packages/flutter/lib/src/material/paginated_data_table.dart - mirrors/flutter - Git at Google

 // Copyright 2014 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'dart:math' as math;

 import 'package:flutter/widgets.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/gestures.dart' show DragStartBehavior;

 import 'button_bar.dart';
 import 'card.dart';
 import 'constants.dart';
 import 'data_table.dart';
 import 'data_table_source.dart';
 import 'debug.dart';
 import 'dropdown.dart';
 import 'icon_button.dart';
 import 'icons.dart';
 import 'ink_decoration.dart';
 import 'material_localizations.dart';
 import 'progress_indicator.dart';
 import 'theme.dart';

 /// A material design data table that shows data using multiple pages.
 ///
 /// A paginated data table shows [rowsPerPage] rows of data per page and
 /// provides controls for showing other pages.
 ///
 /// Data is read lazily from from a [DataTableSource]. The widget is presented
 /// as a [Card].
 ///
 /// See also:
 ///
 ///  * [DataTable], which is not paginated.
 ///  * <https://material.io/go/design-data-tables#data-tables-tables-within-cards>
 class PaginatedDataTable extends StatefulWidget {
   /// Creates a widget describing a paginated [DataTable] on a [Card].
   ///
   /// The [header] should give the card's header, typically a [Text] widget. It
   /// must not be null.
   ///
   /// The [columns] argument must be a list of as many [DataColumn] objects as
   /// the table is to have columns, ignoring the leading checkbox column if any.
   /// The [columns] argument must have a length greater than zero and cannot be
   /// null.
   ///
   /// If the table is sorted, the column that provides the current primary key
   /// should be specified by index in [sortColumnIndex], 0 meaning the first
   /// column in [columns], 1 being the next one, and so forth.
   ///
   /// The actual sort order can be specified using [sortAscending]; if the sort
   /// order is ascending, this should be true (the default), otherwise it should
   /// be false.
   ///
   /// The [source] must not be null. The [source] should be a long-lived
   /// [DataTableSource]. The same source should be provided each time a
   /// particular [PaginatedDataTable] widget is created; avoid creating a new
   /// [DataTableSource] with each new instance of the [PaginatedDataTable]
   /// widget unless the data table really is to now show entirely different
   /// data from a new source.
   ///
   /// The [rowsPerPage] and [availableRowsPerPage] must not be null (they
   /// both have defaults, though, so don't have to be specified).
   PaginatedDataTable({
     Key key,
     @required this.header,
     this.actions,
     @required this.columns,
     this.sortColumnIndex,
     this.sortAscending = true,
     this.onSelectAll,
     this.dataRowHeight = kMinInteractiveDimension,
     this.headingRowHeight = 56.0,
     this.horizontalMargin = 24.0,
     this.columnSpacing = 56.0,
     this.showCheckboxColumn = true,
     this.initialFirstRowIndex = 0,
     this.onPageChanged,
     this.rowsPerPage = defaultRowsPerPage,
     this.availableRowsPerPage = const <int>[defaultRowsPerPage, defaultRowsPerPage * 2, defaultRowsPerPage * 5, defaultRowsPerPage * 10],
     this.onRowsPerPageChanged,
     this.dragStartBehavior = DragStartBehavior.start,
     @required this.source,
   }) : assert(header != null),
        assert(columns != null),
        assert(dragStartBehavior != null),
        assert(columns.isNotEmpty),
        assert(sortColumnIndex == null || (sortColumnIndex >= 0 && sortColumnIndex < columns.length)),
        assert(sortAscending != null),
        assert(dataRowHeight != null),
        assert(headingRowHeight != null),
        assert(horizontalMargin != null),
        assert(columnSpacing != null),
        assert(showCheckboxColumn != null),
        assert(rowsPerPage != null),
        assert(rowsPerPage > 0),
        assert(() {
          if (onRowsPerPageChanged != null)
            assert(availableRowsPerPage != null && availableRowsPerPage.contains(rowsPerPage));
          return true;
        }()),
        assert(source != null),
        super(key: key);

   /// The table card's header.
   ///
   /// This is typically a [Text] widget, but can also be a [ButtonBar] with
   /// [FlatButton]s. Suitable defaults are automatically provided for the font,
   /// button color, button padding, and so forth.
   ///
   /// If items in the table are selectable, then, when the selection is not
   /// empty, the header is replaced by a count of the selected items.
   final Widget header;

   /// Icon buttons to show at the top right of the table.
   ///
   /// Typically, the exact actions included in this list will vary based on
   /// whether any rows are selected or not.
   ///
   /// These should be size 24.0 with default padding (8.0).
   final List<Widget> actions;

   /// The configuration and labels for the columns in the table.
   final List<DataColumn> columns;

   /// The current primary sort key's column.
   ///
   /// See [DataTable.sortColumnIndex].
   final int sortColumnIndex;

   /// Whether the column mentioned in [sortColumnIndex], if any, is sorted
   /// in ascending order.
   ///
   /// See [DataTable.sortAscending].
   final bool sortAscending;

   /// Invoked when the user selects or unselects every row, using the
   /// checkbox in the heading row.
   ///
   /// See [DataTable.onSelectAll].
   final ValueSetter<bool> onSelectAll;

   /// The height of each row (excluding the row that contains column headings).
   ///
   /// This value is optional and defaults to kMinInteractiveDimension if not
   /// specified.
   final double dataRowHeight;

   /// The height of the heading row.
   ///
   /// This value is optional and defaults to 56.0 if not specified.
   final double headingRowHeight;

   /// The horizontal margin between the edges of the table and the content
   /// in the first and last cells of each row.
   ///
   /// When a checkbox is displayed, it is also the margin between the checkbox
   /// the content in the first data column.
   ///
   /// This value defaults to 24.0 to adhere to the Material Design specifications.
   final double horizontalMargin;

   /// The horizontal margin between the contents of each data column.
   ///
   /// This value defaults to 56.0 to adhere to the Material Design specifications.
   final double columnSpacing;

   /// {@macro flutter.material.dataTable.showCheckboxColumn}
   final bool showCheckboxColumn;

   /// The index of the first row to display when the widget is first created.
   final int initialFirstRowIndex;

   /// Invoked when the user switches to another page.
   ///
   /// The value is the index of the first row on the currently displayed page.
   final ValueChanged<int> onPageChanged;

   /// The number of rows to show on each page.
   ///
   /// See also:
   ///
   ///  * [onRowsPerPageChanged]
   ///  * [defaultRowsPerPage]
   final int rowsPerPage;

   /// The default value for [rowsPerPage].
   ///
   /// Useful when initializing the field that will hold the current
   /// [rowsPerPage], when implemented [onRowsPerPageChanged].
   static const int defaultRowsPerPage = 10;

   /// The options to offer for the rowsPerPage.
   ///
   /// The current [rowsPerPage] must be a value in this list.
   ///
   /// The values in this list should be sorted in ascending order.
   final List<int> availableRowsPerPage;

   /// Invoked when the user selects a different number of rows per page.
   ///
   /// If this is null, then the value given by [rowsPerPage] will be used
   /// and no affordance will be provided to change the value.
   final ValueChanged<int> onRowsPerPageChanged;

   /// The data source which provides data to show in each row. Must be non-null.
   ///
   /// This object should generally have a lifetime longer than the
   /// [PaginatedDataTable] widget itself; it should be reused each time the
   /// [PaginatedDataTable] constructor is called.
   final DataTableSource source;

   /// {@macro flutter.widgets.scrollable.dragStartBehavior}
   final DragStartBehavior dragStartBehavior;

   @override
   PaginatedDataTableState createState() => PaginatedDataTableState();
 }

 /// Holds the state of a [PaginatedDataTable].
 ///
 /// The table can be programmatically paged using the [pageTo] method.
 class PaginatedDataTableState extends State<PaginatedDataTable> {
   int _firstRowIndex;
   int _rowCount;
   bool _rowCountApproximate;
   int _selectedRowCount;
   final Map<int, DataRow> _rows = <int, DataRow>{};

   @override
   void initState() {
     super.initState();
     _firstRowIndex = PageStorage.of(context)?.readState(context) as int ?? widget.initialFirstRowIndex ?? 0;
     widget.source.addListener(_handleDataSourceChanged);
     _handleDataSourceChanged();
   }

   @override
   void didUpdateWidget(PaginatedDataTable oldWidget) {
     super.didUpdateWidget(oldWidget);
     if (oldWidget.source != widget.source) {
       oldWidget.source.removeListener(_handleDataSourceChanged);
       widget.source.addListener(_handleDataSourceChanged);
       _handleDataSourceChanged();
     }
   }

   @override
   void dispose() {
     widget.source.removeListener(_handleDataSourceChanged);
     super.dispose();
   }

   void _handleDataSourceChanged() {
     setState(() {
       _rowCount = widget.source.rowCount;
       _rowCountApproximate = widget.source.isRowCountApproximate;
       _selectedRowCount = widget.source.selectedRowCount;
       _rows.clear();
     });
   }

   /// Ensures that the given row is visible.
   void pageTo(int rowIndex) {
     final int oldFirstRowIndex = _firstRowIndex;
     setState(() {
       final int rowsPerPage = widget.rowsPerPage;
       _firstRowIndex = (rowIndex ~/ rowsPerPage) * rowsPerPage;
     });
     if ((widget.onPageChanged != null) &&
         (oldFirstRowIndex != _firstRowIndex))
       widget.onPageChanged(_firstRowIndex);
   }

   DataRow _getBlankRowFor(int index) {
     return DataRow.byIndex(
       index: index,
       cells: widget.columns.map<DataCell>((DataColumn column) => DataCell.empty).toList(),
     );
   }

   DataRow _getProgressIndicatorRowFor(int index) {
     bool haveProgressIndicator = false;
     final List<DataCell> cells = widget.columns.map<DataCell>((DataColumn column) {
       if (!column.numeric) {
         haveProgressIndicator = true;
         return const DataCell(CircularProgressIndicator());
       }
       return DataCell.empty;
     }).toList();
     if (!haveProgressIndicator) {
       haveProgressIndicator = true;
       cells[0] = const DataCell(CircularProgressIndicator());
     }
     return DataRow.byIndex(
       index: index,
       cells: cells,
     );
   }

   List<DataRow> _getRows(int firstRowIndex, int rowsPerPage) {
     final List<DataRow> result = <DataRow>[];
     final int nextPageFirstRowIndex = firstRowIndex + rowsPerPage;
     bool haveProgressIndicator = false;
     for (int index = firstRowIndex; index < nextPageFirstRowIndex; index += 1) {
       DataRow row;
       if (index < _rowCount || _rowCountApproximate) {
         row = _rows.putIfAbsent(index, () => widget.source.getRow(index));
         if (row == null && !haveProgressIndicator) {
           row ??= _getProgressIndicatorRowFor(index);
           haveProgressIndicator = true;
         }
       }
       row ??= _getBlankRowFor(index);
       result.add(row);
     }
     return result;
   }

   void _handlePrevious() {
     pageTo(math.max(_firstRowIndex - widget.rowsPerPage, 0));
   }

   void _handleNext() {
     pageTo(_firstRowIndex + widget.rowsPerPage);
   }

   final GlobalKey _tableKey = GlobalKey();

   @override
   Widget build(BuildContext context) {
     // TODO(ianh): This whole build function doesn't handle RTL yet.
     assert(debugCheckHasMaterialLocalizations(context));
     final ThemeData themeData = Theme.of(context);
     final MaterialLocalizations localizations = MaterialLocalizations.of(context);
     // HEADER
     final List<Widget> headerWidgets = <Widget>[];
     double startPadding = 24.0;
     if (_selectedRowCount == 0) {
       headerWidgets.add(Expanded(child: widget.header));
       if (widget.header is ButtonBar) {
         // We adjust the padding when a button bar is present, because the
         // ButtonBar introduces 2 pixels of outside padding, plus 2 pixels
         // around each button on each side, and the button itself will have 8
         // pixels internally on each side, yet we want the left edge of the
         // inside of the button to line up with the 24.0 left inset.
         // TODO(ianh): Better magic. See https://github.com/flutter/flutter/issues/4460
         startPadding = 12.0;
       }
     } else {
       headerWidgets.add(Expanded(
         child: Text(localizations.selectedRowCountTitle(_selectedRowCount)),
       ));
     }
     if (widget.actions != null) {
       headerWidgets.addAll(
         widget.actions.map<Widget>((Widget action) {
           return Padding(
             // 8.0 is the default padding of an icon button
             padding: const EdgeInsetsDirectional.only(start: 24.0 - 8.0 * 2.0),
             child: action,
           );
         }).toList()
       );
     }

     // FOOTER
     final TextStyle footerTextStyle = themeData.textTheme.caption;
     final List<Widget> footerWidgets = <Widget>[];
     if (widget.onRowsPerPageChanged != null) {
       final List<Widget> availableRowsPerPage = widget.availableRowsPerPage
         .where((int value) => value <= _rowCount || value == widget.rowsPerPage)
         .map<DropdownMenuItem<int>>((int value) {
           return DropdownMenuItem<int>(
             value: value,
             child: Text('$value'),
           );
         })
         .toList();
       footerWidgets.addAll(<Widget>[
         Container(width: 14.0), // to match trailing padding in case we overflow and end up scrolling
         Text(localizations.rowsPerPageTitle),
         ConstrainedBox(
           constraints: const BoxConstraints(minWidth: 64.0), // 40.0 for the text, 24.0 for the icon
           child: Align(
             alignment: AlignmentDirectional.centerEnd,
             child: DropdownButtonHideUnderline(
               child: DropdownButton<int>(
                 items: availableRowsPerPage.cast<DropdownMenuItem<int>>(),
                 value: widget.rowsPerPage,
                 onChanged: widget.onRowsPerPageChanged,
                 style: footerTextStyle,
                 iconSize: 24.0,
               ),
             ),
           ),
         ),
       ]);
     }
     footerWidgets.addAll(<Widget>[
       Container(width: 32.0),
       Text(
         localizations.pageRowsInfoTitle(
           _firstRowIndex + 1,
           _firstRowIndex + widget.rowsPerPage,
           _rowCount,
           _rowCountApproximate,
         ),
       ),
       Container(width: 32.0),
       IconButton(
         icon: const Icon(Icons.chevron_left),
         padding: EdgeInsets.zero,
         tooltip: localizations.previousPageTooltip,
         onPressed: _firstRowIndex <= 0 ? null : _handlePrevious,
       ),
       Container(width: 24.0),
       IconButton(
         icon: const Icon(Icons.chevron_right),
         padding: EdgeInsets.zero,
         tooltip: localizations.nextPageTooltip,
         onPressed: (!_rowCountApproximate && (_firstRowIndex + widget.rowsPerPage >= _rowCount)) ? null : _handleNext,
       ),
       Container(width: 14.0),
     ]);

     // CARD
     return LayoutBuilder(
       builder: (BuildContext context, BoxConstraints constraints) {
         return Card(
           semanticContainer: false,
           child: Column(
             crossAxisAlignment: CrossAxisAlignment.stretch,
             children: <Widget>[
               Semantics(
                 container: true,
                 child: DefaultTextStyle(
                   // These typographic styles aren't quite the regular ones. We pick the closest ones from the regular
                   // list and then tweak them appropriately.
                   // See https://material.io/design/components/data-tables.html#tables-within-cards
                   style: _selectedRowCount > 0 ? themeData.textTheme.subtitle1.copyWith(color: themeData.accentColor)
                                                : themeData.textTheme.headline6.copyWith(fontWeight: FontWeight.w400),
                   child: IconTheme.merge(
                     data: const IconThemeData(
                       opacity: 0.54
                     ),
                     child: Ink(
                       height: 64.0,
                       color: _selectedRowCount > 0 ? themeData.secondaryHeaderColor : null,
                       child: Padding(
                         padding: EdgeInsetsDirectional.only(start: startPadding, end: 14.0),
                         child: Row(
                           mainAxisAlignment: MainAxisAlignment.end,
                           children: headerWidgets,
                         ),
                       ),
                     ),
                   ),
                 ),
               ),
               SingleChildScrollView(
                 scrollDirection: Axis.horizontal,
                 dragStartBehavior: widget.dragStartBehavior,
                 child: ConstrainedBox(
                   constraints: BoxConstraints(minWidth: constraints.minWidth),
                   child: DataTable(
                     key: _tableKey,
                     columns: widget.columns,
                     sortColumnIndex: widget.sortColumnIndex,
                     sortAscending: widget.sortAscending,
                     onSelectAll: widget.onSelectAll,
                     dataRowHeight: widget.dataRowHeight,
                     headingRowHeight: widget.headingRowHeight,
                     horizontalMargin: widget.horizontalMargin,
                     columnSpacing: widget.columnSpacing,
                     rows: _getRows(_firstRowIndex, widget.rowsPerPage),
                   ),
                 ),
               ),
               DefaultTextStyle(
                 style: footerTextStyle,
                 child: IconTheme.merge(
                   data: const IconThemeData(
                     opacity: 0.54
                   ),
                   child: Container(
                     // TODO(bkonyi): this won't handle text zoom correctly, https://github.com/flutter/flutter/issues/48522
                     height: 56.0,
                     child: SingleChildScrollView(
                       dragStartBehavior: widget.dragStartBehavior,
                       scrollDirection: Axis.horizontal,
                       reverse: true,
                       child: Row(
                         children: footerWidgets,
                       ),
                     ),
                   ),
                 ),
               ),
             ],
           ),
         );
       },
     );
   }
 }
	// Copyright 2014 The Flutter Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'dart:math' as math;

	import 'package:flutter/widgets.dart';
	import 'package:flutter/rendering.dart';
	import 'package:flutter/gestures.dart' show DragStartBehavior;

	import 'button_bar.dart';
	import 'card.dart';
	import 'constants.dart';
	import 'data_table.dart';
	import 'data_table_source.dart';
	import 'debug.dart';
	import 'dropdown.dart';
	import 'icon_button.dart';
	import 'icons.dart';
	import 'ink_decoration.dart';
	import 'material_localizations.dart';
	import 'progress_indicator.dart';
	import 'theme.dart';

	/// A material design data table that shows data using multiple pages.
	///
	/// A paginated data table shows [rowsPerPage] rows of data per page and
	/// provides controls for showing other pages.
	///
	/// Data is read lazily from from a [DataTableSource]. The widget is presented
	/// as a [Card].
	///
	/// See also:
	///
	/// * [DataTable], which is not paginated.
	/// * <https://material.io/go/design-data-tables#data-tables-tables-within-cards>
	class PaginatedDataTable extends StatefulWidget {
	/// Creates a widget describing a paginated [DataTable] on a [Card].
	///
	/// The [header] should give the card's header, typically a [Text] widget. It
	/// must not be null.
	///
	/// The [columns] argument must be a list of as many [DataColumn] objects as
	/// the table is to have columns, ignoring the leading checkbox column if any.
	/// The [columns] argument must have a length greater than zero and cannot be
	/// null.
	///
	/// If the table is sorted, the column that provides the current primary key
	/// should be specified by index in [sortColumnIndex], 0 meaning the first
	/// column in [columns], 1 being the next one, and so forth.
	///
	/// The actual sort order can be specified using [sortAscending]; if the sort
	/// order is ascending, this should be true (the default), otherwise it should
	/// be false.
	///
	/// The [source] must not be null. The [source] should be a long-lived
	/// [DataTableSource]. The same source should be provided each time a
	/// particular [PaginatedDataTable] widget is created; avoid creating a new
	/// [DataTableSource] with each new instance of the [PaginatedDataTable]
	/// widget unless the data table really is to now show entirely different
	/// data from a new source.
	///
	/// The [rowsPerPage] and [availableRowsPerPage] must not be null (they
	/// both have defaults, though, so don't have to be specified).
	PaginatedDataTable({
	Key key,
	@required this.header,
	this.actions,
	@required this.columns,
	this.sortColumnIndex,
	this.sortAscending = true,
	this.onSelectAll,
	this.dataRowHeight = kMinInteractiveDimension,
	this.headingRowHeight = 56.0,
	this.horizontalMargin = 24.0,
	this.columnSpacing = 56.0,
	this.showCheckboxColumn = true,
	this.initialFirstRowIndex = 0,
	this.onPageChanged,
	this.rowsPerPage = defaultRowsPerPage,
	this.availableRowsPerPage = const <int>[defaultRowsPerPage, defaultRowsPerPage * 2, defaultRowsPerPage * 5, defaultRowsPerPage * 10],
	this.onRowsPerPageChanged,
	this.dragStartBehavior = DragStartBehavior.start,
	@required this.source,
	}) : assert(header != null),
	assert(columns != null),
	assert(dragStartBehavior != null),
	assert(columns.isNotEmpty),
	assert(sortColumnIndex == null \|\| (sortColumnIndex >= 0 && sortColumnIndex < columns.length)),
	assert(sortAscending != null),
	assert(dataRowHeight != null),
	assert(headingRowHeight != null),
	assert(horizontalMargin != null),
	assert(columnSpacing != null),
	assert(showCheckboxColumn != null),
	assert(rowsPerPage != null),
	assert(rowsPerPage > 0),
	assert(() {
	if (onRowsPerPageChanged != null)
	assert(availableRowsPerPage != null && availableRowsPerPage.contains(rowsPerPage));
	return true;
	}()),
	assert(source != null),
	super(key: key);

	/// The table card's header.
	///
	/// This is typically a [Text] widget, but can also be a [ButtonBar] with
	/// [FlatButton]s. Suitable defaults are automatically provided for the font,
	/// button color, button padding, and so forth.
	///
	/// If items in the table are selectable, then, when the selection is not
	/// empty, the header is replaced by a count of the selected items.
	final Widget header;

	/// Icon buttons to show at the top right of the table.
	///
	/// Typically, the exact actions included in this list will vary based on
	/// whether any rows are selected or not.
	///
	/// These should be size 24.0 with default padding (8.0).
	final List<Widget> actions;

	/// The configuration and labels for the columns in the table.
	final List<DataColumn> columns;

	/// The current primary sort key's column.
	///
	/// See [DataTable.sortColumnIndex].
	final int sortColumnIndex;

	/// Whether the column mentioned in [sortColumnIndex], if any, is sorted
	/// in ascending order.
	///
	/// See [DataTable.sortAscending].
	final bool sortAscending;

	/// Invoked when the user selects or unselects every row, using the
	/// checkbox in the heading row.
	///
	/// See [DataTable.onSelectAll].
	final ValueSetter<bool> onSelectAll;

	/// The height of each row (excluding the row that contains column headings).
	///
	/// This value is optional and defaults to kMinInteractiveDimension if not
	/// specified.
	final double dataRowHeight;

	/// The height of the heading row.
	///
	/// This value is optional and defaults to 56.0 if not specified.
	final double headingRowHeight;

	/// The horizontal margin between the edges of the table and the content
	/// in the first and last cells of each row.
	///
	/// When a checkbox is displayed, it is also the margin between the checkbox
	/// the content in the first data column.
	///
	/// This value defaults to 24.0 to adhere to the Material Design specifications.
	final double horizontalMargin;

	/// The horizontal margin between the contents of each data column.
	///
	/// This value defaults to 56.0 to adhere to the Material Design specifications.
	final double columnSpacing;

	/// {@macro flutter.material.dataTable.showCheckboxColumn}
	final bool showCheckboxColumn;

	/// The index of the first row to display when the widget is first created.
	final int initialFirstRowIndex;

	/// Invoked when the user switches to another page.
	///
	/// The value is the index of the first row on the currently displayed page.
	final ValueChanged<int> onPageChanged;

	/// The number of rows to show on each page.
	///
	/// See also:
	///
	/// * [onRowsPerPageChanged]
	/// * [defaultRowsPerPage]
	final int rowsPerPage;

	/// The default value for [rowsPerPage].
	///
	/// Useful when initializing the field that will hold the current
	/// [rowsPerPage], when implemented [onRowsPerPageChanged].
	static const int defaultRowsPerPage = 10;

	/// The options to offer for the rowsPerPage.
	///
	/// The current [rowsPerPage] must be a value in this list.
	///
	/// The values in this list should be sorted in ascending order.
	final List<int> availableRowsPerPage;

	/// Invoked when the user selects a different number of rows per page.
	///
	/// If this is null, then the value given by [rowsPerPage] will be used
	/// and no affordance will be provided to change the value.
	final ValueChanged<int> onRowsPerPageChanged;

	/// The data source which provides data to show in each row. Must be non-null.
	///
	/// This object should generally have a lifetime longer than the
	/// [PaginatedDataTable] widget itself; it should be reused each time the
	/// [PaginatedDataTable] constructor is called.
	final DataTableSource source;

	/// {@macro flutter.widgets.scrollable.dragStartBehavior}
	final DragStartBehavior dragStartBehavior;

	@override
	PaginatedDataTableState createState() => PaginatedDataTableState();
	}

	/// Holds the state of a [PaginatedDataTable].
	///
	/// The table can be programmatically paged using the [pageTo] method.
	class PaginatedDataTableState extends State<PaginatedDataTable> {
	int _firstRowIndex;
	int _rowCount;
	bool _rowCountApproximate;
	int _selectedRowCount;
	final Map<int, DataRow> _rows = <int, DataRow>{};

	@override
	void initState() {
	super.initState();
	_firstRowIndex = PageStorage.of(context)?.readState(context) as int ?? widget.initialFirstRowIndex ?? 0;
	widget.source.addListener(_handleDataSourceChanged);
	_handleDataSourceChanged();
	}

	@override
	void didUpdateWidget(PaginatedDataTable oldWidget) {
	super.didUpdateWidget(oldWidget);
	if (oldWidget.source != widget.source) {
	oldWidget.source.removeListener(_handleDataSourceChanged);
	widget.source.addListener(_handleDataSourceChanged);
	_handleDataSourceChanged();
	}
	}

	@override
	void dispose() {
	widget.source.removeListener(_handleDataSourceChanged);
	super.dispose();
	}

	void _handleDataSourceChanged() {
	setState(() {
	_rowCount = widget.source.rowCount;
	_rowCountApproximate = widget.source.isRowCountApproximate;
	_selectedRowCount = widget.source.selectedRowCount;
	_rows.clear();
	});
	}

	/// Ensures that the given row is visible.
	void pageTo(int rowIndex) {
	final int oldFirstRowIndex = _firstRowIndex;
	setState(() {
	final int rowsPerPage = widget.rowsPerPage;
	_firstRowIndex = (rowIndex ~/ rowsPerPage) * rowsPerPage;
	});
	if ((widget.onPageChanged != null) &&
	(oldFirstRowIndex != _firstRowIndex))
	widget.onPageChanged(_firstRowIndex);
	}

	DataRow _getBlankRowFor(int index) {
	return DataRow.byIndex(
	index: index,
	cells: widget.columns.map<DataCell>((DataColumn column) => DataCell.empty).toList(),
	);
	}

	DataRow _getProgressIndicatorRowFor(int index) {
	bool haveProgressIndicator = false;
	final List<DataCell> cells = widget.columns.map<DataCell>((DataColumn column) {
	if (!column.numeric) {
	haveProgressIndicator = true;
	return const DataCell(CircularProgressIndicator());
	}
	return DataCell.empty;
	}).toList();
	if (!haveProgressIndicator) {
	haveProgressIndicator = true;
	cells[0] = const DataCell(CircularProgressIndicator());
	}
	return DataRow.byIndex(
	index: index,
	cells: cells,
	);
	}

	List<DataRow> _getRows(int firstRowIndex, int rowsPerPage) {
	final List<DataRow> result = <DataRow>[];
	final int nextPageFirstRowIndex = firstRowIndex + rowsPerPage;
	bool haveProgressIndicator = false;
	for (int index = firstRowIndex; index < nextPageFirstRowIndex; index += 1) {
	DataRow row;
	if (index < _rowCount \|\| _rowCountApproximate) {
	row = _rows.putIfAbsent(index, () => widget.source.getRow(index));
	if (row == null && !haveProgressIndicator) {
	row ??= _getProgressIndicatorRowFor(index);
	haveProgressIndicator = true;
	}
	}
	row ??= _getBlankRowFor(index);
	result.add(row);
	}
	return result;
	}

	void _handlePrevious() {
	pageTo(math.max(_firstRowIndex - widget.rowsPerPage, 0));
	}

	void _handleNext() {
	pageTo(_firstRowIndex + widget.rowsPerPage);
	}

	final GlobalKey _tableKey = GlobalKey();

	@override
	Widget build(BuildContext context) {
	// TODO(ianh): This whole build function doesn't handle RTL yet.
	assert(debugCheckHasMaterialLocalizations(context));
	final ThemeData themeData = Theme.of(context);
	final MaterialLocalizations localizations = MaterialLocalizations.of(context);
	// HEADER
	final List<Widget> headerWidgets = <Widget>[];
	double startPadding = 24.0;
	if (_selectedRowCount == 0) {
	headerWidgets.add(Expanded(child: widget.header));
	if (widget.header is ButtonBar) {
	// We adjust the padding when a button bar is present, because the
	// ButtonBar introduces 2 pixels of outside padding, plus 2 pixels
	// around each button on each side, and the button itself will have 8
	// pixels internally on each side, yet we want the left edge of the
	// inside of the button to line up with the 24.0 left inset.
	// TODO(ianh): Better magic. See https://github.com/flutter/flutter/issues/4460
	startPadding = 12.0;
	}
	} else {
	headerWidgets.add(Expanded(
	child: Text(localizations.selectedRowCountTitle(_selectedRowCount)),
	));
	}
	if (widget.actions != null) {
	headerWidgets.addAll(
	widget.actions.map<Widget>((Widget action) {
	return Padding(
	// 8.0 is the default padding of an icon button
	padding: const EdgeInsetsDirectional.only(start: 24.0 - 8.0 * 2.0),
	child: action,
	);
	}).toList()
	);
	}

	// FOOTER
	final TextStyle footerTextStyle = themeData.textTheme.caption;
	final List<Widget> footerWidgets = <Widget>[];
	if (widget.onRowsPerPageChanged != null) {
	final List<Widget> availableRowsPerPage = widget.availableRowsPerPage
	.where((int value) => value <= _rowCount \|\| value == widget.rowsPerPage)
	.map<DropdownMenuItem<int>>((int value) {
	return DropdownMenuItem<int>(
	value: value,
	child: Text('$value'),
	);
	})
	.toList();
	footerWidgets.addAll(<Widget>[
	Container(width: 14.0), // to match trailing padding in case we overflow and end up scrolling
	Text(localizations.rowsPerPageTitle),
	ConstrainedBox(
	constraints: const BoxConstraints(minWidth: 64.0), // 40.0 for the text, 24.0 for the icon
	child: Align(
	alignment: AlignmentDirectional.centerEnd,
	child: DropdownButtonHideUnderline(
	child: DropdownButton<int>(
	items: availableRowsPerPage.cast<DropdownMenuItem<int>>(),
	value: widget.rowsPerPage,
	onChanged: widget.onRowsPerPageChanged,
	style: footerTextStyle,
	iconSize: 24.0,
	),
	),
	),
	),
	]);
	}
	footerWidgets.addAll(<Widget>[
	Container(width: 32.0),
	Text(
	localizations.pageRowsInfoTitle(
	_firstRowIndex + 1,
	_firstRowIndex + widget.rowsPerPage,
	_rowCount,
	_rowCountApproximate,
	),
	),
	Container(width: 32.0),
	IconButton(
	icon: const Icon(Icons.chevron_left),
	padding: EdgeInsets.zero,
	tooltip: localizations.previousPageTooltip,
	onPressed: _firstRowIndex <= 0 ? null : _handlePrevious,
	),
	Container(width: 24.0),
	IconButton(
	icon: const Icon(Icons.chevron_right),
	padding: EdgeInsets.zero,
	tooltip: localizations.nextPageTooltip,
	onPressed: (!_rowCountApproximate && (_firstRowIndex + widget.rowsPerPage >= _rowCount)) ? null : _handleNext,
	),
	Container(width: 14.0),
	]);

	// CARD
	return LayoutBuilder(
	builder: (BuildContext context, BoxConstraints constraints) {
	return Card(
	semanticContainer: false,
	child: Column(
	crossAxisAlignment: CrossAxisAlignment.stretch,
	children: <Widget>[
	Semantics(
	container: true,
	child: DefaultTextStyle(
	// These typographic styles aren't quite the regular ones. We pick the closest ones from the regular
	// list and then tweak them appropriately.
	// See https://material.io/design/components/data-tables.html#tables-within-cards
	style: _selectedRowCount > 0 ? themeData.textTheme.subtitle1.copyWith(color: themeData.accentColor)
	: themeData.textTheme.headline6.copyWith(fontWeight: FontWeight.w400),
	child: IconTheme.merge(
	data: const IconThemeData(
	opacity: 0.54
	),
	child: Ink(
	height: 64.0,
	color: _selectedRowCount > 0 ? themeData.secondaryHeaderColor : null,
	child: Padding(
	padding: EdgeInsetsDirectional.only(start: startPadding, end: 14.0),
	child: Row(
	mainAxisAlignment: MainAxisAlignment.end,
	children: headerWidgets,
	),
	),
	),
	),
	),
	),
	SingleChildScrollView(
	scrollDirection: Axis.horizontal,
	dragStartBehavior: widget.dragStartBehavior,
	child: ConstrainedBox(
	constraints: BoxConstraints(minWidth: constraints.minWidth),
	child: DataTable(
	key: _tableKey,
	columns: widget.columns,
	sortColumnIndex: widget.sortColumnIndex,
	sortAscending: widget.sortAscending,
	onSelectAll: widget.onSelectAll,
	dataRowHeight: widget.dataRowHeight,
	headingRowHeight: widget.headingRowHeight,
	horizontalMargin: widget.horizontalMargin,
	columnSpacing: widget.columnSpacing,
	rows: _getRows(_firstRowIndex, widget.rowsPerPage),
	),
	),
	),
	DefaultTextStyle(
	style: footerTextStyle,
	child: IconTheme.merge(
	data: const IconThemeData(
	opacity: 0.54
	),
	child: Container(
	// TODO(bkonyi): this won't handle text zoom correctly, https://github.com/flutter/flutter/issues/48522
	height: 56.0,
	child: SingleChildScrollView(
	dragStartBehavior: widget.dragStartBehavior,
	scrollDirection: Axis.horizontal,
	reverse: true,
	child: Row(
	children: footerWidgets,
	),
	),
	),
	),
	),
	],
	),
	);
	},
	);
	}
	}