gesture recognizer: Add a function to remove a registered gesture rec…

…ognizer in gestures (ampproject#12271)

src/gesture.js

@@ -18,6 +18,8 @@ import {Observable} from './observable';
 import {Pass} from './pass';
 import {dev} from './log';
 import {toWin} from './types';
+import {findIndex} from './utils/array';
+
 
 const PROP_ = '__AMP_Gestures';
 
@@ -173,6 +175,35 @@ export class Gestures {
     return overserver.add(handler);
   }
 
+  /**
+   * Unsubscribes all handlers from the given gesture recognizer. Returns
+   * true if anything was done. Returns false if there were no handlers
+   * registered on the given gesture recognizer in first place.
+   *
+   * @param {function(new:GestureRecognizer<DATA>, !Gestures)} recognizerConstr
+   * @return {boolean}
+   */
+  removeGesture(recognizerConstr) {
+    const type = new recognizerConstr(this).getType();
+    const overserver = this.overservers_[type];
+    if (overserver) {
+      overserver.removeAll();
+      const index = findIndex(this.recognizers_, e => e.getType() == type);
+      if (index < 0) {
+        return false;
+      }
+      // Remove the recognizer as well as all associated tracking state
+      this.recognizers_.splice(index, 1);
+      this.ready_.splice(index, 1);
+      this.pending_.splice(index, 1);
+      this.tracking_.splice(index, 1);
+      delete this.overservers_[type];
+      return true;
+    } else {
+      return false;
+    }
+  }
+
   /**
    * Subscribes to pointer down events, such as "touchstart" or "mousedown".
    * @param {!Function} handler

test/functional/test-gesture.js

@@ -355,6 +355,16 @@ describe('Gestures', () => {
     expect(event.stopPropagation).to.have.not.been.called;
   });
 
+  it('should gesture recognizer on removeGesture', () => {
+    expect(gestures.recognizers_.length).to.equal(1);
+    expect(gestures.removeGesture(TestRecognizer)).to.equal(true);
+    expect(gestures.removeGesture(Test2Recognizer)).to.equal(false);
+    expect(gestures.recognizers_.length).to.equal(0);
+    expect(gestures.ready_.length).to.equal(0);
+    expect(gestures.tracking_.length).to.equal(0);
+    expect(gestures.pending_.length).to.equal(0);
+  });
+
   it('should remove listeners and shared cache instance on cleanup', () => {
     const eventNames = ['touchstart', 'touchend', 'touchmove', 'touchcancel'];
     const prop = '__AMP_Gestures';