dart upload file input type file

问题

Using Dart and Golang for a small app and looking to upload a file to server.

Found something like this and placed it in my .dart file:

InputElement uploadInput = query('#file'); // my input type file

  uploadInput.on.change.add((e) {
    // read file content as dataURL
    final files = uploadInput.files;
    if (files.length == 1) {
      final file = files[0];
      final reader = new FileReader();
      reader.on.load.add((e) {
       sendDatas(reader.result);
      });
      reader.readAsDataURL(file);
    }
  });

but getting the following error:

Uncaught TypeError: Cannot read property 'get$on' of null 

any idea how to handle this?

my goal: using input type file upload file to server (file size, < 1MB)

回答1:

This syntax has changed about a year ago.

try instead

uploadInput.onChange.listen((e) {

the same change is necessary here

reader.onLoad.listen((e) {

the xxx.on... syntax is only for custom events or browser events where Dart doesn't yet have direct getters.

This also works for standard browser events. You can use it like

uploadInput.on['change'].listen((e) => doSomething());

回答2:

Finally changed the code and this is the final working function, uploading file with DART:

updatefileToPlay(Event e, dynamic data, FileUploadInputElement el) {

    final files = el.files;
        if (files.length == 1) {
          final file = files[0];
          final reader = new FileReader();

          reader.onLoad.listen((e) {

            FormData data = new FormData(); // from dart:html
                data.append("file", file);

                HttpRequest.request('/upload?id='+message.id, method: 'POST', sendData: data).then((HttpRequest r) {
                  if (r.readyState == HttpRequest.DONE &&
                      (r.status == 200 || r.status == 0)) {
                    window.alert("upload complete");
                  }
                });
          });
          reader.readAsDataUrl(file);
        }
  }

来源：https://stackoverflow.com/questions/25568326/dart-upload-file-input-type-file