GTKmm entry to console output lags 1 character

Question

So I am trying to make a program, which copies the input of an Gtk::Entry and outputs it to the console. However, currently when I enter the first character, nothing happens. Once I enter a second character, the first character gets printed, once I enter a third character, the first 2 characters get printed. When I enter the 4th character, the first 3 get printed. I want it so that when I enter the first character, the first character gets printed, once I enter the second character, the first 2 get printed, and so on.

This is my current inputbox.cpp

#include "inputbox.h"
#include <iostream>

inputBox::inputBox(){
    this->signal_key_press_event().connect(sigc::mem_fun(*this, &inputBox::onKeyPress),false);
}

bool inputBox::onKeyPress(GdkEventKey* event){
    huidigeInput = get_text();
    std::cout << huidigeInput;
    set_text("");
    return false;
}

and this is my inputbox.h file

class inputBox : public::Gtk::Entry{
public:
    inputBox();
    bool onKeyPress(GdkEventKey*);

    Glib::ustring huidigeInput;
};

I hope someone can find the bug problem!

Answer 1

Let's look at the series of actions when a key press event is triggered.

1. Your callback grabs the text in the Entry and sends it to std::cout.
2. The default handler converts the keystroke to a character and adds it to the text in the Entry.

Naturally, if you grab the text before a character is added to the text, then you will not grab that character. You have to wait until after the character has been added.

The reason that your callback runs before the default handler is that you specified false as the after argument to connect(). If you omitted this parameter or specified true, then the default handler would run before yours. Of course, the default handler might think the event is fully handled and block handlers that run after it.

To be sure you get the behavior you want, it might be better to override the virtual function on_key_press_event() than to explicitly connect to signal_key_press_event(). This allows you to insert your code just before the default processing returns its value.

bool inputBox::on_key_press_event(GdkEventKey * key_event)
{
    // Start with the default processing.
    bool retval = Gtk::Entry::on_key_press_event(key_event);
    
    // Now your functionality:
    huidigeInput = get_text();
    std::cout << huidigeInput;
    set_text("");
    
    // Preserve what the default processing wanted to return.
    return retval;
}