how to obtain the UITableViewCell within heightFor

问题:

How does one obtain the UITableViewCell when within the heightForRowAtIndexPath method, i.e. given the indexPath?

(then I could access the content views I have created to add their heights up)

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
  // How to get the UITableViewCell associated with this indexPath?
}

thanks

EDIT: In fact is there really a valid way to do this? When I put some NSLog statements it seems that heightForRowAtIndexPath it called several times before the calls to cellForRowAtIndexPath (which is where I set up the UILabels in the cell)? This kind implies that I may be tried to use a technique that will not work, i.e. I was hoping in heightForRowAtIndexPath to access the already created labels in each cell to get their heights and add them together for the overall cell row height, HOWEVER if they haven't been set up yet (within cellForRowAtIndexPath) then I guess my approach can't really work?

回答1:

For iOS8:

override func viewDidLoad() {
        super.viewDidLoad()

        self.tableView.estimatedRowHeight = 80
        self.tableView.rowHeight = UITableViewAutomaticDimension
    }

OR

func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
            return UITableViewAutomaticDimension

    }

But for iOS7, the key is calculate the height after autolayout,

func calculateHeightForConfiguredSizingCell(cell: GSTableViewCell) -> CGFloat {
        cell.setNeedsLayout()
        cell.layoutIfNeeded()
        let height = cell.contentView.systemLayoutSizeFittingSize(UILayoutFittingExpandedSize).height + 1.0
        return height

    }

Note:

1) If multiple lines labels, don't forget set the numberOfLines to 0.

2) Don't forget label.preferredMaxLayoutWidth = CGRectGetWidth(tableView.bounds)

回答2:

You can use the tableview's delegate instead of the tableView itself.

id cell = [self tableView:tableView cellForRowAtIndexPath:indexPath];

Check the answer here

UPDATED

In new iOS versions and using correct auto constraints you don't need to reference the cell anymore to calculate the cell's height.

Check here

https://www.raywenderlich.com/129059/self-sizing-table-view-cells

回答3:

This question has no sense because in

heightForRowAtIndexPath

no cells are created yet. Here's how tableView works:

1. TableView asks it's datasource how many sections it will have. -numberOfSectionsInTableView
2. Asks it's datasource how many rows each section will have (to know how big scroller should be etc.) -numberOfRowsInSection
3. Asks it's delegate height of each visible row. To know where cells will be located. - heightForRowAtIndexPath
4. Lastly it asks datasource to give it a cell to display at given index path -cellForRowAtIndexPath

So you can't access to cells from heightForRowAtIndexPath because with a most likely cell is not created yet.

---

However in case I misunderstood your question go try:

UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];

回答4:

The obvious answer is to call cellForRowAtIndexPath, but you may have already discovered there are some issues with that. See this question if you haven't already: UITableView flexible/dynamic heightForRowAtIndexPath

For my last project I used a custom subclass of UICell and implemented a method like this. I then called this from table:heightForRowAtIndexPath: (after looking up the content for that row).

+ (CGFloat) heightOfContent: (NSString *)content
{
    CGFloat contentHeight = 
           [content sizeWithFont: DefaultContentLabelFont
               constrainedToSize: CGSizeMake( DefaultCellSize.width, DefaultContentLabelHeight * DefaultContentLabelNumberOfLines )
                   lineBreakMode: UILineBreakModeWordWrap].height;
    return contentHeight + DefaultCellPaddingHeight;
}

回答5:

i would suggest you to calculate the correct height of a row in table:heightForRowAtIndexPath: by using your data structure (Height of text,images,mutliline text etc..).

And change the component height in their -(void) layoutSubviews method.

回答6:

If you want to access the cells use tags. But as @Jhaliya has said it is better to calculate the height based on the content of the cell. If your regard is with the position of the cell then I would suggest you to use scroll view and implement the cells yourself wherever you want.