I have a custom UITableViewCell with a UIScrollView in it that is wired to the cell controller. When I assign text to the scrollview, some cells get the correct text, some are blank, some redisplay old text and others have the scrollview clipped around the 2nd or 3rd line of text. It seems random on what will happen. I followed the suggestion here of using a timer to fix blank cells, http://www.bdunagan.com/2008/12/08/uitextview-in-a-uitableview-on-the-iphone/, but that didn't help. I placed the timer code in the cellForRowAtIndexPath method.
I've also tried calling
[cell.textview setNeedsDisplay];
after text is assigned to the textview but it doesn't have any affect.
When I use a textfield or label, everything looks fine. However, I need something that can scroll text. Any suggestions on a fix or better way?
Update: Found this on the dev forums (specifically mentions your problem):
https://devforums.apple.com/message/38944#38944
I would follow the link it has some more detailed info.
// view controller
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
NSArray* visibleCells = [self.tableView visibleCells];
for (UITableViewCell* cell in visibleCells)
{
if ([cell.reuseIdentifier isEqualToString:kTextViewCellID])
{
[(MTextViewCell*)cell refresh];
}
}
}
// MTextViewCell
- (void)refresh
{
// mucking with the contentOffset causes the textView to redraw itself
CGPoint contentOffset = mTextView.contentOffset;
CGPoint contentOffset1 = { contentOffset.x, contentOffset.y + 1.0f };
mTextView.contentOffset = contentOffset1;
mTextView.contentOffset = contentOffset;
}
Try calling:
[tableView reloadData];
After you update all the textViews.
Related
According to Apple's documentation (and touted at WWDC 2012), it is possible to set the layout on UICollectionView dynamically and even animate the changes:
You normally specify a layout object when creating a collection view but you can also change the layout of a collection view dynamically. The layout object is stored in the collectionViewLayout property. Setting this property directly updates the layout immediately, without animating the changes. If you want to animate the changes, you must call the setCollectionViewLayout:animated: method instead.
However, in practice, I've found that UICollectionView makes inexplicable and even invalid changes to the contentOffset, causing cells to move incorrectly, making the feature virtually unusable. To illustrate the problem, I put together the following sample code that can be attached to a default collection view controller dropped into a storyboard:
#import <UIKit/UIKit.h>
#interface MyCollectionViewController : UICollectionViewController
#end
#implementation MyCollectionViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:#"CELL"];
self.collectionView.collectionViewLayout = [[UICollectionViewFlowLayout alloc] init];
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
return 1;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewCell *cell = [self.collectionView dequeueReusableCellWithReuseIdentifier:#"CELL" forIndexPath:indexPath];
cell.backgroundColor = [UIColor whiteColor];
return cell;
}
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(#"contentOffset=(%f, %f)", self.collectionView.contentOffset.x, self.collectionView.contentOffset.y);
[self.collectionView setCollectionViewLayout:[[UICollectionViewFlowLayout alloc] init] animated:YES];
NSLog(#"contentOffset=(%f, %f)", self.collectionView.contentOffset.x, self.collectionView.contentOffset.y);
}
#end
The controller sets a default UICollectionViewFlowLayout in viewDidLoad and displays a single cell on-screen. When the cells is selected, the controller creates another default UICollectionViewFlowLayout and sets it on the collection view with the animated:YES flag. The expected behavior is that the cell does not move. The actual behavior, however, is that the cell scroll off-screen, at which point it is not even possible to scroll the cell back on-screen.
Looking at the console log reveals that the contentOffset has inexplicably changed (in my project, from (0, 0) to (0, 205)). I posted a solution for the solution for the non-animated case (i.e. animated:NO), but since I need animation, I'm very interested to know if anyone has a solution or workaround for the animated case.
As a side-note, I've tested custom layouts and get the same behavior.
UICollectionViewLayout contains the overridable method targetContentOffsetForProposedContentOffset: which allows you to provide the proper content offset during a change of layout, and this will animate correctly. This is available in iOS 7.0 and above
I have been pulling my hair out over this for days and have found a solution for my situation that may help.
In my case I have a collapsing photo layout like in the photos app on the ipad. It shows albums with the photos on top of each other and when you tap an album it expands the photos. So what I have is two separate UICollectionViewLayouts and am toggling between them with [self.collectionView setCollectionViewLayout:myLayout animated:YES] I was having your exact problem with the cells jumping before animation and realized it was the contentOffset. I tried everything with the contentOffset but it still jumped during animation. tyler's solution above worked but it was still messing with the animation.
Then I noticed that it happens only when there were a few albums on the screen, not enough to fill the screen. My layout overrides -(CGSize)collectionViewContentSize as recommended. When there are only a few albums the collection view content size is less than the views content size. That's causing the jump when I toggle between the collection layouts.
So I set a property on my layouts called minHeight and set it to the collection views parent's height. Then I check the height before I return in -(CGSize)collectionViewContentSize I ensure the height is >= the minimum height.
Not a true solution but it's working fine now. I would try setting the contentSize of your collection view to be at least the length of it's containing view.
edit:
Manicaesar added an easy workaround if you inherit from UICollectionViewFlowLayout:
-(CGSize)collectionViewContentSize { //Workaround
CGSize superSize = [super collectionViewContentSize];
CGRect frame = self.collectionView.frame;
return CGSizeMake(fmaxf(superSize.width, CGRectGetWidth(frame)), fmaxf(superSize.height, CGRectGetHeight(frame)));
}
2019 actual solution
Say you have a number of layouts for your "Cars" view.
Let's say you have three.
CarsLayout1: UICollectionViewLayout { ...
CarsLayout2: UICollectionViewLayout { ...
CarsLayout3: UICollectionViewLayout { ...
It will jump when you animate between layouts.
It's just an undeniable mistake by Apple. It jumps when you animate, without question.
The fix is this:
You must have a global float, and, the following base class:
var avoidAppleMessupCarsLayouts: CGPoint? = nil
class FixerForCarsLayouts: UICollectionViewLayout {
override func prepareForTransition(from oldLayout: UICollectionViewLayout) {
avoidAppleMessupCarsLayouts = collectionView?.contentOffset
}
override func targetContentOffset(
forProposedContentOffset proposedContentOffset: CGPoint) -> CGPoint {
if avoidAppleMessupCarsLayouts != nil {
return avoidAppleMessupCarsLayouts!
}
return super.targetContentOffset(forProposedContentOffset: proposedContentOffset)
}
}
So here are the three layouts for your "Cars" screen:
CarsLayout1: FixerForCarsLayouts { ...
CarsLayout2: FixerForCarsLayouts { ...
CarsLayout3: FixerForCarsLayouts { ...
That's it. It now works.
Incredibly obscurely, you could have different "sets" of layouts (for Cars, Dogs, Houses, etc.), which could (conceivably) collide. For this reason, have a global and a base class as above for each "set".
This was invented by passing user #Isaacliu, above, many years ago.
A detail, FWIW in Isaacliu's code fragment, finalizeLayoutTransition is added. In fact it's not necessary logically.
The fact is, until Apple change how it works, every time you animate between collection view layouts, you do have to do this. That's life!
This issue bit me as well and it seems to be a bug in the transition code. From what I can tell it tries to focus on the cell that was closest to the center of the pre-transition view layout. However, if there doesn't happen to be a cell at the center of the view pre-transition then it still tries to center where the cell would be post-transition. This is very clear if you set alwaysBounceVertical/Horizontal to YES, load the view with a single cell and then perform a layout transition.
I was able to get around this by explicitly telling the collection to focus on a specific cell (the first cell visible cell, in this example) after triggering the layout update.
[self.collectionView setCollectionViewLayout:[self generateNextLayout] animated:YES];
// scroll to the first visible cell
if ( 0 < self.collectionView.indexPathsForVisibleItems.count ) {
NSIndexPath *firstVisibleIdx = [[self.collectionView indexPathsForVisibleItems] objectAtIndex:0];
[self.collectionView scrollToItemAtIndexPath:firstVisibleIdx atScrollPosition:UICollectionViewScrollPositionCenteredVertically animated:YES];
}
Jumping in with a late answer to my own question.
The TLLayoutTransitioning library provides a great solution to this problem by re-tasking iOS7s interactive transitioning APIs to do non-interactive, layout to layout transitions. It effectively provides an alternative to setCollectionViewLayout, solving the content offset issue and adding several features:
Animation duration
30+ easing curves (courtesy of Warren Moore's AHEasing library)
Multiple content offset modes
Custom easing curves can be defined as AHEasingFunction functions. The final content offset can be specified in terms of one or more index paths with Minimal, Center, Top, Left, Bottom or Right placement options.
To see what I mean, try running the Resize demo in the Examples workspace and playing around with the options.
The usage is like this. First, configure your view controller to return an instance of TLTransitionLayout:
- (UICollectionViewTransitionLayout *)collectionView:(UICollectionView *)collectionView transitionLayoutForOldLayout:(UICollectionViewLayout *)fromLayout newLayout:(UICollectionViewLayout *)toLayout
{
return [[TLTransitionLayout alloc] initWithCurrentLayout:fromLayout nextLayout:toLayout];
}
Then, instead of calling setCollectionViewLayout, call transitionToCollectionViewLayout:toLayout defined in the UICollectionView-TLLayoutTransitioning category:
UICollectionViewLayout *toLayout = ...; // the layout to transition to
CGFloat duration = 2.0;
AHEasingFunction easing = QuarticEaseInOut;
TLTransitionLayout *layout = (TLTransitionLayout *)[collectionView transitionToCollectionViewLayout:toLayout duration:duration easing:easing completion:nil];
This call initiates an interactive transition and, internally, a CADisplayLink callback that drives the transition progress with the specified duration and easing function.
The next step is to specify a final content offset. You can specify any arbitrary value, but the toContentOffsetForLayout method defined in UICollectionView-TLLayoutTransitioning provides an elegant way to calculate content offsets relative to one or more index paths. For example, in order to have a specific cell to end up as close to the center of the collection view as possible, make the following call immediately after transitionToCollectionViewLayout:
NSIndexPath *indexPath = ...; // the index path of the cell to center
TLTransitionLayoutIndexPathPlacement placement = TLTransitionLayoutIndexPathPlacementCenter;
CGPoint toOffset = [collectionView toContentOffsetForLayout:layout indexPaths:#[indexPath] placement:placement];
layout.toContentOffset = toOffset;
Easy.
Animate your new layout and collectionView's contentOffset in the same animation block.
[UIView animateWithDuration:0.3 animations:^{
[self.collectionView setCollectionViewLayout:self.someLayout animated:YES completion:nil];
[self.collectionView setContentOffset:CGPointMake(0, -64)];
} completion:nil];
It will keep self.collectionView.contentOffset constant.
If you are simply looking for the content offset to not change when transition from layouts, you can creating a custom layout and override a couple methods to keep track of the old contentOffset and reuse it:
#interface CustomLayout ()
#property (nonatomic) NSValue *previousContentOffset;
#end
#implementation CustomLayout
- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset
{
CGPoint previousContentOffset = [self.previousContentOffset CGPointValue];
CGPoint superContentOffset = [super targetContentOffsetForProposedContentOffset:proposedContentOffset];
return self.previousContentOffset != nil ? previousContentOffset : superContentOffset ;
}
- (void)prepareForTransitionFromLayout:(UICollectionViewLayout *)oldLayout
{
self.previousContentOffset = [NSValue valueWithCGPoint:self.collectionView.contentOffset];
return [super prepareForTransitionFromLayout:oldLayout];
}
- (void)finalizeLayoutTransition
{
self.previousContentOffset = nil;
return [super finalizeLayoutTransition];
}
#end
All this is doing is saving the previous content offset before the layout transition in prepareForTransitionFromLayout, overwriting the new content offset in targetContentOffsetForProposedContentOffset, and clearing it in finalizeLayoutTransition. Pretty straightforward
If it helps add to the body of experience: I encountered this problem persistently regardless of the size of my content, whether I had set a content inset, or any other obvious factor. So my workaround was somewhat drastic. First I subclassed UICollectionView and added to combat inappropriate content offset setting:
- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated
{
if(_declineContentOffset) return;
[super setContentOffset:contentOffset];
}
- (void)setContentOffset:(CGPoint)contentOffset
{
if(_declineContentOffset) return;
[super setContentOffset:contentOffset];
}
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated
{
_declineContentOffset ++;
[super setCollectionViewLayout:layout animated:animated];
_declineContentOffset --;
}
- (void)setContentSize:(CGSize)contentSize
{
_declineContentOffset ++;
[super setContentSize:contentSize];
_declineContentOffset --;
}
I'm not proud of it but the only workable solution seems to be completely to reject any attempt by the collection view to set its own content offset resulting from a call to setCollectionViewLayout:animated:. Empirically it looks like this change occurs directly in the immediate call, which obviously isn't guaranteed by the interface or the documentation but makes sense from a Core Animation point of view so I'm perhaps only 50% uncomfortable with the assumption.
However there was a second issue: UICollectionView was now adding a little jump to those views that were staying in the same place upon a new collection view layout — pushing them down about 240 points and then animating them back to the original position. I'm unclear why but I modified my code to deal with it nevertheless by severing the CAAnimations that had been added to any cells that, actually, weren't moving:
- (void)setCollectionViewLayout:(UICollectionViewLayout *)layout animated:(BOOL)animated
{
// collect up the positions of all existing subviews
NSMutableDictionary *positionsByViews = [NSMutableDictionary dictionary];
for(UIView *view in [self subviews])
{
positionsByViews[[NSValue valueWithNonretainedObject:view]] = [NSValue valueWithCGPoint:[[view layer] position]];
}
// apply the new layout, declining to allow the content offset to change
_declineContentOffset ++;
[super setCollectionViewLayout:layout animated:animated];
_declineContentOffset --;
// run through the subviews again...
for(UIView *view in [self subviews])
{
// if UIKit has inexplicably applied animations to these views to move them back to where
// they were in the first place, remove those animations
CABasicAnimation *positionAnimation = (CABasicAnimation *)[[view layer] animationForKey:#"position"];
NSValue *sourceValue = positionsByViews[[NSValue valueWithNonretainedObject:view]];
if([positionAnimation isKindOfClass:[CABasicAnimation class]] && sourceValue)
{
NSValue *targetValue = [NSValue valueWithCGPoint:[[view layer] position]];
if([targetValue isEqualToValue:sourceValue])
[[view layer] removeAnimationForKey:#"position"];
}
}
}
This appears not to inhibit views that actually do move, or to cause them to move incorrectly (as if they were expecting everything around them to be down about 240 points and to animate to the correct position with them).
So this is my current solution.
I've probably spent about two weeks now trying to get various layout to transition between one another smoothly. I've found that override the proposed offset is working in iOS 10.2, but in version prior to that I still get the issue. The thing that makes my situation a bit worse is I need to transition into another layout as a result of a scroll, so the view is both scrolling and transitioning at the same time.
Tommy's answer was the only thing that worked for me in pre 10.2 versions. I'm doing the following thing now.
class HackedCollectionView: UICollectionView {
var ignoreContentOffsetChanges = false
override func setContentOffset(_ contentOffset: CGPoint, animated: Bool) {
guard ignoreContentOffsetChanges == false else { return }
super.setContentOffset(contentOffset, animated: animated)
}
override var contentOffset: CGPoint {
get {
return super.contentOffset
}
set {
guard ignoreContentOffsetChanges == false else { return }
super.contentOffset = newValue
}
}
override func setCollectionViewLayout(_ layout: UICollectionViewLayout, animated: Bool) {
guard ignoreContentOffsetChanges == false else { return }
super.setCollectionViewLayout(layout, animated: animated)
}
override var contentSize: CGSize {
get {
return super.contentSize
}
set {
guard ignoreContentOffsetChanges == false else { return }
super.contentSize = newValue
}
}
}
Then when I set the layout I do this...
let theContentOffsetIActuallyWant = CGPoint(x: 0, y: 100)
UIView.animate(withDuration: animationDuration,
delay: 0, options: animationOptions,
animations: {
collectionView.setCollectionViewLayout(layout, animated: true, completion: { completed in
// I'm also doing something in my layout, but this may be redundant now
layout.overriddenContentOffset = nil
})
collectionView.ignoreContentOffsetChanges = true
}, completion: { _ in
collectionView.ignoreContentOffsetChanges = false
collectionView.setContentOffset(theContentOffsetIActuallyWant, animated: false)
})
This finally worked for me (Swift 3)
self.collectionView.collectionViewLayout = UICollectionViewFlowLayout()
self.collectionView.setContentOffset(CGPoint(x: 0, y: -118), animated: true)
I'm trying to mimic the iMessage bubble text behaviour with an UITableView. In order to always scroll to the bottom I'm using scrollToRowAtIndexPath when viewDidLoad and viewDidAppear. This is because when the viewDidLoad method is called, the table has not been completely loaded, so I need that extra scroll in viewDidAppear. This code makes the trick. However, what I want is not an animated scroll (setting animated to NO does not solve this), I want the table to be displayed always from the bottom, not load the table and then go to the last row.
Is this possible? I can't find any solution that fits completely with the desired behaviour.
This is the best solution!
Just reverse everything!
tableView.transform = CGAffineTransformMakeRotation(-M_PI);
cell.transform = CGAffineTransformMakeRotation(M_PI);
Swift 4.0:
tableView.transform = CGAffineTransform(rotationAngle: -CGFloat.pi)
cell.transform = CGAffineTransform(rotationAngle: CGFloat.pi)
Be careful though, because now the headerView and footerView positions are reversed as well.
You can avoid the call from viewDidLoad because scrolling from within viewDidAppear makes that first call redundant. viewDidAppear is called every time you navigate back to the view but viewDidLoad is only called once when the view is initialized.
I would agree with earlier suggestions of hiding the scroll from the user instead of changing the way a UITableView is loading data. My suggestion would be to use the scrollToRowAtIndexPath method in the viewWillAppear method with animation set to NO. After that if you have to add a new row while the table is visible to the user, use insertRowsAtIndexPaths:withRowAnimation: to add a row at the bottom of the table view. Be sure to take care of adding the data at the end of your data model so that when the user navigates away and comes back, s/he comes back to the same layout.
Hope this helps.
edit:
Just saw your reason for not accepting the previous answers and thought I'd elaborate a little more. The solution I propose would require minimum effort, avoid calling reloadData time and again and thus avoid calling the scrollToRowAtIndexPath method again and again. You only need to make one call to scrollToRowAtIndexPath in viewWillAppear to scroll to the bottom of the table view (hiding the transition from the user when doing so) and you wouldn't need to do that again.
I do something similar in an RPN calculator I've built. I have a table view with all the numbers in it and when a number is added to the stack, everything pops up one cell. When I load the view I call:
[self.myTableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:NumOfStackItems - 1 inSection:0]
atScrollPosition:UITableViewScrollPositionTop animated:NO];
In my viewWillAppear. This way my table view starts shown at the bottom of the stack and no animation is seen. By putting this in the viewWillAppear, every time I navigate to the view, it shows up at the bottom of the table.
When I add numbers to the stack, I just add it in an array that holds all the numbers and then put the text in the proper row like this:
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
// Cell initialization here...
NSUInteger row_num = [indexPath row];
cell.rowNumber.text = [NSString stringWithFormat:#"%g", [DataArray objectAtIndex:NumberOfStackItems-row_num-1];// subtract the row number off to get the correct array index
return cell
}
I also make sure that whenever I update the tableview with a new value i first call the reloadData function, and then call the scrollToRowAtIndexPath function I cited above, this way I stay at the bottom of the table.
You can have your UITableView hidden on viewDidLoad, and then change it to visible on viewDidAppear right after you scroll the table to the bottom. This way the user won't see the scrolling animation.
The solution is to override viewWillAppear and let it scroll (non-animated) to the bottom:
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self goToBottom];
}
-(void)goToBottom
{
NSIndexPath *lastIndexPath = [self lastIndexPath];
[self.tableView scrollToRowAtIndexPath:lastIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:NO];
}
-(NSIndexPath *)lastIndexPath
{
NSInteger lastSectionIndex = MAX(0, [self.tableView numberOfSections] - 1);
NSInteger lastRowIndex = MAX(0, [self.tableView numberOfRowsInSection:lastSectionIndex] - 1);
return [NSIndexPath indexPathForRow:lastRowIndex inSection:lastSectionIndex];
}
By performing this at viewWillAppear it will be done before the user sees the table.
You can fix it by making an invisible footer and do the calculations in there. When the footer is loaded the contentSize is updated. To make it scroll I check set the contentOffset of the tableview.
I have commented out the animation part, since you wanted it without, but it also works.
-(CGFloat)tableView:(UITableView *)tableView heightForFooterInSection:(NSInteger)section
{
return 1;
}
-(UIView *)tableView:(UITableView *)tableView viewForFooterInSection:(NSInteger)section
{
if( tableView.contentOffset.y != tableView.contentSize.height - tableView.frame.size.height && automaticScroll ){
//[UIView animateWithDuration:0.0 animations:^{
self.contentTableView.contentOffset = CGPointMake(0, tableView.contentSize.height - self.contentTableView.frame.size.height);
//} completion:^(BOOL finished) {
[tableView reloadData];
//}];
automaticScroll = NO;
}
UIView *emptyFooter = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 1)];
emptyFooter.backgroundColor = [UIColor clearColor];
return emptyFooter;
}
I created a BOOL automaticScroll to trigger the scroll to the bottom. This should be set in the viewWillAppear method, or whenever you load the data and reload the tableView.
If you want to add rows, you also need to set the BOOL, like:
-(void)addItemButtonClicked:(id)sender
{
automaticScroll = YES;
//Add object to data
[self.contentTableView reloadData];
}
If you need more help, please let me know.
scrollToRowAtIndexPath
use to scroll the row in tableview to particular position
just change content inset after load data to move content view of table view if height is less than parent view.
[self.tableView reloadData];
[self.tableView setContentInset:UIEdgeInsetsMake(self.view.frame.size.height - self.tableView.contentSize.height < 0 ? 0 : self.view.frame.size.height - self.tableView.contentSize.height, 0, 0, 0)];
Swift 3.1
tableView.transform = CGAffineTransform(rotationAngle: CGFloat.pi)
cell.transform = CGAffineTransform(rotationAngle: CGFloat.pi)
Credits: #Christos Hadjikyriacou
I am using Xcode's SplitView template.
I have placed a bunch of text fields on the 'detail' side of the view however I forgot about the keyboard taking up half the screen.
How do I move this detail view up when the keyboard comes onto the screen?
I used this solution from the always-useful Cocoa With Love when I could not use a UIScrollView.
If you want to add a UIScrollView you your hierarchy, it gets even easier. Just insert the UIScrollview in the hierarchy above the text fields and use this code when the user taps the text item to begin editing:
UIScrollView* v = (UIScrollView*) self.view ;
CGRect rc = [textField bounds];
rc = [textField convertRect:rc toView:v];
rc.origin.x = 0 ;
rc.origin.y -= 60 ;
rc.size.height = 400;
[self.scroll scrollRectToVisible:rc animated:YES];
Good Luck!
I had that problem once. My app used a table view to show the fields, so the solution I came up with is to listen the textViewDidBeginEditing to perform a scrollToRowAtIndexPath on the table view:
- (void)textViewDidBeginEditing:(UITextView *)textView{
UITableViewCell *cell = (UITableViewCell*) [[textView superview] superview];
[self.myTableView scrollToRowAtIndexPath:[self.myTableView indexPathForCell:cell] atScrollPosition:UITableViewScrollPositionMiddle animated:YES];
}
If you don't have a table view but a scroll view I think you could take same similar approach but telling the scrollview to scroll to the section you need just as #MystikSpiral told.
Is there any way that I can get a specific cell to change its style or background image while scrolling the table view?
I want to change the image of a cell which is on top of the visible cells. But only its image is going to be changed the others will stay same, until after scrolling the others come to top of the cells which are shown on the screen. Then the top one's image is going to change this time.
You need to implement scrollViewDidScroll: method of UIScrollViewDelegate in your controller then use visibleCells property of UITableView to get the visible cells of the table.
Something like the following code should work
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
UITableView* tableView;
NSArray* visibleCells;
BOOL first;
tableView = (UITableView*)scrollView;
visibleCells = tableView.visibleCells;
first = YES;
for (UITableViewCell* cell in visibleCells) {
if (first) {
//customize the top cell
first = NO;
}else {
//customize the other visible cells
}
}
}
I have implemented a custom UITableViewCell which includes a UITextView that auto-resizes as the user types, similar to the "Notes" field in the Contacts app. It is working properly on my iPhone, but when I am testing it in the iPad, I am getting some very strange behavior: When you get to the end of a line, the keyboard hides for a millisecond and then shows itself again immediately. I would write it off as just a quirky bug, but it actually causes some data loss since if you are typing, it loses a character or two. Here's my code:
The Code
// returns the proper height/size for the UITextView based on the string it contains.
// If no string, it assumes a space so that it will always have one line.
- (CGSize)textViewSize:(UITextView*)textView {
float fudgeFactor = 16.0;
CGSize tallerSize = CGSizeMake(textView.frame.size.width-fudgeFactor, kMaxFieldHeight);
NSString *testString = #" ";
if ([textView.text length] > 0) {
testString = textView.text;
}
CGSize stringSize = [testString sizeWithFont:textView.font constrainedToSize:tallerSize lineBreakMode:UILineBreakModeWordWrap];
return stringSize;
}
// based on the proper text view size, sets the UITextView's frame
- (void) setTextViewSize:(UITextView*)textView {
CGSize stringSize = [self textViewSize:textView];
if (stringSize.height != textView.frame.size.height) {
[textView setFrame:CGRectMake(textView.frame.origin.x,
textView.frame.origin.y,
textView.frame.size.width,
stringSize.height+10)]; // +10 to allow for the space above the text itself
}
}
// as per: https://stackoverflow.com/questions/3749746/uitextview-in-a-uitableviewcell-smooth-auto-resize
- (void)textViewDidChange:(UITextView *)textView {
[self setTextViewSize:textView]; // set proper text view size
UIView *contentView = textView.superview;
// (1) the padding above and below the UITextView should each be 6px, so UITextView's
// height + 12 should equal the height of the UITableViewCell
// (2) if they are not equal, then update the height of the UITableViewCell
if ((textView.frame.size.height + 12.0f) != contentView.frame.size.height) {
[myTableView beginUpdates];
[myTableView endUpdates];
[contentView setFrame:CGRectMake(0,
0,
contentView.frame.size.width,
(textView.frame.size.height+12.0f))];
}
}
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
int height;
UITextView *textView = myTextView;
[self setTextViewSize:textView];
height = textView.frame.size.height + 12;
if (height < 44) { // minimum height of 44
height = 44;
[textView setFrame:CGRectMake(textView.frame.origin.x,
textView.frame.origin.y,
textView.frame.size.width,
44-12)];
}
return (CGFloat)height;
}
The Problems
So, here's what's happening
This code is working 100% properly on my iPhone and in the iPhone simulator. As I type the text, the UITextView grows smoothly, and the UITableViewCell along with it.
On the iPad simulator, however, it gets screwy. It works fine while you are typing on the first line, but when you get to the end of a line, the keyboard disappears and then reappears immediately, so that if the user continues typing the app misses a character or two.
Here are some additional notes on the weird behaviors that I have noticed which may help explain it:
Also, I have found that removing the lines [myTableView beginUpdates]; [myTableView endUpdates]; in the function textViewDidChange:(UITextView *)textView makes the UITextView grow properly and also doesn't show and hide the keyboard, but unfortunately, then the UITableViewCell doesn't grow to the proper height.
UPDATE: Following these instructions, I am now able to stop the strange movement of the text; but the keyboard is still hiding and showing, which is very strange.
Does anyone have any ideas as to how to get the keyboard to continually show, rather than hide and show when you get to the end of the line on the iPad?
P.S.: I am not interested in using ThreeTwenty.
you should return NO in:
-(BOOL) textViewShouldEndEditing:(UITextView *)textView
if you would like to show keyboard at all times. You should handle cases, which keyboard should be hidden, by returning YES to this delegate function.
edit:
I dug a little more, when [tableView endUpdates] called, it basically does 3 things :
Disables user interaction on the tableView
Updates cell changes
Enables user interaction on the tableView
The difference between SDKs(platforms) is at [UIView setUserInteractionEnabled] method. As UITableView does not overrite setUserInteractionEnabled method, it is called from super (UIView).
iPhone when setUserInteractionEnabled called, looks for a private field _shouldResignFirstResponderWithInteractionDisabled which returns NO as default, so does not resign the first responder (UITextView)
But on iPad there is no such check AFAIK, so it resignes UITextView on step 1, and sets focus and makes it first responder on step 3
Basically, textViewShouldEndEditing, which allows you to keep focus, according to SDK docs, is your only option ATM.
This method is called when the text
view is asked to resign the first
responder status. This might occur
when the user tries to change the
editing focus to another control.
Before the focus actually changes,
however, the text view calls this
method to give your delegate a chance
to decide whether it should.
I had the same issue for an iPad app and came up with another solution without having calculating the height of the text itself.
First create a custom UITableViewCell in IB with an UITextField placed in the cell's contentView. It's important to set the text view's scrollEnabled to NO and the autoresizingMask to flexibleWidth and flexibleHeight.
In the ViewController implement the text view's delegate method -textViewDidChanged: as followed, where textHeight is a instance variable with type CGFloat and -tableViewNeedsToUpdateHeight is a custom method we will define in the next step.
- (void)textViewDidChange:(UITextView *)textView
{
CGFloat newTextHeight = [textView contentSize].height;
if (newTextHeight != textHeight)
{
textHeight = newTextHeight;
[self tableViewNeedsToUpdateHeight];
}
}
The method -tableViewNeedsToUpdateHeight calls the table view's beginUpdates and endUpdates, so the table view itself will call the -tableView:heightForRowAtIndexPath: delegate method.
- (void)tableViewNeedsToUpdateHeight
{
BOOL animationsEnabled = [UIView areAnimationsEnabled];
[UIView setAnimationsEnabled:NO];
[table beginUpdates];
[table endUpdates];
[UIView setAnimationsEnabled:animationsEnabled];
}
In the table view's -tableView:heightForRowAtIndexPath: delegate method we need to calculate the new height for the text view's cell based on the textHeight.
First we need to resize the text view cells height to the maximum available height (after subtracting the height of all other cells in the table view). Then we check if the textHeight is bigger than the calculated height.
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
CGFloat heightForRow = 44.0;
if ([indexPath row] == kRowWithTextViewEmbedded)
{
CGFloat tableViewHeight = [tableView bounds].size.height;
heightForRow = tableViewHeight - ((kYourTableViewsNumberOfRows - 1) * heightForRow);
if (heightForRow < textHeight)
{
heightForRow = textHeight;
}
}
return heightForRow;
}
For a better user experience set the table view's content insets for bottom to e.g. 50.0.
I've tested it on the iPad with iOS 4.2.1 and works as expected.
Florian