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我正在尝试使用 gtk4 绑定来学习 rust,并决定尝试ListStore作为ListBox. 为了绑定模型,Widget需要返回的函数,但我需要一个Label. 为什么Label继承Widget(实现IsA<Widget>)的不满足Widget类型?

错误:

error[E0308]: mismatched types
  --> src/main.rs:22:5
   |
21 | fn create_widget<'r>(label: &'r Object) -> Widget {
   |                                            ------ expected `gtk4::Widget` because of return type
22 |     Label::new(Some(label.property_value("name").get().unwrap()))
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `gtk4::Widget`, found struct `gtk4::Label`

完整代码:

use gtk::prelude::*;
use gtk::{Application, ApplicationWindow, Paned, Label, Orientation, ListBox, ListBoxRow, Widget};
use gtk::gio::ListStore;
use gtk::glib::Type;
use gtk::glib::Object;


fn main() {
    println!("Hello, world!");// Create a new application
    let app = Application::builder()
        .application_id("org.gtk-rs.example")
        .build();

    // Connect to "activate" signal of `app`
    app.connect_activate(build_ui);

    // Run the application
    app.run();
}

fn create_widget<'r>(label: &'r Object) -> Widget {
    Label::new(Some(label.property_value("name").get().unwrap()))
}

fn build_ui(app: &Application) {
    let listbox_left = ListBox::new();
    let listbox_right = ListBox::new();

    let list_model = ListStore::new(Type::STRING);

    listbox_right.bind_model(Some(&list_model), create_widget);


    let paned = Paned::builder()
        .start_child(&listbox_left)
        .end_child(&listbox_right)
        .orientation(Orientation::Horizontal)
        .build();


    // Create a window
    let window = ApplicationWindow::builder()
        .application(app)
        .title("My GTK App")
        .child(&paned)
        .build();

    for n in 1..11 {
        let n_as_string =(n as u32).to_string();
        let mut my = String::from("Left:");
        my.push_str(&n_as_string);

        let m = Object::with_values(Type::STRING, &[("name", my.to_value())]);

        list_model.append(&m.unwrap());
    }

    // Present window
    window.present();
}
4

1 回答 1

1

继承不是 Rust 的语言特性。相反,gtk4板条箱有Labelimpl IsA<Widget>( here ),它允许您这样调用Cast::upcast

Label::new(Some(label.property_value("name").get().unwrap())).upcast()

您可能需要添加

use gtk4::glib::object::Cast;

到文件的顶部。相反,您也可以让您的方法返回impl IsA<Widget>

于 2022-02-20T20:54:31.967 回答