How to get rotation angle in ionic gesture API?

Question

I'm working on canvas and was handling gesture events with hammerjs. But there I was facing an issue which I already asked here and other places but nobody responded. So now I'm working with ionic gestures but there also I can't find rotation angle property. Can anybody help me with that?

Here's the code:

ngAfterViewInit() {
      const gesture: Gesture = this.gestureCtrl.create({
      el: this.transCanvasElement,
      gestureName: 'rotate',
      onStart: ev => this.onStartHandler(ev)
    }, true);
    gesture.enable();
}
onStartHandler(ev) {
    console.log('ionic gesture ev angle: ', ev.rotation); // ev.rotation is undefined
}

Answer 1

Meaning of this in JS depends on the scope. See here for more info. You could either bind this to the callback or make it an arrow function.

Try the following

Option 1: bind this

ngAfterViewInit() {
  const gesture: Gesture = this.gestureCtrl.create({
    el: this.transCanvasElement,
    gestureName: 'rotate',
    onStart: this.onStartHandler.bind(this)  // <-- bind `this` to the callback
  }, true);
  gesture.enable();
}

onStartHandler(ev) {
  console.log('ionic gesture ev angle: ', ev.rotation);
}

Option 2: arrow function

ngAfterViewInit() {
  const gesture: Gesture = this.gestureCtrl.create({
    el: this.transCanvasElement,
    gestureName: 'rotate',
    onStart: ev => this.onStartHandler(ev)
  }, true);
  gesture.enable();
}

onStartHandler = (ev) => {                           // <-- arrow function
  console.log('ionic gesture ev angle: ', ev.rotation);
}