How to call a function directly in a Component in React Native - react-native

Question

I made a CameraComponent.js having function launchCamera(). I am calling CameraComponent.js in my BottamTab navigation. I had make simple button to launch camera by calling launchCamera(). But i want to launch camera directly when component call in BottamTab navigation just like in whatsapp moving topTab to left. I tried to call function in constructor instead of ComponentWillMount(as it is removed in react native). But nothing work. Here is my below code
export default class CameraComponent extends React.Component {
constructor(props) {
super(props);
launchCamera();
this.state = {
filePath: {},
};
}
launchCamera = () => {
let options = {
storageOptions: {
skipBackup: true,
path: 'images',
},
};
ImagePicker.launchCamera(options, response => {
// console.log('Response = ', response);
if (response.didCancel) {
console.log('User cancelled image picker');
} else if (response.error) {
console.log('ImagePicker Error: ', response.error);
} else {
let source = response;
// You can also display the image using data:
// let source = { uri: 'data:image/jpeg;base64,' + response.data };
this.setState({
filePath: source,
});
}
});
};
render() {
return (
<View style={styles.container}>
<TouchableOpacity onPress={this.launchCamera.bind(this)} >
<Text>Launch Camera</Text>
</TouchableOpacity>
</View>
);
}
}