Drawing A Simple GUI

Let us design a classical GUI library using our new knowledge of traits and trait objects. We’ll only implement the drawing of it (as text) for simplicity.

我们的库中有许多 widget：

• “Window”：具有“title”且包含其他 widget。
• Button: has a label. In reality, it would also take a callback function to allow the program to do something when the button is clicked but we won’t include that since we’re only drawing the GUI.
• “Label”：具有“label”。

这些 widget 将实现“Widget”trait，如下所示。

将以下代码复制到 https://play.rust-lang.org/，然后填入缺少的“draw_into”方法，以便实现“Widget”trait：

// TODO: remove this when you're done with your implementation.
#![allow(unused_imports, unused_variables, dead_code)]

pub trait Widget {
    /// Natural width of `self`.
    fn width(&self) -> usize;

    /// Draw the widget into a buffer.
    fn draw_into(&self, buffer: &mut dyn std::fmt::Write);

    /// Draw the widget on standard output.
    fn draw(&self) {
        let mut buffer = String::new();
        self.draw_into(&mut buffer);
        println!("{buffer}");
    }
}

pub struct Label {
    label: String,
}

impl Label {
    fn new(label: &str) -> Label {
        Label {
            label: label.to_owned(),
        }
    }
}

pub struct Button {
    label: Label,
}

impl Button {
    fn new(label: &str) -> Button {
        Button {
            label: Label::new(label),
        }
    }
}

pub struct Window {
    title: String,
    widgets: Vec<Box<dyn Widget>>,
}

impl Window {
    fn new(title: &str) -> Window {
        Window {
            title: title.to_owned(),
            widgets: Vec::new(),
        }
    }

    fn add_widget(&mut self, widget: Box<dyn Widget>) {
        self.widgets.push(widget);
    }

    fn inner_width(&self) -> usize {
        std::cmp::max(
            self.title.chars().count(),
            self.widgets.iter().map(|w| w.width()).max().unwrap_or(0),
        )
    }
}


impl Widget for Label {
    fn width(&self) -> usize {
        unimplemented!()
    }

    fn draw_into(&self, buffer: &mut dyn std::fmt::Write) {
        unimplemented!()
    }
}

impl Widget for Button {
    fn width(&self) -> usize {
        unimplemented!()
    }

    fn draw_into(&self, buffer: &mut dyn std::fmt::Write) {
        unimplemented!()
    }
}

impl Widget for Window {
    fn width(&self) -> usize {
        unimplemented!()
    }

    fn draw_into(&self, buffer: &mut dyn std::fmt::Write) {
        unimplemented!()
    }
}

fn main() {
    let mut window = Window::new("Rust GUI Demo 1.23");
    window.add_widget(Box::new(Label::new("This is a small text GUI demo.")));
    window.add_widget(Box::new(Button::new(
        "Click me!"
    )));
    window.draw();
}

上述程序的输出可能非常简单，例如：

========
Rust GUI Demo 1.23
========

This is a small text GUI demo.

| Click me! |

如果要绘制对齐的文本，可以使用填充/对齐格式设置运算符。需要特别注意的是您填充不同字符（此处是“/”）的方式以及控制对齐的方式：

fn main() {
    let width = 10;
    println!("left aligned:  |{:/<width$}|", "foo");
    println!("centered:      |{:/^width$}|", "foo");
    println!("right aligned: |{:/>width$}|", "foo");
}

使用这些对齐技巧，您可以生成如下的输出内容：

+--------------------------------+
|       Rust GUI Demo 1.23       |
+================================+
| This is a small text GUI demo. |
| +-----------+                  |
| | Click me! |                  |
| +-----------+                  |
+--------------------------------+