What is the Alternative for elevation attribute in HarmonyOS?

In HarmonyOS, an alternative to the elevation property used in traditional Android systems is called 'shadow management'. With its UI framework differing from Android, HarmonyOS offers a distinct approach for managing the hierarchy and shadow effects of UI elements.

In Android, the elevation property primarily defines the height hierarchy of View elements, automatically generating corresponding shadow effects to enhance visual hierarchy. In HarmonyOS, however, shadow implementation does not directly rely on similar properties.

HarmonyOS achieves this through its component visual effect management mechanism. The Shadow class is used to add shadows to components, providing key properties such as offsetX and offsetY (horizontal and vertical offset), blurRadius (blur radius), and color (shadow color), enabling precise control over shadow effects.

For example, to add a shadow to a button, you can write the following code:

java
import ohos.agp.components.AttrSet;
import ohos.agp.components.Button;
import ohos.agp.components.ComponentContainer;
import ohos.agp.render.Canvas;
import ohos.agp.render.Paint;
import ohos.agp.render.Shadow;
import ohos.app.Context;

public class MyButton extends Button {
    private Paint paint;

    public MyButton(Context context, AttrSet attrSet) {
        super(context, attrSet);
        
        paint = new Paint();
        paint.setShadow(new Shadow(10, 0, 0, Color.BLACK));
    }

    @Override
    public void onDraw(Component component, Canvas canvas) {
        super.onDraw(component, canvas);
        setLayerPaint(paint);
    }
}

In this example, a custom Button class is created where a Paint object is instantiated and its shadow effect is set. Within the onDraw method, this Paint is applied to the button's drawing layer, resulting in the button displaying a shadow effect.

This approach enables HarmonyOS to provide flexible shadow management, allowing developers to freely adjust shadow parameters to achieve effects comparable to or superior to those implemented via the elevation property in Android systems.