2011-08-24 Dependency Injection in ASP.NET WebForms

2011-08-24 dependency-injection-in-asp.net-webforms

# Title: Dependency Injection in ASP.NET WebForms
# Author: Mikael Lundin
# Link: http://blog.mikaellundin.name/2011/08/24/dependency-injection-in-asp.net-webforms.html

Product.aspx

<form id="form1" runat="server">
<div>
    <h1>Products</h1>
    <h2>Electronics</h2>
    <asp:DataGrid
        runat="server"
        DataSource='<%# GetByType("Electronics") %>' 
        AutoGenerateColumns="true" OnLoad="DataBind" />
    <h2>Candy</h2>
    <asp:DataGrid
        runat="server"
        DataSource='<%# GetByType("Candy") %>' 
        AutoGenerateColumns="true" OnLoad="DataBind" />
</div>
</form>

Product.aspx.cs

public partial class ProductList : System.Web.UI.Page
{
 [Dependency]
 public IRepository<Product> Repository { get; set; }
 
 protected void Page_Load(object sender, EventArgs e)
 {
 }
 
 protected IEnumerable<Product> GetByType(string type)
 {
  return Repository.Get(p => p.Type == type);
 }
 
 protected void DataBind(object sender, EventArgs e)
 {
  ((Control) sender).DataBind();
 }
}

ProductListCodeBehindShould.cs

[TestFixture]
public class ProductListCodeBehindShould
{
 private class Template : ProductList
 {
  public Template()
  {
   Repository = new StubRepository();
  }
 
  public new IEnumerable<Product> GetByType(string type)
  {
   return base.GetByType(type);
  }
 
  private class StubRepository : IRepository<Product>
  {
   public IEnumerable<Product> Get(Func<Product, bool> criteria)
   {
    return new[]
    {
     new Product("Stereo", 120.0, "Electronics"),
     new Product("Candy bar", 1.2, "Candy"),
     new Product("Soda", 1.8, "Candy"),
     new Product("Deep fried snickers bar", 0.2, "Candy")
    }.Where(criteria);
   }
  }
 }
 
 [TestCase("Electronics", 120.0)]
 [TestCase("Candy", 3.2)]
 public void GetProductsBySpecifiedType(string type, double totalPrice)
 {
  /* Setup */
  var template = new Template();
 
  /* Test */
  var products = template.GetByType(type);
 
  /* Assert */
  Assert.That(products.Sum(p => p.Price), Is.EqualTo(totalPrice));
 }
}

UnityHttpModule.cs

public class UnityHttpModule : IHttpModule
{
 private const string NamespacePrefix = "DIWebFormsExample";
  
 public void Init(HttpApplication context)
 {
  context.PreRequestHandlerExecute += OnPreRequestHandlerExecute;
 }
 
 public void Dispose()
 {
  // Nothing to dispose
 }
 
 // Get the controls in the page's control tree excluding the page itself
 private static IEnumerable GetControlTree(Control root)
 {
  foreach (Control child in root.Controls)
  {
   yield return child;
   foreach (Control c in GetControlTree(child))
   {
    yield return c;
   }
  }
 }
 
 private static void OnPreRequestHandlerExecute(object sender, EventArgs e)
 {
  /* Static content */
  if (HttpContext.Current.Handler == null)
  {
   return;
  }
 
  var handler = HttpContext.Current.Handler;
  Unity.Instance.Container.BuildUp(handler.GetType(), handler);
 
  // User Controls are ready to be built up after the page initialization is complete
  var page = HttpContext.Current.Handler as Page;
  if (page != null)
  {
   page.InitComplete += OnPageInitComplete;
  }
 }
 
 // Build up each control in the page's control tree
 private static void OnPageInitComplete(object sender, EventArgs e)
 {
  var page = (Page)sender;
  foreach (Control c in GetControlTree(page))
  {
   var typeFullName = c.GetType().FullName ?? string.Empty;
   var baseTypeFullName = c.GetType().FullName ?? string.Empty;
 
   // Filter on namespace to avoid build up of System.Web components
   if (typeFullName.StartsWith(NamespacePrefix) || 
    baseTypeFullName.StartsWith(NamespacePrefix))
   {
    Unity.Instance.Container.BuildUp(c.GetType(), c);
   }
  }
 }
}

Web.config.xml

<configuration>
 <!-- IIS 6.0 and below -->
    <system.web>
      <httpModules>
        <add name="UnityHttpModule" type="DIWebFormsExample.Lib.UnityHttpModule, DIWebFormsExample.Lib"/>
      </httpModules>
    </system.web>
 
 <!-- IIS 7.0 and above -->
    <system.webServer>
      <modules>
        <remove name="UnityHttpModule"/>
        <add name="UnityHttpModule" type="DIWebFormsExample.Lib.UnityHttpModule, DIWebFormsExample.Lib"/>
      </modules>
    </system.webServer>
</configuration>