A way to use BitmapMetadata outside the main thread?

Question

Hi,

I'm developing a multi-threaded C# application and have run into problems while using the BitmapMetadata component outside the main (UI) thread and UI class. My app throws 'System.Runtime.InteropServices.COMException' occurred in PresentationCore.dll and when I try to debug it and put a Watch on the BitmapMetadata object, it takes forever to access its properties and when it does so, most of them are marked with "Function evaluation disabled because a previous function evaluation timed out."
 
In view of the articles:

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1646928&SiteID=1
http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1653994&SiteID=1

I figured that my problems are due to the fact that WPF components are not to be used outside the STAThread. My question now is whether I am right (:-) and if there is some kind of workaround to the BitmapMetadata object working outside the main thread? Unfortunately, I'm not only dealing with a different thread, but also the BitmapMetadata object is to be used by a class different from the UI class.

Any suggestions?

Thanks in advance!!!

Answer 1

Does freezing the BitmapMetadata before your non-ui thread accesses it help?

 

-Jer

Answer 2

Hey Jer, thanks for your response!

I'm sorry! I should have posted some code to make my issue clearer. Below is an excerpt. Basically it's a modfication of an example I found on the web that I use for testing.

Code Snippet
namespace IPTC_Test
{
  class Program
  {
    [STAThread]
    static void Main()
    {
      Thread t = new Thread(startApp);
      t.Start();
      Application.Run(new Form1());
    }

    static void startApp()
    {
      Program p = new Program();
      p.writeMetadataDotNet();
    }

    private void writeMetadataDotNet()
    {
      string originalPath = "test.jpg";
      string outputPath = "test2.jpg";

BitmapCreateOptions createOptions = BitmapCreateOptions.PreservePixelFormat | BitmapCreateOptions.IgnoreColorProfile;

      uint paddingAmount = 2048;

      using (Stream originalFile = File.Open(originalPath, FileMode.Open, FileAccess.Read))
      {
        BitmapDecoder original = BitmapDecoder.Create(originalFile, createOptions, BitmapCacheOption.None);
        if (!original.CodecInfo.FileExtensions.Contains("jpg"))
        {
          Console.WriteLine("The file you passed in is not a JPEG.");
          return;
        }

        JpegBitmapEncoder output = new JpegBitmapEncoder();

        if (original.Frames[0] != null && original.Frames[0].Metadata != null)
        {
          try
          {
            BitmapMetadata metadata = new BitmapMetadata("jpg");


// If I set a breakpoint after here and try to access/debug the metadata object, it fails. If I let it run through, the "output.Save" function below throws the exception mentioned in the first post


                      metadata.SetQuery("/app1/ifd/PaddingSchema:Padding", paddingAmount);
            metadata.SetQuery("/app1/ifd/exif/PaddingSchema:Padding", paddingAmount);
            metadata.SetQuery("/xmp/PaddingSchema:Padding", paddingAmount);

            string[] strArr = new string[2];
            strArr[0] = "one";
            strArr[1] = "two";
            metadata.SetQuery("/app13/irb/8bimiptc/iptc/keywords", strArr);
            output.Frames.Add(BitmapFrame.Create(original.Frames[0], original.Frames[0].Thumbnail, metadata, original.Frames[0].ColorContexts));
            using (Stream outputFile = new FileStream("test2.jpg", FileMode.Create, FileAccess.ReadWrite, FileShare.ReadWrite))
            {
              output.Save(outputFile);
            }
          }
          catch (Exception e)
          {
            int einienv = 3883;
          }
        }     
      }  
  }
}

Answer 3

You can set thread apartment to STA and IsBackground property to false to do this.

 

Code Snippet

Thread.SetApartmentState(ApartmentState.STA);

Thread.IsBackground = false;

 

 

Best Regards,

Wei Zhou

Answer 4

Thanks Wei Zhou!

That did the job!