MicroStation .NET: Enumerating DGN Models

DgnPlatformNet

Introduction

This article is for C# developers who want to write an AddIn for MicroStation CONNECT. It is an introduction to the coding required to enumerate DGN models contained in a DGN file.

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Open a DGN File for Reading

The purpose of the code below is to obtain model information from a DGN file or cell library. We don't want to open the file to edit any model — opening the file for read-only is fine. A consequence of this approach is that the user does not see the file we've opened: MicroStation continues to show the active DGN model with no change.

IDisposable

A pecularity of this code is the requirement to create a DgnFileOwner as an intermediate step. The DgnPlatformNET tells us that DgnFileOwner implements IDisposable and moreover that we must call DgnFileOwner.Dispose() when finished. The exception-safe way to ensure that happens is to wrap the object in a using statement.

Models and Cells

A DGN file is a container. It contains one or more models. Each DGN model contains graphic elements.

A DGN file can be a cell library, in which case the models it contains are marked 'can be placed as cell' by the library designer. My requirement to find the cells in a cell library prompted this article: I wanted to enumerate the cells in a DGN cell library, which is the same process as enumerating the models in a DGN file.

The process to enumerate models is …

Open a DGN file for reading
Get the list of models in the DGN file

The process to enumerate cells is similar …

Open a DGN cell library for reading
Get the list of models in the library
Check whether the model is intended to be used as a cell

Namespaces

MicroStation .NET code lives in the Bentley namespace, or a namespace within the scope of Bentley. In this example we're using classes and methods in the Bentley.DgnPlatformNET namespace. Put the following using statements in any C# code module that uses a class in those namespaces …

using Bentley.DgnPlatformNET;

Open a DGN file for Reading

This is a multi-step process (if anyone can tell me a simpler way, I'll be happy) …

Create a DgnDocument
Create a read-only DgnFileOwner
Get the DgnFile from the DgnFileOwner
Get a ModelIndexCollection from the DgnFile
Do something with each ModelIndex in the ModelIndexCollection
Dispose of the DgnFileOwner

Here's the code that implements the above …

using (DgnDocument document = DgnDocument.CreateForLocalFile(fileName))
  using (DgnFileOwner dgnFileOwner = DgnFile.Create(document, DgnFileOpenMode.ReadOnly))
  {
    DgnFile file = dgnFileOwner.DgnFile;
    StatusInt status;
    file.LoadDgnFile(out status);
    ModelIndexCollection models = file.GetModelIndexCollection();
    foreach (ModelIndex model in models)
    {
     msg = $"Model '{model.Name}' Descr '{model.Description}' in DGN file '{fileName}'";
     MessageCenter.Instance.ShowMessage(MessageType.Debug, msg, msg, MessageAlert.None);
    }
    // dgnFileOwner.Dispose() called automatically when wrapped in using statement
  }

Open a Cell Library for Reading

This is a multi-step process similar to the above …

Create a DgnDocument
Create a read-only DgnFileOwner
Get the DgnFile from the DgnFileOwner
Get a ModelIndexCollection from the DgnFile
Do something with each ModelIndex in the ModelIndexCollection
- For example, check the the model can be used as a cell
Dispose of the DgnFileOwner