动态计算自定义 UITableViewCell 的高度

Frome stackoverflow

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Determine which reuse identifier should be used for the cell at this index path,
    // depending on the particular layout required (you may have just one, or may have many).
    NSString *reuseIdentifier = ...;

    // Dequeue a cell for the reuse identifier.
    // Note that this method will init and return a new cell if there isn't one available in the reuse pool,
    // so either way after this line of code you will have a cell with the correct constraints ready to go.
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:reuseIdentifier];

    // Configure the cell with content for the given indexPath, for example:
    // cell.textLabel.text = someTextForThisCell;
    // ...

    // Make sure the constraints have been set up for this cell, since it may have just been created from scratch.
    // Use the following lines, assuming you are setting up constraints from within the cell's updateConstraints method:
    [cell setNeedsUpdateConstraints];
    [cell updateConstraintsIfNeeded];

    // If you are using multi-line UILabels, don't forget that the preferredMaxLayoutWidth needs to be set correctly.
    // Do it at this point if you are NOT doing it within the UITableViewCell subclass -[layoutSubviews] method.
    // For example:
    // cell.multiLineLabel.preferredMaxLayoutWidth = CGRectGetWidth(tableView.bounds);

    return cell;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Determine which reuse identifier should be used for the cell at this index path.
    NSString *reuseIdentifier = ...;

    // Use a dictionary of offscreen cells to get a cell for the reuse identifier, creating a cell and storing
    // it in the dictionary if one hasn't already been added for the reuse identifier.
    // WARNING: Don't call the table view's dequeueReusableCellWithIdentifier: method here because this will result
    // in a memory leak as the cell is created but never returned from the tableView:cellForRowAtIndexPath: method!
    UITableViewCell *cell = [self.offscreenCells objectForKey:reuseIdentifier];
    if (!cell) {
        cell = [[YourTableViewCellClass alloc] init];
        [self.offscreenCells setObject:cell forKey:reuseIdentifier];
    }

    // Configure the cell with content for the given indexPath, for example:
    // cell.textLabel.text = someTextForThisCell;
    // ...

    // Make sure the constraints have been set up for this cell, since it may have just been created from scratch.
    // Use the following lines, assuming you are setting up constraints from within the cell's updateConstraints method:
    [cell setNeedsUpdateConstraints];
    [cell updateConstraintsIfNeeded];

    // Set the width of the cell to match the width of the table view. This is important so that we'll get the
    // correct cell height for different table view widths if the cell's height depends on its width (due to
    // multi-line UILabels word wrapping, etc). We don't need to do this above in -[tableView:cellForRowAtIndexPath]
    // because it happens automatically when the cell is used in the table view.
    // Also note, the final width of the cell may not be the width of the table view in some cases, for example when a
    // section index is displayed along the right side of the table view. You must account for the reduced cell width.
    cell.bounds = CGRectMake(0.0f, 0.0f, CGRectGetWidth(tableView.bounds), CGRectGetHeight(cell.bounds));

    // Do the layout pass on the cell, which will calculate the frames for all the views based on the constraints.
    // (Note that you must set the preferredMaxLayoutWidth on multi-line UILabels inside the -[layoutSubviews] method
    // of the UITableViewCell subclass, or do it manually at this point before the below 2 lines!)
    [cell setNeedsLayout];
    [cell layoutIfNeeded];

    // Get the actual height required for the cell's contentView
    CGFloat height = [cell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;

    // Add an extra point to the height to account for the cell separator, which is added between the bottom
    // of the cell's contentView and the bottom of the table view cell.
    height += 1.0f;

    return height;
}

// NOTE: Set the table view's estimatedRowHeight property instead of implementing the below method, UNLESS
// you have extreme variability in your row heights and you notice the scroll indicator "jumping" as you scroll.
- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Do the minimal calculations required to be able to return an estimated row height that's
    // within an order of magnitude of the actual height.
    // For example:
    if ([self isTallCellAtIndexPath:indexPath]) {
        return 350.0f;
    } else {
        return 40.0f;
    }
}