GUI with c++. lagged when i use button - c++

Question

am new in C++ GUI, am modifying a code sent with a machine to me, i want to make a while loop when i click button, i tried the thread and it is still stuck.
void CDlgWriteEPC::loop()
{
// Do something
}
void CDlgWriteEPC::OnBnClickedOk()
{
std::thread loadingThread(&CDlgWriteEPC::loop, this);
loadingThread.join();
}

Answer 1

join blocks the current thread until the other thread is done, so that's no help.
You should start the worker thread, return immediately and the worker thread
should send some kind of message when it's done.
The function names in your example code seem to look like it's from a MSVC++ MFC
application so we'll work with that.
Simply put, windows GUI applications are event driven, each time a event happens a
WM_MESSAGE is sent. The framework receives these messages and calls the appropriate
functions to handle it. We can define our own messages and message handlers.
This way the worker thread can send such messages to the framework and it will call
our handler function.
WM_APP is defined as a starting point for private user messages, so there won't be
any conflict with already existing system messages.
(https://msdn.microsoft.com/en-us/library/windows/desktop/ms644930%28v=vs.85%29.aspx)
So, imagine we are building a MFC dialog application that searches something in a file.
If the file is big it can take a long time and to prevent blocking the main thread and
getting a 'window is not responding' message we need to do this in a worker thread. We might
also want a progress bar for example.
First, we define our own messages inside our existing dialog class starting from WM_APP + 1
and we add our handler functions, these must be of the following type:
afx_msg LRESULT (CWnd::*)(WPARAM, LPARAM)
WPARAM and LPARAM are parameters passed when posting the message, you can use them to send
custom data. In our example we can use them to send the % progress for our progress bar.
(https://msdn.microsoft.com/en-us/library/k35k2bfs.aspx)
class CMyAppDlg : public CDialogEx
{
public:
//Public so the worker thread class can use these same sames when posting a message.
enum Messages
{
MSG_ThreadProgress = WM_APP + 1,
MSG_ThreadDone
};
private:
afx_msg LRESULT OnThreadProgress(WPARAM wParam, LPARAM lParam)
{
ProgressBar->SetPos(wParam); //Worker thread posts progress as wParam
};
afx_msg LRESULT OnThreadDone(WPARAM wParam, LPARAM lParam)
{
//Get result from worker thread class and use it...
};
};
Then we need to add our messages and handlers to the message map, you should add them to the already
existing message map in the .cpp file for the dialog/document.
BEGIN_MESSAGE_MAP(CMyAppDlg, CDialogEx)
ON_MESSAGE(MSG_ThreadProgress, &CMyAppDlg::OnThreadProgress)
ON_MESSAGE(MSG_ThreadDone, &CMyAppDlg::OnThreadDone)
END_MESSAGE_MAP()
Now we can simply post these messages in our worker thread and the framework main thread will handle
the messages and update the progress bar or use the result:
class ThreadClass
{
public:
//Constructor takes a reference to our dialog class because we need the window handle
//to post a message
ThreadClass(CMyAppDlg& MyAppDlg) : mMyAppDlg(MyAppDlg) {};
void operator()() //Thread worker code...
{
while (what_we_look_for_not_found)
{
int Progress = 0;
//Search for a while and update progress variable...
//Post message to dialog asking it to update the progressbar
PostMessage(mMyAppDlg.m_hWnd, CMyAppDlg::MSG_ThreadProgress, Progress, 0);
}
//Finished searching...
StoreResult();
//Post message to dialog informing it thread is done and result can be retrieved.
PostMessage(mMyAppDlg.m_hWnd, CMyAppDlg::MSG_ThreadDone, 0, 0);
}
private:
CMyAppDlg& mMyAppDlg;
};
QT uses a similar system with SIGNAL and SLOT and other frameworks surely have their own equivalent system.
You should be able to find more information in the manuals if you are using something else then MSVC++ MFC.