How to share Serial port object between two classes

saurabh162

Hello mrjj and MrShawn,

signals and slot approach has solved my problem cleanly.

Thank you very much for help :)

kind regards
Saurabh Jain

saurabh162

Hello Developers,

As mentioned above I was to send command using signals and slot approach to main window.

Now I want also to read data received from serial port in MainWindow from Dialog box.

I have read that signal and slot approach is not good to get data or return values. So can you please guide me what can I do ?

thanks you very much :)

mrjj

@saurabh162
Hi
You mean after serial have read all in main, you want to
send it to a dialog you open ?
Or do you mean that dialog all reads from serial while data is coming in ?

jsulm

@saurabh162 Add a getter method to your dialog:

Dialog dialog(this);
dialog.exec();
MyData data = dialog.data();

saurabh162

@mrjj

Hello Mrji,

thank you for fast reply

Yes, I my application data received from serial port is first stored in buffer in Main Window. I want read this saved data from Dialog box.

In dialog box I am sending serial port commands to Main Window using signal and slot. But do not know what is right way to read serial data saved in Main window from Dialog Box.

saurabh162

@jsulm

Hello jsulm

Thank you for your fast response.

I am sorry but i could not understand your solution. I have serial data collected in Main window. This i want to read inside Dialog box.

So can you please explain your answer in little details

Thank you :)

aha_1980

@saurabh162 said in How to share Serial port object between two classes:

I have read that signal and slot approach is not good to get data or return values. So can you please guide me what can I do ?

Where have you read this? You can surely use signals&slots to exchange data. That's what signals&slots are all about :)

jsulm

@saurabh162 You should explain better what you want to do.
Pass the data from main window to dialog via constructor:

Dialog dialog(this, mySerialData);
dialog.exec();

saurabh162

@aha_1980

Thank you aha for reply

I have read it in following posts

https://forum.qt.io/topic/11000/getting-a-return-value-from-an-emitted-signal/3

https://stackoverflow.com/questions/5842124/can-qt-signals-return-a-value

According to above posts we should be cautious when we are returning data from a slot.

Additionally I have tried it and got segmentation fault. Following are the steps I have taken.

I have a array " char receive_buffer[RBSIZE]" declared in Main window class with private access. This buffer is always filled with new data when we send serial command from Dialog Box using signal and slot.
In order to read this buffer, I declared char pointer in my Dialog Box and intialize this pointer to address of "receive_buffer" in Serial communication slot in Main Window.
After this when I try to read data in receive_buffer[RBSIZE] from Dialog Box using char pointer I get segementation fault.

Please let me know if you need any other information.

thank you :)

aha_1980

@saurabh162

https://forum.qt.io/topic/11000/getting-a-return-value-from-an-emitted-signal/3

Yes, thats bad design. But you don't need to do it like this. You can emit another signal from your dialog when data is ready, and connect it to a slot in your main window.

Regards

saurabh162

@aha_1980

ok aha_1980 I try this and will update you ..thanks :)

saurabh162

hello aha_1980,

Thank you very much it worked.

I have taken following steps to achieve it. It is working but I also want to ensure whether it is correct way of programming.

I have created signal (in Dialog Box) and slot (in main window) with same name
"void ReadSerialBuffer(void);"
Declared a array char serialReceivebuffer[RBSIZE]; in dialog box. Additionally a public function "UpdateSerialReadBuffer"in Dialog box to copy data from source buffer to serialReceivebuffer in Dialog Box.
After this I defined slot in main window which is calling "UpdateSerialReadBuffer" function of dialog box to copy data from buffer in Main window to buffer in Dialog box.
In end I connected both signal and slot using "connect" method

Thank you very much :)

viniltc

@saurabh162

I also came across a similar situation. I'm a beginner of Qt and c++. It will be very helpful if you could share a sample code to communicate the serial port object in two forms.

many thanks