title: Error:(8, 35) cvc-elt.1.a: Cannot find the declaration of element 'android.support.constraint.ConstraintLayout'
body: <p>I am completely new to Android app devlopement and just started watching one video training and have installed andriod studio. I have created a program to print "hello world"" but it's giving few errors which I have no idea as that training is very basic and has no info on errors.</p>
  
  <p>My code is:(Basically this is auto generated code when I started new project)</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  
  &lt;android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      tools:context=".MainActivity"&gt;
  
      &lt;TextView
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="Hello World!"
          app:layout_constraintBottom_toBottomOf="parent"
          app:layout_constraintLeft_toLeftOf="parent"
          app:layout_constraintRight_toRightOf="parent"
          app:layout_constraintTop_toTopOf="parent" /&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p>And it is giving following errors:</p>
  
  <pre><code>Error:(8, 35) cvc-elt.1.a: Cannot find the declaration of element 'android.support.constraint.ConstraintLayout'.
  Error:(1, 56) s4s-elt-schema-ns: The namespace of element 'x' must be from the schema namespace, 'http://www.w3.org/2001/XMLSchema'.
  Error:(1, 56) s4s-elt-invalid: Element 'x' is not a valid element in a schema document.
  Error:(1, 56) schema_reference.4: Failed to read schema document 'null', because 1) could not find the document; 2) the document could not be read; 3) the root element of the document is not &lt;xsd:schema&gt;.
  </code></pre>