GWT: Create Canvas widget from CanvasElement

Question

I want to wrap a CanvasElement (<canvas> in HTML) in a Canvas widget.

Many widgets (e.g. Label) have a static method SomeWidget.wrap(Element) for wrapping an existing DOM element. I imagine Canvas does not feature such a method because not all browser support and therefore the user should be forced to go through createIfSupported().

Unfortunately the constructor in Canvas is private (protected would work), which means that Canvas can not be subclassed. (There isn't any constructor available in the derived class.)

Code snippets of createIfSupported and the constructor in the Canvas class:

  public static Canvas createIfSupported() {
    // check if canvas is supported; if it is not supported: return null
    return new Canvas(element);
  }

  private Canvas(CanvasElement element) {
    setElement(element);
  }

I ended up copying the Canvas class and making the constructor public.

Is there a better way to do this? If not, what is the reasoning behind it (besides that <canvas> might not be supported)?

I am using GWT version 2.4.0.rc1.

Thanks, Julian

Gilberto Torrezan Gilberto Torrezan · Accepted Answer · 2015-05-25T19:52:55

This question is old, but there is a solution in newer versions of GWT:

Canvas.wrap(canvasElement);

See javadocs.

I don't know in which version of GWT it was added, but It works on 2.7.0.

GWT: Create Canvas widget from CanvasElement

1 Answers