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Type conversion problem#2375

feketeimre started this conversation inGeneral
May 7, 2024· 2 comments· 1 reply
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I am trying to interface with a .NET dll to read stuff from a camera and i have trouble figuring out the types for a function call. Admittedly i have just started using pythonnet so my problem might be trivial.

Here is the truncated version of my program:

importclrfromSystemimport*clr.AddReference('PylonC.NET')fromPylonC.NETimportPylonfromPylonC.NETimportPylonBufferfromPylonC.NETimportPylonGrabResult_thDev=Pylon.CreateDeviceByIndex(0)imgBuf=PylonBuffer[Byte](None)#PylonBuffer<Byte> imgBuf = null; Is None correct here ?grabResult=PylonGrabResult_t()ret=Pylon.DeviceGrabSingleFrame(hDev,Int32(0),imgBuf,grabResult,UInt32(500))# the above raises an exception:# System.ArgumentException: PylonC.NET.PylonBuffer`1[System.Byte] value cannot be converted to PylonC.NET.PylonBuffer`1[T] in method# Boolean DeviceGrabSingleFrame[T](PylonC.NET.PYLON_DEVICE_HANDLE, Int32, PylonC.NET.PylonBuffer`1[T] ByRef, PylonC.NET.PylonGrabResult_t ByRef, UInt32)

I have doubts if the imgBuf = PylonBufferByte is equivalent to the original c: PylonBuffer imgBuf = null;
But mainly the type conversion error is what i have no idea why it doesnt work. I am certain that Byte is a valid type for PylonBuffer.
With dnSpy i looked into the problematic function and found this:
grab 2024-05-07 210235

Also im not sure how to deal with the ref and out keywords.

Any help is welcomed,
Thank you

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Replies: 2 comments 1 reply

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Hi I got the same question. Did you figure it out? Like how to convert imgBuf into the ref type needed in C# function? Thank you!

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1 reply
@feketeimre
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Hi, unfortunately no, i stopped trying.

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I spent time on this and managed to figure it out, sort of...
The function expects a generic type [T] but i have [Byte]. When passing Byte to this function it gives the exception as previously mentioned:

# System.ArgumentException: PylonC.NET.PylonBuffer`1[System.Byte] value cannot be converted to PylonC.NET.PylonBuffer`1[T] in method .....

Apparently, you can construct a specific type of the function like:

grabFrame=Pylon.DeviceGrabSingleFrame[Byte]ret=grabFrame(hDev,Int32(0),imgBuf,grabResult,UInt32(500))

In most cases i think this would work, but in my case i need to pass imgBuf and grabResult by reference that cannot be done in pythonnet.

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