title: Jetpack Compose Preview not showing
body: <p>I seem to be having trouble with Preview in compose, the layout panel doesn't appear when I annotate a compose method with @preview. I assume I'm missing a dependency, but I've copied and pasted the code from here <a href="https://developer.android.com/jetpack/compose/setup" rel="noreferrer">https://developer.android.com/jetpack/compose/setup</a>. Any suggestions? (tried the usual clear cache, reopen project etc) :)</p>
  <pre><code>buildFeatures {
          compose true
      }
      composeOptions {
          kotlinCompilerExtensionVersion '1.0.0-alpha10'
          kotlinCompilerVersion '1.4.21'
      }
  }
  
  dependencies {
      implementation 'androidx.compose.ui:ui:1.0.0-alpha10'
      // Tooling support (Previews, etc.)
      implementation 'androidx.compose.ui:ui-tooling:1.0.0-alpha10'
      // Foundation (Border, Background, Box, Image, Scroll, shapes, animations, etc.)
      implementation 'androidx.compose.foundation:foundation:1.0.0-alpha10'
      // Material Design
      implementation 'androidx.compose.material:material:1.0.0-alpha10'
      // Material design icons
      implementation 'androidx.compose.material:material-icons-core:1.0.0-alpha10'
      implementation 'androidx.compose.material:material-icons-extended:1.0.0-alpha10'
      // Integration with observables
      implementation 'androidx.compose.runtime:runtime-livedata:1.0.0-alpha10'
      implementation 'androidx.compose.runtime:runtime-rxjava2:1.0.0-alpha10'
  
      // UI Tests
      androidTestImplementation 'androidx.compose.ui:ui-test-junit4:1.0.0-alpha10'
  
      implementation 'com.google.android.material:material:1.2.1'
  }
  </code></pre>
  <p>Here is my attempt at using preview (in AS it says Function &quot;DefaultPreview&quot; is never used)</p>
  <pre><code>import androidx.compose.ui.tooling.preview.Preview
  .....
  @Preview
  @Composable
  fun DefaultPreview() {
      Text(text = &quot;Hello!&quot;)
  }
  </code></pre>