C# Can'；t在使用“添加用户”之后，在PeopleEditor中以编程方式添加用户帐户；浏览对话框"；

我有一个带有SharePoint PeopleEditor的简单页面： PickerPage.aspx中的代码：

<asp:Content ID="Main" ContentPlaceHolderID="PlaceHolderMain" runat="server">
<table border="0" cellspacing="0" cellpadding="0" class="ms-propertysheet" width="100%">
<wssuc:InputFormSection Title="People Editor" runat="server">
<Template_InputFormControls>
<wssuc:InputFormControl LabelText="Select Users:" runat="server">
<Template_Control>
<SharePoint:PeopleEditor AllowEmpty="true" ValidatorEnabled="true" ID="RespondentPeopleEditor" runat="server" MultiSelect="true" Width="280"
DialogHeight="400" DialogWidth="500" DialogTitle="Choose"
ShowCreateButtonInActiveDirectoryAccountCreationMode="true" SelectionSet="User" />
</Template_Control>
</wssuc:InputFormControl>
</Template_InputFormControls>
</wssuc:InputFormSection>
</table>
<asp:Button runat="server" ID="AddBtn" Text="Add User1" OnClick="AddBtn_Click" UseSubmitBehavior="false" />
</asp:Content>

当我加载我的页面并单击“添加User1”按钮时，User1已成功添加到PeopleEditor。但当我加载页面并使用默认对话框（浏览）在PeopleEditor中添加User2，然后单击按钮添加第二个用户（User1）时，User2仍保留在PeopleEditor中，但User1未添加到PeopleEditor中。

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如何在使用standart添加对话框后以编程方式在PeopleEditor中添加用户？

当我尝试在代码“RespondentPeopleEditor.CommaSeparatedAccounts=accs”后克隆PeopleEditor控件时，新控件会同时拥有两个用户帐户。而在我的控件中，不知何故，新帐户不会添加到此.HiddenSpanData.Value中

public partial class PickerPage2 : LayoutsPageBase
{
    protected PeopleEditor RespondentPeopleEditor;
    protected Label ResultLbl;
    protected Button AddBtn;

    protected void Page_Load(object sender, EventArgs e)
    {}
    protected void AddBtn_Click(object sender, EventArgs e)
    {
        string accs = RespondentPeopleEditor.CommaSeparatedAccounts;
        if (!String.IsNullOrEmpty(accs)) accs += ",";
        accs += "domain\\user1";
        RespondentPeopleEditor.CommaSeparatedAccounts = accs;

    }
}