Walkthrough: Downloading Assemblies on Demand with the ClickOnce Deployment API
By default, all of the assemblies included in a ClickOnce application are downloaded when the application is first run. However, you may have parts of your application that are used by a small set of your users. In this case, you want to download an assembly only when you create one of its types. The following walkthrough demonstrates how to mark certain assemblies in your application as "optional", and how to download them by using classes in the System.Deployment.Application namespace when the common language runtime (CLR) demands them.
Your application will have to run in full trust to use this procedure.
To create a project that uses an on-demand assembly
Create a directory named ClickOnceOnDemand.
Open the Windows SDK Command Prompt or the Visual Studio Command Prompt.
Change to the ClickOnceOnDemand directory.
Generate a public/private key pair using the following command:
sn -k TestKey.snk
Using Notepad or another text editor, define a class named DynamicClass with a single property named Message.
Save the text as a file named ClickOnceLibrary.cs or ClickOnceLibrary.vb, depending on the language you use, to the ClickOnceOnDemand directory.
Compile the file into an assembly.
To get the public key token for the assembly, use the following command:
sn -T ClickOnceLibrary.dll
Create a new file using your text editor and enter the following code. This code creates a Windows Forms application that downloads the ClickOnceLibrary assembly when it is required.
Imports System Imports System.Windows.Forms Imports System.Deployment.Application Imports System.Drawing Imports System.Reflection Imports System.Collections.Generic Imports Microsoft.Samples.ClickOnceOnDemand Namespace Microsoft.Samples.ClickOnceOnDemand <System.Security.Permissions.SecurityPermission(System.Security.Permissions.SecurityAction.Demand, Unrestricted:=true)> _ Class Form1 Inherits Form ' Maintain a dictionary mapping DLL names to download file groups. This is trivial for this sample, ' but will be important in real-world applications where a feature is spread across multiple DLLs, ' and you want to download all DLLs for that feature in one shot. Dim DllMapping as Dictionary(Of String, String) = new Dictionary(of String, String)() Public Sub New() ' Add button to form. Dim GetAssemblyButton As New Button() GetAssemblyButton.Location = New Point(100, 100) GetAssemblyButton.Text = "Get assembly on demand" AddHandler GetAssemblyButton.Click, AddressOf GetAssemblyButton_Click Me.Controls.Add(GetAssemblyButton) DllMapping("ClickOnceLibrary") = "ClickOnceLibrary" AddHandler AppDomain.CurrentDomain.AssemblyResolve, AddressOf CurrentDomain_AssemblyResolve End Sub <STAThread()> _ Shared Sub Main() Application.EnableVisualStyles() Application.Run(New Form1()) End Sub Private Function CurrentDomain_AssemblyResolve(ByVal sender As Object, ByVal args As ResolveEventArgs) As Assembly If ApplicationDeployment.IsNetworkDeployed Then Dim deploy As ApplicationDeployment = ApplicationDeployment.CurrentDeployment ' Get the DLL name from the Name argument. Dim nameParts() as String = args.Name.Split(",") Dim dllName as String = nameParts(0) Dim downloadGroupName as String = DllMapping(dllName) Try deploy.DownloadFileGroup(downloadGroupName) Catch de As DeploymentException End Try ' Load the assembly. Dim newAssembly As Assembly = Nothing Try newAssembly = Assembly.LoadFile(Application.StartupPath & "\\" & dllName & ".dll," & _ "Version=188.8.131.52, Culture=en, PublicKeyToken=03689116d3a4ae33") Catch ex As Exception MessageBox.Show("Could not download assembly on demand.") End Try CurrentDomain_AssemblyResolve = newAssembly Else CurrentDomain_AssemblyResolve = Nothing End If End Function Private Sub GetAssemblyButton_Click(ByVal sender As Object, ByVal e As EventArgs) Dim ourClass As New DynamicClass() MessageBox.Show("DynamicClass string is: " + ourClass.Message) End Sub End Class End Namespace
In the code, locate the call to LoadFile.
Set PublicKeyToken to the value that you retrieved earlier.
Save the file as either Form1.cs or Form1.vb.
Compile it into an executable using the following command.
To mark assemblies as optional in your ClickOnce application by using MageUI.exe
Using MageUI.exe, create an application manifest as described in Walkthrough: Manually Deploying a ClickOnce Application. Use the following settings for the application manifest:
Name the application manifest ClickOnceOnDemand.
On the Files page, in the ClickOnceLibrary.dll row, set the File Type column to None.
On the Files page, in the ClickOnceLibrary.dll row, type ClickOnceLibrary.dll in the Group column.
Using MageUI.exe, create a deployment manifest as described in Walkthrough: Manually Deploying a ClickOnce Application. Use the following settings for the deployment manifest:
Name the deployment manifest ClickOnceOnDemand.
To test your on-demand assembly
Upload your ClickOnce deployment to a Web server.
Start your application deployed with ClickOnce from a Web browser by entering the URL to the deployment manifest. If you call your ClickOnce application ClickOnceOnDemand, and you upload it to the root directory of adatum.com, your URL would look like this:
When your main form appears, press the Button. You should see a string in a message box window that reads "Hello, World!".