I am trying to increase the count value on button

Question

this.state = { count: 0 };

_incrementCount = () => {
    this.setState(prevState => ({ count: prevState.count + 1 }));    
}

Answer 1

state of a Component depend on The component's life circle. When your component unMount and reMount the state will be reset to your default value.

Thus, just store your count value outside your element. (AsyncStorage, Redux, Mobx, or just simple in your custom logic)

Answer 2

This is the correct behaviour. If you want to persist changes after page reload, use AsyncStorage to save it.

componentDidMount() {
    let response = await AsyncStorage.getItem('count'); 
    if(response)
        this.state = { count : response};
}

componentWillUnmount() {
    AsyncStorage.setItem('count', this.state.count + '');    
}