display an UIImageView in two or more cells at the same time, it won't work. You need an UIImageView for each cell on screen.
I suggest that for each cell you create the UIImageView. The tableviewcells will be reused alongside with their accessoryview, so I wouldn't worry too much about performance or memoryproblems.
Related
I making app with collection view and different layout for portrait and landscape orientation and i am allocating UIlabel for every cell.
This is how i do it.
UILabel *scheduleCellLabel = [[UILabel alloc] init];
scheduleCellLabel.textAlignment = NSTextAlignmentCenter;
scheduleCellLabel.frame = CGRectMake(0, 0,scheduleCell.bounds.size.width, scheduleCell.bounds.size.height);
[scheduleCell addSubview:scheduleCellLabel];
Problem is that i reload collection view everytime the orientation changes, but the old cells stays in collection view. I tried to remove the label from cell on load, but that is not the issue.
This is how it looks:
Thanks in advance.
In my opinion, it's not good practice to put subview-adding code in cellForRowAtIndexPath unless you need to; for instance, if some cells have a subview, and some do not based on the indexPath. You should either make the cell in IB, or subclass the cell, and add any subviews in the cell's init method. That way, you don't have to remove views before you re-add them, or check if they exist before you add one; that just complicates your cellForRowAtIndexPath method.
Delete and add the label in cellForItemAtIndexPath. First ull check if label is in the cell, if yes, remove it from superview, then create new label and add it to its contentview.
Probably, you allocate your uilabel in cellForRowAtIndexPath method and it appears again and again when you reload your collectionView.
To solve your problem,just define your label as a property and allocate it in the viewDidLoad method and do what you want in cellForRowAtIndexPath method. Hope this will help.
For example, this is your header file:
#property (retain,nonatomic) IBOutlet UILabel *label;
and this is the viewDidLoad method of implemantation file:
_label = [[UILabel alloc] init];
I have a UITableViewCell which contains an UIView.
This UIView is larger than the UITableViewCell and should also be visible in the cell above.
clipsToBounds=NO
did not work.
This does only work when I remove the content from the upper cell and set the background color to clear.
This means, the content in my upper cell covers my UIView, that's why I tried to call bringSubViewToFront, but this did also not work.
What am I doing wrong?
This is how I add the custom UIView to the cell's contentView:
CustomView *view=[[CustomView alloc] initWithFrame:CGRectMake(0, 0, [DeviceInformation getWidth], [self tableView:tableView heightForRowAtIndexPath:indexPath])];
[cell.contentView addSubview:view];
and in my CustomView I am adding another UIView, which should be then presented among multiple Cells.
Thanks!
I've got a UITableView with several different elements added programmatically. The one I'm having trouble with is the UITextView that displays correctly with correct color, size, font, etc... I have a button in one cell that increases the size of the font in the UITextView in another cell. It works fine and has no issues. The numerical value is placed in a Plist, and when you leave the view with the table and come back the size changes perfectly.
I've placed a reloadData in the button which does reload the table and gives the textView new size and resizes it to fit the new content plus resizes the cell perfectly. The issue I'm having is that when the reloadData is called, the old textView remains. So I have two texts, at two different sizes, or three or four and so on. How can I remove the previous textView when it's not set to global?
Everything is set up exactly how one would expect:
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"Cell" forIndexPath:indexPath];
// cell with textView. Everything is instanced and created for just that cell with tags
UITextView *t = [self setSizeAndTextOfTextView];
[cell.contentView addSubview:t];
// cell with button. simple, alloc's and init inside cell. Calls method in same class
cell.contentView addSubview:button];
//method to increases font size
write to Plist the new size
[self.tableView reloadData]; <-- tableView is iboutlet that does reload table
How are you getting the cell in the first place? Are you reusing? If you are you don't want to add the textview as a subview again you want to retrieve the existing one and adjust it
UPDATE:
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"Cell" forIndexPath:indexPath];
if ([cell.contentView viewWithTag:1]) {
UITextView *t = (UITextView *)[cell.contentView viewWithTag:1];
//This version will take an existing textview and just resize it
[self setSizeAndTextOfTextView:t];
} else {
//This version creates a new text view
UITextView *t = [self setSizeAndTextOfTextView];
t.tag = 1
[cell.contentView addSubview:t];
}
You'll probably need to do something similar with you button as well
The reloadData won't wipe the existing cells, just the data displayed, so you'll get an old one to reuse
You may consider creating a custom subclass of UITableViewCell and associate that with your cell identifier. In your subclass, override the prepareForReuse method to set the cell back to a neutral state. Since cell objects are reused but are only initialized once, prepareForReuse is available to restore an already existing cell to its freshly initialized state.
I'm having an issue,
I have a simple UICollectionView with a static 200 cells that load images from Flickr.
my CellForItemAtIndexPath looks like this:
- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell = [cv dequeueReusableCellWithReuseIdentifier:#"FlickrCell" forIndexPath:indexPath];
cell.backgroundColor = [self generateRandomUIColor];
if(![[cell.subviews objectAtIndex:0] isKindOfClass:[PFImageView class]])
{
NSURL *staticPhotoURL = [self.context photoSourceURLFromDictionary:[self.photos objectAtIndex:indexPath.row] size:OFFlickrSmallSize];
PFImageView *imageView = [[PFImageView alloc] initWithFrame:CGRectMake(0, 0, cell.frame.size.height, cell.frame.size.width) andImageURL:staticPhotoURL andOwningCell:cell];
[cell addSubview:imageView];
}
return cell;
}
PFImageView is a subclass of UIImageView that loads a Flickr photo URL on a background thread and then updates it's own image on the main thread - this works fine.
The logic is really simple - I create a cell if there isn't one dequeueable.
If the cell (which I'm expecting to be dequeued and already have a PFImageView) doesn't have a PFImageView, I alloc and init an imageView for the cell and add it as a subview of the cell.
Thus I expect if the cell has been dequeued it should already have a PFImageView as a subview and as we should not get into the if statement to create a new imageView and kick off a new photo download request
Instead what I see is that the cells at the top and bottom of the UICollectionView that 'go off screen' momentarily - when they come back on screen they are not being reused and seemingly a new cell is created and the picture refreshed.
1) How can I achieve a static image once the cell has been created (i.e. not refreshing when the cell goes slightly off screen.
2) Why are the cells not being reused?
Many thanks for your time.
John
UICollectionView will reuse cells for maximum efficiency. It does not guarantee any particular reuse or population strategies. Anecdotally, it seems to place and remove cells based on integer power of two regions — e.g. on a non-retina iPad it might divide your scroll area up into regions of 1024x1024 and then populate and depopulate each of those regions as they transition into and out of the visible area. However you should not predicate any expectations on its exact behaviour.
In addition, your use of collection view cells is incorrect. See the documentation. A cell explicitly has at least two subviews — backgroundView and contentView. So if you add a subview it will be at index 2 at the absolute least and, in reality, the index will be undefined. In any case you should add subviews to contentView, not to the cell itself.
The most normal way of doing what you're doing would be to create a custom UICollectionView subclass that inherently has a PFImageView within it.
I see several potential issues:
You are looking specifically at index 0 of the cell for the child class that you are adding. The UICollectionViewCell may have other views as children, so you can't just assume that the only (or first) child is the one you added.
I don't see that you are calling registerClass:forCellWithReuseIdentifier: or registerNib:forCellWithReuseIdentifier:, one of which is required for proper use of dequeue (https://developer.apple.com/library/ios/documentation/uikit/reference/UICollectionViewCell_class/Reference/Reference.html).
You are only setting the URL of the PFImageView in the case that you have to construct the PFImageView. The idea with dequeuing reusable views is that you will only construct a small subset of the views needed, and the UITableView will recycle them as they move offscreen. You need to reset the value for the indexPath that is being requested, even when you don't construct the new content.
If your case is as simple as you describe, you can probably get away with adding your PFImageView to the contentView property of your dequeued UICollectionView.
In your controller:
// solve problem 2
[self.collectionView registerClass:[UICollectionViewCell class] forReuseIdentifer:#"FlickrCell"];
In collectionView:cellForItemAtIndexPath
UICollectionViewCell *cell = [cv dequeueReusableCellWithReuseIdentifier:#"FlickrCell" forIndexPath:indexPath];
cell.backgroundColor = [self generateRandomUIColor];
// solve problem 1 by looking in the contentView for your subview (and looping instead of assuming at 0)
PFImageView *pfImageView = nil;
for (UIView *subview in cell.contentView.subviews)
{
if ([subview isKindOfClass:[PFImageView class]])
{
pfImageView = (PFImageView *)subview;
break;
}
}
NSURL *staticPhotoURL = [self.context photoSourceURLFromDictionary:[self.photos objectAtIndex:indexPath.row] size:OFFlickrSmallSize];
if (pfImageView == nil)
{
// No PFImageView, create one
// note the use of contentView!
pfImageView = [[PFImageView alloc] initWithFrame:CGRectMake(0, 0, cell.contentView.frame.size.height, cell.frame.size.width) andImageURL:staticPhotoURL andOwningCell:cell.contentView];
[cell.contentView addSubview:pfImageView];
}
else
{
// Already have recycled view.
// need to reset the url for the pfImageView. (Problem 3)
// not sure what PFImageView looks like so this is an e.g. I'd probably remove the
// URL loading from the ctr above and instead have a function that loads the
// image. Then, you could do this outside of the if, regardless of whether you had
// to alloc the child view or not.
[pfImageView loadImageWithUrl:staticPhotoURL];
// if you really only have 200 static images, you might consider caching all of them
}
return cell;
For less simple cases (e.g. where I want to visually lay out the cell, or where I have multiple children in the content), I typically customize my UICollectionViewCell's using Interface Builder.
Create a subclass of UICollectionViewCell in the project (In your case, call it PFImageCell).
Add an IBOutlet property to that subclass for the view I want to change in initialization (In your case, a UIImageView).
#property (nonatomic, assign) IBOutlet UIImageView *image;
In Interface Builder, create a prototype cell for the UITableView.
In the properties sheet for that prototype cell, identify the UICollectionViewCell subclass as the class.
Give the prototype cell an identifier (the reuse identifier) in the property sheet.
Add the view child in interface builder to the prototype cell (here, a UIImageView).
Use IB to map the IBOutlet property to the added UIImageView
Then, on dequeue in cellForRowAtIndexPath, cast the dequeued result to the subclass (PFImageCell) and set the value of the IBOutlet property instance. Here, you'd load the proper image for your UIImageView.
I am not sure if the cell is being re-used or not. It may be being reused but the subview may not be there. My suggestion would be to create a PFImageViewCollectionViewCell Class (sub class of UICollectionViewCell) and register it as the CollectionView Cell and try. That's how I do and would do if I need a subview inside a cell.
Try adding a tag on this particular UIImageView
- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath {
static int photoViewTag = 54353532;
UICollectionViewCell *cell = [cv dequeueReusableCellWithReuseIdentifier:#"FlickrCell" forIndexPath:indexPath];
cell.backgroundColor = [self generateRandomUIColor];
PFImageView *photoView = [cell.contentView viewWithTag:photoViewTag];
// Create a view
//
if (!photoView) {
photoView = [[PFImageView alloc] initWithFrame:CGRectMake(0, 0, cell.frame.size.height, cell.frame.size.width) andImageURL:staticPhotoURL andOwningCell:cell];
imageView.tag = photoViewTag;
[cell.contentView addSubview:imageView];
}
// Update the current view
//
else {
NSURL *staticPhotoURL = [self.context photoSourceURLFromDictionary:[self.photos objectAtIndex:indexPath.row] size:OFFlickrSmallSize];
photoView.imageURL = staticPhotoURL;
}
return cell;
}
I would really recommend to create your own UICollectionViewCell subclass though.
EDIT: Also, note that I used the contentView property instead of adding it directly to the cell.
Problem:
I use the following code inside the method cellForRowAtIndexPath to set the size of the image for the cell, yet at runtime the image gets blown up to the maximum height and width that the table row will allow.
UIImage *_image = [imageDictionary objectForKey:#"image"]; // Get image data
[_image drawInRect:CGRectMake(0,0,50,50)]; // set size
[cell.imageView setImage: _image]; // assign image to cell
cell.imageView.frame = CGRectMake(cell.imageView.frame.origin.x,cell.imageView.frame.origin.y,50,50);
return cell;
Question: Is there a more robust method of controlling the size of the image in a UITableViewCell? The approach I'm taking comes from several other posts but for some reason its being ignored in my code.
Side-note: I'm using Xcode 5 and developing on an iOS 7 platform.
Use UITableViewCell contentView .
The content view of a UITableViewCell object is the default superview for content displayed by the cell. If you want to customize cells by simply adding additional views, you should add them to the content view so they will be positioned appropriately as the cell transitions into and out of editing mode.
Example:
UIImage *_image = [imageDictionary objectForKey:#"image"]; // Get image data
[_image drawInRect:CGRectMake(0,0,50,50)]; // set size
UIImageView *imageView = [[UIImageView alloc] initWithImage: _image];
[imageView setFrame:yourFrame];
[cell.contentView addSubview:imageView];
This doesn't answer the question but your underlying problem is your approach. You should be customizing your cells by subclassing UITableViewCell. To add to that it's a lot easier to manipulate cell contents as views than to play around with the default picture and text label they give you. To carify, the contents of the cell sit on a view known as contentView accessible as cell.contentView. You can add text labels, buttons, and images as subviews to any location with any size you want the same way you would do with any view added as a subview.