js-apis-display.md

# Display

> **NOTE**
>
> The initial APIs of this module are supported since API version 7. Newly added APIs will be marked with a superscript to indicate their earliest API version.

## Modules to Import

```js
import display from '@ohos.display';
```


## DisplayState

Provides the state of a display.

**System capability**: SystemCapability.WindowManager.WindowManager.Core

| Name| Default Value| Description|
| -------- | -------- | -------- |
| STATE_UNKNOWN | 0 | Unknown.|
| STATE_OFF | 1 | The display is shut down.|
| STATE_ON | 2 | The display is powered on.|
| STATE_DOZE | 3 | The display is in sleep mode.|
| STATE_DOZE_SUSPEND | 4 | The display is in sleep mode, and the CPU is suspended.|
| STATE_VR | 5 | The display is in VR mode.|
| STATE_ON_SUSPEND | 6 | The display is powered on, and the CPU is suspended.|


## Display

Describes the attributes of a display.

**System capability**: SystemCapability.WindowManager.WindowManager.Core

| Name| Type| Readable| Writable| Description|
| -------- | -------- | -------- | -------- | -------- |
| id | number | Yes| No| ID of the display.|
| name | string | Yes| No| Name of the display.|
| alive | boolean | Yes| No| Whether the display is alive.|
| state | [DisplayState](#displaystate) | Yes| No| State of the display.|
| refreshRate | number | Yes| No| Refresh rate of the display.|
| rotation | number | Yes| No| Screen rotation angle of the display.|
| width | number | Yes| No| Width of the display, in pixels.|
| height | number | Yes| No| Height of the display, in pixels.|
| densityDPI | number | Yes| No| Screen density of the display, in DPI.|
| densityPixels | number | Yes| No| Screen density of the display, in pixels.|
| scaledDensity | number | Yes| No| Scaling factor for fonts displayed on the display.|
| xDPI | number | Yes| No| Exact physical dots per inch of the screen in the horizontal direction.|
| yDPI | number | Yes| No| Exact physical dots per inch of the screen in the vertical direction.|


## display.getDefaultDisplay

getDefaultDisplay(callback: AsyncCallback<Display>): void

Obtains the default display object.

**System capability**: SystemCapability.WindowManager.WindowManager.Core

**Parameters**

| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| callback | AsyncCallback<[Display](#display)> | Yes| Callback used to return the default display object.|

**Example**

```js
var displayClass = null;
display.getDefaultDisplay((err, data) => {
    if (err.code) {
        console.error('Failed to obtain the default display object. Code:  ' + JSON.stringify(err));
        return;
    }
    console.info('Succeeded in obtaining the default display object. Data:' + JSON.stringify(data));
    displayClass = data;
});
```

## display.getDefaultDisplay

getDefaultDisplay(): Promise<Display>

Obtains the default display object.

**System capability**: SystemCapability.WindowManager.WindowManager.Core

**Return value**

| Type                              | Description                                          |
| ---------------------------------- | ---------------------------------------------- |
| Promise<[Display](#display)> | Promise used to return the default display object.|

**Example**

```js
let promise = display.getDefaultDisplay();
promise.then(() => {
    console.log('getDefaultDisplay success');
}).catch((err) => {
    console.log('getDefaultDisplay fail: ' + JSON.stringify(err));
});
```

## display.getAllDisplay

getAllDisplay(callback: AsyncCallback<Array<Display>>): void

Obtains all the display objects.

**System capability**: SystemCapability.WindowManager.WindowManager.Core

**Parameters**

| Name  | Type                                                | Mandatory| Description                           |
| -------- | ---------------------------------------------------- | ---- | ------------------------------- |
| callback | AsyncCallback<Array<[Display](#display)>> | Yes  | Callback used to return all the display objects.|

**Example**

```js
display.getAllDisplay((err, data) => {
    if (err.code) {
        console.error('Failed to obtain all the display objects. Code: ' + JSON.stringify(err));
        return;
    }
    console.info('Succeeded in obtaining all the display objects. Data: ' + JSON.stringify(data))
});
```

## display.getAllDisplay

getAllDisplay(): Promise<Array<Display>>

Obtains all the display objects.

**System capability**: SystemCapability.WindowManager.WindowManager.Core

**Return value**

| Type                                           | Description                                                   |
| ----------------------------------------------- | ------------------------------------------------------- |
| Promise<Array<[Display](#display)>> | Promise used to return an array containing all the display objects.|

**Example**

```js
let promise = display.getAllDisplay();
promise.then(() => {
    console.log('getAllDisplay success');
}).catch((err) => {
    console.log('getAllDisplay fail: ' + JSON.stringify(err));
});
```

## display.on('add'|'remove'|'change')

on(type: 'add'|'remove'|'change', callback: Callback<number>): void

Enables listening.

**System capability**: SystemCapability.WindowManager.WindowManager.Core

**Parameters**

| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| type | string | Yes| Listening type. The available values are as follows:<br>-&nbsp;**add**: listening for whether a display is added<br>-&nbsp;**remove**: listening for whether a display is removed<br>-&nbsp;**change**: listening for whether a display is changed|
| callback | Callback&lt;number&gt; | Yes| Callback used to return the ID of the display.|

**Example**

```js
var type = "add";
var callback = (data) => {
    console.info('Listening enabled. Data: ' + JSON.stringify(data))
}
display.on(type, callback);
```


## display.off('add'|'remove'|'change')

off(type: 'add'|'remove'|'change', callback?: Callback&lt;number&gt;): void

Disables listening.

**System capability**: SystemCapability.WindowManager.WindowManager.Core

**Parameters**

| Name| Type| Mandatory| Description|
| -------- | -------- | -------- | -------- |
| type | string | Yes| Listening type. The available values are as follows:<br>-&nbsp;**add**: listening for whether a display is added<br>-&nbsp;**remove**: listening for whether a display is removed<br>-&nbsp;**change**: listening for whether a display is changed|
| callback | Callback&lt;number&gt; | No| Callback used to return the ID of the display.|

**Example**

```js
var type = "remove";
display.off(type);
```