使用Dart中的Blockly的addChangeListener（）函数（js互操作）

Question

I've been writing some wrapper code to access the Blockly API from Dart, using dart:js. All is going smoothly until I need to pass a function to one of Blockly's event registration functions on the JS side.

The function in question in Blockly is addChangeListener() (see https://developers.google.com/blockly/installation/code-generators ). It takes a 0-arg function as a callback. So my goal is to wrap a Dart function, pass it over, and have that function get called when the event fires.

In Dart:

var blockly = context['Blockly'];

context['codeChangedCallback'] = (){
   print('This should work, right?');
};  

blockly.callMethod('addChangeListener', [context['codeChangedCallback']]);

When Blockly initializes, I get this stack trace:

I'm hoping someone can point out something obvious that I've missed.

I have a feeling this may have to do specifically with the way blockly is handling the function internally, because I tried passing the function outside of blockly and it worked fine.

Answer 1

The problem is that the addChangeListener() callback has an arity of one, and Dart cares about arity. Your call should look like:

var blockly = context['Blockly'];

blockly.callMethod('addChangeListener', [(var event) => print('Success!')]);

Answer 2

I think this should work

var blockly = context['Blockly'];

context['codeChangedCallback'] = (){
   print('This should work, right?');
};  

blockly.callMethod('addChangeListener', [(){
   print('This should work, right?');
}]);