| Hosting .NET Windows Forms Controls in IE By Thiru Thangarathinam |
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Introduction
In the past, Web developers often used ActiveX controls to provide rich client-side functionality in their Web applications. Now developers can easily build objects using the Microsoft .NET Framework that are more compact, lightweight, secure and can be hosted within Internet Explorer. By hosting .NET Windows Forms controls in Internet Explorer, developers can accomplish many client-side Web development goals. In this article, we will understand how to create Windows Forms controls and deploy them within Internet Explorer. While using Windows Forms controls from within IE, we will also demonstrate how to provide rich user experience in the client side by invoking a remote Web service from the Windows Forms control. Along the way, we will also understand how to take advantage of the .NET Security Model to provide a seamless secured execution environment for our control. If you have developed Web applications using Java based languages, you are familiar with Java applets. Java applets are small programs that are basically designed to run in a Web browser. Java applets are executed when the browser loads an HTML document that contains the applet tag. Windows Forms within Web pages work in a manner similar to Java applets. In this approach, you create Windows Forms controls using the rich classes supplied by the Windows Forms technology and then deploy the control in a Web page. When the browser loads the Web page, it also executes the code contained in the Windows Forms control. This could be very useful on an Intranet or Extranet application scenario where you need to deploy an enterprise-wide application that requires dynamic rich user experience as provided by a fat-client application. This model is based on the same deployment and maintainability characteristics of a thin client n-tier application. One of the great features of .NET is the seamless integration it provides with Internet Explorer. For example, we can activate a Windows Forms control from IE without even prompting the user. This is accomplished without having to do any registration while still utilizing all the features of Code Access Security provided by the .NET CLR. When you build Windows Forms controls, you have all the features provided by the Windows Forms class hierarchy. For example, you can use Windows Forms control validation techniques to perform extensive validation on the input data entered by the user. Similarly, you can even invoke a remote Web service from your forms control. By using all of these techniques, you can create rich, powerful, dynamic state-of-the-art applications using the .NET platform.
Implementation In this section, we will see how to create a simple Windows Forms control and host it in Internet Explorer. The following list describes five steps to activate a Windows Forms control within IE.
Now we will look at each of the above steps in detail. Create a Windows Forms Control
Once the project is created, we will rename the default user control to HelloWorldCtl. To the user control, we will add a label control named lblMessage and a button named btnClick. When the user clicks the button, we will execute the following code to display a simple message to the user. private void btnClick_Click(object sender, System.EventArgs e)
{
lblDisplayMessage.Text = "Hello World";
}
Now that we have created the control, let us compile the project and create the assembly.
Create an HTML Page <html>
<body>
<p>Hello World Control<br> <br></body>
<object id="HelloWorldControl1"
classid="http:HelloWorldControl.dll#HelloWorldControl.HelloWorldCtl"
height="500" width="500" VIEWASTEXT>
</object>
<br><br>
</html>
In the classid attribute of the object tag, we specify the path to the control library assembly and the fully qualified name of the control. This fully qualified name of the control includes the namespace as well as the name of the control class. As you can see from the above code, the assembly and the fully qualified name of the control are separated by # sign. The combination of these two parameters serves as the unique identifier to identify the control. It is also possible to write client side script against the control since it is identified by the unique id named HelloWorldControl1.
Configure the Virtual Directory
Configuration of Code Access Permissions Run the Control
In this example, we looked at how to create a simple Windows Forms control and host it in Internet Explorer. In the next section, we will see how to access a Web service directly from the client machine using a Windows Forms control. Accessing the Web Service from the Windows Forms Control One of the main advantages of Windows Forms control is that it allows you to bring a rich user experience to the client machine. For example, you can access a Web service directly from the client machine and display the results to the user without even refreshing the page. To demonstrate this, we will first create a Web service and then show how to invoke the Web service from the Windows Forms control. Creation of Web Service
Once the Web service is created, we will change the name of the Web service class to AuthorsService. After that, we will add a new method named GetAuthors to the AuthorsService class. The GetAuthors method looks like the following. [WebMethod]
public DataSet GetAuthors()
{
//Get the connection string from the configuration file
string connString = System.Configuration.ConfigurationSettings.AppSettings["connectionString"];
SqlConnection sqlConn = new SqlConnection(connString);
DataSet dstAuthors = new DataSet("Authors");
SqlDataAdapter adapter = new SqlDataAdapter("Select * from Authors",sqlConn);
//Fill the Dataset with the results of the executed query
adapter.Fill(dstAuthors,"Author");
//Close and dispose the opened database connection
sqlConn.Close();
sqlConn.Dispose();
//Return the Authors Dataset to the caller
return dstAuthors;
}
The code for the GetAuthors method is straightforward. We start off by retrieving the connection string from the web.config file. The connection string is stored in the appSettings section of the web.config file.
<appSettings>
<add key="connectionString"
value="server=localhost;uid=sa;pwd=thiru;database=Pubs">
</add>
</appSettings>
Then we create an instance of SqlConnection object passing in the connection string as an argument. After that, we create an instance of the SqlDataAdapter object and supply the query to be executed and the SqlConnection object as arguments. Then we invoke the Fill method of SqlDataAdapter object to execute the query and fill the DataSet with the results. Finally, we release all the resources and return the DataSet to the callers of the Web service. Now that the Web service is created, you are ready to start creating the client application for the Web service.
Creation of Windows Forms Control That Acts as the Web Service Client
Once the project is created, we will rename the default user control to AuthorsControl. To the user control, we will add a DataGrid named gridAuthors and a command button named btnClick. In the click event of the command button, we will write code to invoke the Web service. Before that, we will add reference to the Web service using Add Web Reference option in Visual Studio .NET. In the Add Web Reference dialog box, we will type in the location of our Web service and press Enter. Then we click on Add Reference button to add the reference to the Web service. This basically creates the proxy for the Authors Web service.
Now that the proxy is created, we are ready to add code to invoke the Web service. We do this in the click event of the command button that we added earlier. private void btnClick_Click(object sender, System.EventArgs e)
{
this.Cursor = Cursors.WaitCursor;
AuthorsWebServiceProxy.AuthorsService authorsSvc = new
AuthorsWebServiceProxy.AuthorsService();
gridAuthors.DataSource = authorsSvc.GetAuthors();
this.Cursor = Cursors.Default;
}
In the above lines of code, we create an instance of the Web service proxy class and then invoke the GetAuthors method. We assign the DataSet that is returned from the Web service to the DataSource property of the DataGrid control. Now compile the project to create an assembly, which we can deploy to the virtual directory.
Creation of HTML page and Virtual Directory <html>
<body>
<p>Authors Display Control<br> <br></body>
<object id="AuthorsControl1"
classid="http:AuthorsWebServiceClientControl.dll#AuthorsWebServiceClientControl.AuthorsControl"
height="500" width="500" VIEWASTEXT>
</object>
<br><br>
</html>
Now that we have created the HTML page, we need to create a virtual directory that can be used to host the HTML page as well as the control. Once the virtual directory is created, copy over the HTML page and the control to the physical folder that is mapped to the virtual directory. Now you can test the control by navigating to the HTML page that we created earlier. In the HTML page, you will see a command button that is part of the forms control. If you click on the command button, it will invoke the Web service from the client browser and display the results of the Web service in a DataGrid. The output from the HTML page looks like the following.
Debugging the Windows Forms Control To debug the control, you need to perform the following steps.
Code Access Permissions and Windows Forms Controls As we have already discussed, when the control executes in IE, it utilizes the code access permissions provided by the .NET runtime. To understand how forms controls running in IE work with the code access security provided by the .NET runtime, let us go ahead and add a few lines of code to our Authors forms control and create a new event log source. After modification, the load event of the control looks like the following. private void AuthorsControl_Load(object sender, System.EventArgs e)
{
if (!EventLog.SourceExists("TestSource"))
EventLog.CreateEventSource("TestSource", "TestLog");
else
{
EventLog.DeleteEventSource("TestSource");
EventLog.CreateEventSource("TestSource", "TestLog");
}
}
}
In the above lines of code, we check for the existence of an EventLog source named TestSource. If the event source does not exist, we create one. Otherwise we delete the existing event source and create a new event source from scratch. As you might expect, performing this kind of operation requires more privileges, and the controls downloaded from the Internet should not be allowed to perform this kind of operation. To validate this, copy the output of the control to the virtual directory. After copying the output of the control to the virtual directory, if you navigate to the HTML page that hosts the control in the browser, you will see the following dialog.
The above dialog box clearly shows that the code in our control is clearly restricted by the code access security of the .NET runtime. Putting It All Together However before using Windows Forms controls in IE, you need to be aware of the benefits and limitations. The main benefits include:
The constraints include:
Due to all of the above constraints, it might be beneficial to detect the capabilities of the client machine and then deliver content that is appropriate to them. For example, since forms controls hosted in IE require the presence of the .NET runtime on the client machine, we can write code to check if the client machine has the .NET runtime installed. You can do this by checking the value of the Request.Browser.ClrVersion property. If the client machine has .NET installed, this property will return the version number; otherwise it will return 0.0. Conclusion In this article, we have discussed how to host Windows Forms controls in IE and demonstrated the steps to be followed for debugging the control. We have also seen how to utilize the .NET Code Access Security to configure what the control can do when running within Internet Explorer. Even though this technology requires the presence of platform specific elements in the client machine, it holds a lot of promise, especially when you consider the fact that future versions of Windows operating systems are likely to have the .NET Framework as an integral part. The recent release of Windows Server 2003 is an example of this. I hope you find this article useful and thanks for reading. About the Author Thiru has almost six years of experience in architecting, designing, developing and implementing applications using Object Oriented Application development methodologies. He also possesses a thorough understanding of software life cycle (design, development and testing). He is an expert with ASP.NET, .NET Framework, Visual C#.NET, Visual Basic.NET, ADO.NET, XML Web Services and .NET Remoting and holds MCAD for .NET, MCSD and MCP certifications. Thiru has authored numerous books and articles. He can be reached at [email protected]. |
