Custom UITableViewCell backgrounds, when to reload, etc

Question

I've set up a custom grouped tableview style using the following code in cellForRowAtIndexPath. Each cell is given a new background view and it's corners are rounded according to its position in the section. I use this style throughout my app and in various views I use animations to add and delete rows. (Using [tableview insertRowsAtIndexPaths:], etc).

If the last row of a section is inserted or removed I need to be able to reload the cells background view corners. How can I do this without calling [tableview reloadData] or even reloadCellsAtIndexPaths? Both of those functions mess up the animations of inserting and deleting cells. Is there somewhere I can put this background corner definition that would get called at the appropriate time? How does the default grouped tableview do this?

Sorry if this is unclear. Ask for clarification and I will edit. Thanks! :)

UITableViewCell *cell = [aTableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:[self styleForCellAtIndexPath:indexPath] 
                                       reuseIdentifier:cellIdentifier] autorelease];

        // Theme the cell
            TableCellBackgroundView *backgroundView = [[TableCellBackgroundView alloc] initWithFrame:cell.frame];
            TableCellBackgroundView *selectedBackgroundView = [[TableCellBackgroundView alloc] initWithFrame:cell.frame];
            selectedBackgroundView.selectedStyle = YES;
            // top row, without header
            BOOL header = [self tableView:aTableView heightForHeaderInSection:indexPath.section]!=0;
            if (indexPath.row == 0 && (!header || tableTheme==kTableThemeSimple)) {
                backgroundView.topRadius = 6;
                selectedBackgroundView.topRadius = 6;
            }
            // bottom row
            if (indexPath.row == [self tableView:aTableView numberOfRowsInSection:indexPath.section]-1) {
                backgroundView.bottomRadius = 6;
                selectedBackgroundView.bottomRadius = 6;
            }
            cell.backgroundView = backgroundView;
            cell.selectedBackgroundView = selectedBackgroundView;
            cell.contentView.backgroundColor = [UIColor clearColor];
            cell.backgroundColor = [UIColor clearColor];
        }
    }

Would there be a clean way to detect in the cells layoutSubviews or drawRect which corners should be drawn? I don't mind subclassing UITableViewCell, I just can't think of a way it would help.. — Dash
– Dash, Commented Apr 19, 2012 at 0:26

geenen124 · Accepted Answer · 2012-04-19 00:38:10Z

If you have a method that you call for the custom animation, when the animation is completed, or rather prior to the display of the new cell, using a subclass of UITableViewCell make a call to a method named something like - (void) fixCornersWithIndexPath: (NSIndexPath *) indexPath.

- (void) customAnimationForCellAtIndexPath: (NSIndexPath *) path {
    //your animation things
    CustomCell *cell = [self.tableView cellForRowAtIndexPath: indexPath];
    [cell fixCornersWithIndexPath: path andRowCount: [self tableView:aTableView numberOfRowsInSection:indexPath.section]];
}

and then fix corners should be something like this:

- (void) fixCornersWithIndexPath: (NSIndexPath *) indexPath andRowCount: (NSInteger *) rowCount {
      if (indexPath.row == 0 && (!header || tableTheme==kTableThemeSimple)) {
            self.backgroundView.topRadius = 6;
            self.selectedBackgroundView.topRadius = 6;
        }
        // bottom row
        if (indexPath.row == rowCount-1) {
            self.backgroundView.bottomRadius = 6;
            self.selectedBackgroundView.bottomRadius = 6;
        }
}

Hope this helps!

danh · Accepted Answer · 2012-04-19 00:52:51Z

0

I think this is what you're looking for. After you've altered your model, call:

- (void)reloadRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation:(UITableViewRowAnimation)animation

This will cause your cellAtIndexPath method to be invoked. Send an array with a single index path of the row that's out of date (I guess for the rounded corners problem, that's either the last row after a row was removed, or the row before a newly added last row).

You can call it along with your other update methods in between begin/end updates.

answered Apr 19, 2012 at 0:52

danh

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Comments

Jerry · Accepted Answer · 2012-07-31 16:25:10Z

The solution that worked for me is this:

Set the background in tableView:willDisplayCell:forRowAtIndexPath:
Create a convenience method called reloadBackgroundForRowAtIndexPath that calls willDisplayCell manually

When I add a row, call the convenience method after a delay to allow the table animations to finish

- (void)reloadBackgroundForRowAtIndexPath:(NSIndexPath*)indexPathToReload {
    [self tableView:self.tableView willDisplayCell:[self.tableView cellForRowAtIndexPath:indexPathToReload] forRowAtIndexPath:indexPathToReload];
}

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
    // Logic to determine the background image
}

// elsewhere, update the table, then
NSIndexPath *indexPathToFix = [NSIndexPath indexPathForRow:count-1 inSection:0];
// If the new row is coming out, we want to update the background right away.  If the new row is going away, we want to wait to update until the animation is done.
// I don't like hard-coding the animation length here, but I don't think I have a choice.
[self performSelector:@selector(reloadBackgroundForRowAtIndexPath:)  withObject:indexPathToFix afterDelay:(self.tableView.isEditing ? 0.0 : 0.2)];

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