scrollViewDidScroll method not giving reference to all scrollviews from table view - ios

Question

I have created tableView with custom cells that contain image view and scrollView. All scroll views contain labels wider than screen bounds, so when I scroll to left/right I want all scrollViews to scroll in same direction. Problem is I don't know how to get reference to each scrollView in scrollViewDidScroll method.
my viewController class:
#import "EPGViewController.h"
#interface EPGViewController (){
NSArray *EPGList;
int scrollPositionX;
}
#end
#implementation EPGViewController
- (void)viewDidLoad
{
[super viewDidLoad];
self.navigationController.navigationBarHidden = false;
EPGList = [NSMutableArray arrayWithObjects:#"1",#"2",#"3",#"4",#"5",#"6",#"7",#"8",#"9",#"10",#"11",#"12", nil];
}
#pragma mark - Table view data source
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
return EPGList.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *hlCellID = #"EPGCell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:hlCellID];
if(cell == nil) {
cell = [[UITableViewCell alloc]
initWithStyle:UITableViewCellStyleDefault reuseIdentifier:hlCellID];
cell.accessoryType = UITableViewCellAccessoryNone;
cell.selectionStyle = UITableViewCellSelectionStyleNone;
}
UILabel *label = (UILabel *)[cell viewWithTag:15];
label.text = EPGList[indexPath.row];
UIScrollView *scrolView = (UIScrollView *)[cell viewWithTag:16];
scrolView.backgroundColor = [UIColor colorWithRed:1.0 green:0.0 blue:0.0 alpha:1.0];
scrolView.delegate = self;
scrolView.tag = indexPath.row+101;
scrolView.scrollEnabled = YES;
scrolView.contentSize = CGSizeMake(scrolView.frame.size.width,scrolView.frame.size.height);
[scrolView setShowsHorizontalScrollIndicator:NO];
[scrolView setShowsVerticalScrollIndicator:NO];
int i=0;
for(i=0;i<15;i++){
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0+i*100, 0, 100, 100)];
label.text = #"HELLO";
label.textColor = [UIColor blackColor];
label.backgroundColor = [UIColor clearColor];
label.textAlignment = NSTextAlignmentCenter;
label.font = [UIFont fontWithName:#"ArialMT" size:18];
[scrolView addSubview:label];
scrolView.contentSize = CGSizeMake(scrolView.frame.size.width+i*label.frame.size.width,scrolView.frame.size.height);
}
[cell addSubview:scrolView];
return cell;
}
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{
return 80.0;
}
- (void)scrollViewDidScroll:(UIScrollView *)callerScrollView {
scrollPositionX = callerScrollView.contentOffset.x;
//if this is called with table view exit
if (callerScrollView == self.tableView) return;
int indexPath = callerScrollView.tag-101;
NSLog(#"TAG: %d",indexPath);
for (UITableViewCell *cell in self.tableView.visibleCells) {
//TODO: Don’t use tags.
UIScrollView *cellScrollView = (UIScrollView *)[cell viewWithTag:16];
if (callerScrollView == cellScrollView) continue;
cellScrollView.contentOffset = CGPointMake(scrollPositionX, 0);
}
}
#end
EDIT:
I managed to solve my problem by deleting line where I add different tags to scrollviews in table view. now I just set offset to scrollview with tag 16.

Answer 1

There are multiple wrong things in your code. Here is better implementation:
- (void)scrollViewDidScroll:(UIScrollView *)callerScrollView {
scrollPositionX = callerScrollView.contentOffset.x;
if (callerScrollView == self.tableView) return;
for (UITableViewCell *cell in self.tableView.visibleCells) {
//TODO: Don’t use tags.
UIScrollView *cellScrollView = (UIScrollView *)[cell viewWithTag:16];
if (callerScrollView == cellScrollView) continue;
cellScrollView.contentOffset = CGPointMake(scrollPositionX, 0);
}
}
Some additonal notes:
This method will be called by table view too, so you will have to check that.
Don’t use any indexes, just plain iteration.
I used checking of scrollViews, but basically there it would be OK without it.
Using tags to identify subviews is not a good idea.
Don’t call reloadData every time!

Answer 2

You should use [tableView visibleCells]; in order to get all cells that are visible at this moment.

Answer 3

You could use UITableView's visibleCells method to get all visible cells and get your scrollviews from there (you can use viewwithTag like you do, but on all cells).
Then you would have to remember to adjust the scrollview position as cells are reused/recreated - probably keep the scrolled offset as a property of your View Controller.

Answer 4

The problem is that you're using dequeueReusableCellWithIdentifier rather than just looping through the cells that have already been displayed.
Do something like:
for (NSInteger j = 0; j < [tableView numberOfSections]; ++j)
{
for (NSInteger i = 0; i < [tableView numberOfRowsInSection:j]; ++i)
{
if (!(indexPath.section == j && indexPath.row == i))
{
UITableViewCell *cell = [tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:i inSection:j]]];
UIScrollView *scrollView = (UIScrollView *)[cell viewWithTag:16];
scrollView.contentOffset = CGPointMake(position_x, scrollView.frame.size.height);
}
}
}