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POCalling a function in another thread C#
 

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    <p>I don't know how to put this but I'll try my best.</p> <p>I have a Windows form application which uses a webcam to take a photo of a user which works fine, I'm using the directshownet library found here <a href="http://directshownet.sourceforge.net/" rel="nofollow">http://directshownet.sourceforge.net/</a> and have used the DxSnap sample to take the photo.</p> <p>The next part of the application uses an RFID tag reader that once a tag is scanned, it calls the take photo method. And this is where the problem is coming in, because the RFID listen method is run in a separate thread to the GUI thread, because it is an infinite while loop.</p> <p>The class that is used to take the picture takes an instance of a picturebox control as a parameter for it's constructor, which is created in the main thread, and i think this is where the problem is.</p> <p>Each part of the application works fine separately but when i try to call the method to take the photo from the listener thread all hell breaks loose and the app crashes.</p> <p>Does anybody know how I could call a method of the object that is initialized in the main thread (that takes the photo) from the listener thread?</p> <p>I've tried delegate and invoke, but can't figure it out as i don't want to manipulate the control directly, but rather let the object do it in the main thread.</p> <p>Here's some code:</p> <pre><code> private Capture cam; private int portIndex = -1; private ArrayList AlreadyOpenPortList = new ArrayList(); private byte readerAddr = 0; private Thread listenThread; IntPtr m_ip = IntPtr.Zero; public podiumForm() { InitializeComponent(); // scanner and camera startup startCam(); openComs(); openRF(); startListening(); } private void startListening() { listenThread = new Thread(new ThreadStart(this.Listen)); listenThread.Start(); } /// &lt;summary&gt; /// Method of retrieving code tag details from reader /// &lt;/summary&gt; private void Listen() { int fCmdRet = 0x30; byte state = 1; byte AFI = 00; byte[] DSFIDAndUID = new byte[9]; byte cardNumber = 0; string strDSFIDAndUID = ""; byte outputSet; if (!GetCurrentUsePort()) { MessageBox.Show("Open ComPort, Please"); return; } while (true) { fCmdRet = StaticClassReaderA.Inventory(ref readerAddr, ref state, ref AFI, DSFIDAndUID, ref cardNumber, portIndex); if (fCmdRet == 0) { outputSet = 0; fCmdRet = StaticClassReaderA.SetGeneralOutput(ref readerAddr, ref outputSet, portIndex); strDSFIDAndUID = ByteArrayToHexString(DSFIDAndUID).Replace(" ", ""); outputSet = 3; fCmdRet = StaticClassReaderA.SetGeneralOutput(ref readerAddr, ref outputSet, portIndex); SavePic(strDSFIDAndUID.Substring(2, 16)); //MessageBox.Show(strDSFIDAndUID.Substring(2, 16)); //ShutDown(); } } } private void SavePic(string text) { Cursor.Current = Cursors.WaitCursor; // Release any previous buffer if (m_ip != IntPtr.Zero) { Marshal.FreeCoTaskMem(m_ip); m_ip = IntPtr.Zero; } // here's where it crashes // capture image m_ip = cam.Click(); Bitmap b = new Bitmap(cam.Width, cam.Height, cam.Stride, PixelFormat.Format24bppRgb, m_ip); cam.Dispose(); // If the image is upsidedown b.RotateFlip(RotateFlipType.RotateNoneFlipY); pbPic.Image = b; Cursor.Current = Cursors.Default; MessageBox.Show("Here " + text); } private void startCam() { const int VIDEODEVICE = 0; // zero based index of video capture device to use const int VIDEOWIDTH = 640; // Depends on video device caps const int VIDEOHEIGHT = 480; // Depends on video device caps const int VIDEOBITSPERPIXEL = 24; // BitsPerPixel values determined by device cam = new Capture(VIDEODEVICE, VIDEOWIDTH, VIDEOHEIGHT, VIDEOBITSPERPIXEL, pbPic); } // method in capture class public IntPtr Click() { int hr; // get ready to wait for new image m_PictureReady.Reset(); m_ipBuffer = Marshal.AllocCoTaskMem(Math.Abs(m_stride) * m_videoHeight); try { m_WantOne = true; // If we are using a still pin, ask for a picture if (m_VidControl != null) { // CRASHES HERE with : System.InvalidCastException was unhandled // Tell the camera to send an image hr = m_VidControl.SetMode(m_pinStill, VideoControlFlags.Trigger); DsError.ThrowExceptionForHR(hr); } // Start waiting if (!m_PictureReady.WaitOne(9000, false)) { throw new Exception("Timeout waiting to get picture"); } } catch { Marshal.FreeCoTaskMem(m_ipBuffer); m_ipBuffer = IntPtr.Zero; throw; } // Got one return m_ipBuffer; } </code></pre>
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    1. COShow us some code.
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    2. COit's 500+ lines
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    3. COThe answer is Control.Invoke, show us what didn't work there.
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      1. USHenk Holterman
 

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