title: import "android.support.v4.view.ViewPager" in activity_main.xml file
body: <p>i want to learn swipe technology to change my pages from a tutorial. in that tutorial, he used "android.support.v4.view.ViewPager" in main xml  file. but i dont know where must i attach  this code in my file in android studio environment.my main problem is when i attached "android.support.v4.view.ViewPager" in every place in my xml code, it indicate an error and i dont know where is the right place to attach it.  this is my  main xml file:</p>
  
  <pre><code>&lt;RelativeLayout
  
      android.support.v4.view.ViewPager  // error  is here
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:paddingLeft="@dimen/activity_horizontal_margin"
      android:paddingRight="@dimen/activity_horizontal_margin"
      android:paddingTop="@dimen/activity_vertical_margin"
      android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity"&gt;
  
      &lt;TextView android:text="@string/hello_world" android:layout_width="wrap_content"
          android:layout_height="wrap_content" /&gt;
  
  &lt;/RelativeLayout&gt;
  </code></pre>
  
  <p>and error in gradle is :</p>
  
  <pre><code>Error:(3) Error parsing XML: not well-formed (invalid token)
  Error:Execution failed for task ':app:processDebugResources'.
  &gt; com.android.ide.common.process.ProcessException: org.gradle.process.internal.ExecException: Process 'command 'C:\Users\iman\AppData\Local\Android\sdk\build-tools\22.0.1\aapt.exe'' finished with non-zero exit value 1
  </code></pre>