title: Disable TouchableHighlight until I submit the form
body: <p>I am working on a react native project, the user need to enter his basic details to move forward into the application ,so as a part of validation i want to disable the touchable highlight until the user fill all the form details( here in my case i am using  react native picker for making user comfortable to fill the form )how can i disable the touchablehighlight until the user selects all the picker values ?
  Can some one help me with that?
  Following is the sample code of my project.</p>
  
  <pre><code>&lt;View&gt;
    &lt;Picker
      selectedValue={this.state.bloodgrp}
      style={{ height: 50, width: 170, color: 'black' }}
      baseColor="#FFF" //for initial text color
      onValueChange={(itemValue) =&gt; this.setState({bloodgrp: itemValue})}&gt;
      &lt;Picker.Item label="Select" value='Select' /&gt;
      &lt;Picker.Item label="A+" value='A+' /&gt;
      &lt;Picker.Item label="A-" value='A-' /&gt;
      &lt;Picker.Item label="B+" value='B+' /&gt;
      &lt;Picker.Item label="B-" value='B-' /&gt;
      &lt;Picker.Item label="O+" value='O+' /&gt;
      &lt;Picker.Item label="O-" value='O-' /&gt;
      &lt;Picker.Item label="AB+" value='AB+' /&gt;
      &lt;Picker.Item label="AB-" value='AB-' /&gt;
  &lt;/Picker&gt;
  &lt;/View&gt;
  
  &lt;View style={styles.inputContainer}&gt;
    &lt;Text style={styles.textLabel}&gt;Gender :&lt;/Text&gt;
    &lt;Picker
      selectedValue={this.state.gender}
      style={{ height: 50, width: 170, color: 'black' }}
      baseColor="#FFF" //for initial text color
      onValueChange={(itemValue) =&gt; this.setState({gender: itemValue})}&gt;
      &lt;Picker.Item label="Select" value=''/&gt;
      &lt;Picker.Item label="Male" value='Male' /&gt;
      &lt;Picker.Item label="Female" value='Female' /&gt;
    &lt;/Picker&gt;
  &lt;/View&gt;
  
  &lt;View style={styles.inputContainer}&gt;
    &lt;Text style={styles.textLabel}&gt;Height :&lt;/Text&gt;
    &lt;View style={{flexDirection:'row'}}&gt;
      &lt;Picker
        selectedValue={this.state.height}
        style={{ height: 50, width: 150, color: 'black'}}
        baseColor="#FFF" //for initial text color
        onValueChange={(itemValue) =&gt; this.setState({height: itemValue})}&gt;
        &lt;Picker.Item label="Select"  value='' /&gt;
        &lt;Picker.Item label="121.92" value='121.92' /&gt;
        &lt;Picker.Item label="124.46" value='124.46' /&gt;
        &lt;Picker.Item label="127.00" value='127.00' /&gt;
      &lt;/Picker&gt;
      &lt;TouchableHighlight
        underlayColor={ 'rgb(32, 53, 70)'}
        activeOpacity={0.9}&gt;
        &lt;View style={styles.button}&gt;
          &lt;Text style={styles.buttonText}&gt;Get your BMI&lt;/Text&gt;
        &lt;/View&gt;
      &lt;/TouchableHighlight&gt;
    &lt;/View&gt;
  &lt;/View&gt;
  </code></pre>
  
  <p>thanks in advance</p>