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LAttribute Class

#include <Layers/lattribute.h>

Inherits:

LObject

Public Functions

	LAttribute(const LString& name, LObject* parent = nullptr)
	LAttribute(const LString& name, const char* value, LObject* parent = nullptr)
	LAttribute(const LString& name, LVariant value, LObject* parent = nullptr)
	LAttribute(const LString& name, LJsonObject json_object, LObject* parent = nullptr)
T	as(const std::vector<LString>& state_combo = std::vector<LString>())
T*	as_if(const std::vector<LString>& state_combo = std::vector<LString>())
void	break_link()
void	clear_overrides()
void	clear_theme_attribute()
void	create_override(const LString& name, const char* value)
void	create_override(const LString& name, LVariant value)
LAttributeList	dependent_attributes(bool include_indirect_dependencies = false) const
void	disconnect_change(const LConnectionID& connection)
void	disconnect_link_change(const LConnectionID& connection)
bool	has_overrides() const
LJsonObject&	json_object()
LAttribute*	link_attribute() const
LString	link_path() const
LConnectionID	on_change(std::function<void()> callback)
LConnectionID	on_link_change(std::function<void()> callback)
LAttribute*	override_attribute(const std::vector<LString>& state_combo)
LAttributeMap	overrides() const
LString	path() const
void	set_link_attribute(LAttribute* link_attr)
void	set_link_path(const LString& link_path)
void	set_theme_attribute(LAttribute* theme_attr)
void	set_value(const char* value)
void	set_value(const LVariant& value)
LJsonObject	to_json_object()
LJsonValue	to_json_value()
size_t	type_index() const
LVariant	value()

Related Non-Members

LAttributeList

LAttributeMap

LVariant

Detailed Description

An LAttribute is a LObject that serves as a value container for Layers widgets and themes.

An attribute stores its value as an LVariant object.

Usage varies depending on the parent type. Typically, an LAttribute is owned by either a Layers widget (LThemeable subclass), an LThemeItem, or another LAttribute. These are referred to as widget attributes, theme attributes, and override attributes, respectively.

Widget attributes change the appearance of their parent widgets.

Theme attributes modify the value of widget attributes.

Override attributes overtake the value of their parent attributes when the value is requested with a state-combination that matches the override attribute.

Applying Theme Attributes to Widget Attributes

When a theme is applied to a Layers widget via LThemeable::apply_theme_item(), the theme attributes are applied to the widget's attributes using set_theme_attribute(). After this, when the value is requested from one of the widget attributes, the value of the theme attribute is returned instead.

Attribute Linking

An attribute can be linked to another attribute. In this case, it will use the value of the other attribute instead of its own. For example:

LAttribute* slider_value = new LAttribute("Slider Value", 0);
LAttribute* thickness = new LAttribute("Thickness", 10);
 
slider_value->set_link_attribute(thickness);
 
//  After set_link_attribute() is called above, slider_value is linked to
//  thickness, so the thickness value represents both attributes.
 
slider_value.set_value(15);
 
//  The above call actually sets the value of thickness to 15.

In the example above, slider_value is linked to thickness. After the relationship is established, slider_value is considered a dependency of thickness. A list of dependent attributes can be obtained through calling dependent_attributes():

//  ... continued from above
 
LAttributeList thickness_dependencies = thickness->dependent_attributes();
 
//  thickness_dependencies should contain the slider_value attribute.

Linking Theme Attributes (Soft Linking)

Themes support linking through their theme attributes. Most links are handled within themes so that they can be manipulated during theme editing. These links are referred to as soft links since they are intended to be changeable.

A theme attribute links to another by storing a link path which is a string that identifies the theme attribute being linked to. Themes do not resolve these path-based links until the end of the loading process.

Linking Widget Attributes (Hard Linking)

Links can also be established outside of themes between widget attributes directly. This is typical for control widgets where users interact with the widget to control a particular value. For example:

// Example using classes from QLayers:
 
QLWidget* widget = new QLWidget;
QLSlider* thickness_slider = new QLSlider;
 
thickness_slider->value()->set_link_attribute(widget->border_thickness());
 
//  After the above link is established, when the user interacts with
//  thickness_slider, the widget's border thickness will change.

These links are referred to as hard links since they are established by the developer and not intended to be changeable.

Override Attributes

Sometimes, you want one attribute to have multiple values. Consider a button whose fill value changes when the mouse hovers over it. This can be handled by adding an override attribute to the fill attribute:

// Initialize button_fill with green color
LAttribute* button_fill = new LAttribute("Button Fill", "#23d143");

// Create override that changes the fill to a light-green color when selected
button_fill->create_override("Selected", "#2bf250");

Override attributes can not have other override attributes.

JSON Data Format

The JSON data for an attribute is formatted as follows:

{
    "value": <int,string,object>,    // The attribute's value (if not linked)
    "linked_to": <link_path>,        // The attribute's link path (if linked)
    "overrides": {                   // The attribute's overrides (if any)
        <attr_name>: <attr_object>,  // First override attribute
        ...                          // Any other override attributes follow (if any)
    }
}

If the attribute is linked, it will store a linked_to value containing the link-path.

If the attribute is not linked, it will store a value value containing the attribute's value. The attribute values can have different types. The following are some examples of attribute values in JSON format:

"value": 10           // Stores a number as an integer

"value": "#36393f"    // Stores a color-name as a string

"value": {            // Stores a gradient as an object
    "gradient": [
        "0:#3a3c42",
        "1:#42454d"
    ]
}

Member Function Documentation

Related Non-Members