How do I get a property of a component that may or may not be created?

[LeeeSe]

import { VideoCompress } from "pages/video_compress.slint";
import { Button, VerticalBox , ListView, StandardListView, HorizontalBox, StandardButton, ComboBox, ProgressIndicator} from "std-widgets.slint";

export component AppWindow inherits Window {
    title: "Dali";
    callback choose_video_file();
    callback compress_video();
    in-out property <float> compressing_progress_value: 0;
    in property <bool> compress-enabled: false;
    in property <string> compress_video_input_file_path: "None" ;
    out property <string> video-type: v_c.video-type;

    HorizontalBox { 
        side_bar := StandardListView { 
            horizontal-stretch: 0;
            width: 100px;
            current-item: 0;
            model: [ { 
                text: "视频压缩",
            }];
        }
        
        if side_bar.current-item == 0 : 
            v_c := VideoCompress {
                choose_video_file => {choose_video_file()}
                compress_video => {compress_video()}
                compressing_progress_value: compressing_progress_value;
                compress_enabled: compress-enabled;
                input_file_path: compress_video_input_file_path;
            }
    }
}

My sidebar has a number of optional pages and I don't always choose which one, when I wanted to pass a v_c.video-type to mian.rs I tried a couple of ways the way I wanted to do it and realized I couldn't do it by myself, is there a standard way to do it and is the way I'm passing the variable very unscientific?

video_compress.slint

import { Button, VerticalBox , ListView, StandardListView, HorizontalBox, StandardButton, ComboBox, ProgressIndicator, StandardTableView} from "std-widgets.slint";

export component VideoCompress inherits VerticalBox {
    callback choose_video_file();
    callback compress_video();
    in-out property <float> compressing_progress_value;
    in property <bool> compress_enabled;
    in property <string> input_file_path;
    out property <string> video_type <=> type-cbx.current-value;
    Button {
        text: "选择文件";
        clicked => {
            choose_video_file();
        }
    }

    if (input-file-path != "None") : Text {
        text: "已选择文件:\n\{input_file_path}";   
    }

    HorizontalBox {
        Text {
            text: "输出格式：";
        }
        type_cbx := ComboBox { 
            height: 20px;
            width: 70px;
            model: ["mp4", "avi", "mov"];
        }
    }
    Button {
        text: "开始压缩";
        enabled: compress_enabled;
        clicked => {
            compress_video();
        }
        
    }
    ProgressIndicator { 
        progress: compressing_progress_value;
    }
}

[ogoffart]

What you can do is use two way binding in the inner component like so:

out property <string> video-type;
//...
    if side_bar.current-item == 0 : 
            VideoCompress {
               video-type <=> root.video-type;
               //...

[LeeeSe]

I tried, but
Cannot assign to output property 'video-type'

[bjorn]

Did you try making your property in-out? Though I do think this should have worked for out properties, since the assignment happens from within the component.

[LeeeSe]

You're right.