Adding a button to take the picture

App.js

render() {
  const { photo } = this.state;

  return (
    <Camera
      style={{ flex: 1 }}
      type={Camera.Constants.Type.back}
      ref={cam => this.camera = cam}>
      <TouchableOpacity
        style={{ flex: 1 }}
        onPress={this.takePicture}/>
    </Camera>
  );
}