以react-native@0.71.7环境为例，开发Android应用。

MetaMask一键登录

示例Demo

import {WebView} from 'react-native-webview';
import {useRef} from 'react';
const address = '<personal address>';
const injectedJavaScript = `
    window.ethereum = {};
    window.ethereum.isMetaMask = true;
    window.ethereum.isConnected = function() {
      console.log('-----------连接成功后调用---------')
      return true
    };
    window.ethereum.wallet = {};
    window.ethereum.wallet.address = '${address}';
    window.ethereum.selectedAddress = '${address}';
    window.ethereum.request = function(args = {}) {
      console.log('---------Dapp交互触发该事件-----------', args)
      const { method, params } = args
      return window.ethereum.send(method, params)
    };
    window.ethereum.send = function(method, params) {
      console.log('---------send-----------', method, params)
      return new Promise(function(resolve, reject) {
        window.ReactNativeWebView.postMessage(JSON.stringify({
            type: 'bsc',
            payload: {
                method: method,
                params: params,
            }
        }));
        document.addEventListener("message", function(event) {
          /**
          * wallet端主动调用postMessage触发该事件
          * 将webviewRef.current.postMessage回调的event.data作为Promise的值返回
          */
          const data = JSON.parse(event.data) || {}
          if (data.type === 'ethereum' && data.payload.id === method) {
              if (data.payload.error) {
                  reject(data.payload.error);
              } else {
                  resolve(data.payload.result);
              }
          }
        }, { once: true });
      });
    };
`;

const BrowserTab = function () {
  const webviewRef = useRef(null);
  const handleWebViewMessage = async function (event: any) {
    /**
    * Dapp端交互调用window.ethereum.request时触发
    * 根据window.ReactNativeWebView.postMessage传递的不同参数，返回对应的结果
    */
    const {data} = event.nativeEvent;
    const {type, payload = {}} = JSON.parse(data) || {};
    const {method} = payload;
    console.log(webviewRef.current);
    if (webviewRef.current) {
      method === 'eth_requestAccounts' &&
        webviewRef.current.postMessage(
          JSON.stringify({
            type: 'ethereum',
            payload: {
              id: 'eth_requestAccounts',
              result: [address],
            },
          }),
          '*',
        );
      method === 'eth_chainId' &&
        webviewRef.current.postMessage(
          JSON.stringify({
            type: 'ethereum',
            payload: {
              id: 'eth_chainId',
              result: 5,
            },
          }),
          '*',
        );
    }
  };
  return (
    <WebView
      ref={webviewRef}
      source={{uri: 'https://app.uniswap.org/'}}
      style={{flex: 1}}
      javaScriptEnabled={true}
      onMessage={handleWebViewMessage}
      injectedJavaScriptBeforeContentLoaded={injectedJavaScript}
    />
  );
};

export default BrowserTab;

流程分析：

1. 借助react-native-webview加载Dapp Web;
2. 绑定webviewRef实例，便于后续通信；
3. 在injectedJavaScriptBeforeContentLoaded内容加载之前注入JS脚本;

• Dapp实现会判断isMetaMask环境展示标识
• 注入业务相关的符合eip-1102等规范的事件实现，如eth_requestAccounts、signTransaction —— 在Dapp中进行操作，会调用对应的注入方法；

4. <WebView>绑定onMessage={handleWebViewMessage}，监听Dapp通过window.ReactNativeWebView.postMessage上报的消息；
5. 格式化event.nativeEvent.data数据，根据method、params进行对应的业务代码，通过 webviewRef.current.postMessage将结果返回；

• webviewRef.current.postMessage会触发注入脚本window.ethereum.send方法中的document.addEventListener("message", handler)回调逻辑；
• Dapp端会通过Promise接收返回结果，执行后续逻辑

Notes:

• injectedJavaScriptBeforeContentLoaded注入window.ethereum后获取该属性为undefined
  • Warning On Android, this may work, but it is not 100% reliable (see #1609 and #1099).
  • 实战演练，发现react-native-webview@11.13.0注入无效，react-native-webview@12.1注入有效
• 由于平台差异，document.addEventListener("message", handler)在Android和IOS环境中有所不同(https://github.com/react-native-webview/react-native-webview/issues/356)。

Metamask相关代码

• webView组件渲染相关代码
  
  Webview组件
  
  其中，onMessage代码实现：

  const onMessage = ({ nativeEvent }) => {
    let data = nativeEvent.data;
    try {
      data = typeof data === 'string' ? JSON.parse(data) : data;
      if (!data || (!data.type && !data.name)) {
        return;
      }
      if (data.name) {
        const origin = new URL(nativeEvent.url).origin;
        backgroundBridges.current.forEach((bridge) => {
          const bridgeOrigin = new URL(bridge.url).origin;
          bridgeOrigin === origin && bridge.onMessage(data);
        });
        return;
      }
    } catch (e) {
      Logger.error(e, `Browser::onMessage on ${url.current}`);
    }
  };

backgroundBridges又是什么呢？

  const initializeBackgroundBridge = (urlBridge, isMainFrame) => {
    const newBridge = new BackgroundBridge({
      webview: webviewRef,  // webview实例，可以通过postMessage向内部渲染的Dapp通信
      url: urlBridge,
      getRpcMethodMiddleware: ({ hostname, getProviderState }) =>
        getRpcMethodMiddleware({
          hostname,
          getProviderState,
          navigation: props.navigation,
          // Website info
          url,
          title,
          icon,
          // Bookmarks
          isHomepage,
          // Show autocomplete
          fromHomepage,
          toggleUrlModal,
          // Wizard
          wizardScrollAdjusted,
          tabId: props.id,
          injectHomePageScripts,
        }),
      isMainFrame,
    });
    backgroundBridges.current.push(newBridge);
  };

getRpcMethodMiddleware的定义

RpcMethod

RpcMethod

参考文档

https://stackoverflow.com/questions/75633905/how-to-inject-a-wallet-into-the-browser-from-mobile-react-native