Add FAQ about ObjectDataSource controls

AspNetDependencyInjection/AspNetDependencyInjection.WebForms/DiObjectDataSource.cs

@@ -0,0 +1,64 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Web;
+using System.Web.Compilation;
+using System.Web.UI.WebControls;
+
+namespace AspNetDependencyInjection.WebForms
+{
+	/// <summary>
+	/// A drop-in replacement for <see cref="ObjectDataSource" /> controls that enables dependency injection
+	/// instantiation for data sources.
+	///
+	/// To use it, register the control namespace by adding the following element to your web.config file:
+	///
+	/// <c>
+	/// &lt;configuration&gt;
+	///   &lt;system.web&gt;
+	///     &lt;pages&gt;
+	///       &lt;controls&gt;
+	///         ...
+	///         &lt;add tagPrefix="di" namespace="AspNetDependencyInjection.WebForms" assembly="AspNetDependencyInjection" /&gt;
+	///         ...
+	///       &lt;/controls&gt;
+	///     &lt;/pages&gt;
+	///   &lt;/system.web&gt;
+	/// &lt;/configuration&gt;
+	/// </c>
+	///
+	/// Then replace the &lt;asp:ObjectDataSource&gt; tags in your code with &lt;di:DiObjectDataSource&gt; tags.
+	/// </summary>
+	/// <remarks>
+	/// Please make sure your <see cref="ObjectDataSource" /> methods are not marked <see langword="static" />.
+	/// </remarks>
+	public class DiObjectDataSource : ObjectDataSource
+	{
+		/// <summary>
+		/// Background: <see cref="ObjectDataSource" /> controls invoke a `Select` method defined
+		/// in the `Page` object in order to retrieve the data to bind to other controls. This select method is
+		/// usually a <see langword="static" /> method on the containing page, which prevents using DI,
+		/// but can also be an instance method, in which case it instantiates a new `Page` object and calls the method
+		/// on the newly created instance.
+		/// That's the scenario when DI should be possible.
+		///
+		/// Unfortunately it seems that Microsoft never updated the <see cref="ObjectDataSource" /> control
+		/// to use <see cref="HttpRuntime.WebObjectActivator" />,
+		/// so it's not able to instantiate DI-enabled `Page` controls.
+		/// However, it is possible to override its <see cref="ObjectDataSource.ObjectCreating" />
+		/// event to make it work the way we want.
+		/// </summary>
+		public DiObjectDataSource()
+		{
+			// We need to use `BuildManager.GetType` instead of `Type.GetType` because this method is actually
+			// able to look for the type in all of the application assemblies - otherwise we'd be restricted
+			// to the current assembly types.
+
+			this.ObjectCreating += ( sender, args ) =>
+				args.ObjectInstance = HttpRuntime.WebObjectActivator.GetService( BuildManager.GetType(
+					( (ObjectDataSourceView)sender ).TypeName, throwOnError: false, ignoreCase: true ) );
+		}
+	}
+}

GETTING_STARTED.md

@@ -186,6 +186,28 @@ Another advantage of this approach is that if you need to use a `DbContext` insi
 * `WebActivatorEx`'s `PreApplicationStartMethod` (the `PreStart` method in our sample above) runs **before** OWIN's Startup method.
 	* See this StackOverflow post: https://stackoverflow.com/questions/21462777/webactivatorex-vs-owinstartup
 
+### How to deal with `ObjectDataSource` controls
+Background: `ObjectDataSource` controls invoke a `Select` method defined in the `Page` object in order to retrieve the data to bind to other controls. This select method is usually a `static` method on the containing page, which prevents using DI, but can also be an instance method, in which case it instantiates a new `Page` object and calls the method on the newly created instance. That's the scenario when DI should be possible.
+
+Unfortunately it seems that Microsoft never updated the `ObjectDataSource` control to use `HttpRuntime.WebObjectActivator`, so it's not able to instantiate DI-enabled `Page` controls. However, it is possible to override its `ObjectCreating` event to make it work the way we want.
+
+For your convenience, this component includes a custom `ObjectDataSource`-derived control called `DiObjectDataSource` that can be used as a drop-in replacement for basic `ObjectDataSource` controls. To use it, register the control namespace by adding the following element to your `web.config` file:
+```
+<configuration>
+  <system.web>
+    <pages>
+      <controls>
+        ...
+        <add tagPrefix="di" namespace="AspNetDependencyInjection.WebForms" assembly="AspNetDependencyInjection" />
+        ...
+      </controls>
+    </pages>
+  </system.web>
+</configuration>
+```
+Then replace the `<asp:ObjectDataSource>` tags in your code with `<di:DiObjectDataSource>` tags.  
+*Note:* Please make sure your `ObjectDataSource` methods are not marked `static`.
+
 ## Included services
 
 All included services are exposed as interfaces so you can replace them with your own implementation for testing purposes or for different production scenarios. They are listed below: