scrollIndicatorBuilder property
Replaces the viewer's built-in main-axis scrollbar with a custom scroll indicator - a compact page number, a draggable page scrubber, a platform-styled bar. See PdfScrollIndicatorBuilder; it receives the live PdfScrollMetrics and the controller for page-aware navigation.
Works in both continuous layouts: it replaces the right-edge bar in a vertical PdfPageLayout.verticalContinuous layout and the bottom-edge bar in a horizontal PdfPageLayout.horizontalContinuous one, and the metrics it receives describe that main axis (with PdfScrollMetrics.scrollAxis telling the host which). Null keeps the stock scrollbar. The cross-axis (zoom-window) scrollbar is unaffected - it still appears when zoomed in. The indicator fills the viewer outside the zoom transform, so it holds its place and size at any zoom.
Implementation
final PdfScrollIndicatorBuilder? scrollIndicatorBuilder;