Extracting Bitmap object from Cache object RSS

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  biomechanic2...

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  Extracting Bitmap object from Cache object

  Jul 02, 2004 04:55 AM|LINK

  Hi folks, I'm creating a set of images dynamically (for a primary navigation), that part is all sweet, however I want to cache the Bitmap objects rather than recreate them each time a page loads. I have the following code:

  Cache cache = System.Web.HttpContext.Current.Cache;
  
  
  			if ( cache[HashImage(_text, _active)] == null )
  			{
                                                                   
  	               			// Set the width and height
  				// Width is calculated by the text length
  				Bitmap image = new Bitmap(100, 20, PixelFormat.Format24bppRgb);
  
  
  				// Set graphic object
  				graphic = Graphics.FromImage(image);
  				
  				Response.ContentType="image/gif";
  				
  
  				cache.Insert( "Image1", (Bitmap)image, null, DateTime.MaxValue, TimeSpan.FromSeconds(30));
  				
  
  				
  
  				image.Save(Response.OutputStream, ImageFormat.Gif);
  				image.Dispose();
  			}
  			
  
  			else
  			{
  				Response.ContentType = "image/gif";
  				Bitmap image = new Bitmap(cache["Image1"]);
  				image.Save(Response.OutputStream, ImageFormat.Gif);
  				image.Dispose();
  			}

  However I get this error: Invalid parameter used. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentException: Invalid parameter used. Any ideas?
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  Atrax

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  Re: Extracting Bitmap object from Cache object

  Jul 02, 2004 06:04 AM|LINK

  and that happens on this line, I expect : cache.Insert( "Image1", (Bitmap)image, null, DateTime.MaxValue, TimeSpan.FromSeconds(30)); ? the second parameter of this call should be type Object, if that clarifies things at all.
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  Jason Brown - MVP, IIS
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  biomechanic2...

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  Re: Extracting Bitmap object from Cache object

  Jul 02, 2004 06:58 AM|LINK

  It happens on this line: image.Save(Response.OutputStream, ImageFormat.Gif);
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  Atrax

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  Re: Extracting Bitmap object from Cache object

  Jul 02, 2004 07:14 AM|LINK

  OK, but there appear to be two of those. does it happen on one or the other or both? (or did I just misread the code? I'll go back in a sec)
  RTFM - straight talk for web developers. Unmoderated, uncensored, occasionally unreadable
  
  Jason Brown - MVP, IIS
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  biomechanic2...

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  Re: Extracting Bitmap object from Cache object

  Jul 02, 2004 07:25 AM|LINK

  It only happens when I refer to the cached object - when it initially creates the image, there's no problems at all.
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  Atrax

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  Re: Extracting Bitmap object from Cache object

  Jul 02, 2004 07:48 AM|LINK

  OK, what if you swap the two method calls? the save to Response and the save to Cache? and what if you write from the Cached copy instead of from the image object?
  RTFM - straight talk for web developers. Unmoderated, uncensored, occasionally unreadable
  
  Jason Brown - MVP, IIS
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  biomechanic2...

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  Re: Extracting Bitmap object from Cache object

  Jul 02, 2004 08:35 AM|LINK

  I'm doing a bit of debugging, after it's added to the Cache, the object is recognised as type System.Drawing.Bitmap - however when I try to get it's Width or Height I get the same error as above...when I write out it's PixelFormat property it says "DontCare"
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  Jigar

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  Re: Extracting Bitmap object from Cache object

  Jul 02, 2004 02:04 PM|LINK

  Response.ContentType = "image/gif";
  
  
  Bitmap image = new Bitmap(cache["Image1"]);  <-- why this?
  
  
  image.Save(Response.OutputStream, ImageFormat.Gif);
  
  
  image.Dispose();

  You already have bitmap object why recreate? You can write like Bitmap image = (Bitmap)cache["Image1"]; PS: I usually do same kind of thing but in slightly different way, I would convert bitmap(bitmap -> save -> to memorystream -> byte array) to byte array and then put byte array in cache, in this process i do not have to do extra processing with bitmap every time when image is served from cache.
  Jigar Desai
  -----------------------
  Do not forget to "Mark as Answer" on the post that helped you.
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  biomechanic2...

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  Re: Extracting Bitmap object from Cache object

  Jul 03, 2004 03:15 AM|LINK

  Thanks mate, that worked a treat!

  MemoryStream mem = new MemoryStream();
  				image.Save(mem, ImageFormat.Gif);
  				Cache.Insert( (string)HashImage(_text, _active), (byte[])mem.ToArray(), null, DateTime.MaxValue, TimeSpan.FromMinutes(30));
  				
  
  				Response.ContentType="image/gif";
  				image.Save(Response.OutputStream, ImageFormat.Gif);
  				image.Dispose();
  			}
  			else
  			{
  				Response.ContentType = "image/gif";
  
  
  				MemoryStream mem = new MemoryStream((byte[])Cache[HashImage(_text, _active)]);
  				Bitmap image = new Bitmap(mem);
  				image.Save(Response.OutputStream, ImageFormat.Gif);
  				image.Dispose();

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  Jigar

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  Re: Extracting Bitmap object from Cache object

  Jul 06, 2004 05:30 PM|LINK

  You can optimize you code by sending bytes directly to ResponseStream (avoids bitmap creation)

  Response.ContentType = "image/gif";
  
  
  byte[] buffer = (byte[])Cache[HashImage(_text, _active)];
  Response.BinaryWrite(buffer);

  Jigar Desai
  -----------------------
  Do not forget to "Mark as Answer" on the post that helped you.