Can't write to Qt5 textEdit box with ui->control->setText(message) - qt

Question

I am trying to put the data passed to a mainwindow.cpp function on the screen with the typical ui->control->setText(message) without success. The same line works if it is in a timer loop or a button function but not from display_that_data function
"MainWindow::display_that_data()" is called from myudp.cpp with the following lines
MainWindow show_tlm;
show_tlm.display_that_data(data_source, buf_copy);
mainwindow.cpp (updated to include emitting a signal for a SIGNAL/SLOT connection)
The SIGNAL/SLOT connection is set up in the constructor with the following line
connect (this, SIGNAL (showdata_signal()), this, SLOT(showdata_slot()));
void MainWindow::display_that_data(QByteArray data_source, QByteArray tlmBuf){
QString msg ;
msg = " in display_that_data";
qDebug() << msg ;
ui->tlm_vals->setText(msg);
//generate a signal which will trigger showdata_slot
emit showdata_signal();
msg = " in display_that_data after emit showdata_signal()";
qDebug() << msg ;
}
void MainWindow::showdata_slot() {
QString msg = "showdata_slot called";
qDebug() << msg ;
ui->tlm_vals->setText(msg);
}
Runtime debug messages show that code is making it to the showdata_slot but it is still not writing to the ui->tlm_vals
" in display_that_data"
"showdata_slot called"
" in display_that_data after emit showdata_signal()"
but.... neither one of the ui->tlm_vals->setText(msg) lines are putting text on the ui
"MainWindow::realtimeDataSlot()" is called by at timer timout signal as follows:
void MainWindow::setupRealtimeDataDemo(QCustomPlot *customPlot) {
// setup a timer that repeatedly calls MainWindow::realtimeDataSlot
connect(&dataTimer, SIGNAL(timeout()), this, SLOT(realtimeDataSlot()));
dataTimer.start(1000);
}
void MainWindow::realtimeDataSlot(){
QString temp = QString("%1").arg(epochTime, 10, 10, QChar('0'));
ui->tlm_vals->setText(temp);
}
And this works perfectly (of course I have to disable it to see if showdata_slot is writing to the ui)
I thought the problem was a needed SIGNAL and SLOT connection to trigger the write to the ui but generating a SIGNAL/SLOT connection (which debug shows as working) still does not write to the ui from the slot function.
For completeness mainwindow.h contains the following
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
void setupRealtimeDataDemo(QCustomPlot *customPlot);
void display_that_data (QByteArray data_source, QByteArray tlmBuf);
private slots:
void realtimeDataSlot();
void showdata_slot();
private:
Ui::MainWindow *ui;
QTimer dataTimer;
What am I missing/doing wrong?

Answer 1

Somewhere deeply embedded in Qt there is a difference between gui mouse click generated event and code generated event and this somehow caues Qt behavior to vary with the same lines of code. I will repost a more more "root level" question on this topic.