To create a custom rounded rectangle view in Android, you must extend the View class and override its drawing methods.

First, define a new class that inherits from View. Provide the necessary constructors to handle different instantiation contexst.

// RoundedRectView.java
public class RoundedRectView extends View {
    public RoundedRectView(Context ctx) {
        super(ctx);
    }

    public RoundedRectView(Context ctx, AttributeSet attrs) {
        super(ctx, attrs);
    }

    public RoundedRectView(Context ctx, AttributeSet attrs, int defStyle) {
        super(ctx, attrs, defStyle);
    }
}

The core drawing logic is placed within the onDraw method. Override this method to define how your view renders itself on the canvas.

// RoundedRectView.java
@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    // Drawing instructions go here.
}

Inside onDraw, use a Paint object to configure the drawing style and a RectF object to define the shape's bounds. The Canvas.drawRoundRect method is then used to render the rounded retcangle.

// RoundedRectView.java
@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    Paint shapePaint = new Paint();
    shapePaint.setAntiAlias(true); // Enable smooth edges
    shapePaint.setColor(Color.BLUE); // Set the fill color

    // Define the rectangle's area to match the view's size
    RectF bounds = new RectF(0, 0, getWidth(), getHeight());
    float cornerRadius = 30f; // Radius for the rounded corners
    canvas.drawRoundRect(bounds, cornerRadius, cornerRadius, shapePaint);
}