WPF vb.net 线程更新UI

'定义委托
    Delegate Sub Gxdjs(ByVal data As String)
    Private Sub UpdateStatus(ByVal n As String)
        Dispatcher.Invoke(New Gxdjs(AddressOf Cdjs), n) '用Invoke跨线程更新UI
    End Sub
    Private Sub Cdjs(ByVal data As String) '这里要和委托定义时的参数保持一致
        lb_Status.Text = data
    End Sub

'引用
Dim Msg As String = "正在下载" + filename + "......"
UpdateStatus(Msg)
APP.DoEvents()

Imports System.Windows.Threading

Partial Class APP
    Inherits Application
    Private Shared exitFrameCallback As New DispatcherOperationCallback(AddressOf ExitFrame)
    Public Shared Sub DoEvents()

        Dim nestedFrame = New DispatcherFrame()
        Dim exitOperation = Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.Background, exitFrameCallback, nestedFrame)
        Dispatcher.PushFrame(nestedFrame)

        If exitOperation.Status <> DispatcherOperationStatus.Completed Then
            exitOperation.Abort()

        End If
    End Sub
    Private Shared Function ExitFrame(ByVal state As Object) As Object


        Dim frame As DispatcherFrame = state
        frame.Continue = False
        Return Nothing
    End Function

End Class