android - toolbar layout is undefined -

i learning how use viewpager actiontabs through tutorial, , main layout hosts toolbar, tablayout , viewpager posted below in act_main.xml. @ run time receive below posted logcat errors , line 21 in posted xml layout contains

<android.support.v7.widget.toolbar 

how fix it

main activitiy class:

public class mainactivity extends appcompatactivity {  private final string tag = this.getclass().getsimplename();  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     log.w(tag, "oncreate()");      setcontentview(r.layout.act_main); } 

act_main.xml

<relativelayout android:id="@+id/main_layout" 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">  <android.support.v7.widget.toolbar     android:id="@+id/toolbar"     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:layout_alignparenttop="true"     android:background="?attr/colorprimary"     android:elevation="6dp"     android:minheight="?attr/actionbarsize"     android:theme="@style/themeoverlay.appcompat.dark.actionbar"     app:popuptheme="@style/themeoverlay.appcompat.light"/>  <android.support.design.widget.tablayout     android:id="@+id/tab_layout"     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:layout_below="@+id/toolbar"     android:background="?attr/colorprimary"     android:elevation="6dp"     android:minheight="?attr/actionbarsize"     android:theme="@style/themeoverlay.appcompat.dark.actionbar"/>  <android.support.v4.view.viewpager     android:id="@+id/pager"     android:layout_width="match_parent"     android:layout_height="fill_parent"     android:layout_below="@id/tab_layout"/>  </relativelayout> 

gradle:

    apply plugin: 'com.android.application'      android {     compilesdkversion 23     buildtoolsversion "23.0.2"      defaultconfig {         applicationid "com.example.com.vpager_00"         minsdkversion 21         targetsdkversion 23         versioncode 1         versionname "1.0"     }     buildtypes {         release {             minifyenabled false             proguardfiles getdefaultproguardfile('proguard-android.txt'), 'proguard-rules.pro'         }     } }  dependencies {     compile filetree(dir: 'libs', include: ['*.jar'])     compile 'com.android.support:appcompat-v7:23.1.1' } 

logcat:

fatal exception: main 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime: process: com.example.com.vpager_00, pid: 23204 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime: java.lang.runtimeexception: unable start activity componentinfo{com.example.com.vpager_00/com.example.com.vpager_00.mainactivity}: android.view.inflateexception: binary xml file line #21: error inflating class android.support.design.widget.tablayout 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ android.app.activitythread.performlaunchactivity(activitythread.java:2689) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ android.app.activitythread.handlelaunchactivity(activitythread.java:2754) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ android.app.activitythread.access$900(activitythread.java:177) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ android.app.activitythread$h.handlemessage(activitythread.java:1448) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ android.os.handler.dispatchmessage(handler.java:102) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ android.os.looper.loop(looper.java:145) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ android.app.activitythread.main(activitythread.java:5938) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ java.lang.reflect.method.invoke(native method) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ java.lang.reflect.method.invoke(method.java:372) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:1400) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:     @ com.android.internal.os.zygoteinit.main(zygoteinit.java:1195) 02-08 13:59:35.031 23204-23204/com.example.com.vpager_00 e/androidruntime:  caused by: android.view.inflateexception: binary xml file line #21: error inflating class android.support.design.widget.tablayout 

add google design library import dependencies {}

compile 'com.android.support:design:23.1.1' 

---

you need add v4 support library

compile 'com.android.support:support-v4:23.1.1' 

to prevent similar error <android.support.v4.view.viewpager />

---

your app.gradle's dependencies {} should this:

dependencies {     compile filetree(dir: 'libs', include: ['*.jar'])     compile 'com.android.support:appcompat-v7:23.1.1'     compile 'com.android.support:design:23.1.1'     compile 'com.android.support:support-v4:23.1.1' }