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How To Get A Website Thumbnail in a C# Application Without Creating A Form (console)

, 5 Jul 2008 CPOL
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The article describes how to get a thumbnail of a Website in .NET Framework 2.0+ without launching a fully interactive WinForms application.

UPDATE

I've updated the code and the binary with the great improvements that Piers Lawson suggested in the comments. The app should no longer have problems taking snapshots of some images with JavaScript or just plain random problems. It is also slightly optimized with suggestions from Frank Herget. It looks like he's based a very nice service around it on his site - check it out!

Thanks again for your great support!

Introduction

The article describes a console-like application that loads a Web page, makes a screenshot of it and saves it as a JPG file.

Our beloved sys admin - (we all bow to him and worship his skills) has recently asked if it's possible to write a .NET application to make a thumbnail of a Website. The task is pretty trivial with Windows Forms actually. But with him being the Linux guy and all... I decided to pick up the more challenging part of it being the console app. An interesting use case anyway.

In WinForms, all you really need to do is drop a WebBrowser from your Toolbox on your form and once it's loaded the page call:

Bitmap bitmap = new Bitmap(width, height);
webBrowser1.DrawToBitmap(bitmap, 
    new Rectangle(webBrowser1.Location.X, webBrowser1.Location.Y, 
        webBrowser1.Width, webBrowser1.Height));

Obvious enough. When it gets tricky is when you want to do it in a console application in a way that can take a shot of multitude of Websites provided in a batch file. There is a dirty way of instantiating a whole form, making it show (or not), doing the work and then exiting the WinForms app. This might probably be enough for a quick solution, but I wanted a clean piece of code, so I would actually NOT take pride in something in that tone.

How is it done then...

So we instantiate the Web control in our class constructor...

public WebPageBitmap(string url, int width, int height, bool scrollBarsEnabled)
{
    this.url = url;
    this.width = width;
    this.height = height;
    webBrowser = new WebBrowser();
    webBrowser.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(documentCompletedEventHandler);
    webBrowser.Size = new Size(width, height);
    webBrowser.ScrollBarsEnabled = scrollBarsEnabled;
}

Easy so far and pretty similar to what the regular app would do anyway. The documentCompletedEventHandler is a delegate to tell that it has loaded. (I initially wanted to use that for drawing the bitmap but deferred that to the point where the bitmap is actually fetched after I added the resizing part.) Now comes the interesting case.

The Neat Part

Since the call is asynchronous, a simple webBrowser.Navigate(URL); just won't cut it. We are in a single thread and the browser does not create a separate thread for that. This makes sense by the canonical windows rule: Only the thread that creates a control, accesses the control. We need to somehow allow the control to take the flow of the thread and do its work. Navigate only tells it that it should perform the action and immediately exits. The developer's responsibility then is to know when the control is ready for consumption. Which is the case when the webBrowser.ReadyState progresses to (or returns to) the state of WebBrowserReadyState.Complete.

The Solution

To pass the flow to the app controls, you need to perform Application.DoEvents(); which was a bit of a wild guess when I used it. Surprise, surprise, it works just like it did in other Windows frameworks that I used before.

public void Fetch()
{
    webBrowser.Navigate(url);
        while (webBrowser.ReadyState != WebBrowserReadyState.Complete)
        {
            Application.DoEvents();
        }
}

The effect is a tiny and neat (I hope) app that pulls a Web page from the net and makes a screenshot off of it (with possible rescaling).

You can get the source code or get the app directly. App usage:

GetSiteThumbnail.exe http://www.yoursite.com/ thumbnail.jpg 
  [browser_width(defaults to 800) browser_height (defaults to 600) ] 
  [thumbnail_width thumbnail_height]

Sample:
GetSiteThumbnail.exe http://www.cognifide.com/ cognifide.jpg 1280 1024 640 480

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

AdamNajmanowicz
Web Developer
Poland Poland
Adam Najmanowicz is a Senior Developer at Cognifide Poland.
 
His previous experience includes Delphi, .Net as well as Java Development.
 
Currently working on ASP.NET + MSSql Server(Oracle) solutions for enterprises.
 
Also developing desktop applications for Stardock Systems.

Comments and Discussions

 
AnswerRe: why I just get blank image? [modified] PinmemberoCasper14-Oct-07 12:42 
GeneralWhy It Does not work with some sites Pinmembermhariri27-Nov-06 6:39 
GeneralAxWebBrowser Vs. WebBrowser (.NET2) events PinmemberAssaf Koren23-Nov-06 9:43 
GeneralRe: AxWebBrowser Vs. WebBrowser (.NET2) events PinmemberAdamNajmanowicz28-Nov-06 9:23 
GeneralGetting it to work in an ASP.NET application [modified] PinmemberdB.20-Nov-06 21:51 
GeneralRe: Getting it to work in an ASP.NET application Pinmemberligaz25-Nov-06 5:06 
GeneralRe: Getting it to work in an ASP.NET application PinmemberdB.25-Nov-06 6:11 
GeneralRe: Getting it to work in an ASP.NET application PinmemberAdamNajmanowicz28-Nov-06 9:19 
Sorry for the dely in reply,
 
wow, incredible research, not sure I didn't learn more from you than the other way round Smile | :)
 
In my esperience with the control from the past was that just suppressing errors was not the path to go to avoid all problems, you may actually want to allow the control to throw the error at you and just mark it as handled. Not sure if that behaves in .Net hwo it did in Delphi for me, where I operated pretty much on the COM control, but try this code:
 
In the constructor make sure you still have the delegate attached to Document completed as in the original class:
 
// Handle DocumentCompleted to gain access to the Document object.
webBrowser.DocumentCompleted +=
new WebBrowserDocumentCompletedEventHandler(documentCompletedEventHandler);
 

and then in the Document completed method add the line for it to look like this:
 
private void documentCompletedEventHandler(object sender, WebBrowserDocumentCompletedEventArgs e)
{
isReady = true;
((WebBrowser)sender).Document.Window.Error +=
new HtmlElementErrorEventHandler(SuppressScriptErrorsHandler);
 
}
 
to attach the error handler to the loaded document.
 
and then add the suppression method:
 
public void SuppressScriptErrorsHandler(object sender, HtmlElementErrorEventArgs e)
{
e.Handled = true;
}

you may want to log the errors here to make sure it actually works.
 

Let me know if that helps you in any way.
 
Thanks again for the great research!
GeneralRe: Getting it to work in an ASP.NET application Pinmemberchr872-Mar-07 3:19 
GeneralRe: Getting it to work in an ASP.NET application PinmemberChris Vann23-Mar-08 11:46 

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