title: android:onclick method doesn't work
body: <p>xml code:</p>
  
  <pre><code> &lt;Button
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:text="Invia"
              android:clickable="true"
              android:onClick="onClick1"
              android:id="@+id/invia" /&gt;
  </code></pre>
  
  <p>java code:</p>
  
  <pre><code>import android.app.Activity;
  import android.content.Intent;
  import android.support.v7.app.AppCompatActivity;
  import android.os.Bundle;
  import android.view.View;
  import android.widget.Button;
  import android.widget.EditText;
  import android.widget.Toast;
  
  import com.android.volley.Request;
  import com.android.volley.RequestQueue;
  import com.android.volley.Response;
  import com.android.volley.VolleyError;
  import com.android.volley.toolbox.StringRequest;
  import com.android.volley.toolbox.Volley;
  
  import java.util.HashMap;
  import java.util.Locale;
  import java.util.Map;
  
  public class CreazioneSondaggio extends AppCompatActivity   {
  
      String URL;
      private EditText titolo;
      private EditText sceltaA;
      private EditText sceltaB;
      private EditText sceltaC;
     private Button invio;
      private EditText server;
      @Override
      protected void onCreate(Bundle savedInstanceState)  {
          titolo = (EditText) findViewById(R.id.titolo);
          sceltaA = (EditText) findViewById(R.id.A);
          sceltaB = (EditText) findViewById(R.id.B);
          sceltaC = (EditText) findViewById(R.id.C);
          server= (EditText) findViewById(R.id.server);
         invio = (Button) findViewById(R.id.invia);
  
         // invio.setOnClickListener(this);
  
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_creazione_sondaggio);
      }
  
      private void inviodati() {
          ......
      }
  
      public void onClick1(View v) {
          Toast.makeText(CreazioneSondaggio.this, "ok", Toast.LENGTH_LONG).show();
  
             inviodati();
  
  
  
      }
  
  
  }
  </code></pre>
  
  <p>Error:</p>
  
  <blockquote>
    <p>Process: com.example.rober.registrazione, PID: 21261
                                                                                     java.lang.IllegalStateException: Could not execute method for
    android:onClick
                                                                                         at
    android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:275)
                                                                                         at android.view.View.performClick(View.java:5210)
                                                                                         at android.view.View$PerformClick.run(View.java:21288)
                                                                                         at android.os.Handler.handleCallback(Handler.java:739)
                                                                                         at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                         at android.os.Looper.loop(Looper.java:148)
                                                                                         at android.app.ActivityThread.main(ActivityThread.java:5527)
                                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                                         at
    com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
                                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
                                                                                      Caused by: java.lang.reflect.InvocationTargetException
                                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                                         at
    android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:270)
                                                                                         at android.view.View.performClick(View.java:5210) 
                                                                                         at android.view.View$PerformClick.run(View.java:21288) 
                                                                                         at android.os.Handler.handleCallback(Handler.java:739) 
                                                                                         at android.os.Handler.dispatchMessage(Handler.java:95) 
                                                                                         at android.os.Looper.loop(Looper.java:148) 
                                                                                         at android.app.ActivityThread.main(ActivityThread.java:5527) 
                                                                                         at java.lang.reflect.Method.invoke(Native Method) 
                                                                                         at
    com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730) 
                                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620) 
                                                                                      Caused by: java.lang.NullPointerException: Attempt to invoke virtual
    method 'android.text.Editable android.widget.EditText.getText()' on a
    null object reference
                                                                                         at
    com.example.rober.registrazione.CreazioneSondaggio.inviodati(CreazioneSondaggio.java:48)
                                                                                         at
    com.example.rober.registrazione.CreazioneSondaggio.onClick1(CreazioneSondaggio.java:87)
                                                                                         at java.lang.reflect.Method.invoke(Native Method) 
                                                                                         at
    android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:270) 
                                                                                         at android.view.View.performClick(View.java:5210) 
                                                                                         at android.view.View$PerformClick.run(View.java:21288) 
                                                                                         at android.os.Handler.handleCallback(Handler.java:739) 
                                                                                         at android.os.Handler.dispatchMessage(Handler.java:95) 
                                                                                         at android.os.Looper.loop(Looper.java:148) 
                                                                                         at android.app.ActivityThread.main(ActivityThread.java:5527) 
                                                                                         at java.lang.reflect.Method.invoke(Native Method) 
                                                                                         at
    com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730) 
                                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)</p>
  </blockquote>
  
  <p>How can I fix it?</p>