Exception loading Facebook Login Button in Android Studio -

i want make app facebook integration. i'm using android studio 1.1.0. i'm able import facebook skd 4.0.0 in build.gradle (module:app) , use in java code:

apply plugin: 'com.android.application'  android {     compilesdkversion 21     buildtoolsversion "22.0.1"      defaultconfig {         applicationid "package.test"         minsdkversion 15         targetsdkversion 21         versioncode 1         versionname "1.0"     }     buildtypes {         release {             minifyenabled false             proguardfiles getdefaultproguardfile('proguard-android.txt'), 'proguard-rules.pro'         }     } }  repositories {     mavencentral() }  dependencies {     compile filetree(dir: 'libs', include: ['*.jar'])     compile 'com.android.support:appcompat-v7:22.0.0'     compile 'com.facebook.android:facebook-android-sdk:4.0.0' } 

i put loginbutton layout file activity:

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     ...     tools:context=".mainactivity">      <com.facebook.login.widget.loginbutton         android:id="@+id/login_button"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_gravity="center_horizontal"         android:layout_marginbottom="30dp"         android:layout_margintop="30dp" />  </relativelayout> 

this exception thrown @ setcontentview(layoutfile).

i checked samples in facebook sdk on github doesn't helped me fix problem. import of facebook sdk correctly?

thanks in advance!

you need call facebooksdk.sdkinitialize in activity or application oncreate.