[Canvas] getContext error for canvas

[treatmaster]

Hi everyone, i'm developing an feature using canvas in QT 5.6. It's ok but when i downgrade to QT 5.3, it occurs error with method getContext for canvas.
Here is the error message:

Canvas {
   id: canvas
   onImageLoaded: {
      var ctx = canvas.getContext('2d');    ===> QML Canvas: Unable to use getContext() at this time, please wait for available: true
   }
}