Allow multi-line text fields with no line limit (#10576)

packages/flutter/lib/src/material/text_field.dart

@@ -62,6 +62,12 @@ class TextField extends StatefulWidget {
   /// To remove the decoration entirely (including the extra padding introduced
   /// by the decoration to save space for the labels), set the [decoration] to
   /// null.
+  ///
+  /// The [maxLines] property can be set to null to remove the restriction on
+  /// the number of lines. By default, it is 1, meaning this is a single-line
+  /// text field. If it is not null, it must be greater than zero.
+  ///
+  /// The [keyboardType], [autofocus], and [obscureText] arguments must not be null.
   const TextField({
     Key key,
     this.controller,
@@ -76,7 +82,11 @@ class TextField extends StatefulWidget {
     this.onChanged,
     this.onSubmitted,
     this.inputFormatters,
-  }) : super(key: key);
+  }) : assert(keyboardType != null),
+       assert(autofocus != null),
+       assert(obscureText != null),
+       assert(maxLines == null || maxLines > 0),
+       super(key: key);
 
   /// Controls the text being edited.
   ///
@@ -98,6 +108,8 @@ class TextField extends StatefulWidget {
   final InputDecoration decoration;
 
   /// The type of keyboard to use for editing the text.
+  ///
+  /// Defaults to [TextInputType.text]. Cannot be null.
   final TextInputType keyboardType;
 
   /// The style to use for the text being edited.
@@ -116,7 +128,7 @@ class TextField extends StatefulWidget {
   /// If true, the keyboard will open as soon as this text field obtains focus.
   /// Otherwise, the keyboard is only shown after the user taps the text field.
   ///
-  /// Defaults to false.
+  /// Defaults to false. Cannot be null.
   // See https://github.com/flutter/flutter/issues/7035 for the rationale for this
   // keyboard behavior.
   final bool autofocus;
@@ -126,13 +138,16 @@ class TextField extends StatefulWidget {
   /// When this is set to true, all the characters in the text field are
   /// replaced by U+2022 BULLET characters (•).
   ///
-  /// Defaults to false.
+  /// Defaults to false. Cannot be null.
   final bool obscureText;
 
   /// The maximum number of lines for the text to span, wrapping if necessary.
   ///
   /// If this is 1 (the default), the text will not wrap, but will scroll
   /// horizontally instead.
+  ///
+  /// If this is null, there is no limit to the number of lines. If it is not
+  /// null, the value must be greater than zero.
   final int maxLines;
 
   /// Called when the text being edited changes.

packages/flutter/lib/src/material/text_form_field.dart

@@ -30,7 +30,8 @@ import 'text_field.dart';
 class TextFormField extends FormField<String> {
   /// Creates a [FormField] that contains a [TextField].
   ///
-  /// For a documentation about the various parameters, see [TextField].
+  /// For documentation about the various parameters, see the [TextField] class
+  /// and [new TextField], the constructor.
   TextFormField({
     Key key,
     TextEditingController controller,
@@ -44,7 +45,11 @@ class TextFormField extends FormField<String> {
     FormFieldSetter<String> onSaved,
     FormFieldValidator<String> validator,
     List<TextInputFormatter> inputFormatters,
-  }) : super(
+  }) : assert(keyboardType != null),
+       assert(autofocus != null),
+       assert(obscureText != null),
+       assert(maxLines == null || maxLines > 0),
+       super(
     key: key,
     initialValue: controller != null ? controller.value.text : '',
     onSaved: onSaved,

packages/flutter/lib/src/painting/text_painter.dart

@@ -35,6 +35,8 @@ class TextPainter {
   ///
   /// The text argument is optional but [text] must be non-null before calling
   /// [layout].
+  ///
+  /// The [maxLines] property, if non-null, must be greater than zero.
   TextPainter({
     TextSpan text,
     TextAlign textAlign,
@@ -43,6 +45,7 @@ class TextPainter {
     String ellipsis,
   }) : assert(text == null || text.debugAssertIsValid()),
        assert(textScaleFactor != null),
+       assert(maxLines == null || maxLines > 0),
        _text = text,
        _textAlign = textAlign,
        _textScaleFactor = textScaleFactor,
@@ -134,7 +137,9 @@ class TextPainter {
   /// After this is set, you must call [layout] before the next call to [paint].
   int get maxLines => _maxLines;
   int _maxLines;
+  /// The value may be null. If it is not null, then it must be greater than zero.
   set maxLines(int value) {
+    assert(value == null || value > 0);
     if (_maxLines == value)
       return;
     _maxLines = value;

packages/flutter/lib/src/painting/text_style.dart

@@ -234,12 +234,18 @@ class TextStyle {
   }
 
   /// The style information for paragraphs, encoded for use by `dart:ui`.
+  ///
+  /// The `textScaleFactor` argument must not be null. If omitted, it defaults
+  /// to 1.0. The other arguments may be null. The `maxLines` argument, if
+  /// specified and non-null, must be greater than zero.
   ui.ParagraphStyle getParagraphStyle({
       TextAlign textAlign,
       double textScaleFactor: 1.0,
       String ellipsis,
       int maxLines,
-   }) {
+  }) {
+    assert(textScaleFactor != null);
+    assert(maxLines == null || maxLines > 0);
     return new ui.ParagraphStyle(
       textAlign: textAlign,
       fontWeight: fontWeight,

packages/flutter/lib/src/rendering/editable.dart

@@ -84,6 +84,15 @@ class TextSelectionPoint {
 /// responsibility of higher layers and not handled by this object.
 class RenderEditable extends RenderBox {
   /// Creates a render object that implements the visual aspects of a text field.
+  ///
+  /// If [showCursor] is not specified, then it defaults to hiding the cursor.
+  ///
+  /// The [maxLines] property can be set to null to remove the restriction on
+  /// the number of lines. By default, it is 1, meaning this is a single-line
+  /// text field. If it is not null, it must be greater than zero.
+  ///
+  /// The [offset] is required and must not be null. You can use [new
+  /// ViewportOffset.zero] if you have no need for scrolling.
   RenderEditable({
     TextSpan text,
     TextAlign textAlign,
@@ -96,7 +105,7 @@ class RenderEditable extends RenderBox {
     @required ViewportOffset offset,
     this.onSelectionChanged,
     this.onCaretChanged,
-  }) : assert(maxLines != null),
+  }) : assert(maxLines == null || maxLines > 0),
        assert(textScaleFactor != null),
        assert(offset != null),
        _textPainter = new TextPainter(text: text, textAlign: textAlign, textScaleFactor: textScaleFactor),
@@ -180,13 +189,21 @@ class RenderEditable extends RenderBox {
   }
 
   /// The maximum number of lines for the text to span, wrapping if necessary.
+  ///
   /// If this is 1 (the default), the text will not wrap, but will extend
   /// indefinitely instead.
+  ///
+  /// If this is null, there is no limit to the number of lines.
+  ///
+  /// When this is not null, the intrinsic height of the render object is the
+  /// height of one line of text multiplied by this value. In other words, this
+  /// also controls the height of the actual editing widget.
   int get maxLines => _maxLines;
   int _maxLines;
+  /// The value may be null. If it is not null, then it must be greater than zero.
   set maxLines(int value) {
-    assert(value != null);
-    if (_maxLines == value)
+    assert(value == null || value > 0);
+    if (maxLines == value)
       return;
     _maxLines = value;
     markNeedsTextLayout();
@@ -261,7 +278,7 @@ class RenderEditable extends RenderBox {
     super.detach();
   }
 
-  bool get _isMultiline => maxLines > 1;
+  bool get _isMultiline => maxLines != 1;
 
   Axis get _viewportAxis => _isMultiline ? Axis.vertical : Axis.horizontal;
 
@@ -359,14 +376,30 @@ class RenderEditable extends RenderBox {
   // This does not required the layout to be updated.
   double get _preferredLineHeight => _textPainter.preferredLineHeight;
 
+  double _preferredHeight(double width) {
+    if (maxLines != null)
+      return _preferredLineHeight * maxLines;
+    if (width == double.INFINITY) {
+      final String text = _textPainter.text.toPlainText();
+      int lines = 1;
+      for (int index = 0; index < text.length; index += 1) {
+        if (text.codeUnitAt(index) == 0x0A) // count explicit line breaks
+          lines += 1;
+      }
+      return _preferredLineHeight * lines;
+    }
+    _layoutText(width);
+    return math.max(_preferredLineHeight, _textPainter.height);
+  }
+
   @override
   double computeMinIntrinsicHeight(double width) {
-    return _preferredLineHeight;
+    return _preferredHeight(width);
   }
 
   @override
   double computeMaxIntrinsicHeight(double width) {
-    return _preferredLineHeight * maxLines;
+    return _preferredHeight(width);
   }
 
   @override
@@ -434,7 +467,7 @@ class RenderEditable extends RenderBox {
       return;
     final double caretMargin = _kCaretGap + _kCaretWidth;
     final double availableWidth = math.max(0.0, constraintWidth - caretMargin);
-    final double maxWidth = _maxLines > 1 ? availableWidth : double.INFINITY;
+    final double maxWidth = _isMultiline ? availableWidth : double.INFINITY;
     _textPainter.layout(minWidth: availableWidth, maxWidth: maxWidth);
     _textLayoutLastWidth = constraintWidth;
   }
@@ -444,9 +477,7 @@ class RenderEditable extends RenderBox {
     _layoutText(constraints.maxWidth);
     _caretPrototype = new Rect.fromLTWH(0.0, _kCaretHeightOffset, _kCaretWidth, _preferredLineHeight - 2.0 * _kCaretHeightOffset);
     _selectionRects = null;
-    size = new Size(constraints.maxWidth, constraints.constrainHeight(
-      _textPainter.height.clamp(_preferredLineHeight, _preferredLineHeight * _maxLines)
-    ));
+    size = new Size(constraints.maxWidth, constraints.constrainHeight(_preferredHeight(constraints.maxWidth)));
     final Size contentSize = new Size(_textPainter.width + _kCaretGap + _kCaretWidth, _textPainter.height);
     final double _maxScrollExtent = _getMaxScrollExtent(contentSize);
     _hasVisualOverflow = _maxScrollExtent > 0.0;
@@ -506,13 +537,13 @@ class RenderEditable extends RenderBox {
   @override
   void debugFillDescription(List<String> description) {
     super.debugFillDescription(description);
-    description.add('cursorColor: $_cursorColor');
-    description.add('showCursor: $_showCursor');
-    description.add('maxLines: $_maxLines');
-    description.add('selectionColor: $_selectionColor');
+    description.add('cursorColor: $cursorColor');
+    description.add('showCursor: $showCursor');
+    description.add('maxLines: $maxLines');
+    description.add('selectionColor: $selectionColor');
     description.add('textScaleFactor: $textScaleFactor');
-    description.add('selection: $_selection');
-    description.add('offset: $_offset');
+    description.add('selection: $selection');
+    description.add('offset: $offset');
   }
 
   @override

packages/flutter/lib/src/rendering/paragraph.dart

@@ -31,7 +31,11 @@ const String _kEllipsis = '\u2026';
 class RenderParagraph extends RenderBox {
   /// Creates a paragraph render object.
   ///
-  /// The [text], [overflow], and [softWrap] arguments must not be null.
+  /// The [text], [overflow], [softWrap], and [textScaleFactor] arguments must
+  /// not be null.
+  ///
+  /// The [maxLines] property may be null (and indeed defaults to null), but if
+  /// it is not null, it must be greater than zero.
   RenderParagraph(TextSpan text, {
     TextAlign textAlign,
     bool softWrap: true,
@@ -43,6 +47,7 @@ class RenderParagraph extends RenderBox {
        assert(softWrap != null),
        assert(overflow != null),
        assert(textScaleFactor != null),
+       assert(maxLines == null || maxLines > 0),
        _softWrap = softWrap,
        _overflow = overflow,
        _textPainter = new TextPainter(
@@ -77,7 +82,11 @@ class RenderParagraph extends RenderBox {
 
   /// Whether the text should break at soft line breaks.
   ///
-  /// If false, the glyphs in the text will be positioned as if there was unlimited horizontal space.
+  /// If false, the glyphs in the text will be positioned as if there was
+  /// unlimited horizontal space.
+  ///
+  /// If [softWrap] is false, [overflow] and [textAlign] may have unexpected
+  /// effects.
   bool get softWrap => _softWrap;
   bool _softWrap;
   set softWrap(bool value) {
@@ -116,9 +125,11 @@ class RenderParagraph extends RenderBox {
 
   /// An optional maximum number of lines for the text to span, wrapping if necessary.
   /// If the text exceeds the given number of lines, it will be truncated according
-  /// to [overflow].
+  /// to [overflow] and [softWrap].
   int get maxLines => _textPainter.maxLines;
+  /// The value may be null. If it is not null, then it must be greater than zero.
   set maxLines(int value) {
+    assert(value == null || value > 0);
     if (_textPainter.maxLines == value)
       return;
     _textPainter.maxLines = value;
@@ -127,8 +138,7 @@ class RenderParagraph extends RenderBox {
   }
 
   void _layoutText({ double minWidth: 0.0, double maxWidth: double.INFINITY }) {
-    final bool wrap = _softWrap || (_overflow == TextOverflow.ellipsis && maxLines == null);
-    _textPainter.layout(minWidth: minWidth, maxWidth: wrap ? maxWidth : double.INFINITY);
+    _textPainter.layout(minWidth: minWidth, maxWidth: _softWrap ? maxWidth : double.INFINITY);
   }
 
   void _layoutTextWithConstraints(BoxConstraints constraints) {

packages/flutter/lib/src/widgets/basic.dart

@@ -3028,7 +3028,11 @@ class Flow extends MultiChildRenderObjectWidget {
 class RichText extends LeafRenderObjectWidget {
   /// Creates a paragraph of rich text.
   ///
-  /// The [text], [softWrap], and [overflow] arguments must not be null.
+  /// The [text], [softWrap], [overflow], nad [textScaleFactor] arguments must
+  /// not be null.
+  ///
+  /// The [maxLines] property may be null (and indeed defaults to null), but if
+  /// it is not null, it must be greater than zero.
   const RichText({
     Key key,
     @required this.text,
@@ -3041,6 +3045,7 @@ class RichText extends LeafRenderObjectWidget {
        assert(softWrap != null),
        assert(overflow != null),
        assert(textScaleFactor != null),
+       assert(maxLines == null || maxLines > 0),
        super(key: key);
 
   /// The text to display in this widget.
@@ -3066,6 +3071,9 @@ class RichText extends LeafRenderObjectWidget {
   /// An optional maximum number of lines for the text to span, wrapping if necessary.
   /// If the text exceeds the given number of lines, it will be truncated according
   /// to [overflow].
+  ///
+  /// If this is 1, text will not wrap. Otherwise, text will be wrapped at the
+  /// edge of the box.
   final int maxLines;
 
   @override

packages/flutter/lib/src/widgets/editable_text.dart

@@ -128,6 +128,10 @@ class TextEditingController extends ValueNotifier<TextEditingValue> {
 class EditableText extends StatefulWidget {
   /// Creates a basic text input control.
   ///
+  /// The [maxLines] property can be set to null to remove the restriction on
+  /// the number of lines. By default, it is 1, meaning this is a single-line
+  /// text field. If it is not null, it must be greater than zero.
+  ///
   /// The [controller], [focusNode], [style], and [cursorColor] arguments must
   /// not be null.
   EditableText({
@@ -152,9 +156,9 @@ class EditableText extends StatefulWidget {
        assert(obscureText != null),
        assert(style != null),
        assert(cursorColor != null),
-       assert(maxLines != null),
+       assert(maxLines == null || maxLines > 0),
        assert(autofocus != null),
-       inputFormatters = maxLines == 1 
+       inputFormatters = maxLines == 1
            ? (
                <TextInputFormatter>[BlacklistingTextInputFormatter.singleLineFormatter]
                  ..addAll(inputFormatters ?? const Iterable<TextInputFormatter>.empty())
@@ -192,8 +196,12 @@ class EditableText extends StatefulWidget {
   final Color cursorColor;
 
   /// The maximum number of lines for the text to span, wrapping if necessary.
+  ///
   /// If this is 1 (the default), the text will not wrap, but will scroll
   /// horizontally instead.
+  ///
+  /// If this is null, there is no limit to the number of lines. If it is not
+  /// null, the value must be greater than zero.
   final int maxLines;
 
   /// Whether this input field should focus itself if nothing else is already focused.
@@ -218,7 +226,7 @@ class EditableText extends StatefulWidget {
   /// Called when the user indicates that they are done editing the text in the field.
   final ValueChanged<String> onSubmitted;
 
-  /// Optional input validation and formatting overrides. Formatters are run 
+  /// Optional input validation and formatting overrides. Formatters are run
   /// in the provided order when the text input changes.
   final List<TextInputFormatter> inputFormatters;
 
@@ -340,7 +348,7 @@ class EditableTextState extends State<EditableText> implements TextInputClient {
   }
 
   bool get _hasFocus => widget.focusNode.hasFocus;
-  bool get _isMultiline => widget.maxLines > 1;
+  bool get _isMultiline => widget.maxLines != 1;
 
   // Calculate the new scroll offset so the cursor remains visible.
   double _getScrollOffsetForCaret(Rect caretRect) {
@@ -417,7 +425,7 @@ class EditableTextState extends State<EditableText> implements TextInputClient {
   void _handleSelectionChanged(TextSelection selection, RenderEditable renderObject, bool longPress) {
     widget.controller.selection = selection;
 
-    // Note that this will show the keyboard for all selection changes on the
+    // This will show the keyboard for all selection changes on the
     // EditableWidget, not just changes triggered by user gestures.
     requestKeyboard();
 

packages/flutter/lib/src/widgets/text.dart

@@ -14,6 +14,14 @@ class DefaultTextStyle extends InheritedWidget {
   ///
   /// Consider using [DefaultTextStyle.merge] to inherit styling information
   /// from the current default text style for a given [BuildContext].
+  ///
+  /// The [style] and [child] arguments are required and must not be null.
+  ///
+  /// The [softWrap] and [overflow] arguments must not be null (though they do
+  /// have default values).
+  ///
+  /// The [maxLines] property may be null (and indeed defaults to null), but if
+  /// it is not null, it must be greater than zero.
   const DefaultTextStyle({
     Key key,
     @required this.style,
@@ -25,6 +33,7 @@ class DefaultTextStyle extends InheritedWidget {
   }) : assert(style != null),
        assert(softWrap != null),
        assert(overflow != null),
+       assert(maxLines == null || maxLines > 0),
        assert(child != null),
        super(key: key, child: child);
 
@@ -48,6 +57,15 @@ class DefaultTextStyle extends InheritedWidget {
   /// for the [BuildContext] where the widget is inserted, and any of the other
   /// arguments that are not null replace the corresponding properties on that
   /// same default text style.
+  ///
+  /// This constructor cannot be used to override the [maxLines] property of the
+  /// ancestor with the value null, since null here is used to mean "defer to
+  /// ancestor". To replace a non-null [maxLines] from an ancestor with the null
+  /// value (to remove the restriction on number of lines), manually obtain the
+  /// ambient [DefaultTextStyle] using [DefaultTextStyle.of], then create a new
+  /// [DefaultTextStyle] using the [new DefaultTextStyle] constructor directly.
+  /// See the source below for an example of how to do this (since that's
+  /// essentially what this constructor does).
   static Widget merge({
     Key key,
     TextStyle style,
@@ -91,6 +109,12 @@ class DefaultTextStyle extends InheritedWidget {
   /// An optional maximum number of lines for the text to span, wrapping if necessary.
   /// If the text exceeds the given number of lines, it will be truncated according
   /// to [overflow].
+  ///
+  /// If this is 1, text will not wrap. Otherwise, text will be wrapped at the
+  /// edge of the box.
+  ///
+  /// If this is non-null, it will override even explicit null values of
+  /// [Text.maxLines].
   final int maxLines;
 
   /// The closest instance of this class that encloses the given context.
@@ -213,9 +237,17 @@ class Text extends StatelessWidget {
   /// [MediaQuery], or 1.0 if there is no [MediaQuery] in scope.
   final double textScaleFactor;
 
-  /// An optional maximum number of lines the text is allowed to take up.
+  /// An optional maximum number of lines for the text to span, wrapping if necessary.
   /// If the text exceeds the given number of lines, it will be truncated according
   /// to [overflow].
+  ///
+  /// If this is 1, text will not wrap. Otherwise, text will be wrapped at the
+  /// edge of the box.
+  ///
+  /// If this is null, but there is an ambient [DefaultTextStyle] that specifies
+  /// an explicit number for its [DefaultTextStyle.maxLines], then the
+  /// [DefaultTextStyle] value will take precedence. You can use a [RichText]
+  /// widget directly to entirely override the [DefaultTextStyle].
   final int maxLines;
 
   @override
@@ -232,7 +264,7 @@ class Text extends StatelessWidget {
       maxLines: maxLines ?? defaultTextStyle.maxLines,
       text: new TextSpan(
         style: effectiveTextStyle,
-        text: data
+        text: data,
       )
     );
   }

packages/flutter/test/material/text_field_test.dart

@@ -46,7 +46,7 @@ void main() {
     'First line of text is '
     'Second line goes until '
     'Third line of stuff ';
-  const String kFourLines =
+  const String kMoreThanFourLines =
     kThreeLines +
     'Fourth line won\'t display and ends at';
 
@@ -462,7 +462,7 @@ void main() {
       );
     }
 
-    await tester.pumpWidget(builder(3));
+    await tester.pumpWidget(builder(null));
 
     RenderBox findInputBox() => tester.renderObject(find.byKey(textFieldKey));
 
@@ -470,28 +470,44 @@ void main() {
     final Size emptyInputSize = inputBox.size;
 
     await tester.enterText(find.byType(TextField), 'No wrapping here.');
-    await tester.pumpWidget(builder(3));
+    await tester.pumpWidget(builder(null));
     expect(findInputBox(), equals(inputBox));
     expect(inputBox.size, equals(emptyInputSize));
 
-    await tester.enterText(find.byType(TextField), kThreeLines);
     await tester.pumpWidget(builder(3));
     expect(findInputBox(), equals(inputBox));
     expect(inputBox.size, greaterThan(emptyInputSize));
 
     final Size threeLineInputSize = inputBox.size;
 
+    await tester.enterText(find.byType(TextField), kThreeLines);
+    await tester.pumpWidget(builder(null));
+    expect(findInputBox(), equals(inputBox));
+    expect(inputBox.size, greaterThan(emptyInputSize));
+
+    await tester.enterText(find.byType(TextField), kThreeLines);
+    await tester.pumpWidget(builder(null));
+    expect(findInputBox(), equals(inputBox));
+    expect(inputBox.size, threeLineInputSize);
+
     // An extra line won't increase the size because we max at 3.
-    await tester.enterText(find.byType(TextField), kFourLines);
+    await tester.enterText(find.byType(TextField), kMoreThanFourLines);
     await tester.pumpWidget(builder(3));
     expect(findInputBox(), equals(inputBox));
     expect(inputBox.size, threeLineInputSize);
 
-    // But now it will.
-    await tester.enterText(find.byType(TextField), kFourLines);
+    // But now it will... but it will max at four
+    await tester.enterText(find.byType(TextField), kMoreThanFourLines);
     await tester.pumpWidget(builder(4));
     expect(findInputBox(), equals(inputBox));
     expect(inputBox.size, greaterThan(threeLineInputSize));
+
+    final Size fourLineInputSize = inputBox.size;
+
+    // Now it won't max out until the end
+    await tester.pumpWidget(builder(null));
+    expect(findInputBox(), equals(inputBox));
+    expect(inputBox.size, greaterThan(fourLineInputSize));
   });
 
   testWidgets('Can drag handles to change selection in multiline', (WidgetTester tester) async {
@@ -594,7 +610,7 @@ void main() {
     await tester.pumpWidget(builder());
     await tester.pump(const Duration(seconds: 1));
 
-    await tester.enterText(find.byType(TextField), kFourLines);
+    await tester.enterText(find.byType(TextField), kMoreThanFourLines);
 
     await tester.pumpWidget(builder());
     await tester.pump(const Duration(seconds: 1));
@@ -603,8 +619,8 @@ void main() {
     final RenderBox inputBox = findInputBox();
 
     // Check that the last line of text is not displayed.
-    final Offset firstPos = textOffsetToPosition(tester, kFourLines.indexOf('First'));
-    final Offset fourthPos = textOffsetToPosition(tester, kFourLines.indexOf('Fourth'));
+    final Offset firstPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('First'));
+    final Offset fourthPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('Fourth'));
     expect(firstPos.dx, fourthPos.dx);
     expect(firstPos.dy, lessThan(fourthPos.dy));
     expect(inputBox.hitTest(new HitTestResult(), position: inputBox.globalToLocal(firstPos)), isTrue);
@@ -622,8 +638,8 @@ void main() {
     await tester.pump();
 
     // Now the first line is scrolled up, and the fourth line is visible.
-    Offset newFirstPos = textOffsetToPosition(tester, kFourLines.indexOf('First'));
-    Offset newFourthPos = textOffsetToPosition(tester, kFourLines.indexOf('Fourth'));
+    Offset newFirstPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('First'));
+    Offset newFourthPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('Fourth'));
 
     expect(newFirstPos.dy, lessThan(firstPos.dy));
     expect(inputBox.hitTest(new HitTestResult(), position: inputBox.globalToLocal(newFirstPos)), isFalse);
@@ -633,7 +649,7 @@ void main() {
 
     // Long press the 'i' in 'Fourth line' to select the word.
     await tester.pump(const Duration(seconds: 1));
-    final Offset untilPos = textOffsetToPosition(tester, kFourLines.indexOf('Fourth line')+8);
+    final Offset untilPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('Fourth line')+8);
     gesture = await tester.startGesture(untilPos, pointer: 7);
     await tester.pump(const Duration(seconds: 1));
     await gesture.up();
@@ -645,7 +661,7 @@ void main() {
 
     // Drag the left handle to the first line, just after 'First'.
     final Offset handlePos = endpoints[0].point + const Offset(-1.0, 1.0);
-    final Offset newHandlePos = textOffsetToPosition(tester, kFourLines.indexOf('First') + 5);
+    final Offset newHandlePos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('First') + 5);
     gesture = await tester.startGesture(handlePos, pointer: 7);
     await tester.pump(const Duration(seconds: 1));
     await gesture.moveTo(newHandlePos + const Offset(0.0, -10.0));
@@ -655,8 +671,8 @@ void main() {
 
     // The text should have scrolled up with the handle to keep the active
     // cursor visible, back to its original position.
-    newFirstPos = textOffsetToPosition(tester, kFourLines.indexOf('First'));
-    newFourthPos = textOffsetToPosition(tester, kFourLines.indexOf('Fourth'));
+    newFirstPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('First'));
+    newFourthPos = textOffsetToPosition(tester, kMoreThanFourLines.indexOf('Fourth'));
     expect(newFirstPos.dy, firstPos.dy);
     expect(inputBox.hitTest(new HitTestResult(), position: inputBox.globalToLocal(newFirstPos)), isTrue);
     expect(inputBox.hitTest(new HitTestResult(), position: inputBox.globalToLocal(newFourthPos)), isFalse);

packages/flutter/test/rendering/paragraph_test.dart

@@ -79,12 +79,13 @@ void main() {
       const TextSpan(
         text: 'This\n' // 4 characters * 10px font size = 40px width on the first line
               'is a wrapping test. It should wrap at manual newlines, and if softWrap is true, also at spaces.',
-        style: const TextStyle(fontFamily: 'Ahem', fontSize: 10.0)),
+        style: const TextStyle(fontFamily: 'Ahem', fontSize: 10.0),
+      ),
       maxLines: 1,
       softWrap: true,
     );
 
-    void relayoutWith({int maxLines, bool softWrap, TextOverflow overflow}) {
+    void relayoutWith({ int maxLines, bool softWrap, TextOverflow overflow }) {
       paragraph
         ..maxLines = maxLines
         ..softWrap = softWrap
@@ -147,5 +148,34 @@ void main() {
     relayoutWith(maxLines: 100, softWrap: true, overflow: TextOverflow.fade);
     expect(paragraph.debugHasOverflowShader, isFalse);
   });
+
+
+  test('maxLines', () {
+    final RenderParagraph paragraph = new RenderParagraph(
+      const TextSpan(
+        text: 'How do you write like you\'re running out of time? Write day and night like you\'re running out of time?',
+            // 0123456789 0123456789 012 345 0123456 012345 01234 012345678 012345678 0123 012 345 0123456 012345 01234
+            // 0          1          2       3       4      5     6         7         8    9       10      11     12
+        style: const TextStyle(fontFamily: 'Ahem', fontSize: 10.0),
+      ),
+    );
+    layout(paragraph, constraints: const BoxConstraints(maxWidth: 100.0));
+    void layoutAt(int maxLines) {
+      paragraph.maxLines = maxLines;
+      pumpFrame();
+    }
+
+    layoutAt(null);
+    expect(paragraph.size.height, 130.0);
+
+    layoutAt(1);
+    expect(paragraph.size.height, 10.0);
+
+    layoutAt(2);
+    expect(paragraph.size.height, 20.0);
+
+    layoutAt(3);
+    expect(paragraph.size.height, 30.0);
+  });
 }