Report Generation Implementation in Mobile App

Report Generation Implementation in Mobile Apps

Report export in mobile apps is a task where users expect "Download PDF" button, but developers hit memory limits, asynchronous generation, complex multi-page document layout and sharing in needed format.

PDF Generation: Three Approaches

1. Native Rendering via Canvas (iOS: PDFKit, Android: PdfDocument)

On iOS — UIGraphicsPDFRenderer, most controlled variant. Draw each element manually via Core Graphics:

func generateReport(data: ReportData) -> Data {
    let pageRect = CGRect(x: 0, y: 0, width: 595, height: 842) // A4 in points
    let renderer = UIGraphicsPDFRenderer(bounds: pageRect)

    return renderer.pdfData { context in
        context.beginPage()
        let ctx = context.cgContext

        // Title
        let titleFont = UIFont.boldSystemFont(ofSize: 18)
        let title = data.title as NSString
        title.draw(at: CGPoint(x: 40, y: 40), withAttributes: [
            .font: titleFont,
            .foregroundColor: UIColor.black
        ])

        // Data table
        drawTable(ctx, rows: data.rows, startY: 80, pageWidth: pageRect.width)

        // If data doesn't fit — new page
        if needsNewPage {
            context.beginPage()
            // continue...
        }
    }
}

Labor-intensive but result is precise pixel control. Good for fixed report template.

On Android via PdfDocument:

val document = PdfDocument()
val pageInfo = PdfDocument.PageInfo.Builder(595, 842, 1).create()
val page = document.startPage(pageInfo)
val canvas = page.canvas

val paint = Paint().apply { textSize = 18f; isFakeBoldText = true }
canvas.drawText(data.title, 40f, 60f, paint)

document.finishPage(page)
val stream = ByteArrayOutputStream()
document.writeTo(stream)
document.close()

2. HTML → PDF via WebView (Flutter: printing package)

Generate HTML template, convert to PDF. Simpler for complex layouts, tables and text blocks — HTML/CSS more flexible than Canvas. On Flutter printing + pdf package:

import 'package:pdf/widgets.dart' as pw;
import 'package:printing/printing.dart';

Future<Uint8List> buildPdf(ReportData data) async {
  final doc = pw.Document();
  final font = await PdfGoogleFonts.notoSansRegular();
  final boldFont = await PdfGoogleFonts.notoSansBold();

  doc.addPage(
    pw.MultiPage(
      pageFormat: PdfPageFormat.a4,
      build: (context) => [
        pw.Header(text: data.title, textStyle: pw.TextStyle(font: boldFont, fontSize: 18)),
        pw.SizedBox(height: 16),
        pw.TableHelper.fromTextArray(
          headers: data.headers,
          data: data.rows,
          cellStyle: pw.TextStyle(font: font, fontSize: 10),
        ),
      ],
    ),
  );
  return doc.save();
}

pw.MultiPage automatically splits to pages — solves long report main problem.

3. Server-Side Generation (Recommended for Complex Reports)

Reports with large data volume, complex diagrams or corporate branding better generated on server. Puppeteer (Node.js) renders HTML + Charts to PDF with browser engine precision. Client gets link or file via WebSocket after completion.

This is the only right path if report must include interactive charts (Echarts, Highcharts) — can't render on device without WebView.

CSV Export

Simpler than PDF, but has encoding nuances. Excel expects UTF-8 with BOM — otherwise Cyrillic shows as garbage. On Flutter:

String buildCsv(List<List<dynamic>> rows) {
  final buffer = StringBuffer();
  buffer.write('\uFEFF'); // UTF-8 BOM for correct Excel opening
  for (final row in rows) {
    buffer.writeln(row.map((cell) {
      final str = cell.toString();
      // Escape cells with commas and quotes
      return str.contains(',') || str.contains('"')
          ? '"${str.replaceAll('"', '""')}"'
          : str;
    }).join(','));
  }
  return buffer.toString();
}

Sharing Generated File

share_plus on Flutter, UIActivityViewController on iOS, FileProvider + Intent.ACTION_SEND on Android. Save to gallery / Files — via path_provider + open_filex.

On iOS need NSPhotoLibraryAddUsageDescription in Info.plist for saving to Photos, UIFileSharingEnabled for file access via Files.app.

Typical Problems

Generating PDF with table of 10,000 rows on device — OutOfMemoryError on Android or memory warning on iOS. Solution: data pagination, page-by-page generation, for large volumes — server.

Cyrillic in PDF without embedded font — white rectangles instead of letters. Must embed custom font with Unicode support via pw.Font.ttf(...).

Scope of Work

• Approach choice per data specifics and layout (native / HTML→PDF / server)
• Report template implementation (PDF/CSV/Excel)
• File sharing and saving integration
• Edge cases handling: empty data, large volumes, page breaks

Timeframe

One PDF report template with basic formatting: 2–3 days. Multiple report types with diagrams and server generation: 1–2 weeks. Cost calculated individually.