Focus is a graphical user interface concept. A component, for example, a UI component, has a focus when it is selected to receive input from the user. The input can be an event, such as mouse button click or key press.
Focusing can be immediate (selected by the touchscreen or mouse) or relative (selected by a key press).
There are mainly two ways to set focus on a graphical elements:
Direct selection does not really need any kind of special treatment as the user explicitly selects the UI component to interact with.
Relative selection' default order is the one the UI components have been added to the canvas. That may not be appropriate, if they are added programmatically in different order than they appear on-screen.
The order the focus goes from a UI component to another is called the focus chain. As said before, the default focus chain is set to the order the UI components have been added to the canvas.
An object can be focused if the following conditions apply:
If any of these conditions do not apply, the object is unfocusable.
Handling of the keys is done automatically by Elementary. According to which
key the user pressed, Elementary switches the focus in the selected direction.
For example, using the
Tab key the focus goes to the next object in the
natural order, whereas using the direction keys the focus goes to the next
object in the requested direction.
When a UI component is hidden, deleted, or disabled, it becomes unfocusable.
When a focused object is unfocusable, the focus is moved to another object.
When the user wants to switch the focus to the next object (i.e. cycle focus), Elementary searches the first object which is focusable.
If there is a disabled or read-only object in the focus chain, the focus goes to the following object in the requested direction.
There are several reasons why to customize the focus chain of an application, for example:
Set the object to focus after other object in a specific direction using
elm_object_focus_next_object_set(object, next, direction). Use the
ELM_FOCUS_NEXT: next UI component in natural order
ELM_FOCUS_PREVIOUS: previous UI component in natural order
ELM_FOCUS_UP: UI component to focus when going up
ELM_FOCUS_DOWN: UI component to focus when going down
ELM_FOCUS_RIGHT: UI component to focus when going right
ELM_FOCUS_LEFT: UI component to focus when going left
Set the object next to another in a specific direction using
To customize the application's custom chain:
Evas_Object *main, *obj1, *obj2, *obj3, *obj4, *obj5; Eina_List *focus_chain = NULL; focus_chain = eina_list_append(focus_chain, obj3); focus_chain = eina_list_append(focus_chain, obj2); // The chain is obj3, then obj2. We set it. elm_object_focus_custom_chain_set(main, focus_chain); // Here we prepend obj5 at the beginning of the chain. elm_object_focus_chain_prepend(main, NULL, obj5); // We append obj1 after obj3. elm_object_focus_chain_append(main, obj3, obj1); // We prepend obj4 before obj1. elm_object_focus_chain_prepend(main, obj1, obj4);
The focus chain is
obj5, obj3, obj4, obj1, obj2.
This actually applies to any container: it is possible to set the focus chain of, for example, a box.
If an object is part of a focus chain and has the next focused object defined, the next object takes precedence over the focus chain.
Following on the previous example, if
obj5 defined as its
next object, the actual focus chain is
obj5, obj3, obj4, and loop back to
If your Evas object has several sub-objects, set its focus chain using the same functions as for the application. Elementary first follows the main focus chain, and then the focus chain of each UI component if applicable.
elm_object_focus_get(object) to set whether a specific object has the
focus. Set the focus to an object using
set is a Boolean value. If it is set to
EINA_TRUE, the focus is
set to that given object. If it is set to
EINA_False, the focus is unset
and passed back to the previous element in the focus chain. Set the focus only
after the object is shown, that is, after
been called. Call the function back when the object receives or loses focus by
registering on smart event “focused” or “unfocused”
elm_object_tree_focus_allow_set(object, focusable) to tell Elementary
whether an object and its children are focusable, where
focusable is a
Boolean value. Get the current value using
The similar functions for a specific object are
elm_object_focus_allow_set(object, focusable) and