USB Via .NET 2 Notifications And Marshal?
Jan 14, 2009
I'm a VB6 programmer who was forced to upgrade to Visual Studio 2005 Version 8.0.50727.42 .NET Framework Version 2.0.50727. I am trying to write a call-back which will intercept a Windows message for when our USB HID device is plugged or unplugged. We have a custom .dll which handles the majority of the HID interface. I just need to call a few API's to connect to the device. I can connect and communicate.
I am looking at USB Complete Third Edition. The code examples do not compile. I'm unsure if this is because of the .NET version 2 or the 2005 dialog of VB. I cannot resolve "StructLayout..." statements, but the program appears to be working without them. I cannot get any "Marshal." statements to compile, which is where I am finding it difficult to get around.
[Code]...
Although OnDeviceChange() is being called six times, both IF statements fail. m.msg is 0x219, which is Device Change. m.WParm is always 7, m.lParm is always 0. And, this is where I'm stuck. m.lParm should be a pointer which gets me to the device path? Don't know what 7 is.
So, maybe I'm not registered to receive the proper messages from the device (or I'm looking in the wrong place). The missing step might be to call the RegisterDeviceNotification() API. This book is telling me to use frmMy.Handle declared globally as Friend frmMy As frmUSB - that gives me a null reference runtime error, so I swapped in Me.Handle for the first parameter to RegisterDeviceNotification(). It likes that. But, then it has heartburn with the buffer pointer - not so easy to resolve in Visual Basic. The call wants a LONG. I have DevBroadcastDeviceInterfaceBuffer, which the book says to use Marshal.AllocHGlobal(Size) and Size is Marshal.Sizeof(DevBroadcastDeviceInterface). Neither Marshal statement compiles and I'm not sure if it was removed in this version of .NET? Anyone? I really don't need a dynamically allocated buffer. This is quickie VB app for a single USB device.
Can anyone tell me how far down the rabbit hole I am and what I'm missing. I can tell when something changes to some USB device. I have a handle to that device supplied to me by a custom API library - probably is the HID handle.
How can I setup to receive a message when my HID USB device is unplugged or plugged in?
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Aug 16, 2010
Also, once i get that done, How would i make it display notifications?(Similar to that of when someone logs on in MSN messenger.)
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Apr 12, 2010
I need to be able to raise different types of audio notifications to the user. I need an "ok" and an "error" type sounds, I was hoping to be able to raise a simple beep and a critical stop type sound but I can only find the Beep() command which doesn't allow for differing sounds. Is there a library that does what I need or will I need to roll my own using the system wavs.
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Jun 30, 2009
I am currently using Snarl to generate notifications whenever an event / error occurs in my program. How would I go about coding a native VB notification instead of using a 3rd party program?
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Sep 23, 2011
I have a vb.net application in which there is a main form. There are around 10 classes each having their own functionalities like tcpactions, fileactions, serialport actions etc. The user interacts with the main form and does certain actions which will invoke the methods in these classes. Now I have a notifications textarea in the mainform and i want to show the current action being performed in those classes and their results in the notifications area.
for example when a user clicks a "Start Process" Button in the form i invoke the method "launchprocess" in a class "ProcessActions". Now this method tries to launch about 7 different process and after launching it sends notification such as "process 1 launched" or if it fails it sends notifications such as "process 1 launch failed".
I currently use event handlers and use them to show notifications but with the amount of events i have to handle it is getting cumbersome and i might have to add even more classes in the future. So is there a better way of handling notifications from other classes.
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Apr 15, 2012
I have a database of asset information with asset age as one of the columns..now i wish to display all the assets which crossed 4 years in the current year
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Feb 20, 2012
I need an array with fix String lenghts and fix rows... I do this...
Imports System.Runtime.InteropServices
Public Class Class1
Public WPFFunktion As String
[code]....
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May 22, 2010
What is the most timers you have used in an application? I think the most I have ever used is 2.In another forum this question was asked. "I have a Timer ... I have a situation where I want to run the code in the Tick event ONLY ONCE not on the interval i have the timer set too."
I responded with Timer1_Tick(New Object, New System.EventArgs) Which led to this "The 'sender' object is VERY important when you have more than one Timer being handled by the Tick event procedure. This is because in a multi-timer tick event procedure, the only way your program knows which timer just fired is by querying the 'sender' object.When you use code like this you are putting nothing into the 'sender' object, so that if you were ever going to query it a 'kaboom' is going to happen.""...this 9 timer Tick event handler job done. Remember, all that is required is the correct timer name gets put into the ListBox." "The need for multi-timers to be handled by a single Tick event handler happens all the time. How would a real life programmer handle this? "Oh, to test the "kaboom" theory I wrote this and ran it overnight successfully:
[code]...
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Dec 15, 2009
I am using a COM library in my VB.NET app that has an asynchronous execution method and signals my application via an event when it completes. The event handler is on a different thread from the calling thread. I want to invoke another execution on the main thread when I receive the completion event. If I call directly in the event handler for another execution it starts on the new thread. How do I marshal back to the main thread. This is done in a dll not in a form.
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Jun 8, 2010
I'm trying to call the GetInterfaceInfo Windows API - it accepts a structure as one of its parameters and this structure has a member that is an array. The API populates the contents of the array when it is called and there can be any number of items in the array. How can I define such an array in my structure?
If I just use a normal .NET array like so then the program just crashes (no exception thrown)
<StructLayoutAttribute(LayoutKind.Sequential)> _
Public Structure IP_INTERFACE_INFO
Public NumAdapters As Integer
[Code]...
and this works fine, but the problem is I have to define the SizeConst attribute as you can see to something large (64 in this example) so that the API doesnt fail because the array wasnt big enough. Firstly this is a waste of memory as in most cases the number of items the API sticks in the array will be less than 10, but secondly if there was ever a case where the API wanted to put more than 64 items in then it would fail.
Using ReDim to set the length of the array at runtime seems to have no effect, and that SizeConst attribute has to be set to a constant value so there's no way I can dynamically set it.
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Jan 24, 2010
creating a business layer in a .dll which at the moment is being used on a windows forms application. I have some objects with properties that use iNotifyPropertyChanged to update the UI which has all been working fine. My problem is tarted to explore using multiple threads and ing a cross-thread error because the properties are being changed on a different thread to the UI and iNotifyPropertyChanged is attempting to update the values (shown in labels) on the UI thread... shows the best way to solve my problem. The .dll will never know what Forms application is using it so I really dt want to hard code references into the objects. From what I gather this code allows you to register a form with the .dll and then add the invoke to OnPropertyChanged to avoid any threading issues. Is this correct?
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Dec 24, 2010
I get an AccessViolationException using this code (attempted to access protected memory, this is often an indication that other memory is corrupt) on the line in DoWaitNotify that copies the pixel data back to the location in memory. In my experience, that usually means that the array is too large, but it all seems to check out. Does image data expire after a certain time or something?
Public Class Form1
Private Const NUM_THREADS As Integer = 3
Private Original As Bitmap
[Code]....
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Jan 11, 2010
VS 2010 [RESOLVED] Marshal.ReadInt32 -> AccessViolationException
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Apr 28, 2012
I tried to translate this code to vb.net using Marshal.copy but I can't get it to work
for (int y = 0; y < bitmapdata.Height; y++)
{
byte* destPixels = (byte*)bitmapdata.Scan0 + (y * bitmapdata.Stride);
[Code]...
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Jun 20, 2012
I'm just needing a simple bit of code for vb.net that will allow me to marshal an object into a string, allowing for the saving and loading of this string so I can save my classes, needs to be simple and easy!
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Sep 24, 2010
Marshal attributes to be passed as an argument in this Declare statement? [code]...
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May 17, 2010
I've created a simple Windows Forms Application and the idea is I want to identify all instances of Excel, save any open workbooks to my desktop and close all the Excel instances down.[code]I'm pretty new to this C# business so hints on the following two possible issues I've identified would be much appreciated:The ForEach loop doesn't seem to be successfully looping through the XlApp.Workbooks collection as I was hoping.
It seems that I can't quit each Excel application which, with my current code structure, is causing an infinite loop. My suspicion is that Marshal.GetActiveObject() is locking it up and preventing it from closing?If nothing obvious jumps out then I might try the alternative method by Andrew Whitechapel mentioned and linked to on this thread.
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Dec 5, 2010
I get this error on this line: System.Runtime.InteropServices.Marshal.Copy _
(Scan0, Data2, 0, Data2.Length)
"Attempted to read or write protected memory. This is often an indication that other memory is corrupt."
I also sometimes get an error on this line:
Dim dc1 As IntPtr = CreateDC("DISPLAY", Nothing, Nothing, CType(Nothing, IntPtr))
What I'm trying to do is take a screenshot and then read the colors of pixels. I currently have a working vb.net copyfromscreen method but it's SLOW and using 100% cpu usage.
[Code]...
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Jun 14, 2011
I didn't think it fair to post a comment on Fredrik Mörk's answer in this 2 year old post, so I thought I'd just ask it as a new question instead..NB: This is not a critiscm of the answer in any way, I'm simply trying to understand this all before delving into memory management / the marshal class.
In that answer, the function GetByteArray allocates memory to each object within the given array, within a loop.Would the GetByteArray function on the aforementioned post have benefited at all from allocating memory for the total size of the provided array:
Dim arrayBufferPtr = Marshal.AllocHGlobal(Marshal.SizeOf(<arrayElement>) * <array>.Count)
I just wonder if allocating the memory, as shown in the answer, causes any kind of fragmentation? Assuming there may be fragmentation, would there be much of an impact to be concerned with? Would allocating the memory in the way I've shown force you to call IntPtr.ToInt## to obtain pointer offsets from the overall allocation pointer, and therefore force you to check the underlying architecture to ensure the correct method is used*1 or is there a better way? (ToInt32/ToInt64 depending on x86/64?)
*1 I read elsewhere that calling the wrong IntPtr.ToInt## will cause overflow exceptions. What I mean by that statement is would I use:
Dim anOffsetPtr As New IntPtr(arrayBufferPtr.ToInt## + (loopIndex * <arrayElementSize>))
I've read through a few articles on the VB.Net Marshal class and memory allocation; listed below, but if you know fo any other good articles I'm all ears![URL]..
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Mar 14, 2012
I've got a structure that's giving me fits. I have been searching the net looking for help on this and one posting says that you shouldn't use Marshal.SizeOf but to use SizeOf instead. However, I can't seem to figure out how to do this in VB.Net.
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