Gist that demonstrates Pop up functionality with aspx markup

SurveyMaint.cs

[PXCopyPasteHiddenView]
public SelectFrom<Contact>.
            Where<Contact.contactType.IsEqual<ContactTypesAttribute.employee>.
                And<Contact.isActive.IsEqual<True>>.
                And<Contact.userID.IsNotNull>>.OrderBy<Asc<Contact.displayName>>.View UsersForAddition;
 
public PXAction<Survey> AddRecipients;
 
[PXButton]
[PXUIField(DisplayName = "Add Recipients", MapViewRights = PXCacheRights.Select,
    MapEnableRights = PXCacheRights.Select)]
public virtual IEnumerable addRecipients(PXAdapter adapter)
{
    if (UsersForAddition.AskExt((graph, viewName) =>
    {
        graph.Views[UsersForAddition.View.Name].Cache.Clear();
        graph.Views[viewName].Cache.Clear();
        graph.Views[viewName].Cache.ClearQueryCache();
        graph.Views[viewName].ClearDialog();
    }, true) != WebDialogResult.OK) 
             	return adapter.Get();
 
    return addUsers(adapter);
}
 
public PXAction<Survey> AddUsers;
 
[PXUIField(DisplayName = "Add", MapEnableRights = PXCacheRights.Select, MapViewRights = PXCacheRights.Select)]
[PXButton(VisibleOnDataSource = false)]
public virtual IEnumerable addUsers(PXAdapter adapter)
{
    var users = UsersForAddition.Select().Where(a => a.GetItem<Contact>().Selected == true).ToList();
 
    foreach (var user in users)
    {
        var surveyUser = new SurveyUser();
        surveyUser.Active = true;
        surveyUser.SurveyID = SurveyCurrent.Current.SurveyID;
        surveyUser.ContactID = user.GetItem<Contact>().ContactID;
        surveyUser = SurveyUsers.Insert(surveyUser);
    }
 
    return adapter.Get();
}

SV201000.aspx

<px:PXDataSource ID="ds" runat="server" Visible="True" Width="100%"
                     TypeName="PX.Survey.Ext.SurveyMaint" PrimaryView="SurveyCurrent">
        <CallbackCommands>
            <px:PXDSCallbackCommand Name="AddRecipients" Visible="False" />
        </CallbackCommands>
    </px:PXDataSource>

<px:PXSmartPanel ID="PanelAddRecipients" runat="server" Key="UsersForAddition" LoadOnDemand="true" Width="1100px" Height="500px"
                     Caption="Select Recipients" CaptionVisible="true" AutoRepaint="true" DesignView="Content" ShowAfterLoad="true">
	    <px:PXGrid ID="grdRecipientContacts" runat="server" DataSourceID="ds" Height="150px" Width="100%" ActionsPosition="Top" SkinID="Inquire" 
                   SyncPosition="True" NoteIndicator="False" FilesIndicator="False" TabIndex="4900" AllowPaging="true">       
            <Levels>
                <px:PXGridLevel DataMember="UsersForAddition">
                    <RowTemplate>
                    </RowTemplate>
                    <Columns>
                        

                        <px:PXGridColumn CommitChanges="true" DataField="Selected" TextAlign="Center" Type="CheckBox" />
                        <px:PXGridColumn DataField="DisplayName" Width="280px" />
                        <px:PXGridColumn DataField="ContactType" />
                        
                        <%--some more columns--%>

                        <px:PXGridColumn DataField="UsrUsingMobileApp" Width="180px" TextAlign="Center" Type="CheckBox" />
                        <px:PXGridColumn DataField="FirstName" Width="180px" />
                        <px:PXGridColumn DataField="LastName" Width="220px" />
                        <px:PXGridColumn DataField="BAccountID_BAccount_acctName" Width="280px" />
                        <px:PXGridColumn DataField="EMail" Width="280px" />
                        <px:PXGridColumn DataField="Phone1" Width="180px" />
                    </Columns>
                </px:PXGridLevel>
            </Levels>
            <AutoSize Enabled="True" MinHeight="150" />
        </px:PXGrid>
        <px:PXPanel ID="pnlButtons" runat="server" SkinID="Buttons">
            <px:PXButton ID="btnAdd" runat="server" CommandSourceID="ds" Text="Add" CommandName="AddUsers" /> <%--as you guessed this is markup of button add--%>
            <px:PXButton ID="btnAddAndClose" runat="server" Text="Add & Close" DialogResult="OK" /> <%--and this is markup of button Add and close. Pay attention to DialogResult part--%>
            <px:PXButton ID="btnCancel" runat="server" DialogResult="Cancel" Text="Cancel" /> <%--and this button just will close the dialog window--%>
        </px:PXPanel>
    </px:PXSmartPanel>