RevitAPI: 注意Revit 2016事件注册和注销行为的改变

在以前的Revit版本中， 我们可以在一个非模态对话框中注册或者注销一个事件，但是Revit 2016做了一些改变，不再允许这样做，凡是在非Revit主线程里面的注册或者注销事件，系统会抛出异常，如果您没有捕获这个异常，将会导致系统崩溃。

官方的原话是这样的：

API events - behavioral change

Although the Revit API has never officially supported such a work-flow it is now enforced that registering to and unregistering from events must happen while executing on the main thread. An exception will be thrown if an external application attempts to register to (or unregister from) events from outside of valid API context.

解决办法：

• 使用模态对话框，或者尽量保证事件在ExternalCommand的Execute函数或者ExternalApplication的OnStartup函数里面注册。
• 如果一定要使用非模态对话框，那么请使用ExternalEvent事件的Raise函数，强迫程序进入Revit主线程，然后在里面进行注册事件。

代码示例：

首先定义一个类实现IExternalEventHandler，在Execute函数里面我们注册一个事件。

public class EventRegisterHandler : IExternalEventHandler{    public void Execute(UIApplication app)    {        app.Application.DocumentChanged += Application_DocumentChanged;    }    void Application_DocumentChanged(object sender, Autodesk.Revit.DB.Events.DocumentChangedEventArgs e)    {        // do your stuff    }    public string GetName()    {        return "EventRegisterHandler";    }}

在需要执行注册的时候，创建一个ExternalEvent的实例并调用它的Raise函数，例如，点击一个按钮实现注册，可以使用如下代码：

private void button1_Click(object sender, EventArgs e){    ExternalEvent _exEvent = null;    EventRegisterHandler _exEventHandler = null;    _exEventHandler = new EventRegisterHandler();    _exEvent = ExternalEvent.Create(_exEventHandler);    _exEvent.Raise();}

2016/3/8 更新：

有人指出button1_Click函数会抛出异常

Autodesk.Revit.Exceptions.InvalidOperationException: Attempting to create an ExternalEvent outside of a standard API execution

确实是一个问题。解决方法也比较简单，就是不要在非模态对话框里面创建ExternanlEvent，而是在IExternalCommand的Execute函数，或者IExternalApplication的OnStartup函数里面创建。

下面是一个完整例子的代码，用户运行命令EventRegistrationInModelessDialogViaExternalEvent之后可以点击非模态对话框上的按钮来注册或者注销DocumentChanged事件。

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using Autodesk.Revit.ApplicationServices;using Autodesk.Revit.Attributes;using Autodesk.Revit.DB;using Autodesk.Revit.UI;using System.Windows.Forms;namespace TestScript{    [TransactionAttribute(TransactionMode.Manual)]    public class EventRegistrationInModelessDialogViaExternalEvent         : IExternalCommand    {        public Document doc;        public Autodesk.Revit.ApplicationServices.Application RevitApp;        ExternalEvent _exEvent;        public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)        {            EventRegisterHandler _exeventHander = new EventRegisterHandler();            _exEvent = ExternalEvent.Create(_exeventHander);            MyForm form = new MyForm();            form.ExEvent = _exEvent;            form.Show();            return Result.Succeeded;        }    }    public class MyForm : System.Windows.Forms.Form    {        public MyForm()            : base()        {            Button btn = new Button();            btn.Text = "Toggle DocumentChanged Event Registration";            btn.Click += btn_Click;            btn.Width = 250;            this.Controls.Add(btn);        }        public ExternalEvent ExEvent { get; set; }        void btn_Click(object sender, EventArgs e)        {            if (ExEvent != null)                ExEvent.Raise();            else                MessageBox.Show("external event handler is null");        }    }    public class EventRegisterHandler : IExternalEventHandler    {        public bool EventRegistered { get; set; }        public void Execute(UIApplication app)        {            if (EventRegistered)            {                EventRegistered = false;                app.Application.DocumentChanged -= Application_DocumentChanged;            }            else            {                EventRegistered = true;                app.Application.DocumentChanged += Application_DocumentChanged;            }        }        void Application_DocumentChanged(object sender,             Autodesk.Revit.DB.Events.DocumentChangedEventArgs e)        {            var sb = new StringBuilder();            var added = "added:" + e.GetAddedElementIds()                .Aggregate("", (ss, el) => ss + "," + el).TrimStart(',');            var modified = "modified:" + e.GetModifiedElementIds()                .Aggregate("", (ss, el) => ss + "," + el).TrimStart(',');            var deleted = "deleted:" + e.GetDeletedElementIds()                .Aggregate("", (ss, el) => ss + "," + el).TrimStart(',');            sb.AppendLine(added);            sb.AppendLine(modified);            sb.AppendLine(deleted);            TaskDialog.Show("Changes", sb.ToString());        }        public string GetName()        {            return "EventRegisterHandler";        }    }}