Here is what i have problem

i have following code :

  //Get All master record
        entryE_QuestMaster = new ObservableCollection<E_QuestMaster>();
        QuestVM.getExamsMasterbyExamID(eUtility.ConvertInt32(this.txtID.Text), ref entryE_QuestMaster);
        //

        //Loop to show questions
        int iNumber=1;
        foreach (var oIn in entryE_QuestMaster)
        {
            Node subNode = new Node();
            subNode.Content = oIn.e_Question;
            subNode.Name = "Quest_" + iNumber.ToString().Trim();
            subNode.Tag = oIn.e_QID.ToString();
            subNode.Icon = "/Images/Number/" + iNumber.ToString().Trim() + ".gif";
            iNumber++;
            this.tvMainNode.Nodes.Add(subNode);
        }

here is async method calling wcf service

  /// <summary>
    /// 
    /// </summary>
    /// <param name="ID"></param>
    public void getExamsMasterbyExamID(int ID, ref ObservableCollection<E_QuestMaster> iCollectionData)
    {
        ObservableCollection<E_QuestMaster> iCollectionDataResult = iCollectionData;
        eLearningDataServiceClient client = new eLearningDataServiceClient();
        client.getExamsMasterCompleted+=(s,e)=>
            {
                iCollectionDataResult = e.Result;
            };
        client.getExamsMasterAsync(ID);
    }

problem : when ever system run --> QuestVM.getExamsMasterbyExamID(eUtility.ConvertInt32(this.txtID.Text), ref entryE_QuestMaster);

its does not wait till i get e.result its just move to next line of code which is foreach loop.

plssss help any one or give idea with sample code what should i do to wait till e.result

i wanted to some how wait till i get e.result

any idea ?