ios – uitablviewcell动态高度从systemLayoutSizeFittingSize不正确

- (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,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;
}
}

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