CODEWITHSUNDEEP
c++multithreadingqt
Daniel Lauss
Daniel Lauss

Reputation: 17

Qt Threads call Function

I have a Class 'A' and in this class there is a method 'method1()' and method1 run in a qthread. In method1 I'd like to call a function in the MainWindow class like this: 'MainWindow window; window.func()'

When I do this i get this error message: QObject::setParent: Cannot set parent, new parent is in a different thread

Here is my Code:

void gCode_int::parse_File(char* gCode_file, int file_length,MainWindow *window)
{
    window->fahre_on_pos(NULL,atoi(x_pos.c_str()),atoi(y_pos.c_str()));
}

Here the function in MainWindow:

void MainWindow::fahre_on_pos(char* g_command ,int x_pos, int y_pos)
{    
double y_schritte;
double x_schritte;

int j =  1;
int x_length = x_pos-x_pos_old;
int y_length = y_pos-y_pos_old;

digitalWrite(x_treiber,1);
digitalWrite(y_treiber,1);

if(x_length > 0)
{
    digitalWrite(x_richtung, 1);
}
if(x_length <= 0)
{
    digitalWrite(x_richtung,0);
    x_length *= -1;
}

if(y_length > 0)
{
    digitalWrite(y_richtung, 0);
}
if(y_length < 0)
{
    digitalWrite(y_richtung,1);
    y_length *= -1;
}
y_schritte = round((y_length/1.25)*48);

if(y_schritte == 0)
{
    y_schritte =1;
    digitalWrite(y_treiber,0);
}
if(x_schritte == 0)
    digitalWrite(x_treiber,0);

x_schritte = round(((x_length/1.25)*200)/y_schritte);
while(j <= y_schritte)
{
    for(int i=1;i<= x_schritte;i++)
    {
        digitalWrite(x_v, 1);
        delay(1);
        digitalWrite(x_v, 0);
        delay(1);
    }
    if(x_schritte == 0)
    {
        digitalWrite(y_v, 1);
        delay(4);
        digitalWrite(y_v, 0);
        delay(4);
    }
    else
    {
        digitalWrite(y_v, 1);
        delay(1);
        digitalWrite(y_v, 0);
        delay(1);
    }
    j++;
}
x_pos_old = x_pos;
y_pos_old = y_pos;

}

Hope anybody can help me

Upvotes: 0

Views: 974

Answers (2)

Robert Wadowski
Robert Wadowski

Reputation: 1427

From http://doc.qt.io/qt-5/threads-qobject.html

Although QObject is reentrant, the GUI classes, notably QWidget and all its subclasses, are not reentrant. They can only be used from the main thread. As noted earlier, QCoreApplication::exec() must also be called from that thread.

In practice, the impossibility of using GUI classes in other threads than the main thread can easily be worked around by putting time-consuming operations in a separate worker thread and displaying the results on screen in the main thread when the worker thread is finished

Signals and slots should make connection between workers and main window, otherwise as stated it will not work

Upvotes: 0

gengisdave
gengisdave

Reputation: 2050

Create a slot in MainWindow which receive parameters from thread with a signal and invoke the method

Qt - updating main window with second thread

Upvotes: 0

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