NewPage with freeSpace extended #1648

pdf/lib/src/widgets/multi_page.dart

@@ -65,12 +65,20 @@ mixin SpanningWidget on Widget {
  saveContext().apply(context);
 }
 
+/// Trigger a page break if there is not enough free space.
+/// If freeSpace is null, a page break is always performed.
 class NewPage extends Widget {
+ NewPage({this.freeSpace});
+ final double? freeSpace;
+
  @override
  void layout(Context context, BoxConstraints constraints,
  {bool parentUsesSize = false}) {
  box = PdfRect.zero;
  }
+
+ bool newPageNeeded(double availableSpace) =>
+ (freeSpace == null) || (availableSpace < freeSpace!);
 }
 
 @immutable
@@ -230,7 +238,7 @@ class MultiPage extends Page {
  maxHeight: pageFormat.height - _margin.vertical);
  final calculatedTheme = theme ?? document.theme ?? ThemeData.base();
  Context? context;
- late double offsetEnd;
+ var offsetEnd = 0.0;
  double? offsetStart;
  var _index = 0;
  var sameCount = 0;
@@ -252,8 +260,13 @@ class MultiPage extends Page {
  'This widget created more than $maxPages pages. This may be an issue in the widget or the document. See https://pub.dev/documentation/pdf/latest/widgets/MultiPage-class.html');
  }
 
+ // Calculate available space of the current page
+ final freeSpace = (offsetStart == null)
+ ? fullConstraints.maxHeight
+ : offsetStart - offsetEnd;
+
  // Create a new page if we don't already have one
- if (context == null || child is NewPage) {
+ if (context == null || (child is NewPage) && child.newPageNeeded(freeSpace)) {
  final pdfPage = PdfPage(
  document.document,
  pageFormat: pageFormat,

pdf/test/widget_newpage_test.dart

@@ -0,0 +1,131 @@
+/*
+ * Copyright (C) 2017, David PHAM-VAN <[email protected]>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import 'dart:io';
+
+import 'package:pdf/pdf.dart';
+import 'package:pdf/widgets.dart';
+import 'package:test/test.dart';
+
+late Document pdf;
+
+Widget footer(Context context) {
+ return Footer(
+ trailing: Container(
+ height: 25,
+ child: Text('Page ${context.pageNumber}'),
+ ),
+ );
+}
+
+Widget header(Context context) {
+ return Container(
+ height: 20,
+ child: Text('Test document'),
+ );
+}
+
+List<Widget> contentWithPageBreak(double? freeSpace) {
+ return [
+ Container(
+ color: const PdfColor(0.75, 0.75, 0.75),
+ height: 50,
+ width: 100,
+ child: Text('Page 1'),
+ ),
+ Container(
+ color: const PdfColor(0.6, 0.6, 0.6),
+ height: 40,
+ width: 100,
+ ),
+ Container(
+ color: const PdfColor(0.5, 0.5, 0.5),
+ height: 20,
+ width: 100,
+ ),
+ NewPage(freeSpace: freeSpace),
+ Text('Page 2'),
+ ];
+}
+
+void main() {
+ setUpAll(() {
+ Document.debug = true;
+ RichText.debug = true;
+ pdf = Document();
+ });
+
+ const pageFormatWithoutMargins = PdfPageFormat(200.0, 200.0);
+ const pageFormatWithMargins =
+ PdfPageFormat(200.0, 200.0, marginTop: 10, marginBottom: 20);
+
+ // PageHeight - Content Height
+ // 200 - 110 = 90 available space
+ test('PageBreak normal on page without margins', () {
+ pdf.addPage(MultiPage(
+ pageFormat: pageFormatWithoutMargins,
+ build: (_) => contentWithPageBreak(null),
+ ));
+ });
+
+ test('No PageBreak, because enough space available', () {
+ pdf.addPage(MultiPage(
+ pageFormat: pageFormatWithoutMargins,
+ build: (_) => contentWithPageBreak(90),
+ ));
+ });
+
+ test('PageBreak because more free space needed', () {
+ pdf.addPage(MultiPage(
+ pageFormat: pageFormatWithoutMargins,
+ build: (_) => contentWithPageBreak(91),
+ ));
+ });
+
+ // PageHeight - Margins - Content Height
+ // 200 - 10 - 20 - 20 - 25 - 110 = 15
+ test('PageBreak normal on page with margins, header and footer', () {
+ pdf.addPage(MultiPage(
+ pageFormat: pageFormatWithMargins,
+ build: (_) => contentWithPageBreak(null),
+ header: header,
+ footer: footer,
+ ));
+ });
+
+ test('No PageBreak, because enough space available', () {
+ pdf.addPage(MultiPage(
+ pageFormat: pageFormatWithMargins,
+ build: (_) => contentWithPageBreak(15.0),
+ header: header,
+ footer: footer,
+ ));
+ });
+
+ test('PageBreak because more free space needed', () {
+ pdf.addPage(MultiPage(
+ pageFormat: pageFormatWithMargins,
+ build: (_) => contentWithPageBreak(16.0),
+ header: header,
+ footer: footer,
+ ));
+ });
+
+ tearDownAll(() async {
+ final file = File('widgets-newpage.pdf');
+ await file.writeAsBytes(await pdf.save());
+ });
+}