# Input Device Development

## When to Use

Input device management provides functions such as listening for device hot swap events and querying the keyboard type of a specified device. For example, as a user enters text, the input method determines whether to launch the virtual keyboard based on whether a physical keyboard is currently inserted. Your application can determine whether a physical keyboard is inserted by listening to device hot swap events.

## Modules to Import

```js
import inputDevice from '@ohos.multimodalInput.inputDevice';
```

## Available APIs

The following table lists the common APIs for input device management. For details about the APIs, see [ohos.multimodalInput.inputDevice](../reference/apis/js-apis-inputdevice.md).

| Instance| API | Description|
| ----------- | ------------------------------------------------------------ | -------------------------- |
| inputDevice | function getDeviceList(): Promise\<Array\<number>>; | Obtains the list of input devices.|
| inputDevice | function getKeyboardType(deviceId: number): Promise\<KeyboardType>; | Obtains the keyboard type of the input device.|
| inputDevice | function on(type: "change", listener: Callback\<DeviceListener>): void; | Enables listening for device hot swap events.|
| inputDevice | function off(type: "change", listener?: Callback\<DeviceListener>): void; | Disables listening for device hot swap events.|

## Virtual Keyboard Detection

When a user enters text, the input method determines whether to launch the virtual keyboard based on whether a physical keyboard is currently inserted. Your application can determine whether a physical keyboard is inserted by listening to device hot swap events.

## How to Develop

1. Call the **getDeviceList** API to obtain the list of connected input devices. Call the **getKeyboardType** API to traverse all connected devices to check whether a physical keyboard exists. If a physical keyboard exists, mark the physical keyboard as connected. This step ensures that your application detects all inserted input devices before listening for device hot swap events.
2. Call the **on** API to listen for device hot swap events. If a physical keyboard is inserted, mark the physical keyboard as connected. If a physical keyboard is removed, mark the physical keyboard as disconnected.


```js
import inputDevice from '@ohos.multimodalInput.inputDevice';

let isPhysicalKeyboardExist = true;
try {
  // 1. Obtain the list of input devices and check whether a physical keyboard is connected.
  inputDevice.getDeviceList().then(data => {
    for (let i = 0; i < data.length; ++i) {
      inputDevice.getKeyboardType(data[i]).then(type => {
        if (type === inputDevice.KeyboardType.ALPHABETIC_KEYBOARD) {
          // The physical keyboard is connected.
          isPhysicalKeyboardExist = true;
        }
      });
    }
  });
  // 2. Listen for device hot swap events.
  inputDevice.on("change", (data) => {
    console.log(`Device event info: ${JSON.stringify(data)}`);
    inputDevice.getKeyboardType(data.deviceId).then((type) => {
      console.log("The keyboard type is: " + type);
      if (type === inputDevice.KeyboardType.ALPHABETIC_KEYBOARD && data.type == 'add') {
        // The physical keyboard is inserted.
        isPhysicalKeyboardExist = true;
      } else if (type == inputDevice.KeyboardType.ALPHABETIC_KEYBOARD && data.type == 'remove') {
        // The physical keyboard is removed.
        isPhysicalKeyboardExist = false;
      }
    });
  });
} catch (error) {
  console.log(`Execute failed, error: ${JSON.stringify(error, [`code`, `message`])}`);
}
```