如何使用程序获取或新建一个arcmap对象

在GIS应用中，Arcmap的有些功能在 ArcEngine并不好使，那么使用arcmap进行批处理对于数据处理挺有用的。可是如何在程序中捕获一个已经打开的Arcmap呢？过程下面代码所示：

    Dim app As IApplication = Nothing
    Dim appRot As New AppROT
'寻找打开的ArcMap
    For i As Integer = 0 To appRot.Count - 1
      If TypeOf appRot.Item(i) Is IMxApplication Then
        app = appRot.Item(i)
        Exit For
      End If
    Next
'找不到就新建一个
    If app Is Nothing Then
      Dim pDoc As IDocument = New MxDocument
      app = pDoc.Parent
      app.Visible = True
    End If