# Class (WebDownloadDelegate)

Implements a **WebDownloadDelegate** object to notify users of the download state.

> **NOTE**
>
> - The initial APIs of this module are supported since API version 9. Updates will be marked with a superscript to indicate their earliest API version.
>
> - The initial APIs of this class are supported since API version 11.
>
> - You can preview how this component looks on a real device, but not in DevEco Studio Previewer.

## Modules to Import

```ts
import { webview } from '@kit.ArkWeb';
```

## onBeforeDownload<sup>11+</sup>

onBeforeDownload(callback: Callback\<WebDownloadItem>): void

Invoked to notify users before the download starts. **WebDownloadItem.start("xxx")** must be called in this API, with a download path provided. Otherwise, the download remains in the PENDING state.

> **NOTE**
>
>The file of the download task in the PENDING state is saved to a temporary directory. After the target path is specified by invoking **WebDownloadItem.start**, the temporary file is renamed as the target file, and the unfinished part is directly downloaded to the target path. To avoid generating temporary files before invoking **WebDownloadItem.start**, you can call **WebDownloadItem.cancel** to cancel the current download task and then call **WebDownloadManager.resumeDownload** to resume it.

**System capability**: SystemCapability.Web.Webview.Core

**Parameters**

| Name | Type  | Mandatory| Description          |
| ------- | ------ | ---- | :------------- |
| callback | Callback\<[WebDownloadItem](./arkts-apis-webview-WebDownloadItem.md)> | Yes  | Callback for triggering a download.|

**Example**

```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';

@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  delegate: webview.WebDownloadDelegate = new webview.WebDownloadDelegate();
  download: webview.WebDownloadItem = new webview.WebDownloadItem();
  failedData: Uint8Array = new Uint8Array();

  build() {
    Column() {
      Button('setDownloadDelegate')
        .onClick(() => {
          try {
            this.delegate.onBeforeDownload((webDownloadItem: webview.WebDownloadItem) => {
              console.log("will start a download.");
              // Pass in a download path and start the download.
              webDownloadItem.start("/data/storage/el2/base/cache/web/" + webDownloadItem.getSuggestedFileName());
            })
            this.delegate.onDownloadUpdated((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download update percent complete: " + webDownloadItem.getPercentComplete());
              this.download = webDownloadItem;
            })
            this.delegate.onDownloadFailed((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download failed guid: " + webDownloadItem.getGuid());
              // Serialize the failed download to a byte array.
              this.failedData = webDownloadItem.serialize();
            })
            this.delegate.onDownloadFinish((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download finish guid: " + webDownloadItem.getGuid());
            })
            this.controller.setDownloadDelegate(this.delegate);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('startDownload')
        .onClick(() => {
          try {
            this.controller.startDownload('https://www.example.com');
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('resumeDownload')
        .onClick(() => {
          try {
            webview.WebDownloadManager.resumeDownload(webview.WebDownloadItem.deserialize(this.failedData));
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('cancel')
        .onClick(() => {
          try {
            this.download.cancel();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('pause')
        .onClick(() => {
          try {
            this.download.pause();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('resume')
        .onClick(() => {
          try {
            this.download.resume();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Web({ src: 'www.example.com', controller: this.controller })
    }
  }
}
```

## onDownloadUpdated<sup>11+</sup>

onDownloadUpdated(callback: Callback\<WebDownloadItem>): void

Invoked when the download progress is updated.

**System capability**: SystemCapability.Web.Webview.Core

**Parameters**

| Name | Type  | Mandatory| Description          |
| ------- | ------ | ---- | :------------- |
| callback | Callback\<[WebDownloadItem](./arkts-apis-webview-WebDownloadItem.md)> | Yes  | Callback invoked when the downloaded progress is updated.|

**Example**

```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';

@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  delegate: webview.WebDownloadDelegate = new webview.WebDownloadDelegate();
  download: webview.WebDownloadItem = new webview.WebDownloadItem();
  failedData: Uint8Array = new Uint8Array();

  build() {
    Column() {
      Button('setDownloadDelegate')
        .onClick(() => {
          try {
            this.delegate.onBeforeDownload((webDownloadItem: webview.WebDownloadItem) => {
              console.log("will start a download.");
              // Pass in a download path and start the download.
              webDownloadItem.start("/data/storage/el2/base/cache/web/" + webDownloadItem.getSuggestedFileName());
            })
            this.delegate.onDownloadUpdated((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download update percent complete: " + webDownloadItem.getPercentComplete());
              this.download = webDownloadItem;
            })
            this.delegate.onDownloadFailed((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download failed guid: " + webDownloadItem.getGuid());
              // Serialize the failed download to a byte array.
              this.failedData = webDownloadItem.serialize();
            })
            this.delegate.onDownloadFinish((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download finish guid: " + webDownloadItem.getGuid());
            })
            this.controller.setDownloadDelegate(this.delegate);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('startDownload')
        .onClick(() => {
          try {
            this.controller.startDownload('https://www.example.com');
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('resumeDownload')
        .onClick(() => {
          try {
            webview.WebDownloadManager.resumeDownload(webview.WebDownloadItem.deserialize(this.failedData));
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('cancel')
        .onClick(() => {
          try {
            this.download.cancel();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('pause')
        .onClick(() => {
          try {
            this.download.pause();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('resume')
        .onClick(() => {
          try {
            this.download.resume();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Web({ src: 'www.example.com', controller: this.controller })
    }
  }
}
```

## onDownloadFinish<sup>11+</sup>

onDownloadFinish(callback: Callback\<WebDownloadItem>): void

Invoked when the download is complete.

**System capability**: SystemCapability.Web.Webview.Core

**Parameters**

| Name | Type  | Mandatory| Description          |
| ------- | ------ | ---- | :------------- |
| callback | Callback\<[WebDownloadItem](./arkts-apis-webview-WebDownloadItem.md)> | Yes  | Callback invoked when the download is complete.|

**Example**

```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';

@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  delegate: webview.WebDownloadDelegate = new webview.WebDownloadDelegate();
  download: webview.WebDownloadItem = new webview.WebDownloadItem();
  failedData: Uint8Array = new Uint8Array();

  build() {
    Column() {
      Button('setDownloadDelegate')
        .onClick(() => {
          try {
            this.delegate.onBeforeDownload((webDownloadItem: webview.WebDownloadItem) => {
              console.log("will start a download.");
              // Pass in a download path and start the download.
              webDownloadItem.start("/data/storage/el2/base/cache/web/" + webDownloadItem.getSuggestedFileName());
            })
            this.delegate.onDownloadUpdated((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download update percent complete: " + webDownloadItem.getPercentComplete());
              this.download = webDownloadItem;
            })
            this.delegate.onDownloadFailed((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download failed guid: " + webDownloadItem.getGuid());
              // Serialize the failed download to a byte array.
              this.failedData = webDownloadItem.serialize();
            })
            this.delegate.onDownloadFinish((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download finish guid: " + webDownloadItem.getGuid());
            })
            this.controller.setDownloadDelegate(this.delegate);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('startDownload')
        .onClick(() => {
          try {
            this.controller.startDownload('https://www.example.com');
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('resumeDownload')
        .onClick(() => {
          try {
            webview.WebDownloadManager.resumeDownload(webview.WebDownloadItem.deserialize(this.failedData));
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('cancel')
        .onClick(() => {
          try {
            this.download.cancel();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('pause')
        .onClick(() => {
          try {
            this.download.pause();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('resume')
        .onClick(() => {
          try {
            this.download.resume();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Web({ src: 'www.example.com', controller: this.controller })
    }
  }
}
```

## onDownloadFailed<sup>11+</sup>

onDownloadFailed(callback: Callback\<WebDownloadItem>): void

Invoked when the download fails.

**System capability**: SystemCapability.Web.Webview.Core

**Parameters**

| Name | Type  | Mandatory| Description          |
| ------- | ------ | ---- | :------------- |
| callback | Callback\<[WebDownloadItem](./arkts-apis-webview-WebDownloadItem.md)> | Yes  | Callback invoked when the download fails.|

**Example**

```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';

@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  delegate: webview.WebDownloadDelegate = new webview.WebDownloadDelegate();
  download: webview.WebDownloadItem = new webview.WebDownloadItem();
  failedData: Uint8Array = new Uint8Array();

  build() {
    Column() {
      Button('setDownloadDelegate')
        .onClick(() => {
          try {
            this.delegate.onBeforeDownload((webDownloadItem: webview.WebDownloadItem) => {
              console.log("will start a download.");
              // Pass in a download path and start the download.
              webDownloadItem.start("/data/storage/el2/base/cache/web/" + webDownloadItem.getSuggestedFileName());
            })
            this.delegate.onDownloadUpdated((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download update percent complete: " + webDownloadItem.getPercentComplete());
              this.download = webDownloadItem;
            })
            this.delegate.onDownloadFailed((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download failed guid: " + webDownloadItem.getGuid());
              // Serialize the failed download to a byte array.
              this.failedData = webDownloadItem.serialize();
            })
            this.delegate.onDownloadFinish((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download finish guid: " + webDownloadItem.getGuid());
            })
            this.controller.setDownloadDelegate(this.delegate);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('startDownload')
        .onClick(() => {
          try {
            this.controller.startDownload('https://www.example.com');
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('resumeDownload')
        .onClick(() => {
          try {
            webview.WebDownloadManager.resumeDownload(webview.WebDownloadItem.deserialize(this.failedData));
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('cancel')
        .onClick(() => {
          try {
            this.download.cancel();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('pause')
        .onClick(() => {
          try {
            this.download.pause();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('resume')
        .onClick(() => {
          try {
            this.download.resume();
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Web({ src: 'www.example.com', controller: this.controller })
    }
  }
}
```