flutter 的 in_app_web_view实现下载功能

flutter与前端交互,利用in_app_web_view实现下载功能:

首先下载库,终端输入

flutter pub add flutter_inappwebview

之后导出

import 'package:flutter_inappwebview/flutter_inappwebview.dart';

即可使用。

创建in_app_web_view:

InAppWebView(
     initialOptions:
          InAppWebViewGroupOptions(
              crossPlatform:InAppWebViewOptions(
                useOnDownloadStart:true,
              ),
              android: AndroidInAppWebViewOptions()
          ),
      //老版本:initialUrl    新版本:initialUrlRequest
      initialUrlRequest: URLRequest(
        url: Uri.parse(widget.url),
      )
)

因为要下载文件,所以请务必手动设置 useOnDownloadStart 为 true(否则出发文件下载的监听)。

initialUrlRequest中可填写自己想首先打开的url地址。

可参考例子:

flutter_inappwebview_examples/main.dart at main · pichillilorenzo/flutter_inappwebview_examples · GitHub
https://github.com/pichillilorenzo/flutter_inappwebview_examples/blob/main/file_download/lib/main.dart

https://github.com/pichillilorenzo/flutter_inappwebview_examples/blob/main/file_download/lib/main.dart

填写自己需要的回调(例子中的一点错误,没有开启 useOnDownloadStart, 因此不会下载成功,在使用时请设置为true)

正常情况下,配合downloader和android_path_provider,普通https链接即可下载文件。

 

而遇到blob链接时,还需要进行更多操作来确保文件的下载:

可参考

javascript - Flutter WebView blob pdf download - Stack Overflow
https://stackoverflow.com/questions/64865972/flutter-webview-blob-pdf-download/64902313#64902313

https://stackoverflow.com/questions/64865972/flutter-webview-blob-pdf-download/64902313#64902313

因为Android不支持blob链接下载,因此我们嵌套javascript处理下载链接,在in_app_web_view的build中重写onWebViewCreated方法,添加javascriptHandler:

onWebViewCreated: (InAppWebViewController controller) {
        if (mounted) {
          setState(() {
            _inAppWebCtrl = controller;
            _inAppWebCtrl!.addJavaScriptHandler(
              handlerName: 'blobToBase64Handler',
              callback: (data) async {
                if (data.isNotEmpty) {
                  final String receivedFileInBase64 = data[0];
                  final String receivedMimeType = data[1];

                  // NOTE: create a method that will handle your extensions
                  final String extension =
                  _mapMimeTypeToExtension(receivedMimeType);
                  String tmpFileName = 'tmpfile';
                  _createFileFromBase64(
                      receivedFileInBase64, tmpFileName, extension);
                }
              },
            );
          });
        }
      },

首先在assets中添加js文件夹,然后创建 base64.js 文件

var xhr = new XMLHttpRequest();
var blobUrl = "blobUrlPlaceholder";
console.log(blobUrl);
xhr.open('GET', blobUrl, true);
xhr.responseType = 'blob';
xhr.onload = function(e) {
  if (this.status == 200) {
    var blob = this.response;
    var reader = new FileReader();
    reader.readAsDataURL(blob);
    reader.onloadend = function() {
      var base64data = reader.result;
      var base64ContentArray = base64data.split(",");
      var mimeType = base64ContentArray[0].match(/[^:\s*]\w+\/[\w-+\d.]+(?=[;| ])/)[0];
      var decodedFile = base64ContentArray[1];
      console.log(mimeType);
      window.flutter_inappwebview.callHandler('blobToBase64Handler', decodedFile, mimeType);
    };
  };
};
xhr.send();

 

注意js中的callhander的名字参数,对应创建webview时addJavascriptHandler中的name。

另外是文件类型映射函数和文件下载函数:

  String _mapMimeTypeToExtension(String mimeType) {
    String extension = '';
    switch(mimeType) {
      case 'image/png': extension = 'png'; break;
      case 'application/msword': extension = 'doc'; break;
      case 'application/vnd.openxmlformats-officedocument.wordprocessingml.document':
        extension = 'docx';
        break;
      case 'image/jpeg': extension = 'jpg'; break;
      case 'image/gif': extension = 'gif'; break;
      case 'image/svg+xml': extension = 'svg'; break;
      case 'image/tiff': extension = 'tif'; break;
      case 'text/plain': extension = 'txt'; break;
      case 'application/vnd.ms-powerpoint': extension = 'ppt'; break;
      case 'application/vnd.openxmlformats-officedocument.presentationml.presentation':
        extension = 'pptx';
        break;
      case 'application/vnd.ms-excel': extension = 'xls'; break;
      case 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet':
        extension = 'xlsx';
        break;
      case 'application/zip': extension = 'zip'; break;
      case 'application/x-7z-compressed': extension = '7z'; break;
      case 'application/pdf': extension = 'pdf'; break;
    }
    return extension;
  }

  _createFileFromBase64(String base64content, String fileName, String yourExtension) async {
    var bytes = base64Decode(base64content.replaceAll('\n', ''));
    final file = File("$_localPath/$fileName.$yourExtension");
    await file.writeAsBytes(bytes.buffer.asUint8List());
    
  }

最后重写inappwebview中的下载请求方法:

      onDownloadStartRequest: (controller, downloadStartRequest) async {
          var jsContent = await rootBundle.loadString("assets/js/base64.js");
// 运行javascript代码解析blob
          await controller.evaluateJavascript(
              source: jsContent.replaceAll("blobUrlPlaceholder",
                  downloadStartRequest.url.toString()));
      },

总结:因为android本身不能解析blob,我们因此使用javascript作为翻译:运行顺序:

onDownloadStartRequest -> javascript文件 -> webviewController中的handler的callback,最后以流的方式写入文件。