ListenEvent

This function sets a callback function that will be executed when an event occurs.

Syntax

void ListenEvent(const EventId id, shared_ptr<Widget> source, bool callback(const Event& event, shared_ptr<Object> extra), shared_ptr<Object> extra = NULL)

Parameter	Description
id	event ID to listen for, or EVENT_NONE to listen for all events
source	event source to listen for, or NULL for events emitted from any source
callback	function to call when event is triggered
extra	extra object to pass to the callback function

Remarks

Internally, this function will store a weak pointer to the event source and a shared pointer to the extra field.

If the callback function returns false no more callbacks will be executed and no event will be added to the event queue.

Example

The first example shows another way to quit the program when the window is closed:

#include "UltraEngine.h"

using namespace UltraEngine;

bool EventCallback(const Event& ev, shared_ptr<Object> extra)
{
    exit(0);
}

int main(int argc, const char* argv[])
{
    //Get the displays
    auto displays = GetDisplays();

    //Create window
    auto window = CreateWindow("Ultra Engine", 0, 0, 800, 600, displays[0]);

    //Create user interface
    auto ui = CreateInterface(window);

    ListenEvent(EVENT_WINDOWCLOSE, window, EventCallback);

    while (true)
    {
        WaitEvent();
    }
    return 0;
}

The example below demonstrates how an event listener can be used for custom resizing behavior:

#include "UltraEngine.h"

using namespace UltraEngine;

bool EventCallback(const Event& ev, shared_ptr<Object> extra)
{
    auto panel = extra->As<Widget>();
    iVec2 sz = panel->GetParent()->ClientSize();
    panel->SetShape(50, 50, sz.x - 100, sz.y - 100);
    panel->SetText(String(sz.x) + " x " + String(sz.y));
    return true;
}

int main(int argc, const char* argv[])
{
    //Get the displays
    auto displays = GetDisplays();

    //Create window
    auto window = CreateWindow("Ultra Engine", 0, 0, 800, 600, displays[0], WINDOW_TITLEBAR | WINDOW_RESIZABLE);

    //Create user interface
    auto ui = CreateInterface(window);
    iVec2 sz = ui->root->ClientSize();
    auto panel = CreatePanel(50, 50, sz.x - 100, sz.y - 100, ui->root);
    panel->SetColor(0, 0, 0);

    //Comment this line out to see why it is needed. ;)
    ListenEvent(EVENT_WINDOWSIZE, window, EventCallback, panel);

    while (true)
    {
        const Event ev = WaitEvent();
        switch (ev.id)
        {
        case EVENT_WINDOWCLOSE:
            if (ev.source == window) return 0;
            break;
        case EVENT_WINDOWSIZE:
            sz = panel->GetParent()->ClientSize();
            panel->SetShape(50, 50, sz.x - 100, sz.y - 100);
            panel->SetText(String(sz.x) + " x " + String(sz.y));
            break;
        }
    }
    return 0;
}