javascript - 回调函数在 JavaScript 中被多次触发

Question

当由于某种原因调用两次回调函数时，我遇到了这样的问题。在这里，我将尝试显示调用堆栈：

Provider.prototype._delegateEvent = function(event, collaboration) {
switch (event.type) {
    case EventTypes.START_SCREEN_SHARING:
        this._isScreenSharingActive = true;
        this._isScreenSharingEnding = false;

        //STEP 1 (addOnContentSharingStartedCallback will be called)
        this.contentSharingHandler.startScreenSharing(collaboration, event); //starting screensharing and addOnContentSharingStartedCallback will be called later
        break;
}};



  startScreenSharing: function(collaboration, startEvent) {
    var startingParticipant = this._getParticipant(collaboration, startEvent);
    var sharingState = collaboration._contentSharing._contentSharingService._sharingState;
    collaboration._contentSharing._contentSharingService._sharingState = Collaboration.ContentSharingState.SHARING;
    if (
        collaboration._contentSharing._isPaused === true &&
        sharingState !== Collaboration.ContentSharingState.NOT_SHARING
    ) {

        //addOnContentSharingResumedCallback will be called
        collaboration._contentSharing._isPaused = false;
        collaboration._contentSharing._onContentSharingResumedCallbacks.fire(collaboration._contentSharing, startingParticipant);
    } else {
        // STEP 2(addOnContentSharingStartedCallback will be called)
        collaboration._contentSharing._onContentSharingStartedCallbacks.fire(collaboration._contentSharing, startingParticipant);
    }
},

(function(angular) {
        'use strict';

        angular
            .module('collaboration')
            .controller('ContentSharingManagementController', ContentSharingManagementController);

        ContentSharingManagementController.$inject = ['promisify', '$scope', '$timeout', ];

        function ContentSharingManagementController(promisify, $scope, $timeout) {
            var vm = this;
            vm.isPaused = false;
            vm.isReceivingPaused = false;
            vm.isStarted = false;
            activate();

            function activate() {//STEP 3
                vm.contentSharing.addOnContentSharingStartedCallback(function() {
                    console.log("addOnContentSharingStartedCallback is called");
                    vm.isStarted = true;
                    showPreview();
                    $scope.$apply();
                });

                vm.contentSharing.addOnContentSharingEndedCallback(function() {
                    console.log("addOnContentSharingEndedCallback is called");
                    vm.isStarted = false;
                    vm.isPaused = false;
                    window.removeEventListener('message', screenSharingListener);
                    window.removeEventListener('message', windowSharingListener);
                    $scope.$applyAsync();
                });

                vm.contentSharing.addOnContentSharingPausedCallback(function() {
                    console.log("addOnContentSharingPausedCallback is called");
                    vm.isPaused = true;
                    $scope.$apply();
                });
                vm.contentSharing.addOnContentSharingResumedCallback(function() {
                    console.log("addOnContentSharingResumedCallback is called");
                    vm.isPaused = false;
                    $scope.$apply();
                });
            }
        }

调用回调函数时我做错了什么？什么会对它被调用两次的事实产生影响？

脚步：

1. 调用函数 _delegateEvent
2. 调用 startScreenSharing
3. 调用 activate() 函数，然后调用回调函数 addOnContentSharingEndedCallback