How to Implement Pagination in Android for Long-Form Text?

Paginating Text in Android

Overview

Pagination involves breaking text into smaller, manageable pages for display on a screen. This process is essential for enhancing user experience, especially for long-form content. TextView, a core Android text rendering component, handles line breaking efficiently, but struggles with page breaking.

Current Limitations with TextView

The primary challenge with TextView is its inability to provide direct feedback on line breaking, making it difficult to determine where the actual text painting ends on the screen. This information is crucial for continuing pagination on subsequent pages.

Proposed Solution

The proposed solution involves leveraging the ViewTreeObserver to obtain the visible text after the text layout is complete. By identifying the firstVisibleLineNumber and lastVisibleLineNumber within the TextView, the algorithm can determine the text that should be displayed on the current page.

Pagination Algorithm

1. Iterate through text lines.


2. Check if a line's bottom exceeds the view's height.


3. If exceeded, break a new page and calculate a new height for line comparison.

Implementation

The Pagination class implements the pagination algorithm and exposes methods for layout, page retrieval, and size determination. It encapsulates the text processing logic and parameters, enabling its use independently of TextView.

Optimization

For text with uniform font size, the algorithm can be optimized by calculating the number of lines that fit on a page and jumping to the appropriate line instead of looping through each line.

Sample Implementation

The provided sample demonstrates pagination of both HTML and Spanned text, dynamically adjusting to screen resizes. It utilizes a custom PaginationActivity for handling page navigation.

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