UITableView-当上面有一定数量的单元格时，删除最后一个单元格

Question

In my UITableView, I have a dedicated cell with an insert control at the bottom to allow the user to insert new rows.

What I want to do is remove/hide this cell when there are a certain number of cells above it (8 in this case).

Here's what I have so far:

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    if (section == 1) {
        if ([sites count] == [[BrowserController sharedBrowserController] maximumTabs]) {
            return [sites count];
        } else {
            return [sites count] + 1;
        }
    } else {
        return 1;
    }
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        ...
    } else if (editingStyle == UITableViewCellEditingStyleInsert) {
        NSString *newSiteAddress = [NSString stringWithString:@"http://"];

        [sites addObject:newSiteAddress];

        if ([sites count] == [[%c(BrowserController) sharedBrowserController] maximumTabs]) {
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
        }

        [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
        [tableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionNone animated:YES];
        [[(BookmarkTextEntryTableViewCell *)[tableView cellForRowAtIndexPath:indexPath] textField] becomeFirstResponder];
    }   
}

Which causes the following exception to be thrown:

2/01/12 4:28:07.956 PM MobileSafari: *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of rows in section 1.  The number of rows contained in an existing section after the update (8) must be equal to the number of rows contained in that section before the update (8), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).'
*** First throw call stack:
(0x2bc0052 0x2d51d0a 0x2b68a78 0x1cf2db 0x747518 0x75282a 0x7528a5 0x812481c 0x75e7bb 0x8b2d30 0x2bc1ec9 0x6c65c2 0x6c655a 0x76bb76 0x76c03f 0x76b2fe 0x984a2a 0x2b949ce 0x2b2b670 0x2af74f6 0x2af6db4 0x2af6ccb 0x491879 0x49193e 0x6c3a9b 0x4430 0x2db5)

Answer 1

Here's a relevant paragraph from Apple's UITableView documentation which has to do with inserting and deleting cells:

Clicking on the insertion or deletion control causes the data source to receive a tableView:commitEditingStyle:forRowAtIndexPath: message. You commit a deletion or insertion by calling deleteRowsAtIndexPaths:withRowAnimation: or insertRowsAtIndexPaths:withRowAnimation:, as appropriate. Also in editing mode, if a table-view cell has its showsReorderControl property set to YES, the data source receives a tableView:moveRowAtIndexPath:toIndexPath: message. The data source can selectively remove the reordering control for cells by implementing tableView:canMoveRowAtIndexPath:.

You should create new methods called "insertLastCell" and "deleteLastCell" (or something along those lines) which explicitly tells your table view to insert and delete that last cell via insertRowsAtIndexPaths:withRowAnimation: and deleteRowsAtIndexPaths:withRowAnimation: .

Once the insert and deletes are "committed", only then can you report back different numbers in your numberOfRowsInSection method.