Cocoa-Touch: How to: custom UITableViewCell with UIColor clearColor background

Question

I have a UITableView with custom cells.
I have MyTableViewCell : UITableViewCell and MyTableViewCellContentView : UIView classes.

What I'm doing is basically what is done in the AdvancedTableViewCells demo app from Apple with a slight change, on some rows I want to use a clearColor background to show the table's background behind the painted text.

So in MyTableView's cellForRowAtIndexPath I'm doing:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *CellIdentifier = @"MyCell";

    MyTableViewCell *cell = (MyTableViewCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[MyTableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }

    cell.someValue = indexPath.section;
    [cell finishedSetup];

    return cell;
}

And in my MyTableViewCell's finishedSetup:

cellContentView = [[MyTableViewCellContentView alloc] initWithFrame:CGRectMake(0, 0, 320, 80) cell:self];
cellContentView.autoresizingMask = UIViewAutoresizingNone;
cellContentView.contentMode = UIViewContentModeRedraw;
[self.contentView addSubview:cellContentView];

And in MyTableViewCellContentView I implement the drawRect method. And plan to not use any subviews but draw my custom content just as the Apple example does in the CompositeSubviewBasedApplication.

The problem is that for a few sections I want to use a clearColor backgroundColor. This works, until a cell with a non-clearColor backgroundColor is reused to draw a clearColor cell, at which time the background is not cleared and will still have the old color.

How can I make the background redraw?

Edit: I forgot to mention, I'm setting the background color in MyTableViewCellContentView's init after calling super's init. Setting it via:

self.backgroundColor = [UIColor clearColor];

I've verified that this in fact does get called and is called as expected with clearColor or redColor.

I've also tried setting the table cell's background color, it didn't help.

Edit #2: Here's my drawRect method:

- (void)drawRect:(CGRect)rect {
    [super drawRect:rect];
    static int i = 0;
    [[NSString stringWithFormat:@"Cell %d", ++i] drawAtPoint:CGPointMake(3, 3) withFont:[UIFont boldSystemFontOfSize:16]];
}

Answer 1

To make the background color setting take effect you need to do the setting in tableView:willDisplayCell:forRowAtIndexPath - the OS will not alter anything you set here. The reason is that some additional setup of the cell gets done by the OS after you return it from tableView:cellForRowAtIndexPath. If you can, get a look at session 101 from WWDC 09 presented by Jason Beaver.

Answer 2

I haven't found out why it was happening. But I've tried a different strategy. I'm no longer reusing table cells, since I don't have that many of them.

Instead I'm creating all cells at startup and actually get a boost in performance when showing them since this way there is no additional setup needed when scrolling.