## `AppBar`
An `AppBar` can be placed at the top of an app and contains a leading button, title and extra content.
### Properties
- **`title`** (_in_ _string_): Defines the title of the app bar.
- **`leading_button_icon`** (_in_ _string_): Defines the icon of the leading button.
- **`style`** (_in_ _`AppBarStyle`_): Defines the style of the button.
### Callbacks
- **`leading_button_clicked()`**: Invoked when leading button clicked.
### Example
```slint
import { AppBar, IconButton, Icons, MagicWindow } from "@vivi/magic.slint";
export component MainWindow inherits MagicWindow {
min_width: 400px;
min_height: 600px;
VerticalLayout {
AppBar {
leading_button_icon: Icons.add;
title: "My app";
IconButton {
icon: Icons.add;
}
}
Rectangle {}
}
}
```