Use dart callback for wrapped js

Question

I wrapped exif-js library via dart:js.

  @JS()
    library exif;

    import 'package:js/js.dart';

    @JS()
    external PhotoDetails get EXIF;

    @JS()
    class PhotoDetails {
      factory PhotoDetails() {
        return EXIF;
      }

      @JS()
      external bool getData(img, callback);
}

And have a little Dart program:

PhotoDetails photoDetails = new PhotoDetails();
    var fileUploadInputElement = new FileUploadInputElement();
    fileUploadInputElement.onChange.listen((e) => photoDetails.getData(
        fileUploadInputElement.files[0], () {
      print(this);
    }));

Here it was already answered, but when I made so, I have this js error: exif.js:351 Uncaught TypeError: callback.call is not a function I tried to cast manually to Function. But it has not helped. With lambda expression it was the same.

Günter Zöchbauer · Accepted Answer · 2016-06-29 16:47:53Z

1

I think you need allowInterop or allowInteropCaptureThis

PhotoDetails photoDetails = new PhotoDetails();
var fileUploadInputElement = new FileUploadInputElement();
fileUploadInputElement.onChange.listen((e) => photoDetails.getData(
    fileUploadInputElement.files[0], allowInteropCaptureThis((self, [_]) {
  print(self);
})));

edited Jun 29, 2016 at 16:47

answered Jun 29, 2016 at 15:15

Günter Zöchbauer

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6 Comments

Leonid Lunin Over a year ago

I am not sure, that your answer is reason, but now it throws

Uncaught Unhandled exception: Closure call with mismatched arguments: function 'call'  NoSuchMethodError: incorrect number of arguments passed to method named 'call' Receiver: Closure: () => dynamic Tried calling: call(Instance of 'FileImpl') Found: call() #0      Object._noSuchMethod (dart:core-patch/object_patch.dart:42) #1      Object.noSuchMethod (dart:core-patch/object_patch.dart:45)

Günter Zöchbauer Over a year ago

I updated my answer (added [_, __]). Can you please try if this has any effect (different error, ...)?

Leonid Lunin Over a year ago

This not crashing, but for a pity print a "". So now I need to go deeper and find my mistake. Thanks a lot.

Günter Zöchbauer Over a year ago

Try print(_); instead of print(this). _ and __ are just names for unused variables. You can use proper names for them instead. [...] is to make them optional because I didn't know how many parameters are tried to pass and just used two of them. I assume the first is this (not sure, it's a while I tried this myself)

Leonid Lunin Over a year ago

Yes, this works. Very big thanks! Can you edit your answer?

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