Parent UIView not resizing after constraint.constant on UILabel changed - ios

Question

UPDATE
Now Solved The problem was that when I was updating the bottomConstraint I was setting the Constant to the bottom padding property. Sounds reasonable but of course the Constant should have been set to 0 - BottomPadding. That explains why the bottom of the text was being not visible, it was being constrained beyond its clipping container.
I have a simple UIView custom control called PaddedLabel that wraps (not inherits) a UILabel
The view hierarchy is
PaddedLabel -> UILabel
When the constraints on the UILabel have their constants updated the outer View does not chnage height. It is as if the outer UIView is seeing only the Height of the Label as the Height it needs rather than the Height of the Label plus constants. This is how it looks
In UpdateConstraints I add some constraints and if there is a Text value I set the Constant on the Constraint to the value I want for padding else I set the Constant to 0.
public override void UpdateConstraints()
{
base.UpdateConstraints();
if (this.constraintsApplied == false)
{
this.leftConstraint =
NSLayoutConstraint.Create(this.NestedLabel, NSLayoutAttribute.Left, NSLayoutRelation.Equal, this, NSLayoutAttribute.Left, 1.0f, this.LeftPadding);
this.AddConstraint(this.leftConstraint);
this.rightConstraint =
NSLayoutConstraint.Create(this.NestedLabel, NSLayoutAttribute.Right, NSLayoutRelation.Equal, this, NSLayoutAttribute.Right, 1.0f, 0 - this.RightPadding);
this.AddConstraint(this.rightConstraint);
this.topConstraint =
NSLayoutConstraint.Create(this.NestedLabel, NSLayoutAttribute.Top, NSLayoutRelation.Equal, this, NSLayoutAttribute.Top, 1.0f, this.TopPadding);
this.AddConstraint(this.topConstraint);
this.bottomConstraint =
NSLayoutConstraint.Create(this.NestedLabel, NSLayoutAttribute.Bottom, NSLayoutRelation.Equal, this, NSLayoutAttribute.Bottom, 1.0f, 0 - this.BottomPadding);
this.AddConstraint(this.bottomConstraint);
this.constraintsApplied = true;
}
if (this.Text.HasValue())
{
this.topConstraint.Constant = this.TopPadding;
// The following code was the problem.
// It should have been 0 - this.BottomPadding Now corrected
// this.bottomConstraint.Constant = this.BottomPadding;</del>
this.bottomConstraint.Constant = 0 - this.BottomPadding;
}
else
{
this.topConstraint.Constant = 0;
this.bottomConstraint.Constant = 0;
}
}
When the Text property is set I set the Text property on the inner UILabel and call SetNeedsUpdateConstraints
public string Text
{
get
{
return this.text;
}
set
{
if (this.text == value)
{
return;
}
this.text = value;
this.nestedLabel.Text = value;
this.SetNeedsUpdateConstraints();
}
}

Answer 1

If you want the PaddedLabel view to expand and fit around the inside UILabel, change the bottom constraint. You want to tie the bottom of PaddedLabel to the bottom of the UILabel, so as the UILabel grows it makes PaddedLabel expand! The way it is now, you're telling the UILabel to squish itself inside of the PaddedLabel view.
Reverse the bottomConstraint and you should be set.