如何将字符串类型转换为任务类型

我有一个由某些任务组成的xml节点字符串，以及一个项目列表字符串，我正在迭代任务和项目列表，并调用另一个类的函数并传递任务和项目列表，但它给了我best overloaded method and it has some invalid argument的错误。我假设这是一个类型转换错误。

下面是我的代码:

private void addtask(object sender,RoutedEventArgs e)
    {
        foreach (object item in tasklistBox.Items)
        {
            var listBoxItem = tasklistBox.ItemContainerGenerator.ContainerFromItem(item);
            var myContentPresenter = FindVisualChild<ContentPresenter>(listBoxItem);
            var myDataTemplate = myContentPresenter.ContentTemplate;
            var mydata = (System.Windows.Controls.Label)myDataTemplate.FindName("tasklabel", myContentPresenter);
            var xmlElement = (XmlElement)mydata.Content;
            //System.Windows.Forms.MessageBox.Show(xmlElement.InnerText);
            foreach (Harvest_Project item1 in Globals._globalController.harvestManager._PROJECTLIST)
            {
                Globals._globalController.harvestManager.assignTaskToProject(xmlElement.InnerText,item1);
            }
        }
    }

和我正在调用的另一个类的函数:

public void assignTaskToProject(Harvest_Task task, Harvest_Project project)
    {
        Console.WriteLine("Assigning Task to Project");
        string assignXML = "<task>" +
                                "<id type='"integer'">" + task._id + "</id>  " +
                           "</task>";
        sendPOSTRequest(uri + _GETALLPROJECTS + "/" + project._id + "/task_assignments", assignXML);
    }

Harvest_Task类在这里:

private bool _billable_by_default;
    private bool _deactivated;
    private float _default_hourly_rate=0;
    public int _id { get; set; }
    private bool _is_default;
    public string _name { get; set; }
    private DateTime _created_at;
    private DateTime _updated_at;
    private XmlNode _node;
    public Harvest_Task()
    { }
    public Harvest_Task(XmlNode node)
    {
        this._node = node;
        this._name = node.SelectSingleNode("name").InnerText;

        this._created_at = Harvest_Base.storeTime(node.SelectSingleNode("created-at").InnerText);
        this._updated_at = Harvest_Base.storeTime(node.SelectSingleNode("updated-at").InnerText);
        this._is_default = bool.Parse(node.SelectSingleNode("is-default").InnerText);
        this._deactivated = bool.Parse(node.SelectSingleNode("deactivated").InnerText);
        float.TryParse(node.SelectSingleNode("default-hourly-rate").InnerText,out this._default_hourly_rate);
        this._id = int.Parse(node.SelectSingleNode("id").InnerText);

    }
    public Harvest_Task(string name, float defaultHourlyRate)
    {
        this._name = name;
        this._default_hourly_rate = defaultHourlyRate;
    }
    public string createXMLAddEntry()
    {
        string returnXML = "<task>" +
                                "<billable-by-default type='"boolean'">true</billable-by-default>" +
                                "<default-hourly-rate type='"decimal'">"+this._default_hourly_rate+"</default-hourly-rate>" +
                                "<is-default type='"boolean'">true</is-default>" +
                                "<name>" + this._name + "</name>  " +
                           "</task>";

        return returnXML;
    }

Harvest_Project类在这里

    public string _name { get; set; }
    private DateTime _over_budget_notified_at;
    private bool _billable;
    private DateTime _created_at;
    private bool _active;
    private enum _bill_by { Tasks, People, none };
    public int _client_id = 0;
    private string _code;
    private string _notes;
    private enum _budget_by { project, project_cost, task, person, none };
    private float _budget = 0; //Budget in hrs
    private DateTime _latest_record_at;
    private DateTime _earliest_record_at;
    private int _fees = 0;
    public int _id { get; set; }
    private DateTime _updated_at;
    private XmlNode _node;
    public int getId() { return this._id; }
    public Harvest_Project(XmlNode node)
    {
        this._node = node;
        this._name = node.SelectSingleNode("name").InnerText;
        this._created_at = storeTime(node.SelectSingleNode("created-at").InnerText);
        this._updated_at = storeTime(node.SelectSingleNode("updated-at").InnerText);
        this._over_budget_notified_at = storeTime(node.SelectSingleNode("over-budget-notified-at").InnerText);
        this._latest_record_at = storeTime(node.SelectSingleNode("hint-latest-record-at").InnerText);
        this._earliest_record_at = storeTime(node.SelectSingleNode("hint-earliest-record-at").InnerText);
        this._billable = bool.Parse(node.SelectSingleNode("billable").InnerText);
        try
        {
            this._id = Convert.ToInt32(getXmlNode("id", node));
            this._client_id = Convert.ToInt32(getXmlNode("client-id", node));
            this._budget = float.Parse(getXmlNode("budget", node));
            this._fees = Convert.ToInt32(getXmlNode("fees", node));
        }
        catch (OverflowException e)
        {
            Console.WriteLine("The number cannot fit in an Int32.");
        }
        catch (FormatException e)
        {
            Console.WriteLine("The string is not a valid integer");
        }
        this._code = node.SelectSingleNode("code").InnerText;
        this._notes = node.SelectSingleNode("notes").InnerText;

    }

这个函数有Harvest_task和Harvest_Project类，我正在调用这个函数，但无法调用。这行给出错误

Globals._globalController.harvestManager.assignTaskToProject(xmlElement.InnerText,item1);使用什么转换?我卡住了

帮忙吗?由于

foreach (Harvest_Project item1 in Globals._globalController.harvestManager._PROJECTLIST)
{
    Globals._globalController.harvestManager.assignTaskToProject(new Harvest_Task(xmlElement), item1);
}

class HarvestTaskConverter {
    public Harvest_Task Convert(string text) {
        var task = new Harvest_Task();
        // parse the text here
        return task;
    }
}