How can I create a new subclass extends a ButtonElement

Question

import dart:html , I can create a new subclass MyButton of ButtonElement with factory constructor ,and add some new function such as getButtonName(){} ...
when it's running ,I get a instance
```
MyButton btn=new MyButton()
```
But the instance "btn" runtime type is still ButtonElement, and can't call the getButtonName() function. If I use btn as MyButton then I get this error

Uncaught CastError: Casting value of type ButtonElement to incompatible type MyButton

Here is the code

    class MyButton extends ButtonElement {   
       factory MyButton(){
        return new ButtonElement();   
       }

       String getButtonName(){
        return "ButtonName";   
       } 
    }

Why a super class used a factory constructor ,then forced the subclass must use the factory constructor too ? and the instance cannot access the static method of the class ? Why ? — liu bin, Feb 12 '15 at 05:44

score 1 · Answer 1 · edited May 23 '17 at 12:05

1

Just because this line

return new ButtonElement();

is within a factory constructor or MyButton doesn't mean it has any relation to MyButton it still returns new ButtonElement().

This question extendTag in Dart custom element shows how to create a custom element without Polymer.
See also this discussion https://groups.google.com/a/dartlang.org/forum/#!topic/misc/-z_8sVp_uPY

edited May 23 '17 at 12:05

Community

1
1

answered Feb 12 '15 at 07:00

Günter Zöchbauer

623,577
216
2,003
1,567

How can I create a new subclass extends a ButtonElement

1 Answers1

Linked