title: Android Studio add library error?
body: <p>I want add Picasso library in my project but my project give an error.
  Iusing jdk 7  and android studio  0.2.11 </p>
  
  <p>This is my error. I tryed 8 hours but again error again and again</p>
  
  <p>please help </p>
  
  <p>sorry bad english.</p>
  
  <pre><code>10-05 21:02:45.891  32262-32262/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
      java.lang.NoClassDefFoundError: com.squareup.picasso.Picasso
              at com.medyasef.androidfirsttime.MainActivity.onCreate(MainActivity.java:20)
              at android.app.Activity.performCreate(Activity.java:5133)
              at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
              at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
              at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
              at android.app.ActivityThread.access$600(ActivityThread.java:141)
              at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
              at android.os.Handler.dispatchMessage(Handler.java:99)
              at android.os.Looper.loop(Looper.java:137)
              at android.app.ActivityThread.main(ActivityThread.java:5103)
              at java.lang.reflect.Method.invokeNative(Native Method)
              at java.lang.reflect.Method.invoke(Method.java:525)
              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
              at dalvik.system.NativeStart.main(Native Method)
  </code></pre>
  
  <p>This is MainActivity.java </p>
  
  <pre><code>package com.medyasef.androidfirsttime;
  
  import android.os.Bundle;
  import android.app.Activity;
  import android.view.Menu;
  import android.widget.ImageView;
  
  import com.squareup.picasso.Picasso;
  
  public class MainActivity extends Activity {
  
      private ImageView imageView;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          imageView = (ImageView) findViewById(R.id.imageView);
          Picasso.with(this).load("http://i.imgur.com/DvpvklR.png").into(imageView);
  
      }
  
  
      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
          // Inflate the menu; this adds items to the action bar if it is present.
          getMenuInflater().inflate(R.menu.main, menu);
          return true;
      }
  </code></pre>
  
  <p>build.gradle</p>
  
  <pre><code>buildscript {
      repositories {
          mavenCentral()
      }
      dependencies {
          classpath 'com.android.tools.build:gradle:0.5.+'
      }
  }
  apply plugin: 'android'
  
  repositories {
      mavenCentral()
  }
  
  android {
      compileSdkVersion 18
      buildToolsVersion "18.1.0"
  
      defaultConfig {
          minSdkVersion 9
          targetSdkVersion 16
      }
  }
  
  dependencies {
      compile 'com.android.support:appcompat-v7:18.0.0'
      compile files('libs/picasso-2.1.1.jar')
  }
  </code></pre>