I have the following layout in my view controller. I want to be able to scroll vertically with the header scrolling off the view and the UISegmentedControl sticking to the top of the view, beyond that the remaining scroll should be handled by the Collection View.
However I'm a bit confused as to what is the best approach to implemented this layout.
I tried a few implementations with mixed results:
UIScrollView with UICollectionView as subviews: UIScrollView as the parent view with the header, segmented control and collection views as child controls. The problem with this approach is that the nested scrolling does not seem to work correctly. To be able to scroll the UIScrollView the tap needs to be outside the CollectionView area otherwise only the CollectionView scrolls and the header and segmented control don't move.
Header and Segmented Control in Header cell: I tried another approach by using a single CollectionView. I added the header and Segmented Control as subviews of a single Header cell of the collection view. When the segmented control value was changed, I switch the data source property of the CollectionView to achieve the 3 views required for the collection view. Visually everything works perfectly. The only problem here is the race condition when switching quickly between first,second and third tabs. I load the data from a web service, if the web service takes time and is still loading the data and I quickly switch the tabs then I run into bugs where the data returned is for a different collection view than what is currently selected, a lot of out of order sync issues.
Update constant value for Autolayout Constraint: Another approach I tried is to change the constant value of the auto layout constraint applied to "Header" view. Then I added a gesture to the view controller's view to track the scroll, as the user scrolls vertically I adjust the constant of the auto layout constraint so that the "header" cell pops out of view. Again this doesn't seem to work that smoothly, but I suppose I can tweak it, but it seems sort of a hack.
Is there a better way to implement this layout?
#2 seems like a good solution — the scrolling gestures will be most consistent with what users expect, since it's all a single scroll view. (I agree that #3 sounds like a hack.) You can make the header "sticky" with some custom layout attributes.
The only problem here is the race condition when switching quickly between first, second and third tabs.
This is a common problem with asynchronous loading when views are being switched out (especially when you are loading data into individual cells, which are being reused as you scroll). It is important that upon receiving the data you always check whether the receiver is still expecting it; i.e., you should check the segmented control value before changing the backing data source. You could also:
Use separate data source objects for the different segments, having each one manage its own data fetching so they can't get mixed up.
Cancel the outstanding requests, if you can, when quickly switching tabs, to avoid unnecessary network requests.
Cache data to avoid re-fetching every time you switch tabs.
I think you want the same functionality that pinterest profile page have. To implement such functionality at easy way, you need to do following things.
Step 1 : Add UIView as tableHeaderView those who showing off while scrolling up.
self.tableHeaderView = yourView
Step 2 : Add UISegmentControl in section header view.
- (UITableViewHeaderFooterView *)headerViewForSection:(NSInteger)section{
return your_segmentcontrolView;
}
Step 3 : Add UICollectionView into first row of first section.
By implementing following way, you can got your desire functionality.
Hope this help you.
An alternative approach you could consider:
Use a UITableView to contain your UI
Create a UITableView, and set your header as the UITableView's headerView.
Use a sectionHeader to contain the segmentedControl.
Place your collectionView inside of a single UITableViewCell. Or alternatively, you may be able to use the UITableView's footerView to contain the gridView.
By using the sectionHeader, this should allow the header to scroll out of view, but then the sectionHeader will stick below the navigationBar or top of the contentView until another section comes into view (and in your case you will only have one section.)
Add Header View, Body View (Holding Segment View & Collection View) into scroll view.
Initially set userInteractionEnabled property to "NO" for collection view.
Track the insect of scroll view always.
If the y-coordinate of the scrolled insect is more than the height of header view, then set userInteractionEnabled property to "YES" so that thereafter collection view can be scrolled.
If user scroll outside the scroll view and try to bring the header view down, i.e Scroll view y-coordinate insect is less than the height of header view, then immediately change the user iteration mode of collection view and allow user to scroll the scroll view till the top.
Rather than implementing this by hand, you could use a library/cocoapod to set this up for you. This one looks like a pretty good fit: https://github.com/iosengineer/BMFloatingHeaderCollectionViewLayout
Plus, the code is open-source, so you can always modify as needed.
All I can say is that you need to subclass UIView and make it a delegate of UIGestureRecognizerDelegate and UICollectionViewDelegate, then in your UIView subclass, do the following, I can't give out anymore information on this because the code, although owned by myself, is proprietary to the point of probably enraging quite a few organizations that I've used this for, so here's the secret sauce:
CGPoint contentOffset = [scrollView contentOffset];
CGFloat newHeight = [_headerView maxHeight] - contentOffset.y;
CGRect frame = [_headerView frame];
if (newHeight > [_headerView maxHeight]) {
frame.origin.y = contentOffset.y;
frame.size.height = [_headerView maxHeight];
[_headerView setFrame:frame];
} else if (newHeight < [_headerView minHeight]) {
frame.origin.y = contentOffset.y;
frame.size.height = [_headerView minHeight];
[_headerView setFrame:frame];
} else {
frame.origin.y = contentOffset.y;
frame.size.height = newHeight;
[_headerView setFrame:frame];
}
if ([_delegate respondsToSelector:#selector(scrollViewDidScroll:)]) {
return [_delegate scrollViewDidScroll:scrollView];
}
You must subclass another UIView that is defined as the header for this custom UiCollectionView. Then, you must declare the UIView custom header view inside the custom subview of the UIView/UICollectionView delegate, and then set the header of that custom subview inside the UICollctionViewdelegate. You should then pull in this compounded subclass of UIView/UIcollectionView into your UIViewController. Oh yes, and in your layoutSubViews, make sure you do the height calculations that are passed through a double layered subclass. So, you will have the following files:
UIVew this is the delegate of UICollectionView and what I mentioned before
UIView this is a UISCrollViewDelegate and this is the header view
UIViewController that pulls in the subclassed UIView in number 1
UIView subclass of number 1 that pulls in number 2 and sets it as its header
In the number 4 part, make sure you do something like this:
- (CGFloat)maxHeight
{
if (SCREEN_WIDTH == 414)
{
return 260;
}else if (SCREEN_WIDTH == 375)
{
return 325;
}else
{
return 290;
}
}
- (CGFloat)minHeight
{
if (SCREEN_WIDTH == 414)
{
return 90;
}else if (SCREEN_WIDTH == 375)
{
return 325;
}else
{
return 290;
}
}
This will then pass through to the UIView subclass that is a compounded subclass as I already explained. The idea is to capture the maxHeight of you header in the subclass of this header UIView (number 2 above), and then pass this into the main UIView subclass that intercepts these values in the scrollViewDidScroll.
Last tidbit of information, make sure you set up your layoutSubviews in all methods to intercept scroll events. For example in number 1 above, the layoutsubviews method is this:
- (void)layoutSubviews
{
CGRect frame = [_headerView frame];
frame.size.width = [self frame].size.width;
[_headerView setFrame:frame];
[super layoutSubviews];
}
This is all I can give you, I wish I could post more, but this should give you an idea of how it's done in production environments for the big time apps you see out in the wild.
One more thing to note. When you start going down the road of intense implementations like this, don't be surprised to learn that, for example, a single view controller in an app that works with methods like I've explained will have anywhere from 30-40 custom subclasses that are either subclasses in their own right or compounded subclasses or subclasses of my own subclasses or my own subclasses. I'm telling you this so you get an idea of how much code is required to get this right, not to scare you, but to let you know that it might take a while to get right, and to not kick yourself in the butt if it takes awhile to make work. Good luck!!
I have two table views set up side by side, and I need them to scroll at exactly the same time. So, when you scroll one, the other one will scroll at the same time.
I did some searching and I couldn't find any information, but I assume it must be possible somehow.
My table views are both connected to the same class and I differentiate between them like this:
if tableView == tableView1 {
//
} else if tableView = tableView2 {
//
}
You can get set the scrollView delegate to self on both of your tableView's scrollViews. And in -scrollViewDidScroll, take the contentOffset and set the other scrollView's contentOffset to the same value.
Like Schemetrical said you should use scrollViewDidScroll.
see the first answer of this:
Scrolling two UITableViews together
- (void)scrollViewDidScroll:(UIScrollView *)scrollView;
{
UITableView *slaveTable = nil;
if (self.table1 == scrollView) {
slaveTable = self.table2;
} else if (self.table2 == scrollView) {
slaveTable = self.table1;
}
[slaveTable setContentOffset:scrollView.contentOffset];
}
If you want them to scroll in prefect lock-step then this isn't a trivial problem. UITableView is a subclass of UIScrollview, so you could probably create a custom subclass of UITableView that overrode various UIScrollView methods and when something caused the table view to scroll, it would do the same thing to the other table view.
Edit: #Schemetrical's suggestion of using the scroll view delegate is cleaner than creating subclasses. You might have to monitor quite a few of the scroll view delegate methods and use them to match the behavior in the other scroll view.
EDIT #2:
Apparently I'm wrong and scrollViewDidScroll is called for every change in the scroll view, so it's simpler than I thought to keep them synced. I'm going to leave my answer for context even though I was wrong.
If title isn't telling you anything, here's what I found out recently and am curious about:
In my app I have a UIScrollView with buttons in it. These buttons all have one subview each - an instance of UILabel. Sometimes there is a particular event triggered that changes the text in labels and I also needed to change the frame of both labels and buttons, so that whole text can be displayed (it won't be truncated). So I just grabbed first subview of a button and checked how much space its text needs.
This caused crashes if that event occurred during scrolling. Turns out that besides the label, each button had another subview which was instance of UIImageView. At first I thought that during scrolling, UIScrollView takes "screenshots" of its subviews and kind of puts the images on top so that animating the scrolling is somewhat less expensive in terms of performance. This logic is flawed however, because the UIImageView was a subview at index 0, so it was put below my labels.
Anyone knows why this happens? What did Apple engineers try to achieve with this weird mechanic?
Note that it might actually happen just for buttons though. Also, I checked the labels and they didn't have any subviews.
UIButtons have a UIImageView for the background image (which is nil until you call - (void)setImage:(UIImage *)image forState:(UIControlState)state or set it using Interface Builder). So I would assume that the subview at index 0 would be the background image since that would be drawn first to be below everything else.
What you could do to be sure that you are getting the UILabel that you're looking for is something like this:
- (UILabel *)getLabelForButton:(UIButton *)button
{
for (id subView in button.subviews)
{
if ([subView isKindOfClass:[UILabel class]])
{
return subView;
}
}
return nil;
}
Is it possible to recognise gesture from scrollView so when one scrollView is dragged to simulate same dragging on another scrollView? For example I have tableView with custom cell that have scrollView in it, and I want to simulate dragging on every item in list.
EDIT
I succeeded to recognize movement of scrollView, but now I cant set other scrollViews from table to do same amount of scrolling.
-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
int position_x = scrollView.contentOffset.x;
int i=0;
int indexPath = [self.tableView indexPathForSelectedRow].row;
static NSString *hlCellID = #"EPGCell";
UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:hlCellID];
UIScrollView *scrollView = (UIScrollView *)[cell viewWithTag:16];
for(i=0; i<EPGList.count;i++){
if(i!=indexPath){
scrollView.contentOffset = CGPointMake(position_x, scrollView.frame.size.height);
}
}
}
Problem is that indexPath is not returning correct value when i am clicking on scrollView. It returns correct value only when I am clicking on cell space outside of scrollview.
Yes, yes it is possible. You need to have a delegate assigned to the scrollViews within the cells. Preferrably the same class that implements hour tableview data source and table view delegate protocols. You must implement UIScrollViewDelegate and the delegate must implement the scrollViewDidScroll: method.
Within that scrollViewDidScroll delegate method, you check the contentOffset property for its x and/or y values. Normally people go for the vertical scrolling value, but if you're implementing them in a UITableViewCell, you're probably doing horizontal scrolling.
The you use the value, I am assuming contentOffset.x, to update other scroll views within the other cells of your table! Make sense?
I have just posted an answer to another UIScrollView question yesterday. Please read what I wrote there, it might help you more.
Animation in UIScrollView iOS app
I use custom code to create cells that get displayed on a UITableView. When a row is swiped, the delete button appears on the far right of the cell as expected. However it causes the contents of the cell to move to the left (partly off screen). This kind of behaviour didn't happen when using the cells that are built in to the framework.
The UIView property autoresizingMask allows you to specify how your subviews should behave when their superview (in this case the UITableViewCell's contentView) gets resized.
See the View Programming Guide for iOS for more information.
Isn't it because your content is bound to the right edge?
Although this answer may be too late, I believe the problem is due to the fact that you happen to be adding your content directly to the cell by writing something like:
MyView* myView = [[MyView alloc] init];
[cell addSubview : myView];
This happens to be good; however, your content will be affected by any change that takes place within the cell. If, on the other hand, you want your views to remain intact while anything else happens to the cell, you must add your content as subviews of the cell's contentView:
MyView* myView = [[MyView alloc] init];
[[cell contentView] addSubview : myView];
I do hope this helps.
Cheers!