application-dev/web/web-page-loading-with-web-components.md

# Loading Pages by Using the Web Component


Page loading is a basic function of the **Web** component. Depending on the data source, page loading falls into three types: loading of network pages, loading of local pages, and loading of HTML rich text data.


If acquisition of network resources is involved in page loading, you need to declare the [ohos.permission.INTERNET](../security/AccessToken/declare-permissions.md) permission.


## Loading Network Pages

You can specify the default network page to be loaded when creating a **Web** component. After the default network page is loaded, call [loadUrl()](../reference/apis-arkweb/js-apis-webview.md#loadurl) if you want to change the network page displayed by the **Web** component.


In the following example, after the **www.\example.com** page is loaded by the **Web** component, **loadUrl** is called to change the displayed page to **www\.example1.com**.


```ts
// xxx.ets
import web_webview from '@ohos.web.webview';
import business_error from '@ohos.base';

@Entry
@Component
struct WebComponent {
  webviewController: web_webview.WebviewController = new web_webview.WebviewController();

  build() {
    Column() {
      Button('loadUrl')
        .onClick(() => {
          try {
            // Upon button clicking, call loadUrl to redirect to www.example1.com.
            this.webviewController.loadUrl('www.example1.com');
          } catch (error) {
            let e: business_error.BusinessError = error as business_error.BusinessError;
            console.error(`ErrorCode: ${e.code},  Message: ${e.message}`);
          }
        })
      // When creating a Web component, set the default network page to be loaded to www.example.com.
      Web({ src: 'www.example.com', controller: this.webviewController})
    }
  }
}
```


## Loading Local Pages

Local page files are stored in the application's **rawfile** directory. You can specify the local page to be loaded by default when creating a **Web** component. After page loading is complete, you can call [loadUrl()](../reference/apis-arkweb/js-apis-webview.md#loadurl) to change the displayed page of the **Web** component.


The following example shows how to load a local page file.


- Local page file in the application's resources/rawfile directory:

    **Figure 1** Path of local page files

    ![resource-path](figures/resource-path.png)


- Application code:

  ```ts
  // xxx.ets
  import web_webview from '@ohos.web.webview';
  import business_error from '@ohos.base';

  @Entry
  @Component
  struct WebComponent {
    webviewController: web_webview.WebviewController = new web_webview.WebviewController();

    build() {
      Column() {
        Button('loadUrl')
          .onClick(() => {
            try {
              // Upon button clicking, call loadUrl to redirect to local1.html.
              this.webviewController.loadUrl($rawfile("local1.html"));
            } catch (error) {
              let e: business_error.BusinessError = error as business_error.BusinessError;
              console.error(`ErrorCode: ${e.code},  Message: ${e.message}`);
            }
          })
        // When creating a Web component, load the local.html file through $rawfile.
        Web({ src: $rawfile("local.html"), controller: this.webviewController })
      }
    }
  }
  ```


- Code of the **local.html** page:

  ```html
  <!-- local.html -->
  <!DOCTYPE html>
  <html>
    <body>
      <p>Hello World</p>
    </body>
  </html>
  ```


## Loading HTML Rich Text Data

The **Web** component provides the [loadData()](../reference/apis-arkweb/js-apis-webview.md#loaddata) API for you to load HTML rich text data. This API is applicable if you want to display some page sections instead of the entire page.


```ts
// xxx.ets
import web_webview from '@ohos.web.webview';
import business_error from '@ohos.base';

@Entry
@Component
struct WebComponent {
  controller: web_webview.WebviewController = new web_webview.WebviewController();

  build() {
    Column() {
      Button('loadData')
        .onClick(() => {
          try {
            // Upon button clicking, call loadData to load HTML rich text data.
            this.controller.loadData(
              "<html><body bgcolor=\"white\">Source:<pre>source</pre></body></html>",
              "text/html",
              "UTF-8"
            );
          } catch (error) {
            let e: business_error.BusinessError = error as business_error.BusinessError;
            console.error(`ErrorCode: ${e.code},  Message: ${e.message}`);
          }
        })
      // When creating a Web component, set the default network page to be loaded to www.example.com.
      Web({ src: 'www.example.com', controller: this.controller })
    }
  }
}
```

## Dynamically Creating Web Components
**Web** components can be created with commands. Components created in this mode are not immediately mounted to the component tree, that is, they are not presented to users (their state is **Hidden** or **InActive**). You can dynamically mount the components as required in subsequent use. It is recommended that the number of **Web** instances started in the background be less than or equal to 200.

```ts
// Carrier ability
// EntryAbility.ets
import {createNWeb} from "../pages/common"
onWindowStageCreate(windowStage: window.WindowStage): void {
  windowStage.loadContent('pages/Index', (err, data) => {
    // Dynamically create a Web component (UIContext needs to be passed in). The component can be created at any time after loadContent is called.
    createNWeb("https://www.example.com", windowStage.getMainWindowSync().getUIContext());
    if (err.code) {
      return;
    }
  });
}
```
```ts
// Create a NodeController instance.
// common.ets
import { UIContext } from '@ohos.arkui.UIContext';
import web_webview from '@ohos.web.webview'
import { NodeController, BuilderNode, Size, FrameNode }  from '@ohos.arkui.node';
// @Builder contains the specific content of the dynamically created component.
// Data is the class for input parameter encapsulation.
class Data{
  url: string = "https://www.example.com";
  controller: WebviewController = new web_webview.WebviewController();
}

@Builder
function WebBuilder(data:Data) {
  Column() {
    Web({ src: data.url, controller: data.controller })
      .width("100%")
      .height("100%")
  }
}

let wrap = wrapBuilder<Data[]>(WebBuilder);

// NodeController is used to control and feed back the behavior of the corresponding node in the NodeContainer. It must be used together with NodeContainer.
export class myNodeController extends NodeController {
  private rootnode: BuilderNode<Data[]> | null = null;
  // This method must be overridden. It is used to construct the number of nodes and return the number of nodes mounted to the corresponding NodeContainer.
  // Called when the corresponding NodeContainer is created or called through the rebuild method.
  makeNode(uiContext: UIContext): FrameNode | null {
    console.log(" uicontext is undifined : "+ (uiContext === undefined));
    if (this.rootnode != null) {
      // Return the FrameNode.
      return this.rootnode.getFrameNode();
    }
    // Return null to control the dynamic component to be detached from the bound node.
    return null;
  }
  // Called when the layout size changes.
  aboutToResize(size: Size) {
    console.log("aboutToResize width : " + size.width  +  " height : " + size.height )
  }

  // Called when the NodeContainer bound to the current controller is about to be displayed.
  aboutToAppear() {
    console.log("aboutToAppear")
  }

  // Called when the NodeContainer bound to the current controller is about to be hidden.
  aboutToDisappear() {
    console.log("aboutToDisappear")
  }

  // This function is a custom function and can be used as an initialization function.
  // Initialize BuilderNode through UIContext, and then initialize the content in @Builder through the build API in BuilderNode.
  initWeb(url:string, uiContext:UIContext, control:WebviewController) {
    if(this.rootnode != null)
    {
      return;
    }
    // Create a node. uiContext is required.
    this.rootnode = new BuilderNode(uiContext)
    // Create a dynamic Web component.
    this.rootnode.build(wrap, { url:url, controller:control })
  }
}
 // Create a map to save the required NodeController.
let NodeMap:Map<string, myNodeController | undefined> = new Map();
// Create a map to save the required WebViewController.
let controllerMap:Map<string, WebviewController | undefined> = new Map();

// UIContext is required for initialization and needs to be obtained from the ability.
export const createNWeb = (url: string, uiContext: UIContext) => {
  // Create a NodeController.
  let baseNode = new myNodeController();
  let controller = new web_webview.WebviewController() ;
  // Initialize the custom Web component.
  baseNode.initWeb(url, uiContext, controller);
  controllerMap.set(url, controller)
  NodeMap.set(url, baseNode);
}
// Customize the API for obtaining the NodeController.
export const getNWeb = (url : string) : myNodeController | undefined => {
  return NodeMap.get(url);
}
```
```ts
// Use the Page page of the NodeController.
// Index.ets
import {createNWeb, getNWeb} from "./common"
@Entry
@Component
struct Index {
  build() {
    Row() {
      Column() {
        // NodeContainer is used to bind to the NodeController. A rebuild call triggers makeNode.
        // The Page page is bound to the NodeController through the NodeContainer API to display the dynamic component.
        NodeContainer(getNWeb("https://www.example.com"))
          .height("90%")
          .width("100%")
      }
      .width('100%')
    }
    .height('100%')
  }
}

```