I was trying to change theme in my application but i am getting this error

Setting read-only property: yii\web\Application::view

need a stack trace and the code you run that causes the error. otherwise it is hard to guess what is going wrong there,

not sure what youre trying to do, but i think you tryied something like:

$someObject->someAttribure = $newAttribute;

this throws an error since the attributes are protected, instead you should use setAttribute()