How can custom properties be defined in a user Android component?

In Android, to define custom properties of a user component, XML attributes are usually used, which are described in the attrs.xml file located in the res/values folder.

Example:

1. Create a file res/values/attrs.xml and define your attributes:

<resources>
    <declare-styleable name="MyCustomView">
        <attr name="customColor" format="color" />
        <attr name="customSize" format="dimension" />
    </declare-styleable>
</resources>

2. In your custom component (for example, a subclass of View), read these attributes in the constructor with Context and AttributeSet parameters:

public class MyCustomView extends View {
    private int customColor;
    private float customSize;

    public MyCustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.MyCustomView);
        customColor = a.getColor(R.styleable.MyCustomView_customColor, Color.BLACK);
        customSize = a.getDimension(R.styleable.MyCustomView_customSize, 16f);
        a.recycle();
    }
}

3. These attributes can be used in XML layout:

<com.example.MyCustomView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:customColor="#FF0000"
    app:customSize="24sp" />

Thus, you create your own properties that can be set in XML and used in the component's code.