I would like to get a UICollectionViewCell's position after programattically scrolling to a cell. I'm setting the scroll position like this.
[self.collectionView scrollToItemAtIndexPath:indexPath
atScrollPosition:UICollectionViewScrollPositionCenteredVertically
animated:NO];
I would then like to get the frame of the cell I have scrolled to as I need to position another UIView near it.
This code returns the rect of the cell with the scrollview, but I need the position within the visible rect.
UICollectionViewLayoutAttributes *attributes = [self.collectionView layoutAttributesForItemAtIndexPath:indexPath];
CGRect cellRect = attributes.frame;
The frame of a cell doesn't change, it's the content offset of the enclosing scroll view. Subtract the contentOffset from the frame's origin to get the on-screen position, or use one of the convertRect: methods to get the coordinates in a related view.
Here is the cell X and Center values
UICollectionViewLayoutAttributes *attributes = [collectionView layoutAttributesForItemAtIndexPath:indexPath];
CGPoint cellCenterPoint = attributes.center;
CGPoint contentOffset = [collectionView contentOffset];
NSLog(#"%f , %f",-1*contentOffset.x , cellCenterPoint.x);
int relativeCellCenter = (-1*contentOffset.x) + cellCenterPoint.x +collectionView.frame.origin.x;
int relativeX = (-1*contentOffset.x) +collectionView.frame.origin.x;
Related
I have a collection view that scrolls horizontally and spans its parent view's full width. My cheap way to achieve paging on it is to set the cell widths to be equal to 1/3 of the collection view width, and to set that same amount of width as left and right content insets.
I disable scrolling in IB and replace with left and right swipe recognizers. My code almost works without setting contentInset, but setting the contentInset seems prevent any scrolling from happening
- (void)viewDidLayoutSubviews {
[super viewDidLayoutSubviews];
CGFloat itemWidth = self.collectionView.bounds.size.width/3.0;
NSInteger count = [self collectionView:self.collectionView numberOfItemsInSection:0];
self.collectionView.contentSize = (CGSize){ .width=itemWidth*count, .height=self.collectionView.bounds.size.height };
// uncomment this line, and the scroll code in the swipes below fails to work
//self.collectionView.contentInset = UIEdgeInsetsMake(0, itemWidth, 0, itemWidth);
self.collectionView.contentOffset = (CGPoint){ .x=self.collectionView.contentSize.width/2.0, .y=0 };
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
CGFloat width = self.view.bounds.size.width/3.0;
return (CGSize){ .width=width, .height=collectionView.bounds.size.height };
}
This code handles the swipes...
- (NSIndexPath *)centerIndexPath {
CGRect visibleRect = (CGRect){.origin = self.collectionView.contentOffset, .size = self.collectionView.bounds.size};
CGPoint visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect));
return [self.collectionView indexPathForItemAtPoint:visiblePoint];
}
- (void)swipeLeft:(UISwipeGestureRecognizer *)gr {
NSIndexPath *centerIndexPath = [self centerIndexPath];
NSLog(#"at %#", centerIndexPath);
if (centerIndexPath.row < [self collectionView:self.collectionView numberOfItemsInSection:0]-1) {
[self.collectionView scrollToItemAtIndexPath:centerIndexPath atScrollPosition:UICollectionViewScrollPositionLeft animated:YES];
}
}
- (void)swipeRight:(UISwipeGestureRecognizer *)gr {
NSIndexPath *centerIndexPath = [self centerIndexPath];
NSLog(#"at %#", centerIndexPath);
if (centerIndexPath.row > 0) {
[self.collectionView scrollToItemAtIndexPath:centerIndexPath atScrollPosition:UICollectionViewScrollPositionRight animated:YES];
}
}
All of this works, except when I set the contentInsets in the setup above. Then, even though I reach the scrollToItemAtIndexPath: code in the debugger, no scrolling occurs.
It's important to have those insets, because I want user to understand that center item is the selected item.
Can somebody explain why contentInset spoils scrolling and how to fix?
It looks like UICollectionView has its own built-in way to handle insets:
https://developer.apple.com/library/content/documentation/WindowsViews/Conceptual/CollectionViewPGforIOS/UsingtheFlowLayout/UsingtheFlowLayout.html#//apple_ref/doc/uid/TP40012334-CH3-SW1
Using Section Insets to Tweak the Margins of Your Content
Section insets are a way to adjust the space available for laying out cells. You can use insets to insert space after a section’s header view and before its footer view. You can also use insets to insert space around the sides of the content. Figure 3-5 demonstrates how insets affect some content in a vertically scrolling flow layout.
Figure 3-5 Section insets change the available space for laying out cells
I have five rows of cells each row containing four cells - 5x4. I am trying to accomplish almost an Apple watch like effect. The row in the center of the screen should have cell sizes of 100x100 and the rest return sizes of 80x80. When scrolled, the row moving away from the center should turn to 80x80 and the row moving into the center should turn 100x100.
I have implemented prepareLayout, layoutAttributesForElementsInRect, and layoutAttributesForItemAtIndexPath
So right now I have a center row of 100x100 cells and the rest 80x80.
To make it dynamic I implement shouldInvalidateLayoutForBoundsChange but nothing happens.
- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{
NSMutableArray *allAttributes = [NSMutableArray arrayWithCapacity:self.layoutInfo.count];
[self.layoutInfo enumerateKeysAndObjectsUsingBlock:^(NSString *elementIdentifier,
NSDictionary *elementsInfo,
BOOL *stop) {
[elementsInfo enumerateKeysAndObjectsUsingBlock:^(NSIndexPath *indexPath,
UICollectionViewLayoutAttributes *attributes,
BOOL *innerStop) {
// NSLog(#"%f, %f", newBounds.origin.x, newBounds.origin.y);
if ((newBounds.origin.y < [[UIScreen mainScreen]bounds].size.height/2-50) && (newBounds.origin.y > [[UIScreen mainScreen]bounds].size.height/2+50)) {
CGRect frame = attributes.frame;
frame.size.width = 100.0f;
frame.size.height = 100.0f;
attributes.frame = frame;
}else{
CGRect frame = attributes.frame;
frame.size.width = 80.0f;
frame.size.height = 80.0f;
attributes.frame = frame;
}
[allAttributes addObject:attributes];
}];
}];
return YES;
}
shouldInvalidateLayoutForBoundsChange: is called pretty frequently (whenever the view is resized, or scrolled...), so you probably don't need to be doing all that work there. If you know your cells will always have a fixed size and position then you can just return NO here.
As long as you have implemented prepareLayout, layoutAttributesForElementsInRect, and layoutAttributesForItemAtIndexPath, then make sure you also implement collectionViewContentSize to return the total size of the content.
I have a UITableView with changing height.
I wanted in every cell selection to kind of get the 'focus' on it by moving it to the middle of the screen. The problem is to move the upper and lower cells in the table since they cannot scroll beyond the table upper and lower bounds. I'll also prefer to do this with animations..
Any suggestions?
Thanks!
I created small example of how to achieve this:
https://github.com/vkozlovskyi/CenterCellExample
You just need to calculate scroll offset of UITableView, and and animate the change:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
// Get offset for cell
CGFloat centerOffset = self.tableView.frame.size.height / 2 - self.tableView.rowHeight / 2;
// Content offset
CGFloat total = indexPath.row * self.tableView.rowHeight;
[UIView animateWithDuration:0.3 animations:^{
self.tableView.contentOffset = CGPointMake(0, total - centerOffset);
}];
}
It works for all cells, upper and lower too.
You can add extra space to the content of your table view using the contentInset property. Add extra space above and below your table view will allow your cells to scroll all the way to the middle of your table view.
UITableView * tableView = self.tableView ;
CGRect bounds = self.tableView.bounds ;
CGFloat extraSpaceNeeded = 0.5 * ( bounds.size.height - tableView.rowHeight ) ;
tableView.contentInset = (UIEdgeInsets){ .top = -extraSpaceNeeded, .bottom = -extraSpaceNeeded } ;
Now you can just use
[tableView scrollToRowAtIndexPath:indexPath
atScrollPosition:UITableViewScrollPositionMiddle
animated:animated];
I have a UITableViewCell with multiple items inside. (Not just a textView so I cant follow this option.) I'm trying to dynamically size it's height based on the content it has inside.
The heights I will be changing, are a UITextView and a UIView. The textView will constantly be changing (at another method, if you'd like, I can post it). And the UIView will change if the user clicks a button:
Here is my code:
- (void)viewDidLoad
{
self.tableView.rowHeight = UITableViewAutomaticDimension;
}
- (IBAction)thisButton:(id)sender
{
CGRect frame = self.myView.frame;
frame.size.height = 50;
frame.size.width = self.myView.frame.size.width;
self.myView.frame = frame;
// update 'myView's constraint
self.viewHeight.constant = self.myView.frame.size.height;
self.tableView.rowHeight = UITableViewAutomaticDimension;
[myTableView reloadData];
}
Problem:
What happens is, when I press the button, the UIView's height gets
updated, but then everything else in the cell gets moved up, and the cell stays the same size.
When the UITextView's height changes, it doesn't pull everything else
down, and the cells height stays the same. Though the textView's
height does change and it just goes over everything else.
Constraints:
On the UITextView I have 3 constraints - 2 on each side, and 1 on top. The UIView has 3 constraints - 2 on each side, and 1 on the bottom.
I then have a constraint connecting the UIView to the textView.
You can dynamically manage UITableViewCell size by calculating a max height of your internal views:
NSArray *array = [[NSArray alloc] initWithArray:#[view1, view2, view3]];
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
__block CGFloat maxHeight;
[array enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
UIView *view = obj;
if (view.bounds.size.height > maxHeight) {
maxHeight = view.bounds.size.height;
}
}];
return maxHeight;
}
Then in the end of your method that changes view's dimensions you must call [self.tableView reloadData]
I have a button in a static UITableViewCell. What I want to do is place a UIView at the buttons location.
If I just get the buttons position, it will give me a position relative to the tableviews cell, not from the top of the tableViewController. What I want is get the buttons position from the top of the tableViewController.
For example: If the button is 8px away from the top of the current
cell, but 57px away from the top of the viewController, I want to
place the UIView at 57px.
Here's my code:
- (void)viewDidLoad {
CGPoint buttonPosition = [button convertPoint:CGPointZero fromView:self.tableView];
NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint:buttonPosition];
CGRect rect = [myTableView rectForRowAtIndexPath:indexPath];
NSLog(#"%f, %f", rect.origin.y, rect.origin.x);
self.infoView = [[UIView alloc] initWithFrame:CGRectMake(button.frame.origin.x, button.frame.origin.y, 220, 110)];
}
The output of the nslog is 0.
I would also like to update the UIView's position whenever the iphone goes to landscape mode.
CGPoint originalPoint = button.frame.origin;
CALayer *layer = self;
CGPoint point = originalPoint;
while (layer.superlayer)
{
point = [layer convertPoint:point toLayer:layer.superlayer];
layer = layer.superlayer;
}
//When you reach this code, you should have the position in the rootView