如何更改表格视图单元格内的textview高度约束？

Question

There's been a lot of questions about how to make dynamic cell height using Autolayout and TextView inside it. Here's the story

1. I follow this article iOS dynamic table view cells with varying row height and Autolayout . In this case, we replace the 2nd label in the article with a TextView, with the same set of constraints

2. The TextView does not have intrinsic content size as the Label. So we must use sizeThatFits and creating height constraint on the TextView, like this.

This height constraint is an IBOutlet from the Nib

ViewController.m

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    Item *item = self.dataSource.items[indexPath.row];
    [self.prototypeCell configureWithModel:item];

    [self.prototypeCell updateConstraintsIfNeeded];
    [self.prototypeCell layoutIfNeeded];

    self.prototypeCell.textViewHeightConstraint.constant = [self.prototypeCell.textView sizeThatFits:CGSizeMake(self.prototypeCell.frame.size.width, CGFLOAT_MAX)].height;

    [self.prototypeCell updateConstraintsIfNeeded];
    [self.prototypeCell layoutIfNeeded];

    return [self.prototypeCell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;
}

CustomCell.m

- (void)configureWithModel:(Item *)model {
    self.textView.text = model.content;
}

3. I then see in the console that

 Unable to simultaneously satisfy constraints. Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to 

figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) ( "", "", "", "", "" )

 Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7fa3e3988a90 UITextView:0x7fa3e210f000.height == 200> 

Here you can see that the Autolayout system removes the height constraint on the TextView.

The problem here is that we update the height constraint on the TextView, but the contentView of the cell seems to ignore this.

I know the key to this dynamic height is that the subviews (Label, TextView) must determine its own size (Label has its own intrinsic content size, for TextView we manually set its height constraint) so that the contentSize is then calculated

What am I missing?

Answer 1

只需降低textViewHeightConstraint的优先级（低于1000）即可解决Unable to simultaneously satisfy constraints问题