UICollectionView Drag and Drop update all affected indexPaths - ios

Question

I have a UICollectionView that uses drag and drop functionality to perform manual re-order of the cells.
I only have 1 section that contains two columns of equally sized cells.
To explain my problem properly I would need to upload screenshots but I don't have enough rep, so I will have to explain using numbers.
1 2 3 4 5 6
This represents a CollectionView with 6 cells in 2 columns filling the entire screen.
So the problem i'm encountering is that if I swap, for example, cell 3 and cell 2 everything works correctly because cell 3 becomes cell 2 and vice versa, the issue happens when I swap cell 3 and cell 1 because then cell 3 becomes cell1 and cell1 becomes cell2 and cell2 becomes cell3.
Now it re-arranges but as soon as the app calls [self.collectionView reloadData]; cell3 will stay at 1 where I dropped it, but the new cell 2 and 3 will swap positions as if there indexes havn't updated.
A long press gesture handles the remove and insert of the cell(snapshot of cell) when dragged and all the tiles re-arrange and fit properly into the sections.
-(IBAction)longPressGestureRecognized:(id)sender {
UILongPressGestureRecognizer *longPress = (UILongPressGestureRecognizer *)sender;
UIGestureRecognizerState state = longPress.state;
CGPoint location = [longPress locationInView:self.collectionView];
NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:location];
static UIView *snapshot = nil;
static NSIndexPath *sourceIndexPath = nil;
switch (state) {
case UIGestureRecognizerStateBegan: {
if (indexPath) {
sourceIndexPath = indexPath;
UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:indexPath];
snapshot = [self customSnapshotFromView:(cell)];
__block CGPoint center = cell.center;
snapshot.center = center;
snapshot.alpha = 0.98;
[self.collectionView addSubview:snapshot];
[UIView animateWithDuration:0.25 animations:^{
center.y = location.y;
snapshot.center = center;
snapshot.transform = CGAffineTransformMakeScale(1.05, 1.05);
snapshot.alpha = 0.98;
cell.hidden = YES;
} completion:nil];
}
break;
}
case UIGestureRecognizerStateChanged: {
CGPoint center = snapshot.center;
center.y = location.y;
center.x = location.x;
snapshot.center = center;
if (indexPath && ![indexPath isEqual:sourceIndexPath]) {
[people2 exchangeObjectAtIndex:indexPath.item withObjectAtIndex:sourceIndexPath.item];
[self.collectionView moveItemAtIndexPath:sourceIndexPath toIndexPath:indexPath];
sourceIndexPath = indexPath;
[databaseClass arrangeData:people2];
}
break;
}
default: {
UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:sourceIndexPath];
[UIView animateWithDuration:0.25 animations:^{
snapshot.center = cell.center;
snapshot.transform = CGAffineTransformIdentity;
snapshot.alpha = 0.0;
cell.hidden = NO;
} completion:^(BOOL finished){
[snapshot removeFromSuperview];
snapshot = nil;
}];
sourceIndexPath = nil;
break;
}
}
}
I am using a sqlite method to store the arrangement of the tiles in the database.
+(void)arrangeData:(NSArray*)arrange {
[self databaseInit];
if (sqlite3_open(dbpath, &peopleDB ) == SQLITE_OK)
{
for (int i = 0; i < [arrange count]; i++) {
NSString *insertSQL = [NSString stringWithFormat:#"UPDATE PEOPLE SET ARRANGE = %i WHERE ID = %i",i+1,[[arrange objectAtIndex:i] ID]];
const char *insert_stmt = [insertSQL UTF8String];
sqlite3_prepare_v2( peopleDB, insert_stmt,-1, &statement, NULL);
if (sqlite3_step(statement) == SQLITE_DONE)
{
NSLog(#"Arranged Successfully");
}
else {
NSLog(#"%s SQLITE_ERROR '%s' (%1d)", __FUNCTION__, sqlite3_errmsg(peopleDB), sqlite3_errcode(peopleDB));
}
sqlite3_finalize(statement);
}
sqlite3_close(peopleDB);
}
Not that it matters much but the snapshot :
-(UIView *)customSnapshotFromView:(UIView *)inputView {
UIView *snapshot = [inputView snapshotViewAfterScreenUpdates:YES];
snapshot.layer.masksToBounds = NO;
snapshot.layer.cornerRadius = 0.0;
snapshot.layer.shadowOffset = CGSizeMake(-5.0, 0.0);
snapshot.layer.shadowRadius = 5.0;
snapshot.layer.shadowOpacity = 0.4;
return snapshot;
}
If anyone has any ideas on how to get the cells to stay where they are when the longpress ends I would be hugely appreciative.

Answer 1

I don't understand sqlite, but according to what you say, it seems that you swap data instead of moving the concerned data.
In your example you have to delete dataForCell3 from it's array and then insert it at the index of dataForCell1.
Seems that instead of that you swapped dataForCell3 and dataForCell1.