Creating custom SSRS handler for field with HTML

问题

I have an SSRS 2008 report with a field that contains and is configured to render as HTML. Some of the text in this field may contain IMG tags, and the IMG tag is not among the tags SSRS natively supports within its HTML rendering extension.

I am trying to find a way to write a custom handler to hook into the processing of this field that will let me look at the raw HTML before the SSRS handler processes it, in the hopes of grabbing IMG tags, extracting the SRC URL and getting the raw bytes of an image to insert on the fly in a way SSRS will accept, yet retaining the HTML SSRS will render.

From what I've read and seen so far, if a field is marked to render as HTML, the SSRS processor grabs it and parses it entirely before any handler could modify it, meaning the IMG tag is (would be) discarded before I could do anything with it (or even know it was present). The only option I see is to turn off the HTML rendering entirely, thus losing the benefit of the tags SSRS can recognize.

EDIT: Per Jamie's response below, I'm beginning to think the "2nd half" of this issue may prove harder than I realized: Is it even possible to programmatically add an Image to an SSRS Report at runtime (obviously through code/custom assembly)? That is, I'd like to write some code that might look something like this (pseudocode)

'Conceptual Pseudocode I'd like to be able to write
'for dynamic addition of Image element in SSRS report
'Is this even possible?? Is there a documented Report 
'object model??

Public Function AddImage(imageBytes() as Byte) as Image

    Dim newImage as New Image()
    newImage.SetBytes(imageBytes)
    Report.Add(newImage)

    return newImage

End Function

I'm hoping I'm just overlooking something simple that prevents me from grabbing the raw, unprocessed HTML, and someone else might be able to point me in the right direction on how to grab it.

回答1:

EDIT: I have created and implemented this solution within the SSRS development environment and it works. WOOHOO :) It did require some hoop-jumping with creating a Single-Threaded Apartment thread to host the WebBrowser control, and to create a message pump, but it does work! **

As I was literally typing up the message to a co-worker that this issue was a non-starter, I did have a bit of an inspiration on a way to solve this problem. I know this post hasn't generated a great deal of response, but just in case someone else finds themselves in a similar problem, I'm going to share what I've implemented in a "petri dish" scenario that, provided I get all the code permission issues resolved, should allow me a decent solution to this problem.

With SSRS inability to handle an IMG tag insurmountable, I actually thought of an idea that took the HTML rendering away from SSRS entirely. To do this, I created custom code that hands off the HTML rendering to a WebBrowser control, then copies the rendered result as an image. It does the following:

1. Instantiates a WebBrowser control of a given width and height.
2. Sets the DocumentText property of that control to the HTML from TinyMCE
3. Waits for the DocumentText to completely render.
4. Creates a bitmap equal to the size of the control.
5. Uses the undocumented and presumably unsupported DrawToBitmap method of the WebBrowser to draw the rendered HTML to a bitmap.
6. Copies the Bitmap to an Image
7. Saves the Image as a .png file
8. Returns the path to the .png as the result of the function.

In SSRS, I plan to replace the erstwhile HTML text field with an external Image control that will then call the above method and render the image file. I may alter that to simply draw the image to the SSRS Image control directly, but that's a final detail I'll resolve later. I think this basic design is going to work. Its a little kludgey, but I think it will work.

I have some permissions issues to work out with the code that SSRS will allow me to call at runtime, but I'm confident I'll get those sorted out (even if I end up moving the code to a separate assembly). Once this is tested and working, I plan to mark this as the answer.

Thanks to those who offered suggestions.

回答2:

I've done something similar with success: We had an HTML "Comment" field that was collected on a web form. For a particular report we wanted to truncate this field to the first 1000 characters or so, but preserve valid HTML.

So I created a C# .dll & class with a public function:

public static string TruncateHtml(string html, int characters)
{
   ...
}

(I used the HtmlAgilityPack for most of the HTML parsing, and to create and close off my new HTML string, while I kept track of the content length.)

Then I could call that code with the fully qualified path to the function in an SSRS expression:

=ReportHtmlHandler.HtmlTruncate.TruncateHtml(Fields!Comment.Value, 1000)

I could have added a calculated field to my dataset with this, but I was only using this value for one field, so I kept it at the field expression level.

All of this code gets called well before the HTML is processed or rendered by SSRS. I'm sure that any original IMG tag will be in the string.

This approach might work for you, possibly create a ExtractImg function which could be set as the source of an img on the report. I think some of the tricky bits for your requirement will be to handle multiple images as well as embedding the extracted img. But you might be able to do this simply with a external reference to an image. I haven't done much with external images in SSRS.

An MSDN blog entry on calling a custom dll from SSRS: http://support.microsoft.com/kb/920769

来源：https://stackoverflow.com/questions/19930524/creating-custom-ssrs-handler-for-field-with-html