title: Enable/Disable Header Button on Picker Tap
body: <p>I'm new to react-native. I have used a button in my header and a picker for my project. Initially I have disabled by button, but I want it to enable on tapping the Picker. Below is my code.</p>
  
  <pre><code>static navigationOptions = ({ navigation }) =&gt; ({
      headerRight: (
        &lt;View 
          &lt;Button
            disabled = {true}
            title="Save"
  
          /&gt;
        &lt;/View&gt;
      )
    });
  
  render(){
  return(
    &lt;Picker
      selectedValue={this.state.changedVal}
      style={{ height: 50, width: 100 }}
      onValueChange={(itemValue, itemIndex) =&gt; this.pickerActivity(itemValue)}&gt;
      &lt;Picker.Item label="Java" value="java" /&gt;
      &lt;Picker.Item label="JavaScript" value="js" /&gt;
    &lt;/Picker&gt;
    )
  }
  </code></pre>