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.
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'));