How to Start UITableView on the Last Cell?

前端 未结 8 1222
囚心锁ツ
囚心锁ツ 2020-11-30 01:43

In Apple\'s Messages app, when you click a correspondent\'s name and switch to the table view of the conversation (with balloons for each message), the table appears scrolle

相关标签:
8条回答
  • 2020-11-30 02:22

    scrollToRowAtIndexPath should work.

    In viewWillAppear:, try this:

    [theTableView reloadData];    
    NSIndexPath* ip = [NSIndexPath indexPathForRow:rowNumberHere inSection:sectionNumberHere];
    [theTableView scrollToRowAtIndexPath:ip atScrollPosition:UITableViewScrollPositionTop animated:NO];
    

    rowNumberHere is the row number in the data source you want to scroll to.

    atScrollPosition is just one of the values in the UITableViewScrollPosition enum which can determine where on the screen the row number you want will show up. However, depending on the number of rows and which row you are scrolling to, it may not make a difference.

    Putting reloadData: avoids an exception if the data is not loaded yet in viewWillAppear:. If you put the scrollToRowAtIndexPath in viewDidAppear:, you would not need the reloadData: but you will see the table jump a little which you say you don't want.

    Edit: @Theory, try changing your code as follows...

    [tableView reloadData];
    int lastRowNumber = [tableView numberOfRowsInSection:0] - 1;
    NSIndexPath* ip = [NSIndexPath indexPathForRow:lastRowNumber inSection:0];
    [tableView scrollToRowAtIndexPath:ip atScrollPosition:UITableViewScrollPositionTop animated:NO];
    

    Please note numberOfRowsInSection returns row count, not the last row number (which is row count - 1).

    0 讨论(0)
  • 2020-11-30 02:27

    The issue with scrollToRowAtIndexPath method is its slow and the tableView takes time to scroll to the bottom.

    i had the exact same problem, after trying everything(same as you), this worked, the key is if you're using autolayout initialize scrollToBottom to true and then do this

    - (void)viewDidLayoutSubviews {
        [super viewDidLayoutSubviews];
        // Scroll table view to the last row
        [self scrollToBottom];
    }
    
    -(void)scrollToBottom {
        if (shouldScrollToLastRow)
        {
            CGPoint bottomOffset = CGPointMake(0, self.tableView.contentSize.height - self.tableView.bounds.size.height);
            [self.tableView setContentOffset:bottomOffset animated:NO];
        } }
    

    doing this will ensure you're almost at the bottom of you're tableView but might not be at the very bottom as its impossible to know the exact bottom offset when you're at the top of the tableView, so after that we can implement scrollViewDidScroll

    -(void)scrollViewDidScroll: (UIScrollView*)scrollView
    {
        float scrollViewHeight = scrollView.frame.size.height;
        float scrollContentSizeHeight = scrollView.contentSize.height;
        float scrollOffset = scrollView.contentOffset.y;
    
        // if you're not at bottom then scroll to bottom
        if (!(scrollOffset + scrollViewHeight == scrollContentSizeHeight))
        {
            [self scrollToBottom];
        } else {
        // bottom reached now stop scrolling
            shouldScrollToLastRow = false;
        }
    }
    
    0 讨论(0)
  • 2020-11-30 02:28

    Note for scrolling to the bottom row, the section needs to be last section not 0 (first section):

    int lastSection = [self.myTableView numberOfSections] -1;
    if (lastSection < 0) return;
    
    int lastRow = [self.myTableView numberOfRowsInSection:lastSection] - 1;
    if (lastRow < 0) return;  
    NSIndexPath* ip = [NSIndexPath indexPathForRow:lastRow inSection:lastSection];
    
     [self.myTableView scrollToRowAtIndexPath:ip atScrollPosition:UITableViewScrollPositionTop animated:YES];
    
    0 讨论(0)
  • 2020-11-30 02:30

    Answer of @DyingCactus in Swift 3 & Swift 4:

        let lastRow: Int = self.tableView.numberOfRows(inSection: 0) - 1
        let indexPath = IndexPath(row: lastRow, section: 0);
        self.tableView.scrollToRow(at: indexPath, at: .top, animated: false)
    
    0 讨论(0)
  • 2020-11-30 02:31

    You can call -scrollToRowAtIndexPath:atScrollPosition:animated within the -viewWillAppear: method of your TableViewController.

    atScrollPosition: allows you to set where you want your cell for rowAtIndexPath to appear. There are four options:

    UITableViewScrollPositionTop - puts your cell right at the top of the view

    UITableViewScrollPositionMiddle - centers your cell in the view

    UITableViewScrollPositionBottom - puts your cell at the bottom

    UITableViewScrollPositionNone - Using this setting will position in the cell in user view with minimum scrolling/movement.

    The behavior is different in three scenarios :-

    If the cell is already in view, it does nothing.

    If the cell is above the current view, it scrolls the cell to the top of the view.

    If the cell is beneath the current view, it scrolls the cell to the bottom of the view.

    0 讨论(0)
  • 2020-11-30 02:31

    Following DyingCactus's reply above, I added this method to my controller:

    -(void)viewWillAppear:(BOOL)animated {
          [self.tableView reloadData];    
          NSIndexPath* ip = [NSIndexPath indexPathForRow:[self.tableView numberOfRowsInSection:0] - 1 inSection:0];
          [self.tableView scrollToRowAtIndexPath:ip atScrollPosition:UITableViewScrollPositionTop animated:NO];
    }
    

    And now it works, exactly what I wanted. Thanks!

    0 讨论(0)
提交回复
热议问题