Ajax Control Toolkit这个控件库内包含一些扩展控件，利用这些扩展控件，可以非常方便的为普通的控件添加Ajax效果，例如，利用AutoCompleteExtender控件，可以为文本框添加自动完成的ajax效果。当然，这并不是本文想讨论的内容。
将Ajax Control Toolkit加入到Visual Studio 2008的工具箱中，并打开一个新的aspx文件，向里面拖入一个TextBox。这时，有趣的事情发生了，在TextBox的SmartTasks面板里，竟然出现了一个“添加扩展程序…”的链接！我又试着拖入一个Button，一个Panel，无一例外的，每个控件的SmartTasks面板的底部都出现了“添加扩展程序…”的链接。
最近我正打算把保存、删除、关闭页面等功能抽象成动作，每一种动作对应一个自定义的Web控件，将某个动作控件附加到目标控件（例如Button）上面之后，目标控件就拥有了诸如保存、删除、关闭页面的功能。如何在WebForm设计器里为一个Button控件方便地附加动作？我想要的正是类似“添加扩展程序…”这样的效果。
开发过自定义服务器控件的朋友应该知道，如果想给控件添加SmartTasks，需要重写ControlDesigner的ActionLists属性，并实现自己的DesignerActionList。显然，一个TextBox并不知道AjaxControlToolkit的存在，所以“添加扩展程序…”这么一个DesignerActionMethodItem并不是它加进来的。那么，.net framework是否提供了某种接口，可以让我们为别的控件“动态的注入”DesignerActionItem呢？
通过对AjaxControlToolKit.dll的研究，我发现这些扩展控件的Designer并不负责提供“添加扩展程序”这个Action，他们只负责提供相应扩展程序对应的扩展内容，所以只能从Visual studio的webform designer作为入口来研究。用reflector打开Microsoft Visual Studio 9.0Common7IDEMicrosoft.Web.Design.Client.dll，找到了IWebSmartTasksProvider接口，该接口有一个GetDesignerActionLists的方法，这个方法的返回值应该就是SmartTasks面板里显示的内容了。这个接口有3个实现类，DataFormDesigner、DataFormXslValueOfDesigner、ElementDesigner。从这三个类的命名上可以推断，ElementDesigner应该是用的最多的实现类了。ElementDesigner的GetDesignerActionLists的方法实现如下：
1: DesignerActionListCollection IWebSmartTasksProvider.GetDesignerActionLists()
2: {
3: DesignerActionListCollection componentActions = null;
4: if (this.Designer != null)
5: {
6: DesignerActionService service = (DesignerActionService) base.DesignerHost.GetService(typeof(DesignerActionService));
7: if (service != null)
8: {
9: componentActions = service.GetComponentActions(this.Designer.Component);
10: }
11: }
12: if (componentActions == null)
13: {
14: componentActions = new DesignerActionListCollection();
15: }
16: return componentActions;
17: }
18:
19:
20:
21:
从上面代码里可以看到最终的DesignerActionListCollection是由System.Design程序集下的System.ComponentModel.Design.DesignerActionService类的GetComponentActions决定的，Microsoft.Web.Design.Client.dll下的Microsoft.Web.Design.WebFormDesigner+WebDesignerActionService继承了该类，他的实现如下：
1: protected override void GetComponentDesignerActions(IComponent component, DesignerActionListCollection actionLists)
2: {
3: Control control = component as Control;
4: ElementDesigner parent = null;
5: if (control != null)
6: {
7: parent = ElementDesigner.GetElementDesigner(control);
8: }
9: if ((parent == null) || !parent.InTemplateMode)
10: {
11: base.GetComponentDesignerActions(component, actionLists);
12: if ((parent != null) && (parent.Designer != null))
13: {
14: ControlDesigner designer = parent.Designer as ControlDesigner;
15: if ((designer != null) && (designer.AutoFormats.Count > 0))
16: {
17: actionLists.Insert(0, new AutoFormatActionList(parent));
18: }
19: }
20: if ((parent != null) && (parent.Element != null))
21: {
22: IWebDataFormElementCallback dataFormElementCallback = parent.Element.GetDataFormElementCallback();
23: if (dataFormElementCallback != null)
24: {
25: DataFormElementActionList list = new DataFormElementActionList(parent, parent.Control, dataFormElementCallback);
26: actionLists.Add(list);
27: DataFormElementActionList.ModifyActionListsForListControl(actionLists, list);
28: }
29: }
30: if (((parent != null) && (parent.Designer != null)) && parent.DocumentDesigner.ExtenderControlHelper.ProvidesActionLists)
31: {
32: parent.DocumentDesigner.ExtenderControlHelper.AddActionLists(parent, actionLists);
33: }
34: }
35: if ((parent != null) && (parent.TemplateEditingUI != null))
36: {
37: actionLists.Add(new TemplateEditingActionList(parent.TemplateEditingUI, parent.Element));
38: }
39: }
40:
41:
42:
43:
这个方法里，有这么一段：
1: if (((parent != null) && (parent.Designer != null)) && parent.DocumentDesigner.ExtenderControlHelper.ProvidesActionLists)
2: {
3: parent.DocumentDesigner.ExtenderControlHelper.AddActionLists(parent, actionLists);
4: }
看来“添加扩展程序”这个action就是在这里加进去的了。继续查看ExtenderControlHelper.AddActionLists的实现：
1: public void AddActionLists(ElementDesigner element, DesignerActionListCollection lists)
2: {
3: lists.Add(new ControlExtenderActionList(element));
4: ExtenderControl component = element.Designer.Component as ExtenderControl;
5: Control control = element.Designer.Component as Control;
6: if ((component == null) && (control != null))
7: {
8: IExtenderInformationService service = (IExtenderInformationService) control.Site.GetService(typeof(IExtenderInformationService));
9: if (service != null)
10: {
11: foreach (Control control3 in service.GetAppliedExtenders(control))
12: {
13: lists.Add(new HoistedExtenderActionList(element.Designer, control3));
14: }
15: }
16: }
17: }
18:
19:
20:
21:
这个方法里的第一句是lists.Add(new ControlExtenderActionList(element))，ControlExtenderActionList继承了System.ComponentModel.Design.DesignerActionList，他的GetSortedActionItems方法定义如下：
1: public override DesignerActionItemCollection GetSortedActionItems()
2: {
3: Control component = (Control) this._htmlDesigner.Component;
4: DesignerActionItemCollection items = new DesignerActionItemCollection();
5: IExtenderInformationService service = (IExtenderInformationService) component.Site.GetService(typeof(IExtenderInformationService));
6: string category = SR.GetString(SR.Ids.SmartTasksLabelExtenderSection, CultureInfo.CurrentUICulture);
7: if (service.IsControlExtendible(component))
8: {
9: string displayName = SR.GetString(SR.Ids.SmartTasksAddExtender, CultureInfo.CurrentUICulture);
10: items.Add(new DesignerActionMethodItem(this, "AddExtender", displayName, category, true));
11: }
12: if (service.IsControlExtended(component))
13: {
14: string str3 = SR.GetString(SR.Ids.SmartTasksRemoveExtender, CultureInfo.CurrentUICulture);
15: items.Add(new DesignerActionMethodItem(this, "RemoveExtender", str3, category, true));
16: }
17: return items;
18: }
19:
这下清楚了，“添加扩展程序”这个action，是在Visual studio的web form设计器里，写死进去的，.net framework并没有提供相应接口来供我们添加类似的action。但是我想要的效果是增加一个“添加动作”的action，所以我不能参考AjaxControlToolkit的方法去实现，应该要寻找别的方法。
回过头来，重新查看Microsoft.Web.Design.WebFormDesigner+WebDesignerActionService类的GetComponentActions方法，找到基类System.Web.UI.Design.WebFormsDesignerActionService（在System.Design程序集下）的定义，如下：
1: protected override void GetComponentDesignerActions(IComponent component, DesignerActionListCollection actionLists)
2: {
3: if (component == null)
4: {
5: throw new ArgumentNullException("component");
6: }
7: if (actionLists == null)
8: {
9: throw new ArgumentNullException("actionLists");
10: }
11: IServiceContainer site = component.Site as IServiceContainer;
12: if (site != null)
13: {
14: DesignerCommandSet service = (DesignerCommandSet) site.GetService(typeof(DesignerCommandSet));
15: if (service != null)
16: {
17: DesignerActionListCollection lists = service.ActionLists;
18: if (lists != null)
19: {
20: actionLists.AddRange(lists);
21: }
22: }
23: if ((actionLists.Count == 0) || ((actionLists.Count == 1) && (actionLists[0] is ControlDesigner.ControlDesignerActionList)))
24: {
25: DesignerVerbCollection verbs = service.Verbs;
26: if ((verbs != null) && (verbs.Count != 0))
27: {
28: DesignerVerb[] array = new DesignerVerb[verbs.Count];
29: verbs.CopyTo(array, 0);
30: actionLists.Add(new DesignerActionVerbList(array));
31: }
32: }
33: }
34: }
35:
36:
37:
38:
通过研究上述代码，可以看到DesignerActionListCollection是由DesignerCommandSet这个service的ActionLists属性负责返回的，而这个service是从component的Site里面取得的，只要我另外写一个DesignerCommandSet，并且保证从Site里面取出的DesignerCommandSet是我写的这个service就可以了。终于找到了切入点，下面是具体做法。
首先，创建一个类继承DesignerCommandSet，如下：
1: public class MyDesignerCommandSet : DesignerCommandSet
2: {
3: private ComponentDesigner _componentDesigner;
4:
5: public MyDesignerCommandSet(ComponentDesigner componentDesigner)
6: {
7: _componentDesigner = componentDesigner;
8: }
9:
10: public override ICollection GetCommands(string name)
11: {
12: if (name.Equals("ActionLists"))
13: {
14: return GetActionLists();
15: }
16: return base.GetCommands(name);
17: }
18:
19: private DesignerActionListCollection GetActionLists()
20: {
21: //先取得控件原有的DesignerActionLists
22: DesignerActionListCollection lists = _componentDesigner.ActionLists;
23:
24: //增加“添加动作”这个DesignerActionList
25: lists.Add(new ActionList(_componentDesigner));
26: return lists;
27: }
28:
29: internal class ActionList : DesignerActionList
30: {
31: private DesignerActionItemCollection _actions;
32:
33: public ActionList(IDesigner designer)
34: : base(designer.Component)
35: {
36: }
37: public override DesignerActionItemCollection GetSortedActionItems()
38: {
39: if (_actions == null)
40: {
41: const string actionCategory = "Actions";
42: _actions = new DesignerActionItemCollection();
43: _actions.Add(new DesignerActionMethodItem(this, "AddAction", "添加动作...", actionCategory, true));
44: }
45: return _actions;
46: }
47:
48: public void AddAction()
49: {
50: //添加动作的逻辑，略
51: }
52: }
53: }
下一步就是如何使component的Site这个ServiceProvider返回自己的这个service。方法是自己写一个Site，并使Component的Site变成自己写的SIte类的对象。
自己写的Site类的定义如下：
1: public class SiteProxy : ISite, IServiceContainer
2: {
3: private ISite _site;
4: private ComponentDesigner _designer;
5:
6: public SiteProxy(ISite site, ComponentDesigner designer)
7: {
8: _site = site;
9: _designer = designer;
10:
11: }
12:
13: #region ISite 成员
14:
15: public IComponent Component
16: {
17: get { return _site.Component; }
18: }
19:
20: public System.ComponentModel.IContainer Container
21: {
22: get { return _site.Container; }
23: }
24:
25: public bool DesignMode
26: {
27: get { return _site.DesignMode; }
28: }
29:
30: public string Name
31: {
32: get { return _site.Name; }
33: set { _site.Name = value; }
34: }
35:
36: #endregion
37:
38: #region IServiceProvider 成员
39:
40: public object GetService(Type serviceType)
41: {
42: object service = _site.GetService(serviceType);
43:
44: if (serviceType == typeof(DesignerCommandSet) && !(_designer.Component is ExtenderControl))
45: {
46: if (service == null || !(service is MyDesignerCommandSet))
47: {
48: if (service != null)
49: {
50: RemoveService(typeof(DesignerCommandSet));
51: }
52: //返回自己写的DesignerCommandSet
53: service = new MyDesignerCommandSet(_designer);
54: AddService(typeof(DesignerCommandSet), service);
55: }
56: }
57: return service;
58: }
59:
60: #endregion
61:
62: #region IServiceContainer 成员
63:
64: public void AddService(Type serviceType, ServiceCreatorCallback callback, bool promote)
65: {
66: (_site as IServiceContainer).AddService(serviceType, callback, promote);
67: }
68:
69: public void AddService(Type serviceType, ServiceCreatorCallback callback)
70: {
71: (_site as IServiceContainer).AddService(serviceType, callback);
72: }
73:
74: public void AddService(Type serviceType, object serviceInstance, bool promote)
75: {
76: (_site as IServiceContainer).AddService(serviceType, serviceInstance, promote);
77: }
78:
79: public void AddService(Type serviceType, object serviceInstance)
80: {
81: (_site as IServiceContainer).AddService(serviceType, serviceInstance);
82: }
83:
84: public void RemoveService(Type serviceType, bool promote)
85: {
86: (_site as IServiceContainer).RemoveService(serviceType, promote);
87: }
88:
89: public void RemoveService(Type serviceType)
90: {
91: (_site as IServiceContainer).RemoveService(serviceType);
92: }
93:
94: #endregion
95: }
在这个Site的GetService方法中，判断要get的service类型，如果是DesignerCommandSet，就返回自己创建的MyDesignerCommandSet。
下一步是如何使component的Site变成自己写的SiteProxy。一种方法是新增一种自定义控件，在该控件的ControlDesigner的Initialize方法中改变Container中其他控件的Site，只需要向WebForm中拖入该控件，就可以改变其他控件的Site；另外一种方法是写一个vs package，在package中捕获web form designer的相应事件。下面介绍第一种做法：
新增一个继承自Control的控件，叫做ActionManager，这个控件不用添加任何功能，只需要为它制作ControlDesigner。它的ControlDesigner类主要代码如下：
1: public class ActionManagerDesigner : ControlDesigner
2: {
3: private IDesignerHost _host;
4: private IDictionary<IComponent, ISite> _components;
5:
6: public override void Initialize(IComponent component)
7: {
8: base.Initialize(component);
9:
10: _components = new Dictionary<IComponent, ISite>();
11:
12: _host = GetService(typeof(IDesignerHost)) as IDesignerHost;
13: if (_host != null)
14: {
15: //替换已有控件的Site
16: ProcessComponent();
17:
18: IComponentChangeService service =
19: _host.GetService(typeof(IComponentChangeService)) as IComponentChangeService;
20: if (service != null)
21: {
22: service.ComponentAdded += ComponentAdded;
23: service.ComponentRemoving += ComponentRemoving;
24: }
25: }
26: }
27:
28: #region ProcessComponent
29:
30: private void ProcessComponent()
31: {
32: ComponentCollection components = _host.Container.Components;
33: foreach (IComponent component in components)
34: {
35: if (component is ActionControl)
36: continue;
37: ProcessComponentSite(component);
38: }
39: }
40:
41: #endregion
42:
43: #region 替换Site
44:
45: /// <summary>
46: /// 替换Component原来的Site，换成SiteProxy
47: /// </summary>
48: private void ProcessComponentSite(IComponent component)
49: {
50: ComponentDesigner designer = _host.GetDesigner(component) as ComponentDesigner;
51: _components[component] = component.Site;
52: component.Site = new SiteProxy(component.Site, designer);
53: }
54:
55: /// <summary>
56: /// 恢复Component原来的site
57: /// </summary>
58: /// <param name="component"></param>
59: private void RestoreComponentSite(IComponent component)
60: {
61: if (_components.ContainsKey(component))
62: {
63: ISite site = _components[component];
64: component.Site = site;
65: _components.Remove(component);
66: }
67: }
68:
69: #endregion
70:
71: #region on Component Add, remove, change
72:
73: private void ComponentRemoving(object sender, ComponentEventArgs e)
74: {
75: if (e.Component is ActionControl)
76: {
77: return;
78: }
79: //在删除Component的时候，要把他的Site属性还原回去，否则DesignerHost中还会保留原来的Site,
80: //这样再添加同名的Component的时候，会报“重复的组件名称”错误
81: RestoreComponentSite(e.Component);
82: }
83:
84:
85: private void ComponentAdded(object sender, ComponentEventArgs e)
86: {
87: if (e.Component is ActionControl)
88: {
89: return;
90: }
91: ProcessComponentSite(e.Component);
92: }
93:
94: #endregion
95:
96: #region dispose
97:
98: protected override void Dispose(bool disposing)
99: {
100: if (_host != null)
101: {
102: IComponentChangeService service =
103: _host.GetService(typeof(IComponentChangeService)) as IComponentChangeService;
104: if (service != null)
105: {
106: service.ComponentAdded -= ComponentAdded;
107: service.ComponentRemoving -= ComponentRemoving;
108: }
109: }
110: base.Dispose(disposing);
111: }
112:
113: #endregion
114: }
至此，只要把一个ActionManager控件拖入到web form designer中，就可以在其他控件的smart task面板上看到“添加动作…”这个链接了。但是这种方式需要在webform designer中放入额外的一个控件，该控件只在设计时有用，在运行时则无用，看起来比较奇怪，所以最好的做法是第二种做法，即开发一个vs package，在package的Initialize方法中，注册IDesignerEventService的DesignerCreated事件，进而通过IDesignerHost和IComponentChangeService达到更改控件Site的目的，具体实现和上面差不多，就不再写了。