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Detect whether the value change happened by manual or programmatic

You can check about whether value change happened by manual or programmatic by using change event argument that argument name is isInteracted.

The following example demonstrate, how to check whether value change happened by manual or programmatic.

Source
Preview
index.tsx
index.html
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<{}, {}> {
  // define the array of data
  private sportsData: string[] = ['Badminton', 'Cricket', 'Football', 'Golf', 'Tennis'];
  private dropDownListObject:any;
    public onclick(){
        this.dropDownListObject.value = 'Football';
        }
    public onChange(args: any){
    const element: HTMLElement = document.createElement('p');
        if (args.isInteracted) {
            element.innerText = 'Changes happened by Interaction';
        } else {
            element.innerText = 'Changes happened by programmatic';
        }
        (document.getElementById('event') as any).append(element);
    }
  public render() {
    return (
        // specifies the tag for render the DropDownList component
      <div>
      <DropDownListComponent id="ddlelement" ref={(scope) => { this.dropDownListObject = scope; }} dataSource={this.sportsData}  placeholder="Select a game" change={this.onChange} />
      <button id='btn' className="e-control e-btn" onClick={this.onclick = this.onclick.bind(this)}>
      Set value dynamically</button>
      <div id='event'/>
      </div>
    );
  }
}
ReactDOM.render(<App />, document.getElementById('sample'));
<!DOCTYPE html>
<html lang="en">

<head>
    <title>Syncfusion React DropDownList</title>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta name="description" content="Essential JS 2 for React Components" />
    <meta name="author" content="Syncfusion" />
    <link href="//cdn.syncfusion.com/ej2/ej2-base/styles/material.css" rel="stylesheet" />
    <link href="//cdn.syncfusion.com/ej2/ej2-react-inputs/styles/material.css" rel="stylesheet" />
    <link href="//cdn.syncfusion.com/ej2/ej2-react-dropdowns/styles/material.css" rel="stylesheet" />
    <script src="https://cdnjs.cloudflare.com/ajax/libs/systemjs/0.19.38/system.js"></script>
    <script src="systemjs.config.js"></script>
    <style>
        #loader {
            color: #008cff;
            height: 40px;
            left: 45%;
            position: absolute;
            top: 45%;
            width: 30%;
        }
    </style>
</head>

<body>
    <div id='sample' style="margin: 20px auto 0; width:250px;">
        <div id='loader'>Loading....</div>
    </div>
	<p id='event'> </p>
</body>

</html>
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