Button - Hello, Button!

Keeping the tradition, this is a simple "Hello, World" button example. We will show how to create a button and associate an action to be performed when you click on it.

The first part consists of including the headers. In this case we are only working with the Elementary C++ binding and thus we need only to include him.

#include <Elementary.hh>

If necessary the C and/or the C++ headers should be include here as well.

Now we need to actually start the code and set the elm_policy, which defines for a given policy group/identifier a new policy's value, respectively. In this example the only policy we need to set a value for is ELM_POLICY_QUIT, possibles values for it are:

elm_main (int argc, char *argv[])

As you can see, the policy we chose was to quit when the last win is hidden as opose to examples with the C bindings where we perpetually set it to quit when last win was closed. This changed was necessary because in C++ binding as the elm mainloop stop running all object are destroyed, references are unreferenced and events are stopped at ELM_MAIN().

See also
For more details consult elm_policy_set

Next step is creating an Elementary window, where win calls a constructor and sets the type of the win to ELM_WIN_BASIC (Elm_Win_Type), which is the indicated type for most of our examples. Here we also set the title that will appear at the top of our window and then the autohide state for it.

The autohide works similarly to autodel, automatically handling "delete,request" signals when set to true, with the difference that it will hide the window, instead of destroying it.

It is specially designed to work together with ELM_POLICY_QUIT_LAST_WINDOW_HIDDEN which allows exiting Elementary's main loop when all the windows are hidden.

win.title_set("Hello, World!");

autodel and autohide are not mutually exclusive. The window will be destructed if both autodel and autohide is set to EINA_TRUE or true.

Now we construct the elm background and for this we use the C++ method below, setting it's parent.

::elm::bg bg(efl::eo::parent = win);

The function size_hint_weight_set for C++ bindings originated from C bindings function evas_object_size_hint_weight_set, that is EFL Evas type function. With this function we set the hints for an object's weight. The parameters are:

This is not a size enforcement in any way, it's just a hint that should be used whenever appropriate. This is a hint on how a container object should resize a given child within its area.

Containers may adhere to the simpler logic of just expanding the child object's dimensions to fit its own (see the EVAS_HINT_EXPAND helper weight macro in the EFL Evas Documentation) or the complete one of taking each child's weight hint as real weights to how much of its size to allocate for them in each axis. A container is supposed to, after normalizing the weights of its children (with weight hints), distribute the space it has to layout them by those factors – most weighted children get larger in this process than the least ones.

bg.size_hint_weight_set(EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);

Default weight hint values are 0.0, for both axis.

Now we add the background as a resize_object to win informing that when the size of the win changes so should the background's size. And finally we make it visible.

If a color it's not setted the default color will be used.

There is only one button on this interface. We need to create this button with the C++ method, set the text to be displayed, the size, position and the size hint for weight.

For alignment we'll use the function size_hint_align_set for C++ bindings originated from C bindings function evas_object_size_hint_align_set, that is EFL Evas type function. With this function we set the hints for an object's alignment. The parameters are:

These are hints on how to align an object inside the boundaries of a container/manager. Accepted values are in the 0.0 to 1.0 range, with the special value EVAS_HINT_FILL used to specify "justify" or "fill" by some users. In this case, maximum size hints should be enforced with higher priority, if they are set. Also, any padding hint set on objects should add up to the alignment space on the final scene composition.

For the horizontal component, 0.0 means to the left, 1.0 means to the right. Analogously, for the vertical component, 0.0 to the top, 1.0 means to the bottom.

This is not a size enforcement in any way, it's just a hint that should be used whenever appropriate.

Default alignment hint values are 0.5, for both axis.

Continuing with our button we make it visible.

This button performs a basic action: close the application. This behavior is described by on_click() which is a lambda function, that interrupt the program invoking elm_exit(). The lambda function on_click is the added as a clicked callback to btn.

See also
For more details consult Lambda Functions with Elementary - C++11

Now we set the size for the window, making it visible in the end:

Finally we just have to start the elm mainloop, starting to handle events and drawing operations.

The full code for this example can be found at button_cxx_example_00.cc .

This example will look like this: