Bind UI to Model class

Game.java

package com.myapp;

import com.myapp.util.UiLoader;
import org.mini2Dx.core.Graphics;
import org.mini2Dx.core.assets.AssetManager;
import org.mini2Dx.core.files.*;
import org.mini2Dx.core.game.GameContainer;
import org.mini2Dx.core.graphics.viewport.FitViewport;
import org.mini2Dx.core.graphics.viewport.Viewport;
import org.mini2Dx.ui.UiContainer;
import org.mini2Dx.ui.UiThemeLoader;
import org.mini2Dx.ui.style.UiTheme;

public class Game extends GameContainer {
    public static final String GAME_IDENTIFIER = "com.myapp";
    private UiContainer container;
    private AssetManager assetManager;

    @Override
    public void initialise() {
        FileHandleResolver fileHandleResolver = new FallbackFileHandleResolver(
                new InternalFileHandleResolver(), new LocalFileHandleResolver(), new ExternalFileHandleResolver()
        );
        Viewport viewport = new FitViewport(true, getWidth(), getHeight());

        assetManager = new AssetManager(fileHandleResolver);
        assetManager.setAssetLoader(UiTheme.class, new UiThemeLoader(fileHandleResolver));
        assetManager.load(UiTheme.DEFAULT_THEME_FILENAME, UiTheme.class);

        container = new UiContainer(this, assetManager);
        container.setViewport(viewport);

        UiLoader uiLoader = new UiLoader(fileHandleResolver);
        MyUiModel model = uiLoader.load("test.xml", MyUiModel.class);
        if (model != null) {
            model.initialize();
            container.add(model.getContainer());
        }
    }

    @Override
    public void update(float delta) {
        if (!assetManager.update()) return;
        if (!UiContainer.isThemeApplied()) {
            UiContainer.setTheme(assetManager.get(UiTheme.DEFAULT_THEME_FILENAME, UiTheme.class));
        }
        container.update(delta);
    }

    @Override
    public void render(Graphics g) {
        container.render(g);
    }

    @Override
    public void onPause() {

    }

    @Override
    public void onResume() {

    }
}

MyUiModel.java

package com.myapp;

import com.myapp.util.UiElement;
import com.myapp.util.UiModel;
import org.mini2Dx.ui.element.Container;
import org.mini2Dx.ui.element.TextButton;

public class MyUiModel extends UiModel {
    @UiElement(id = "testContainer")
    Container container;

    @UiElement(id = "testButton")
    TextButton button;

    @Override
    public void initialize() {

        button.setText("IT WORKS!");
    }

    @Override
    public Container getContainer() {
        return container;
    }
}

test.xml

<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="https://github.com/mini2Dx/mini2Dx" id="testContainer">
    <flex-row>
        <text-button id="testButton" text="TestButton"/>
    </flex-row>
</container>

UiElement.java

package com.myapp.util;

import java.lang.annotation.*;

@Documented
@Inherited
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface UiElement {
    String id();
}

UiLoader.java

package com.myapp.util;

import org.mini2Dx.core.exception.MdxException;
import org.mini2Dx.core.files.FileHandleResolver;
import org.mini2Dx.ui.element.UiElement;
import org.mini2Dx.ui.xml.UiXmlLoader;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;

public class UiLoader extends UiXmlLoader {
    public UiLoader(FileHandleResolver fileHandleResolver) {
        super(fileHandleResolver);
    }
    
    public <T extends UiModel> T load(String filename, Class<? extends UiModel> model) {
        UiElement container;
        try {
            container = load(filename);
        } catch (Exception e) {
            throw new MdxException("Failed to load UI file: " + filename, e);
        }
        if (container != null) {
            return populateModel(container, model);
        } else {
            throw new MdxException("Failed to populate Ui file" + filename, new Exception("container is null"));
        }
    }

    private <T extends UiElement, M extends UiModel> M populateModel(T ui, Class<? extends UiModel> model) {
        try {
            var newInstance = model.getConstructor().newInstance();
            var fields = model.getDeclaredFields();
            for (Field field : fields) {
                if (field.isAnnotationPresent(com.myapp.util.UiElement.class)) {
                    String id = field.getAnnotation(com.myapp.util.UiElement.class).id();
                    UiElement element = ui.getElementById(id);
                    try {
                        field.set(newInstance, field.getType().cast(element));
                    } catch (IllegalAccessException ex) {
                        field.setAccessible(true);
                        field.set(newInstance, field.getType().cast(element));
                        field.setAccessible(false);
                    }
                }
            }
            return (M) newInstance;
        } catch (NoSuchMethodException | IllegalAccessException | InstantiationException | InvocationTargetException e) {
            throw new MdxException("could not populate fields", e);
        }
    }
}

UiModel.java

package com.myapp.util;

import org.mini2Dx.ui.element.Container;

public abstract class UiModel {
    public abstract void initialize();

    public abstract Container getContainer();
}