adding an example to illustrate custom QObject nesting

Author: aeyno

Cargo.toml

@@ -9,4 +9,5 @@ members = [
     'examples/todos',
     'examples/webengine',
     'examples/qenum',
+    'examples/nested_qobjects',
 ]

examples/nested_qobjects/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "nested_qobjects"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+qmetaobject = { path = "../../qmetaobject" }
+cstr = "0.2"

examples/nested_qobjects/README.md

@@ -0,0 +1,3 @@
+# Nested QObjects
+
+This example illustrate how to put a `QObject` inside another `QObject` using `RefCell`.

examples/nested_qobjects/src/main.rs

@@ -0,0 +1,95 @@
+use cstr::cstr;
+use qmetaobject::{
+    qml_register_type, qt_base_class, qt_method, qt_property, qt_signal, QObject, QString,
+    QmlEngine,
+};
+use std::cell::RefCell;
+
+// Here we define a custom QObject Person with a property and two methods.
+#[derive(QObject, Default)]
+struct Person {
+    base: qt_base_class!(trait QObject),
+    name: qt_property!(QString; NOTIFY name_changed),
+    name_changed: qt_signal!(),
+}
+
+impl Person {
+    fn set_name(&mut self, name: String) {
+        self.name = name.into();
+        self.name_changed();
+    }
+
+    fn get_name(&self) -> String {
+        self.name.to_string()
+    }
+}
+
+// Now we want to use the Person as a property of another QObject.
+#[derive(QObject, Default)]
+struct Greeter {
+    base: qt_base_class!(trait QObject),
+
+    // To store our Person QObject as a property of another QObject, we need to use a RefCell.
+    person: qt_property!(RefCell<Person>; NOTIFY person_changed),
+    person_changed: qt_signal!(),
+
+    compute_greetings: qt_method!(
+        fn compute_greetings(&self, verb: String) -> QString {
+            // To access the person, we need to borrow it.
+            format!("{} {}", verb, self.person.borrow().get_name()).into()
+        }
+    ),
+    set_person_name: qt_method!(
+        fn set_person_name(&mut self, name: String) {
+            // To modify the nested object we need to borrow it as mutable
+            println!("Person name set to {}", &name);
+            self.person.borrow_mut().set_name(name);
+            self.person_changed();
+        }
+    ),
+}
+
+fn main() {
+    // We need to register our two custom QObjects with the QML engine.
+    qml_register_type::<Greeter>(cstr!("Greeter"), 1, 0, cstr!("Greeter"));
+    qml_register_type::<Person>(cstr!("Person"), 1, 0, cstr!("Person"));
+
+    let mut engine = QmlEngine::new();
+    engine.load_data(
+        r#"
+        import QtQuick 2.6
+        import QtQuick.Window 2.0
+        import Greeter 1.0
+
+        Window {
+            visible: true
+            Greeter {
+                id: greeter;
+                // Here we can directly set the person name inside the Greeter's Person property
+                person.name: "World"
+                // or we can use the set_person_name method to set the name
+                //Component.onCompleted : {
+                //    greeter.set_person_name("foo");
+                //}
+            }
+            Text {
+                id: txt
+                anchors.centerIn: parent
+                text: greeter.compute_greetings("hello")
+
+                // When the person's name changes, we update the text
+                Connections {
+                    target: greeter
+                    function onPersonChanged() {
+                        txt.text = greeter.compute_greetings("hello")
+                    }
+                }
+            }
+
+            
+        }
+    "#
+        .into(),
+    );
+    engine.exec();
+}