title: Exception raised during Rendering: android.support.design.widget.CoordinatorLayout cannot be cast to android.view.ViewGroup
body: <p>Although i was getting preview before, i have not made any changes in the files. As a matter of fact there is not much to change in my code, its just a OK button in app.
  Just to tell, i deleted the toolbar from my design in activity_main.xml file.But undo the changes afterwards as i can see it in MainActivity.java file.
  I am a newbie to android studio, any help would be useful.
  Here's my java file.</p>
  
  <pre><code>package com.learning.pehlaapp;
  
  import android.os.Bundle;
  import android.support.design.widget.FloatingActionButton;
  import android.support.design.widget.Snackbar;
  import android.support.v7.app.AppCompatActivity;
  import android.support.v7.widget.Toolbar;
  import android.view.View;
  import android.view.Menu;
  import android.view.MenuItem;
  
  public class SampleActivity extends AppCompatActivity {
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_sample);
      Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
      setSupportActionBar(toolbar);
  
      FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
      fab.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                      .setAction("Action", null).show();
          }
      });
  }
  
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
      // Inflate the menu; this adds items to the action bar if it is present.
      getMenuInflater().inflate(R.menu.menu_sample, menu);
      return true;
  }
  
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
      // Handle action bar item clicks here. The action bar will
      // automatically handle clicks on the Home/Up button, so long
      // as you specify a parent activity in AndroidManifest.xml.
      int id = item.getItemId();
  
      //noinspection SimplifiableIfStatement
      if (id == R.id.action_settings) {
          return true;
      }
  
      return super.onOptionsItemSelected(item);
  }
  }
  </code></pre>