I have a view which has dynamic height and I am trying to change this view height priority in run time.

Here is my part of code;

```
if (index == 0) {

    surveyViewHeightConstraint.constant = 0;
    surveyViewHeightConstraint.priority = 1000;

} else if (index == 1) {

    surveyViewHeightConstraint.constant = 163;
    surveyViewHeightConstraint.priority = 500;

}

```

I am changing index with a button action. When I run this code, I am getting this error:

```
*** Assertion failure in -[NSLayoutConstraint setPriority:], /SourceCache/Foundation/Foundation-1141.1/Layout.subproj/NSLayoutConstraint.m:174

```

What is my mistake in here?