Get string result from function React Native

问题:

I have created a component that connects to redux and returns the currently loaded item's name as the navigation title.

But when I try to get the title from this component it breaks with this error:

Error: `title` cannot be defined as a function in navigation options for `StockScreen` screen. 

Try replacing the following:
{
    title: ({ state }) => state...
}

with:
({ navigation }) => ({
    title: navigation.state...
})

This is my component:

import { connect } from 'react-redux';

let Title = () => {
    if(this.props.item === null || this.props.item === undefined, this.props.item === {}) {
        return '';
    }else{
        return this.props.item.TradeName;
    }
}

const mapStateToProps = state => ({
    item: state.stockItem.item,
});

export default ConnectedTitle = connect(mapStateToProps)(Title);

And this is how I have attempted to implement it within my react-navigation stack:

const Stack = createStackNavigator(
    {
        Home: {
            screen: Tabs,
            navigationOptions: {
                header: null,
            },
        },
        StockModal: {
            screen: StockModal,
            navigationOptions: {
                header: null,
            },
        },
        StockScreen: {
            screen: StockScreen,
            navigationOptions: {
                headerRight: (<ConnectedSaveButton/>),
                title: ConnectedTitle,
            },
        },
    },
    {}
);

回答1:

You are passing a React Component to the title in navigation options, while it should be a string. I think you need to use the headerTitle to achieve what you want

StockScreen: {
    screen: StockScreen,
    navigationOptions: {
        headerRight: (<ConnectedSaveButton/>),
        headerTitle: (<ConnectedTitle />),
    },
}

From the documentation

title

String that can be used as a fallback for headerTitle. Additionally, will be used as a fallback for tabBarLabel (if nested in a TabNavigator) or drawerLabel (if nested in a DrawerNavigator).

headerTitle

String, React Element or React Component used by the header. Defaults to scene title. When a component is used, it receives allowFontScaling, style and children props. The title string is passed in children.