ExtReact - PickerField picker.show() is not function

Question

I using Picker of ExtReact. I got the code from sencha's documentation. But message error: "picker.show is not function". I don't understand reason. Code here:

 export default class Picker extends Component {
showPicker = () => { console.log('this.picker', this.picker); this.picker.show() };
render() {
    return (
        <ExtContainer>
            <ExtButton ui="action" handler={this.showPicker} text="Show Picker" />
            <ExtPicker
                ref={picker => this.picker = picker}
                slots={[
                    {
                        name: 'limit_speed',
                        title: 'Speed',
                        data: [
                            { text: '50 KB/s', value: 50 },
                            { text: '100 KB/s', value: 100 },
                            { text: '200 KB/s', value: 200 },
                            { text: '300 KB/s', value: 300 }
                        ]
                    }
                ]}
            />
        </ExtContainer>)
}

}

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