xref: /docs/en/application-dev/quick-start/resource-categories-and-access.md

# Resource Categories and Access

During application development, you may need to use different resources, such as colors, fonts, spacing, and images, based on the device or configuration. Depending on the resource type, you can achieve this using the following methods:

- Application resources: Configure device- or configuration-specific resources in the resource files.

- System resources: Use the preset resource definitions<!--Del--> (that is, [layered parameters](../../design/ux-design/design-resources.md), with which each resource ID is assigned different values under different configurations, including device types and color modes)<!--DelEnd-->.

## Resource Categories

Resource files used during application development must be stored in specified directories for management. There are two types of resource directories, namely, resource directories and resource group directories. The resource directories are the **base**, qualifiers, **rawfile**, and **resfile** directories. The resource group directories are the **element**, **media**, and **profile** directories.

> **NOTE**
>
> The common resource files used across projects in the stage model are stored in the **resources** directory under **AppScope**.

Example of the **resources** directory:
```
resources
|---base
|   |---element
|   |   |---string.json
|   |---media
|   |   |---icon.png
|   |---profile
|   |   |---test_profile.json
|---en_US  // Default directory. When the device language is en-us, resources in this directory are preferentially matched.
|   |---element
|   |   |---string.json
|   |---media
|   |   |---icon.png
|   |---profile
|   |   |---test_profile.json
|---zh_CN  // Default directory. When the device language is zh-cn, resources in this directory are preferentially matched.
|   |---element
|   |   |---string.json
|   |---media
|   |   |---icon.png
|   |---profile
|   |   |---test_profile.json
|---en_GB-vertical-car-mdpi // Example of a qualifiers directory, which needs to be created on your own.
|   |---element
|   |   |---string.json
|   |---media
|   |   |---icon.png
|   |---profile
|   |   |---test_profile.json
|---rawfile // Other types of files are saved as raw files and will not be integrated into the resources.index file. You can customize the file name as needed.
|---resfile // Other types of files are saved as raw files and will not be integrated into the resources.index file. You can customize the file name as needed.
```
### Resource Directories

#### base Directory

The **base** directory is provided by default. Under this directory, the **element** subdirectory stores basic elements such as strings, colors, and boolean values, and the **media** and **profile** subdirectories store resource files such as media, animations, and layouts.<br>
Resource files in the subdirectories are compiled into binary files, and each resource file is assigned an ID. Resource files in the subdirectories are referenced based on the resource type and resource name.

#### Qualifiers Directory

**en_US** and **zh_CN** are two default qualifiers directories. You need to create other qualifiers directories on your own. Under this directory, the subdirectories store basic elements such as strings, colors, and boolean values, as well as resource files such as media, animations, and layouts.<br>Resource files in the subdirectories are compiled into binary files, and each resource file is assigned an ID. Resource files in the subdirectories are referenced based on the resource type and resource name.

**Naming Conventions for Qualifiers Directories**

The name of a qualifiers directory consists of one or more qualifiers that represent the application scenarios or device characteristics, covering the mobile country code (MCC), mobile network code (MNC), language, script, country or region, screen orientation, device type, night mode, and screen density. The qualifiers are separated using underscores (\_) or hyphens (\-). Before creating a qualifiers directory, familiarize yourself with the directory naming conventions.

- Qualifiers are ordered in the following sequence: **\_MCC_MNC-language_script_country/region-orientation-device-color mode-density_**. You can select one or multiple qualifiers to name your subdirectory based on your application scenarios and device characteristics.

- Separation between qualifiers: The language, script, and country/region qualifiers are separated using underscores (\_); the MNC and MCC qualifiers are also separated using underscores (\_); other qualifiers are separated using hyphens (\-). For example, **zh_Hant_CN** and **zh_CN-car-ldpi**.

- Value range of qualifiers: The value of each qualifier must meet the requirements specified in the following table. Otherwise, the resource files in the resources directory cannot be matched.

Table 2 Requirements for qualifier values

| Qualifier Type      | Description and Value Range                                 |
| ----------- | ---------------------------------------- |
| MCC&MNC| Indicates the MCC and MNC, which are obtained from the network where the device is registered.<br>The MCC can be either followed by the MNC with an underscore (_) in between or be used independently. For example, **mcc460** represents China, and **mcc460_mnc00** represents China Mobile.<br>For details about the value range, see [ITU-T E.212](https://www.itu.int/rec/T-REC-E.212) (the international identification plan for public networks and subscriptions).|
| Language         | Indicates the language used by the device. The value consists of two or three lowercase letters. For example, **zh** indicates Chinese, **en** indicates English, and **mai** indicates Maithili.<br>For details about the value range, see [ISO 639](https://www.iso.org/iso-639-language-code) (codes for the representation of names of languages).|
| Text         | Indicates the script type used by the device. The value starts with one uppercase letter followed by three lowercase letters. For example, **Hans** indicates simplified Chinese, and **Hant** indicates traditional Chinese.<br>For details about the value range, see [ISO 15924](https://www.iso.org/standard/81905.html) (codes for the representation of names of scripts).|
| Country/Region      | Indicates the country or region where the user is located. The value consists of two or three uppercase letters or three digits. For example, **CN** indicates China, and **GB** indicates the United Kingdom.<br>For details about the value range, see [ISO 3166-1](https://www.iso.org/iso-3166-country-codes.html) (codes for the representation of names of countries and their subdivisions).|
| Screen orientation        | Indicates the screen orientation of the device. The value can be:<br>- **vertical**: portrait orientation<br>- **horizontal**: landscape orientation|
| Device type       | <!--RP1-->Indicates the device type. The value can be:<br>- **car**: head unit<br>- **tablet**: tablet<br>- **tv**: smart TV<br>- **wearable**: smart wearable<!--RP1End--> |
| Color mode       | Indicates the color mode of the device. The value can be:<br>- **dark**: dark mode<br>- **light**: light mode|
| Screen density       | Indicates the screen density of the device, in dpi. The value can be:<br>- **sdpi**: screen density with small-scale dots per inch (SDPI). This value is applicable for devices with a DPI range of (0, 120].<br>- **mdpi**: medium-scale screen density (Medium-scale&nbsp;Dots&nbsp;Per&nbsp;Inch), applicable to DPI whose value is (120, &nbsp;160] device.<br>- **ldpi**: screen density with large-scale dots per inch (LDPI). This value is applicable for devices with a DPI range of (160, 240].<br>- **xldpi**: screen density with extra-large-scale dots per inch (XLDPI). This value is applicable for devices with a DPI range of (240, 320].<br>- **xxldpi**: screen density with extra-extra-large-scale dots per inch (XXLDPI). This value is applicable for devices with a DPI range of (320, 480].<br>- **xxxldpi**: screen density with extra-extra-extra-large-scale dots per inch (XXXLDPI). This value is applicable for devices with a DPI range of (480, 640].|

#### rawfile Directory

You can create multiple levels of subdirectories with custom names to store various resource files.<br>Resource files in the subdirectories are directly packed into the application without being compiled, and no IDs will be assigned to the resource files. The subdirectories are referenced based on the specified file path and file name.

#### resfile Directory

You can create multiple levels of subdirectories with custom names to store various resource files.<br>Resource files in the subdirectories are directly packed into the application without being compiled, and no IDs will be assigned to the resource files. After an application is installed, the **resfile** directory is decompressed to the application sandbox path. You can obtain the path through the [resourceDir](https://gitee.com/openharmony/docs/blob/master/en/application-dev/reference/apis-ability-kit/js-apis-inner-application-context.md#properties) attribute of **Context**.

### Resource Group Directories

Resource group directories include **element**, **media**, and **profile**, which are used to store resources of specific types.

  **Table 3** Resource group directories

| Directory   | Description                                    | Resource File                                    |
| --------- | ---------------------------------------- | ---------------------------------------- |
| element | Element resources. Each type of data is represented by a JSON file. (Only files are supported in this directory.) The options are as follows:<br>- **boolean**: boolean data<br>- **color**: color data<br>- **float**: floating point number ranging from -2^128 to 2^128<br>- **intarray**: array of integers<br>- **integer**: integer ranging from -2^31 to 2^31-1<!--Del--><br>- **pattern**: style (for system applications only)<!--DelEnd--><br>- **plural**: plural form data<br>- **strarray**: array of strings<br>- **string**: string. [See descriptions for formatting strings.](../reference/apis-localization-kit/js-apis-resource-manager.md#getstringsync10)<!--Del--><br>- **theme**: theme (for system applications only)<!--DelEnd-->| It is recommended that files in the **element** subdirectory be named the same as the following files, each of which can contain only data of the same type:<br>-&nbsp;boolean.json<br>-&nbsp;color.json<br>-&nbsp;float.json<br>-&nbsp;intarray.json<br>-&nbsp;integer.json<!--Del--><br>-&nbsp;pattern.json<!--DelEnd--><br>-&nbsp;plural.json<br>-&nbsp;strarray.json<br>-&nbsp;string.json |
| media   | Indicates media resources, including non-text files such as images, audios, and videos. (Only files are supported in this directory.)<br>Table 4 and Table 5 describe the types of images, audios, and videos.             | The file name can be customized, for example, **icon.png**.                    |
| profile  | Indicates a custom configuration file. You can obtain the file content by using the [getProfileByAbility](../reference/apis-ability-kit/js-apis-bundleManager.md#bundlemanagergetprofilebyability) API. (Only JSON files are supported in this directory.)      | The file name can be customized, for example, **test_profile.json**.          |

**Media Resource Types**

Table 4 Image resource types

| Format  | File Name Extension|
| ---- | ----- |
| JPEG | .jpg  |
| PNG  | .png  |
| GIF  | .gif  |
| SVG  | .svg  |
| WEBP | .webp |
| BMP  | .bmp  |

Table 5 Audio and video resource types

| Format                                  | File Name Extension        |
| ------------------------------------ | --------------- |
| H.264 AVC |.3gp |
| Baseline Profile (BP) | .mp4   |

**Resource File Examples**

The content of the **color.json** file is as follows:

```json
{
    "color": [
        {
            "name": "color_hello",
            "value": "#ffff0000"
        },
        {
            "name": "color_world",
            "value": "#ff0000ff"
        }
    ]
}
```

The content of the **float.json** file is as follows:

```json
{
    "float":[
        {
            "name":"font_hello",
            "value":"28.0fp"
        },
	      {
            "name":"font_world",
            "value":"20.0fp"
        }
    ]
}
```

The content of the **string.json** file is as follows:

```json
{
    "string":[
        {
            "name":"string_hello",
            "value":"Hello"
        },
	      {
            "name":"string_world",
            "value":"World"
        },
	      {
            "name":"message_arrive",
            "value":"We will arrive at %1$s."
        },
        {
            "name":"message_notification",
            "value":"Hello, %1$s!,You have %2$d new messages."
        }
    ]
}
```

The content of the **plural.json** file is as follows:

```json
{
    "plural":[
        {
            "name":"eat_apple",
            "value":[
                {
                    "quantity":"one",
                    "value":"%d apple"
                },
                {
                    "quantity":"other",
                    "value":"%d apples"
                }
            ]
        }
    ]
}
```

## Creating a Resource Directory and Resource File

You can create a directory and its files under the **resources** directory based on the preceding descriptions of the qualifiers directories and resource group directories. DevEco Studio provides a wizard for you to create resource directories and resource files.

### Creating a Resource Directory and Resource File

Right-click the **resources** directory and choose **New** > **Resource File**. If no qualifier is selected, the file is created in a resource group directory under **base**. If one or more qualifiers are selected, the system automatically generates a subdirectory and creates the file in this subdirectory.

In **File name**, enter the name of the resource file to create. In **Resource type**, select the type of the resource group, which is **element** by default. In **Root Element**, select a resource type. To select a qualifier, highlight it under **Available qualifiers** and click the right arrow. To deselect a qualifier, highlight it under **Selected qualifiers** and click the left arrow.<br>The created directory is automatically named in the format of *Qualifiers.Resource group type*. For example, if you create a subdirectory by setting **Color Mode** to **Dark** and **Resource type** to **Element**, the system automatically generates a subdirectory named **dark.element**.

  ![create-resource-file-1](figures/create-resource-file-1.png)

### Creating a Resource Directory

Right-click the **resources** directory and choose **New** > **Resource Directory** to create a directory only. By default, the **base** directory is created. You can create qualifiers directories as required, by specifying the qualifier and resource group type.

  ![create-resource-file-2](figures/create-resource-file-2.png)

### Creating a Resource File

Right-click a directory under **resources** and choose **New** > **XXX Resource File**. This operation creates a resource file under this directory. For example, you can create an element resource file in the **element** subdirectory.

  ![create-resource-file-3](figures/create-resource-file-3.png)

## Using the attr Attribute for Resource Translation

### Function Description

You can use the **attr** attribute to specify whether a string should be translated and the translation status. The **attr** attribute is not involved in resource compilation.

If the **attr** attribute is not configured, a string is translated by default.
```
"attr": {
  "translatable": false|true
  "priority": "code|translate|LT|customer"
}
```
**Parameters of attr**

| Name       | Type                   |  Description  |
| --------- | ----------------------- |  ---- |
| translatable |  boolean |  Whether the string needs to be translated.<br>  **true**: The string needs to be translated.<br> **false**: The string does not need to be translated.|
| priority    | string   |  Translation status of the string.<br>**code**: untranslated<br>**translate**: translated but not verified<br>**LT**: translated and verified<br>**customer**: custom  |

### Constraints
The **attr** attribute applies to the string, strarray, and plural resources in the **base** directory.
```
resources
|---base
|   |---element
|   |   |---string.json
|   |   |---strarray.json
|   |   |---plural.json
```
### Example
This example sets the **attr** attribute for strings.

```json
{
  "string": [
    {
      "name": "string1",
      "value": "1",
      "attr": {
        "translatable": false
      }
    },
    {
      "name": "string2",
      "value": "Hello world!",
      "attr": {
        "translatable": true,
        "priority": "LT"
      }
    }
  ]
}
```

## Resource Access

### HAP Resources

 - Use **$r** or **$rawfile** to reference resources.<br>To reference resources of the color, float, string, plural, media, or profile type, use the "$r('app.type.name')" format, where **app** indicates the resource defined in the **resources** directory, **type** indicates the resource type or resource save path, and **name** indicates the name you assign to the resource.<br>To reference strings with multiple placeholders in the **string.json** file, use the "$r('app.string.label','aaa','bbb',444)" format.<br>To reference resources in the **rawfile** subdirectory, use the "$rawfile('filename')" format. Wherein **filename** indicates the relative path of a file in the **rawfile** subdirectory, which must contain the file name extension and cannot start with a slash (/).

   > **NOTE**
   >
   > For details about how to use native APIs to access raw files, see [Raw File Development](../napi/rawfile-guidelines.md).

  As described in [Resource Group Directories](#resource-group-directories), you can reference .json resource files, including **color.json**, **string.json**, and** plural.json**.<br>The usage is as follows:

  ```ts
    Text('Hello')
    .fontColor($r('app.color.ohos_id_color_emphasize'))
    .fontSize($r('app.float.ohos_id_text_size_headline1'))
    .fontFamily($r('app.string.ohos_id_text_font_family_medium'))
    .backgroundColor($r('app.color.ohos_id_color_palette_aux1'))

    Image($r('app.media.ohos_app_icon'))
    .border({
      color: $r('app.color.ohos_id_color_palette_aux1'),
      radius: $r('app.float.ohos_id_corner_radius_button'), width: 2
    })
    .margin({
      top: $r('app.float.ohos_id_elements_margin_horizontal_m'),
      bottom: $r('app.float.ohos_id_elements_margin_horizontal_l')
    })
    .height(200)
    .width(300)
  ```

- Obtain a **ResourceManager** object through the application context, and then call [resource management APIs](../reference/apis-localization-kit/js-apis-resource-manager.md) to access different resources.<br>For example, call **getContext().resourceManager.getStringByNameSync('test')** to obtain string resources; call **getContext().resourceManager.getRawFd('rawfilepath')** to obtain the descriptor of the HAP where a raw file is located, and then use the descriptor ({fd, offset, length}) to access the raw file.

### Cross-HAP/HSP Resources

<!--Del-->
#### Cross-Bundle Access (for System Applications Only)

- Call **createModuleContext(bundleName, moduleName)** to obtain the context of the target HAP/HSP module in another application. Obtain a **ResourceManager** object through the context, and then call [resource management APIs](../reference/apis-localization-kit/js-apis-resource-manager.md) to access different resources.<br>Example: **getContext().createModuleContext(bundleName, moduleName).resourceManager.getStringByNameSync('test')**.
<!--DelEnd-->

#### Inter-Bundle, Cross-Module Access

- Call **createModuleContext(moduleName)** to obtain the context of the target HAP/HSP module in the same application. Obtain a **ResourceManager** object through the context, and then call resource management APIs to access different resources.<br>Example: **getContext().createModuleContext(moduleName).resourceManager.getStringByNameSync('test')**.

- Use **$r** or **$rawfile** to reference resources. Specifically, perform either of the following:

  1. Use *[hsp].type.name*, where **hsp** indicates the HSP module name, **type** indicates the resource type, and **name** indicates the resource name. The following is an example:
  
    ```ts
      Text($r('[hsp].string.test_string'))
        .fontSize($r('[hsp].float.font_size'))
        .fontColor($r('[hsp].color.font_color'))  
      Image($rawfile('[hsp].icon.png'))
    ```
  2. Use variables. The following is an example:

   ```ts
    @Entry
    @Component
    struct Index {
      text: string = '[hsp].string.test_string';
      fontSize: string = '[hsp].float.font_size';
      fontColor: string = '[hsp].color.font_color';
      image: string = '[hsp].media.string';
      rawfile: string = '[hsp].icon.png';
  
      build() {
        Row() {
          Text($r(this.text))
            .fontSize($r(this.fontSize))
            .fontColor($r(this.fontColor))
  
          Image($r(this.image))
  
          Image($rawfile(this.rawfile))
        }
      }
    }
   ```
  > **NOTE**
  >
  > The HSP module name must be placed in the brackets ([]). If the **rawfile** directory contains multiple levels of folders, the path must start from the first level, for example, **\$rawfile('[hsp].oneFile/twoFile/icon.png')**. When **$r** or **$rawfile** is used for cross-HSP resource access, resource verification is not available at compile time, and you need to manually check that the target resources exist in the corresponding location.

### System Resources

Apart from custom resources, you can use system resources to maintain a consistent visual style throughout your application. <!--Del-->For details about the system resource IDs and their values in different configurations, see [Resources](../../design/ux-design/design-resources.md).<!--DelEnd-->

During development, the usage of layered parameters is basically the same as that of qualifiers. To reference a system resource, use the "$r('sys.type.resource_id')" format. Wherein: **sys** indicates a system resource; **type** indicates the resource type, which can be **color**, **float**, **string**, or **media**; **resource_id** indicates the resource ID.

> **NOTE**
>
> - The use of system resources is only supported in the declarative development paradigm.
>
> - For preset applications, you are advised to use system resources.<!--Del--> For third-party applications, you can choose to use system resources or custom application resources as required.<!--DelEnd-->
>
> - You can view the fonts for the system resources in the **system/etc/fontconfig.json** file. The default font is **'HarmonyOS Sans'**.

```ts
Text('Hello')
  .fontColor($r('sys.color.ohos_id_color_emphasize'))
  .fontSize($r('sys.float.ohos_id_text_size_headline1'))
  .fontFamily($r('sys.string.ohos_id_text_font_family_medium'))
  .backgroundColor($r('sys.color.ohos_id_color_palette_aux1'))

Image($r('sys.media.ohos_app_icon'))
  .border({
    color: $r('sys.color.ohos_id_color_palette_aux1'),
    radius: $r('sys.float.ohos_id_corner_radius_button'), width: 2
  })
  .margin({
    top: $r('sys.float.ohos_id_elements_margin_horizontal_m'),
    bottom: $r('sys.float.ohos_id_elements_margin_horizontal_l')
  })
  .height(200)
  .width(300)
```

## Resource Matching

When your application needs to use a resource, the system preferentially searches the qualifiers subdirectories that match the current device state. The system searches the **base** subdirectory for the target resource only when the **resources** directory does not contain any qualifiers subdirectories that match the current device state or the target resource is not found in the qualifiers subdirectories. The **rawfile** directory is not searched for resources.

### Rules for Matching Qualifiers Subdirectories and Device Resources

- Qualifiers are matched with the device resources in the following priorities: MCC&MNC > locale (options: language, language_script, language_country/region, and language_script_country/region) > screen orientation > device type > color mode > screen density

- If the qualifiers subdirectories contain the MCC, MNC, language, script, screen orientation, device type, and color mode qualifiers, their values must be consistent with the current device status so that the subdirectories can be used for matching the device resources. For example, the qualifiers subdirectory **zh_CN-car-ldpi** cannot be used for matching the resource files labeled **en_US**.

- If there are multiple qualifiers subdirectories for the screen density, the closest qualifiers are matched upwards; otherwise, downwards. For example, if qualifiers directories **xldpi** and **xxldpi** exist and the device screen density is **xxldpi**, the qualifier directory **xxldpi** will be matched.

For more information about how resources are loaded in applications, see the internationalization and localization documents.

### Obtaining Resources for a Specific Configuration

#### Background

When using [qualifiers directories](#qualifiers-directory) to apply configuration-specific resources, you may find some resources fail to be obtained due to matching rules of the qualifiers directories.

If this is the case, you can use the following APIs to obtain resources for a specific configuration.

#### Available APIs

| API                                                      | Description                                                        |
| ------------------------------------------------------------ | ------------------------------------------------------------ |
| [getOverrideResourceManager](../reference/apis-localization-kit/js-apis-resource-manager.md#getoverrideresourcemanager12)(configuration?: [Configuration](../reference/apis-localization-kit/js-apis-resource-manager.md#configuration)) : [ResourceManager](../reference/apis-localization-kit/js-apis-resource-manager.md#resourcemanager) | Obtains a **ResourceManager** object for loading resources for a specific configuration. This API returns the result synchronously.|
| [getOverrideConfiguration](../reference/apis-localization-kit/js-apis-resource-manager.md#getoverrideconfiguration12)() : [Configuration](../reference/apis-localization-kit/js-apis-resource-manager.md#configuration) | Obtains the specified configuration. This API returns the result synchronously.                            |
| [updateOverrideConfiguration](../reference/apis-localization-kit/js-apis-resource-manager.md#updateoverrideconfiguration12)(configuration: [Configuration](../reference/apis-localization-kit/js-apis-resource-manager.md#configuration)) : void | Updates the specified configuration.                                              |

#### Example

The following example demonstrates how to obtain the resources for languages other than the one in use. Assume that the following resource files with the same name are defined in the **resources** directories for Chinese, English, and German:

- entry/src/main/resources/zh_CN/element/string.json

```json
{
  "string": [
    {
      "name": "greetings",
      "value": "你好，世界"
    }
  ]
}
```

- entry/src/main/resources/en_US/element/string.json

```json
{
  "string": [
    {
      "name": "greetings",
      "value": "Hello, world"
    }
  ]
}
```

- entry/src/main/resources/de_DE/element/string.json

```json
{
  "string": [
    {
      "name": "greetings",
      "value": "Hallo, Welt"
    }
  ]
}
```

In **Index.ets**, add code to obtain the resources of the three languages and display them in the text box. The current system language is Chinese. The following is sample code in **entry/src/main/ets/pages/Index.ets**:

```ts
@Entry
@Component
struct Index {
  @State englishString: string = ""
  @State germanString: string = ""

  getString(): string {
    let resMgr = getContext().resourceManager
    let resId = $r('app.string.greetings').id

    // Obtain resources that match the current system configuration, including the color mode and resolution, for the current system language.
    let currentLanguageString = resMgr.getStringSync(resId)

    // Obtain resources that match the current system configuration, including the color mode and resolution, for the English language.
    let overrideConfig = resMgr.getOverrideConfiguration()
    overrideConfig.locale = "en_US" // Set the language to English and locale to US.
    let overrideResMgr = resMgr.getOverrideResourceManager(overrideConfig)
    this.englishString = overrideResMgr.getStringSync(resId)

    // Obtain resources that match the current system configuration, including the color mode and resolution, for the German language.
    overrideConfig.locale = "de_DE" // Set the language to German and locale to DE.
    overrideResMgr.updateOverrideConfiguration(overrideConfig) // Equivalent to resMgr.updateOverrideConfiguration(overrideConfig).
    this.germanString = overrideResMgr.getStringSync(resId)

    return currentLanguageString
  }

  build() {
    Row() {
      Column() {
        Text(this.getString())
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
        Text(this.englishString)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
        Text(this.germanString)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
      }
      .width('100%')
    }
    .height('100%')
  }
}
```

### Overlay Mechanism

Overlay is a resource replacement mechanism. With overlay resource packages, you enable your application GUI to adapt to different styles of various brands and products, without having to repack your application HAPs. The overlay mechanism works in dynamic and static modes. Overlay resource packages contain only resource files, resource index files, and configuration files.

- Using overlay in dynamic mode

1. Place the overlay resource package in the target application installation path and install the package using **hdc install**. For example, for the com.example.overlay application, place the overlay resource package in **data/app/el1/bundle/public/com.example.overlay/**.

2. The application uses [addResource(path)](../reference/apis-localization-kit/js-apis-resource-manager.md#addresource10) to load overlay resources and uses [removeResource(path)](../reference/apis-localization-kit/js-apis-resource-manager.md#removeresource10) to remove overlay resources. The path to an overlay resource consists of the application's sandbox root directory (obtained through **getContext().BundleCodeDir**) and the overlay resource package name. For example, **let path = getContext().bundleCodeDir + "Overlay resource package name"**, such as **/data/storage/el1/bundle/overlayResourcePackageName**.

- Using overlay in static mode

The **module.json5** file in the inter-application overlay resource package supports the following fields:
```{
  "app":{
    "bundleName": "com.example.myapplication.overlay",
    "vendor" : "example",
    "versinCode": "1000000",
    "versionName": "1.0.0.1",
    "icon": "$media:app_icon",
    "label": "$string:app_name",
  },
  "module":{
    "name": "entry_overlay_module_name",
    "type": "shared",
    "description": "$string:entry_overlay_desc",
    "deviceTypes": [
      "default",
      "tablet",
    ],
    "deliverywithInstall": true,

    "targetModuleName": "entry_module_name",
    "targetPriority": 1,
  }
}
```
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The **module.json5** file in the cross-application overlay resource package supports the following fields, which are available for system applications only:
```{
  "app":{
    "bundleName": "com.example.myapplication.overlay",
    "vendor" : "example",
    "versinCode": "1000000",
    "versionName": "1.0.0.1",
    "icon": "$media:app_icon",
    "label": "$string:app_name",
    "targetBundleName": "com.example.myapplication",
    "targetPariority": 1,
  },
  "module":{
    "name": "entry_overlay_module_name",
    "type": "shared",
    "description": "$string:entry_overlay_desc",
    "deviceTypes": [
      "default",
      "tablet",
    ],
    "deliverywithInstall": true,

    "targetModuleName": "entry_module_name",
    "targetPriority": 1,
  }
}
```
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> **NOTE**
> - **targetBundleName**: name of the target application to apply the overlay feature. The value is a string.
>
> - **targetModuleName**: name of the target module to apply the overlay feature. The value is a string.
>
> - **targetPriority**: overlay priority. The value is an integer.
>
> - Other fields such as **Ability**, **ExtensionAbility**, and **Permission** are not supported.
>
> - The overlay feature does not support JSON images.

If the **module.json5** file of a module contains the **targetModuleName** and **targetPriority** fields during project creation on DevEco Studio, the module is identified as a module with the overlay feature in the installation phase. Modules with the overlay feature generally provide an overlay resource file for other modules on the device, so that the module specified by **targetModuleName** can display different colors, labels, themes, and the like by using the overlay resource file in a running phase.

The overlay feature is enabled by default. For details about how to enable and disable this feature, see [@ohos.bundle.overlay (overlay)](../reference/apis-ability-kit/js-apis-overlay.md).

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