学习：使用postMessage()建立应用侧与前端页面的数据通道

前端页面和应用侧之间可以用createWebMessagePorts()接口创建消息端口来实现两端的通信。

在下面的示例中，应用侧页面中通过createWebMessagePorts方法创建两个消息端口，再把其中一个端口通过postMessage()接口发送到前端页面，便可以在前端页面和应用侧之间互相发送消息。端口使用完毕后或Webview对象销毁前通过close接口关闭端口。

应用侧代码：

TypeScript 复制代码

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

@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  ports: webview.WebMessagePort[] = [];
  @State sendFromEts: string = 'Send this message from ets to HTML';
  @State receivedFromHtml: string = 'Display received message send from HTML';

  build() {
    Column() {
      // 展示接收到的来自HTML的内容
      Text(this.receivedFromHtml);
      // 输入框的内容发送到HTML
      TextInput({ placeholder: 'Send this message from ets to HTML' })
        .onChange((value: string) => {
          this.sendFromEts = value;
        })

      // 该内容可以放在onPageEnd生命周期中调用。
      Button('postMessage')
        .onClick(() => {
          try {
            // 1、创建两个消息端口。
            this.ports = this.controller.createWebMessagePorts();
            if (this.ports && this.ports[0] && this.ports[1]) {
              // 2、在应用侧的消息端口(如端口1)上注册回调事件。
              this.ports[1].onMessageEvent((result: webview.WebMessage) => {
                let msg = 'Got msg from HTML:';
                if (typeof (result) === 'string') {
                  console.info(`received string message from html5, string is: ${result}`);
                  msg = msg + result;
                } else if (typeof (result) === 'object') {
                  if (result instanceof ArrayBuffer) {
                    console.info(`received arraybuffer from html5, length is: ${result.byteLength}`);
                    msg = msg + 'length is ' + result.byteLength;
                  } else {
                    console.info('not support');
                  }
                } else {
                  console.info('not support');
                }
                this.receivedFromHtml = msg;
              })
              // 3、将另一个消息端口(如端口0)发送到HTML侧，由HTML侧保存并使用。
              this.controller.postMessage('__init_port__', [this.ports[0]], '*');
            } else {
              console.error(`ports is null, Please initialize first`);
            }
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })

      // 4、使用应用侧的端口给另一个已经发送到html的端口发送消息。
      Button('SendDataToHTML')
        .onClick(() => {
          try {
            if (this.ports && this.ports[1]) {
              this.ports[1].postMessageEvent(this.sendFromEts);
            } else {
              console.error(`ports is null, Please initialize first`);
            }
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })

      // 5、关闭端口。
      Button('closePort')
      .onClick(() => {
        try {
          if (this.ports && this.ports.length == 2) {
            this.ports[0].close();
            this.ports = [];
          } else {
            console.error("ports is null, not need close");
          }
        } catch (error) {
          console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
        }
      })
      Web({ src: $rawfile('index.html'), controller: this.controller })
    }
  }
}

前端页面代码：

html 复制代码

<!--index.html-->
<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>WebView Message Port Demo</title>
</head>
<body>
    <h1>WebView Message Port Demo</h1>
    <div>
        <input type="button" value="SendToEts" onclick="PostMsgToEts(msgFromJS.value);"/><br/>
        <input id="msgFromJS" type="text" value="send this message from HTML to ets"/><br/>
    </div>
    <p class="output">display received message send from ets</p>
</body>
<script>
var h5Port;
var output = document.querySelector('.output');
window.addEventListener('message', function (event) {
    if (event.data === '__init_port__') {
        if (event.ports[0] !== null) {
            h5Port = event.ports[0]; // 1. 保存从应用侧发送过来的端口。
            h5Port.onmessage = function (event) {
              // 2. 接收ets侧发送过来的消息。
              var msg = 'Got message from ets:';
              var result = event.data;
              if (typeof(result) === 'string') {
                console.info(`received string message from ets, string is: ${result}`);
                msg = msg + result;
              } else if (typeof(result) === 'object') {
                if (result instanceof ArrayBuffer) {
                  console.info(`received arraybuffer from ets, length is: ${result.byteLength}`);
                  msg = msg + 'length is ' + result.byteLength;
                } else {
                  console.info('not support');
                }
              } else {
                console.info('not support');
              }
              output.innerHTML = msg;
            }
        }
    }
})
// 3. 使用h5Port向应用侧发送消息。
function PostMsgToEts(data) {
    if (h5Port) {
      h5Port.postMessage(data);
    } else {
      console.error('h5Port is null, Please initialize first');
    }
}
</script>
</html>

常见问题

为什么H5向应用侧发送消息接收不到？

检查传递的数据类型是否正确，WebMessage支持的数据类型有string和ArrayBuffer。

如果想要传递对象类型则需要将对象类型通过JSON.stringify方法转换为string类型再进行传递。示例如下：

TypeScript 复制代码

  function PostMsgToEts(data) {
      if (h5Port) {
        let obj = {name:'exampleName',id:10}
        h5Port.postMessage(JSON.stringify(obj));
      } else {
        console.error('h5Port is null. Please initialize it first.');
      }
  }