ios - 在底部添加单元格并滚动 UITableView

Question

我想在 UITableView 的底部添加单元格，然后滚动以使其完全可见(就像在 Whatsapp 中发送或接收消息时一样)。

我试过这样做:

[self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForItem:[self.tableView numberOfRowsInSection:0]-1 inSection:0] atScrollPosition:UITableViewScrollPositionMiddle animated:YES];

但这会造成图形故障，表格会闪烁，滚动效果不佳而不是流畅。

有什么帮助吗？

Answer 1

这里我所做的是，插入一行，然后更改 tableView 的内容插图

-(IBOutlet)sendButton:(id)sender
{
    [array addObject:textView.text];
    [self addAnotherRow];
}
- (void)addAnotherRow {
        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:(array.count - 1) inSection:0];
        [self.messagesTableView beginUpdates];
        [self.messagesTableView insertRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
        [self.messagesTableView endUpdates];
        [self updateContentInsetForTableView:self.messagesTableView animated:YES];

        // TODO: if the scroll offset was at the bottom it can be scrolled down (allow user to scroll up and not override them)

        [self.messagesTableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];
}

- (void)updateContentInsetForTableView:(UITableView *)tableView animated:(BOOL)animated {
    NSUInteger lastRow = [self tableView:tableView numberOfRowsInSection:0];
    NSLog(@"last row: %lu", (unsigned long)lastRow);
    NSLog(@"items count: %lu", (unsigned long)array.count);

    NSUInteger lastIndex = lastRow > 0 ? lastRow - 1 : 0;

    NSIndexPath *lastIndexPath = [NSIndexPath indexPathForItem:lastIndex inSection:0];
    CGRect lastCellFrame = [self.messagesTableView rectForRowAtIndexPath:lastIndexPath];

    // top inset = table view height - top position of last cell - last cell height
    CGFloat topInset = MAX(CGRectGetHeight(self.messagesTableView.frame) - lastCellFrame.origin.y - CGRectGetHeight(lastCellFrame), 0);

    // What about this way? (Did not work when tested)
    // CGFloat topInset = MAX(CGRectGetHeight(self.tableView.frame) - self.tableView.contentSize.height, 0);

    NSLog(@"top inset: %f", topInset);

    UIEdgeInsets contentInset = tableView.contentInset;
    contentInset.top = topInset;
    NSLog(@"inset: %f, %f : %f, %f", contentInset.top, contentInset.bottom, contentInset.left, contentInset.right);

    NSLog(@"table height: %f", CGRectGetHeight(self.messagesTableView.frame));

    UIViewAnimationOptions options = UIViewAnimationOptionBeginFromCurrentState;
    [UIView animateWithDuration:animated ? 0.25 : 0.0 delay:0.0 options:options animations:^{
        tableView.contentInset = contentInset;

    } completion:^(BOOL finished) {
    }];
}

Note: to view existing messages from array, you have to include this also.

- (void)viewDidLayoutSubviews {
    [self updateContentInsetForTableView:self.messagesTableView animated:NO];
}