Method update

Ch06/yew-image-processing/src/app.rs:31–100

(&mut self, msg: Self::Message)

    }

    fn update(&mut self, msg: Self::Message) -> ShouldRender {
        match msg {
            Msg::LoadFile(files) => {
                let file = &files[0];
                    let file_url = web_sys::Url::create_object_url_with_blob(&file).unwrap();
                    let document = web_sys::window().unwrap().document().unwrap();
                    let image = Rc::new(document
                        .create_element("img").unwrap()
                        .dyn_into::<web_sys::HtmlImageElement>().unwrap()
                    );
                    image.set_src(&file_url);


                    let image_clone = image.clone();

                    let callback = Closure::wrap(Box::new(move || {
                        let canvas = document.get_element_by_id("preview").unwrap();
                        let canvas: web_sys::HtmlCanvasElement = canvas
                            .dyn_into::<web_sys::HtmlCanvasElement>()
                            .map_err(|_| ())
                            .unwrap();

                        let context = canvas
                            .get_context("2d")
                            .unwrap()
                            .unwrap()
                            .dyn_into::<web_sys::CanvasRenderingContext2d>()
                            .unwrap();
                        canvas.set_width(image_clone.natural_width());
                        canvas.set_height(image_clone.natural_height());
                        context.draw_image_with_html_image_element(&image_clone, 0.0, 0.0).unwrap();
                    }) as Box<dyn Fn()>);
                    // .as_ref().unchecked_ref() can extract the &Function from the &JsValue
                    image.set_onload(Some(callback.as_ref().unchecked_ref()));
                    // Do not drop the Closure so the JS callback won't be invalidated after the
                    // function exits
                    callback.forget();
            }
            Msg::Shrink => { 
                // DO nothing yet
                let document = web_sys::window().unwrap().document().unwrap();
                let canvas = document.get_element_by_id("preview").unwrap();
                let canvas: web_sys::HtmlCanvasElement = canvas
                    .dyn_into::<web_sys::HtmlCanvasElement>()
                    .map_err(|_| ())
                    .unwrap();

                let context = canvas
                    .get_context("2d")
                    .unwrap()
                    .unwrap()
                    .dyn_into::<web_sys::CanvasRenderingContext2d>()
                    .unwrap();
                let width: u32 = canvas.width();
                let height: u32 = canvas.height();
                let image_buffer = context.get_image_data(0.0, 0.0, width.into(), height.into())
                    .unwrap()
                    .data();