Add PdfPreview Widget

 # Changelog
 
+## 3.4.0
+
+- Add PdfPreview Widget
+
 ## 3.3.1
 
 - Remove width and height parameters from wrapWidget helper

@@ -16,6 +16,7 @@
 
 export 'src/asset_utils.dart';
 export 'src/callback.dart';
+export 'src/pdf_preview.dart';
 export 'src/printer.dart';
 export 'src/printing.dart';
 export 'src/printing_info.dart';

+import 'dart:math';
+import 'dart:typed_data';
+
+import 'package:flutter/material.dart';
+import 'package:pdf/pdf.dart';
+import 'package:pdf/widgets.dart' as pw;
+
+import 'callback.dart';
+import 'printing.dart';
+import 'printing_info.dart';
+import 'raster.dart';
+
+class PdfPreview extends StatefulWidget {
+  const PdfPreview({
+    Key key,
+    @required this.build,
+    this.initialPageFormat,
+    this.allowPrinting = true,
+    this.allowSharing = true,
+    this.canChangePageFormat = true,
+    this.actions,
+    this.pageFormats,
+    this.onError,
+    this.onPrinted,
+    this.onShared,
+  }) : super(key: key);
+
+  final LayoutCallback build;
+
+  final PdfPageFormat initialPageFormat;
+
+  final bool allowPrinting;
+
+  final bool allowSharing;
+
+  final bool canChangePageFormat;
+
+  final List<PdfPreviewAction> actions;
+
+  final Map<String, PdfPageFormat> pageFormats;
+
+  final Widget Function(BuildContext context) onError;
+
+  final void Function(BuildContext context) onPrinted;
+
+  final void Function(BuildContext context) onShared;
+
+  @override
+  _PdfPreviewState createState() => _PdfPreviewState();
+}
+
+class _PdfPreviewState extends State<PdfPreview> {
+  final GlobalKey<State<StatefulWidget>> shareWidget = GlobalKey();
+  final GlobalKey<State<StatefulWidget>> listView = GlobalKey();
+
+  final List<_PdfPreviewPage> pages = <_PdfPreviewPage>[];
+
+  PdfPageFormat pageFormat;
+
+  PrintingInfo info = PrintingInfo.unavailable;
+  bool infoLoaded = false;
+
+  double dpi = 10;
+
+  dynamic error;
+
+  static const Map<String, PdfPageFormat> defaultPageFormats =
+      <String, PdfPageFormat>{
+    'A4': PdfPageFormat.a4,
+    'Letter': PdfPageFormat.letter,
+  };
+
+  Future<void> _raster() async {
+    Uint8List _doc;
+
+    if (!info.canRaster) {
+      return;
+    }
+
+    try {
+      _doc = await widget.build(pageFormat);
+    } catch (e) {
+      error = e;
+      return;
+    }
+
+    if (error != null) {
+      setState(() {
+        error = null;
+      });
+    }
+
+    int pageNum = 0;
+    await for (final PdfRaster page in Printing.raster(_doc, dpi: dpi)) {
+      setState(() {
+        if (pages.length <= pageNum) {
+          pages.add(_PdfPreviewPage(page: page));
+        } else {
+          pages[pageNum] = _PdfPreviewPage(page: page);
+        }
+      });
+
+      pageNum++;
+    }
+
+    pages.removeRange(pageNum, pages.length);
+  }
+
+  @override
+  void initState() {
+    final Locale locale =
+        WidgetsBinding.instance.window.locale ?? const Locale('en', 'US');
+    final String cc = locale.countryCode;
+    if (cc == 'US' || cc == 'CA' || cc == 'MX') {
+      pageFormat = widget.initialPageFormat ?? PdfPageFormat.letter;
+    } else {
+      pageFormat = widget.initialPageFormat ?? PdfPageFormat.a4;
+    }
+
+    super.initState();
+  }
+
+  @override
+  void reassemble() {
+    _raster();
+    super.reassemble();
+  }
+
+  @override
+  void didUpdateWidget(covariant PdfPreview oldWidget) {
+    if (oldWidget.build != widget.build) {
+      pages.clear();
+      _raster();
+    }
+    super.didUpdateWidget(oldWidget);
+  }
+
+  @override
+  void didChangeDependencies() {
+    if (!infoLoaded) {
+      Printing.info().then((PrintingInfo _info) {
+        setState(() {
+          infoLoaded = true;
+          info = _info;
+          _raster();
+        });
+      });
+    }
+
+    final MediaQueryData mq = MediaQuery.of(context);
+    dpi = (mq.size.width - 16) *
+        min(mq.devicePixelRatio, 2) /
+        pageFormat.width *
+        72;
+
+    _raster();
+    super.didChangeDependencies();
+  }
+
+  Widget _showError() {
+    if (widget.onError != null) {
+      return widget.onError(context);
+    }
+
+    return const Center(
+      child: Text(
+        'Unable to display the document',
+        style: TextStyle(
+          fontSize: 20,
+        ),
+      ),
+    );
+  }
+
+  Widget _createPreview() {
+    if (error != null) {
+      Widget content = _showError();
+      assert(() {
+        content = ErrorWidget.withDetails(
+          message: error.toString(),
+        );
+        return true;
+      }());
+      return content;
+    }
+
+    if (!info.canRaster) {
+      return _showError();
+    }
+
+    if (pages.isEmpty) {
+      return const Center(child: CircularProgressIndicator());
+    }
+
+    return Scrollbar(
+      child: ListView.builder(
+        itemCount: pages.length,
+        itemBuilder: (BuildContext context, int index) => pages[index],
+      ),
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final ThemeData theme = Theme.of(context);
+
+    final Widget scrollView = Container(
+      width: double.infinity,
+      decoration: BoxDecoration(
+        gradient: LinearGradient(
+          colors: <Color>[Colors.grey.shade400, Colors.grey.shade200],
+          begin: Alignment.topCenter,
+          end: Alignment.bottomCenter,
+        ),
+      ),
+      child: _createPreview(),
+    );
+
+    final List<Widget> actions = <Widget>[];
+
+    if (widget.allowPrinting && info.canPrint) {
+      actions.add(
+        IconButton(
+          icon: const Icon(Icons.print),
+          color: theme.accentIconTheme.color,
+          onPressed: _print,
+        ),
+      );
+    }
+
+    if (widget.allowSharing && info.canShare) {
+      actions.add(
+        IconButton(
+          key: shareWidget,
+          icon: const Icon(Icons.share),
+          color: theme.accentIconTheme.color,
+          onPressed: _share,
+        ),
+      );
+    }
+
+    if (widget.canChangePageFormat) {
+      final Map<String, PdfPageFormat> _pageFormats =
+          widget.pageFormats ?? defaultPageFormats;
+      final List<String> keys = _pageFormats.keys.toList();
+      actions.add(
+        DropdownButton<PdfPageFormat>(
+          style: theme.accentTextTheme.button,
+          dropdownColor: Colors.grey.shade700,
+          icon: Icon(
+            Icons.arrow_drop_down,
+            color: theme.accentIconTheme.color,
+          ),
+          value: pageFormat,
+          items: List<DropdownMenuItem<PdfPageFormat>>.generate(
+            _pageFormats.length,
+            (int index) {
+              final String key = keys[index];
+              final PdfPageFormat val = _pageFormats[key];
+              return DropdownMenuItem<PdfPageFormat>(
+                child: Text(key),
+                value: val,
+              );
+            },
+          ),
+          onChanged: (PdfPageFormat _pageFormat) {
+            setState(() {
+              pageFormat = _pageFormat;
+              _raster();
+            });
+          },
+        ),
+      );
+    }
+
+    if (widget.actions != null) {
+      for (final PdfPreviewAction action in widget.actions) {
+        actions.add(
+          IconButton(
+            icon: action.icon,
+            color: theme.accentIconTheme.color,
+            onPressed: action.onPressed == null
+                ? null
+                : () => action.onPressed(
+                      context,
+                      widget.build,
+                      pageFormat,
+                    ),
+          ),
+        );
+      }
+    }
+
+    assert(() {
+      if (actions.isNotEmpty) {
+        actions.add(
+          Switch(
+            activeColor: Colors.red,
+            value: pw.Document.debug,
+            onChanged: (bool value) {
+              setState(
+                () {
+                  pw.Document.debug = value;
+                  _raster();
+                },
+              );
+            },
+          ),
+        );
+      }
+
+      return true;
+    }());
+
+    return Column(
+      mainAxisAlignment: MainAxisAlignment.center,
+      children: <Widget>[
+        Expanded(child: scrollView),
+        if (actions.isNotEmpty)
+          Material(
+            elevation: 4,
+            color: theme.primaryColor,
+            child: Row(
+              mainAxisAlignment: MainAxisAlignment.spaceAround,
+              children: actions,
+            ),
+          )
+      ],
+    );
+  }
+
+  Future<void> _print() async {
+    final bool result = await Printing.layoutPdf(onLayout: widget.build);
+
+    if (result && widget.onPrinted != null) {
+      widget.onPrinted(context);
+    }
+  }
+
+  Future<void> _share() async {
+    // Calculate the widget center for iPad sharing popup position
+    final RenderBox referenceBox =
+        shareWidget.currentContext.findRenderObject();
+    final Offset topLeft =
+        referenceBox.localToGlobal(referenceBox.paintBounds.topLeft);
+    final Offset bottomRight =
+        referenceBox.localToGlobal(referenceBox.paintBounds.bottomRight);
+    final Rect bounds = Rect.fromPoints(topLeft, bottomRight);
+
+    final Uint8List bytes = await widget.build(pageFormat);
+    final bool result = await Printing.sharePdf(bytes: bytes, bounds: bounds);
+
+    if (result && widget.onShared != null) {
+      widget.onShared(context);
+    }
+  }
+}
+
+class _PdfPreviewPage extends StatelessWidget {
+  const _PdfPreviewPage({
+    Key key,
+    this.page,
+  }) : super(key: key);
+
+  final PdfRaster page;
+
+  @override
+  Widget build(BuildContext context) {
+    final PdfRasterImage im = PdfRasterImage(page);
+
+    return Container(
+      margin: const EdgeInsets.only(
+        left: 8,
+        top: 8,
+        right: 8,
+        bottom: 12,
+      ),
+      decoration: const BoxDecoration(
+        color: Colors.white,
+        boxShadow: <BoxShadow>[
+          BoxShadow(
+            offset: Offset(0, 3),
+            blurRadius: 5,
+            color: Color(0xFF000000),
+          ),
+        ],
+      ),
+      child: AspectRatio(
+        aspectRatio: page.width / page.height,
+        child: Image(
+          image: im,
+          fit: BoxFit.cover,
+        ),
+      ),
+    );
+  }
+}
+
+typedef OnPdfPreviewActionPressed = void Function(
+  BuildContext context,
+  LayoutCallback build,
+  PdfPageFormat pageFormat,
+);
+
+class PdfPreviewAction {
+  const PdfPreviewAction({
+    @required this.icon,
+    @required this.onPressed,
+  }) : assert(icon != null);
+
+  final Icon icon;
+  final OnPdfPreviewActionPressed onPressed;
+}

@@ -4,7 +4,7 @@ description: Plugin that allows Flutter apps to generate and print documents to
 homepage: https://github.com/DavBfr/dart_pdf/tree/master/printing
 repository: https://github.com/DavBfr/dart_pdf
 issue_tracker: https://github.com/DavBfr/dart_pdf/issues
-version: 3.3.1
+version: 3.4.0
 
 environment:
   sdk: ">=2.3.0 <3.0.0"