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Configure the cascading DropDownList

The cascading DropDownList is a series of DropDownList, where the value of one DropDownList depends upon another’s value. This can be configured by using the change event of the parent DropDownList. Within that change event handler, data has to be loaded to the child DropDownList based on the selected value of the parent DropDownList.

The following example, shows the cascade behavior of country, state, and city DropDownList. Here, the dataBind method is used to reflect the property changes immediately to the DropDownList.

Source
Preview
index.tsx
import { Query } from '@syncfusion/ej2-data';
import { DropDownListComponent } from '@syncfusion/ej2-react-dropdowns';
import * as React from 'react';
import * as ReactDOM from 'react-dom';

export default class App extends React.Component<{}, {}> {
    // country DropDownList instance
    private countryObj: any;

    // state DropDownList instance
    private stateObj: any;

    // city DropDownList instance
    private cityObj: any;

    // define the country DropDownList data
    private countryData: { [key: string]: Object }[] = [
        { CountryName: 'Australia', CountryId: '2' },
        { CountryName: 'United States', CountryId: '1' }
    ];

    // define the state DropDownList data
    private stateData: { [key: string]: Object }[] = [
        { StateName: 'New York', CountryId: '1', StateId: '101' },
        { StateName: 'Virginia ', CountryId: '1', StateId: '102' },
        { StateName: 'Tasmania ', CountryId: '2', StateId: '105' }
    ];

    // define the city DropDownList data
    private cityData: { [key: string]: Object }[] = [
        { CityName: 'Albany', StateId: '101', CityId: 201 },
        { CityName: 'Beacon ', StateId: '101', CityId: 202 },
        { CityName: 'Emporia', StateId: '102', CityId: 206 },
        { CityName: 'Hampton ', StateId: '102', CityId: 205 },
        { CityName: 'Hobart', StateId: '105', CityId: 213 },
        { CityName: 'Launceston ', StateId: '105', CityId: 214 }
    ];

    // maps the country column to fields property
    private countryField: object = { value: 'CountryId', text: 'CountryName' };

    // maps the state column to fields property
    private stateField: object = { value: 'StateId', text: 'StateName' };

    // maps the city column to fields property
    private cityField: object = { text: 'CityName', value: 'CityId' };

    public onCountryChange() {
        // query the data source based on country DropDownList selected value
        this.stateObj.query = new Query().where('CountryId', 'equal', this.countryObj.value);
        // enable the state DropDownList
        this.stateObj.enabled = true;
        // clear the existing selection.
        this.stateObj.text = null;
        // bind the property changes to state DropDownList
        this.stateObj.dataBind();
        // clear the existing selection in city DropDownList
        this.cityObj.text = null;
        // disable the city DropDownList
        this.cityObj.enabled = false;
        // bind the property change to City DropDownList
        this.cityObj.dataBind();
    }
    public onStateChange() {
        // query the data source based on state DropDownList selected value
        this.cityObj.query = new Query().where('StateId', 'equal', this.stateObj.value);
        // enable the city DropDownList
        this.cityObj.enabled = true;
        // clear the existing selection
        this.cityObj.text = null;
        // bind the property change to city DropDownList
        this.cityObj.dataBind();
    }

    public render() {
        return (
            <div>
                {/* specifies the tag for render the country DropDownList component */}
                <DropDownListComponent id="country-ddl" ref={(scope) => { this.countryObj = scope; }} fields={this.countryField} dataSource={this.countryData} placeholder='Select a country' change={this.onCountryChange = this.onCountryChange.bind(this)} />
                <br />

                 {/* specifies the tag for render the state DropDownList component */}
                 <DropDownListComponent id="state-ddl" ref={(scope) => { this.stateObj = scope; }} enabled={false} fields={this.stateField} dataSource={this.stateData} placeholder='Select a state' change={this.onStateChange = this.onStateChange.bind(this)} />
                <br />

                 {/* specifies the tag for render the city DropDownList component */}
                <DropDownListComponent id="city-ddl" ref={(scope) => { this.cityObj = scope; }} enabled={false} fields={this.cityField} dataSource={this.cityData} placeholder='Select a city' />
            </div>
        );
    }
}
ReactDOM.render(<App />, document.getElementById('sample'));