# FormExtensionContext

The **FormExtensionContext** module, inherited from **ExtensionContext**, provides context for Form Extension abilities.

You can use the APIs of this module to start Form Extension abilities.

> **NOTE**
>
> The initial APIs of this module are supported since API version 9. Newly added APIs will be marked with a superscript to indicate their earliest API version.
> The APIs of this module can be used only in the stage model.

## Usage

Before using the **ServiceExtensionContext** module, you must first obtain a **FormExtension** instance.

```ts
import FormExtensionAbility from '@ohos.app.form.FormExtensionAbility';
import formBindingData from '@ohos.app.form.formBindingData';
export default class MyFormExtensionAbility extends FormExtensionAbility {
    onAddForm() {
        let dataObj1 = {
            temperature:"11c",
            "time":"11:00"
        };
        let obj1 = formBindingData.createFormBindingData(dataObj1);
        return obj1;
    }
}
```

## startAbility

startAbility(want: Want, callback: AsyncCallback<void>): void

Starts an ability. This API uses an asynchronous callback to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.Ability.Form

**Parameters**

| Name|                Type              | Mandatory|              Description              |
| ------| --------------------------------- | ---- | -------------------------------------- |
| want| [Want](js-apis-application-want.md) | Yes | Information about the ability to start, such as the bundle name, ability name, and custom parameters.|
| callback| AsyncCallback<void>       | Yes | Callback used to return the result. If the ability is started, **err** is undefined; otherwise, **err** is an error object.|

**Example**

```ts
var want = {
    deviceId: "",
    bundleName: "com.example.formstartability",
    abilityName: "MainAbility",
    action: "action1",
    entities: ["entity1"],
    type: "MIMETYPE",
    uri: "key={true,true,false}",
    parameters: {}
}
this.context.startAbility(want, (error, data) => {
    if (error) {
      console.log('FormExtensionContext startAbility, error:' + JSON.stringify(error));
    } else {
      console.log(`FormExtensionContext startAbility success`);
    }
})
```

## startAbility

startAbility(want: Want): Promise<void>

Starts an ability. This API uses a promise to return the result.

**System API**: This is a system API.

**System capability**: SystemCapability.Ability.Form

**Parameters**

| Name|                Type              | Mandatory|              Description              |
| ------| --------------------------------- | ---- | -------------------------------------- |
| want| [Want](js-apis-application-want.md) | Yes | Information about the ability to start, such as the bundle name, ability name, and custom parameters.|

**Return value**

| Type         | Description                               |
| ------------ | ---------------------------------- |
| Promise<void< | Promise that returns no value.|

**Example**

```ts
var want = {
    deviceId: "",
    bundleName: "com.example.formstartability",
    abilityName: "MainAbility",
    action: "action1",
    entities: ["entity1"],
    type: "MIMETYPE",
    uri: "key={true,true,false}",
    parameters: {}
}
this.context.startAbility(want).then(() => {
    console.info("StartAbility Success");
}).catch((error) => {
    console.info("StartAbility failed");
});
```