uitablviewcell 动态高度与 systemLayoutSizeFittingSize 不正确

Question

我正在使用 xib 和自动布局来构建我的自定义单元格，在我的单元格中，有一个多行标签。在 tableview 的 heightForRowAtIndexPath 中，我将使用

1 dequeueReusableCellWithIdentifier 获取单元格

2 然后调用 [cell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize] 得到正确的高度。

但是在debug中，我发现调用heightForRowAtIndexPath时，我的单元格的宽度不是tableview的宽度，单元格的宽度和xib文件的宽度是一样的（因为在xcode6中，你可以将xib的大小设置为任意）。所以从 systemLayoutSizeFittingSize 得到的高度是不正确的。如何解决此问题以获得正确的单元格高度

从systemLayoutSizeFittingSize得到的尺寸：不正确，这个尺寸可能是340+的宽度（而设备是iPhone5，宽度是320），340+就是cell的xib文件的宽度

最后，我得到了解决方案，感谢 Ashish Gabani 的帮助，事实上，解决方案包括 2 个步骤： 1 将单元格框架重置为您的 tableView 大小 2 在调用systemLayoutSizeFittingSize之前调用cell的layoutSubViews，在自定义cell中，需要重写layoutSubViews方法。 这是解决这个问题的代码，我用红色方块标记它们，享受它

Answer 1

您可以通过像 as 一样传递单元格高度来解决此问题

- (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;
}
}

您也可以从这里找到解决方案Link