角实例在连接事件中不可用

Question

我正在尝试在连接事件中调用我的角度注入实例或本地实例。但是，每当我进行引用时，就会在运行时抛出错误。

ifCall = false;
 constructor(private rtc: WebrtcService, public api: ApiService, private toastr: ToastrService) { 
  }

someFunction(){
connection.checkPresence(x[0].roomId, function(isRoomEists, roomid) {
        if(isRoomEists) {
          connection.join(roomid);
          if(connection.getAllParticipants().length === 0){
            connection.getAllParticipants().forEach(function(participantId) {
              connection.disconnectWith(participantId);
            });
            // ERROR
            this.api.deleteRooms(roomid);
          }
        }
        else {
            // ERROR
          this.ifCall = false;
          this.api.deleteRooms(roomid);

        }
      });
}
``

core.js:15724 ERROR TypeError: Cannot set property 'ifCall' of undefined
    at home.component.ts:77
    at r.<anonymous> (rtc.min.js:18)
    at r.onack (socket.io.js:8)
    at r.onpacket (socket.io.js:8)
    at r.<anonymous> (socket.io.js:8)
    at r.emit (socket.io.js:6)
    at r.ondecoded (socket.io.js:6)
    at a.<anonymous> (socket.io.js:8)
    at a.r.emit (socket.io.js:6)
    at a.add (socket.io.js:6)