Ensemble Graphics Toolkit: Events
Introduction
In this training, you will learn how to create a button widget and add source code for an event to handle a button click.
Steps:
- Create a New Source File
- Event Handling
Prerequisites
You have prepared the Host PC with all the development software tools and Ensemble Graphics Toolkit source code as explained in:
You have installed and prepared the Eclipse IDE for C/C++ Developers as explained in:
Create a New Source File
In this section, you will be creating a new event.cpp source file that you will build in this and later training demonstrating the following classes:
Start the Eclipse IDE
Eclipse will ask you to select a directory for your workspace. Accept the default directory and click on the Launch button.
Eclipse will launch the previous workspace you configured.
You will be adding a new source file with the name: event.cpp. If you have a *.cpp source file from a previous Ensemble Graphics Toolkit training, perform the following steps:
The Exclude from build window will open:
The selected *.cpp will be excluded from the build.
Right click on EgtProject and select New > Source File.
The New Source File window will open:
Enter event.cpp into the Source file: text box. Click on the Finish button.
A new source file tab event.cpp is created within EgtProject.
Enter the following source code to the event.cpp window pane:
#include <iostream>
using namespace std;
using namespace egt;
int main(int argc, const char ** argv)
{
Application app;
TopWindow window;
Button button(window, "Press Me");
center(button);
window.show();
return app.run();
}
You have completed adding a new source file to EgtProject.
Event Handling
In this section, you will modify and build the source code you added in the previous section to create a button widget and an event to handle a button click event.
Modify the event.cpp source code by adding the following lines of code:
#include <iostream>
using namespace std;
using namespace egt;
int main(int argc, const char ** argv)
{
Application app;
TopWindow window;
Button button(window, "Press Me");
center(button);
// event handling
button.on_event([ & ](Event & event)
{
if (event.id() == EventId::pointer_click)
{
cout << "clicked!" << endl;
}
});
window.show();
return app.run();
}
To build the project, hover over EgtProject, right-click, and select Build Project from the menu. Or you can click on the Build icon.
The Console window (bottom pane) will display the build progress.
In the left-hand pane, select EgtProject Debug (under C/C++ Remote Application).
In the Run Configurations window, enter the following in the Remote Absolute File Path for C/C++ Application: text box:
/root/event
This is the location of the event.cpp executable will be loaded and run on the target.
Observe the WVGA Display on the target:
The event.cpp executable is running remotely on the target.
Observe the Press Me button in the center of the WVGA Display. When you click on the button you will see clicked! displayed on the Console.
/root/event; exit
clicked!
clicked!
clicked!
Event class
From ~/egt/docs/html/annotated.html, click on the Event class. All the functions, attributes and constructor associated with the class is documented here.
In this training, you used the id() function to get the id of the button click event (pointer_click) and you handled it by printing a message to the console.
Here is a list of some event identifiers:
| Event Identifier | Description |
|---|---|
| none | |
| raw_pointer_down | Raw pointer event. It's usually preferred to use the normal pointer events instead. |
| raw_pointer_up | Raw pointer event. It's usually preferred to use the normal pointer events instead. |
| raw_pointer_move | Raw pointer event. It's usually preferred to use the normal pointer events instead. |
| pointer_click | pointer event. |
| pointer_dblclick | pointer event. |
| pointer_hold | pointer event. |
| pointer_drag_start | pointer event. |
| pointer_drag | pointer event. |
| pointer_drag_stop | pointer event. |
| keyboard_down | keyboard event. |
| keyboard_up | keyboard event. |
| keyboard_repeat | keyboard event. |
Summary
In this training, you learned how to create a button widget and add source code for an event to handle a button click.
What’s Next?
There’s plenty more to learn. Here are some additional Ensemble Graphics Toolkit training resources to help you gain more knowledge and skills: