react-native-maps - TypeError: undefined is not an object (evaluating '_this.state.region')

First of all getInitialState is deprecated. Check this

and working example. https://snack.expo.io/@nazrdogan/mapview-example?session_id=snack-session-cSA-6uzo9

Second problem is onRegionChange function. you need to bind or use arrow function

You don't have state in the context you are using it. i.e. the function in Home.js

What you should do is pass the region from your component as a prop in your Map stateless component.

Moreover, the onRegionChange is also not available here so pass that too as a prop

Your code should look like :

import MapView from 'react-native-maps';

 export default ({region, onRegionChange}) => (
   <MapView 
     style={{
       position: 'absolute',
       top: 0,
       left: 0,
       right: 0,
       bottom: 0,
     }} 
     region={region} 
     onRegionChange={onRegionChange}
    />
    );

and when you use this in rendering use it like below from your component where you have the region state variable.

import MyMap from './Home' . //Assuming that the Map function is imported as MyMap name.
....
render() {
  ...
   <MyMap region ={this.state.region} onRegionChange ={this.onRegionChange} />
}

Also, you should not use getInitialState as its deprecated and should not be used with the class syntax.

You should initialize your state like this:

export default class App extends React.Component {
   constructor (props) {
      super (props);
      this.state = {
       ...
       region: {
           latitude: 37.78825,
           longitude: -122.4324,
           latitudeDelta: 0.0922,
           longitudeDelta: 0.0421,
      },
     }
   }
}

Also, you have not binded your onRegionChanged function in your class, do it using ES6 => operator.

onRegionChange = (region) => {
   this.setState({ region });
}