GValue
GObject.Value
open in new window is a generic value container, usually only used to implement GObject Properties in projects written with the C programming language. By storing the value type alongside the value, it allows for dynamic type features usually not available to C programmers.
In JavaScript, this behaviour is part of the language (i.e. typeof
) and GJS will usually convert them automatically, but there are some situations that require using GObject.Value
directly.
Basic Usage
Before a newly created GValue can be used, it must be initialized to hold a specific GType:
const {GObject} = imports.gi;
// Create a new GValue
let value = new GObject.Value();
// Initialize it to hold a boolean
value.init(GObject.TYPE_BOOLEAN);
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Although you should always use native JavaScript accessors for properties, the property methods can be used to demonstrate how to work with GValue:
const {GObject, Gio} = imports.gi;
const action = new Gio.SimpleAction({
name: 'test',
enabled: false,
});
// Create a new boolean GValue
const booleanValue = new GObject.Value();
booleanValue.init(GObject.TYPE_BOOLEAN);
// Set the GValue from a property
action.get_property('enabled', booleanValue);
// Check the result
if (booleanValue.get_boolean())
log(`${action.name} is enabled`);
else
log(`${action.name} is disabled`);
// Set the GValue
booleanValue.set_boolean(true);
// Set the property from the GValue
action.set_property('enabled', booleanValue);
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Type Safety
The type of an existing GObject.Value
can be checked by calling GObject.type_check_value_holds()
open in new window:
const {GObject, Gio} = imports.gi;
const booleanValue = new GObject.Value();
booleanValue.init(GObject.TYPE_BOOLEAN);
if (GObject.type_check_value_holds(booleanValue, GObject.TYPE_BOOLEAN)
log('GValue initialized to hold boolean values');
if (!GObject.type_check_value_holds(booleanValue, GObject.TYPE_STRING)
log('GValue not initialized to hold string values');
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