Use TextPainter.preferredLineHeight to estimate line height for Cupertino selection handles (#12833)

Fixes https://github.com/flutter/flutter/issues/12046

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

@@ -399,7 +399,7 @@ class RenderEditable extends RenderBox {
     if (selection.isCollapsed) {
       // TODO(mpcomplete): This doesn't work well at an RTL/LTR boundary.
       final Offset caretOffset = _textPainter.getOffsetForCaret(selection.extent, _caretPrototype);
-      final Offset start = new Offset(0.0, _preferredLineHeight) + caretOffset + paintOffset;
+      final Offset start = new Offset(0.0, preferredLineHeight) + caretOffset + paintOffset;
       return <TextSelectionPoint>[new TextSelectionPoint(start, null)];
     } else {
       final List<ui.TextBox> boxes = _textPainter.getBoxesForSelection(selection);
@@ -441,7 +441,7 @@ class RenderEditable extends RenderBox {
     _layoutText(constraints.maxWidth);
     final Offset caretOffset = _textPainter.getOffsetForCaret(caretPosition, _caretPrototype);
     // This rect is the same as _caretPrototype but without the vertical padding.
-    return new Rect.fromLTWH(0.0, 0.0, _kCaretWidth, _preferredLineHeight).shift(caretOffset + _paintOffset);
+    return new Rect.fromLTWH(0.0, 0.0, _kCaretWidth, preferredLineHeight).shift(caretOffset + _paintOffset);
   }
 
   @override
@@ -456,12 +456,13 @@ class RenderEditable extends RenderBox {
     return _textPainter.maxIntrinsicWidth;
   }
 
-  // This does not required the layout to be updated.
+  /// An estimate of the height of a line in the text. See [TextPainter.preferredLineHeight].
-  double get _preferredLineHeight => _textPainter.preferredLineHeight;
+  /// This does not required the layout to be updated.
+  double get preferredLineHeight => _textPainter.preferredLineHeight;
 
   double _preferredHeight(double width) {
     if (maxLines != null)
-      return _preferredLineHeight * maxLines;
+      return preferredLineHeight * maxLines;
     if (width == double.INFINITY) {
       final String text = _textPainter.text.toPlainText();
       int lines = 1;
@@ -469,10 +470,10 @@ class RenderEditable extends RenderBox {
         if (text.codeUnitAt(index) == 0x0A) // count explicit line breaks
           lines += 1;
       }
-      return _preferredLineHeight * lines;
+      return preferredLineHeight * lines;
     }
     _layoutText(width);
-    return math.max(_preferredLineHeight, _textPainter.height);
+    return math.max(preferredLineHeight, _textPainter.height);
   }
 
   @override
@@ -558,7 +559,7 @@ class RenderEditable extends RenderBox {
   @override
   void performLayout() {
     _layoutText(constraints.maxWidth);
-    _caretPrototype = new Rect.fromLTWH(0.0, _kCaretHeightOffset, _kCaretWidth, _preferredLineHeight - 2.0 * _kCaretHeightOffset);
+    _caretPrototype = new Rect.fromLTWH(0.0, _kCaretHeightOffset, _kCaretWidth, preferredLineHeight - 2.0 * _kCaretHeightOffset);
     _selectionRects = null;
     // We grab _textPainter.size here because assigning to `size` on the next
     // line will trigger us to validate our intrinsic sizes, which will change

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

@@ -344,7 +344,7 @@ class TextSelectionOverlay implements TextSelectionDelegate {
       (endpoints.length == 1) ?
         endpoints[0].point.dx :
         (endpoints[0].point.dx + endpoints[1].point.dx) / 2.0,
-      endpoints[0].point.dy - renderObject.size.height,
+      endpoints[0].point.dy - renderObject.preferredLineHeight,
     );
 
     final Rect editingRegion = new Rect.fromPoints(
@@ -509,7 +509,7 @@ class _TextSelectionHandleOverlayState extends State<_TextSelectionHandleOverlay
               child: widget.selectionControls.buildHandle(
                 context,
                 type,
-                widget.renderObject.size.height / widget.renderObject.maxLines,
+                widget.renderObject.preferredLineHeight,
               ),
             ),
           ],

packages/flutter/test/material/text_field_test.dart

@@ -1664,4 +1664,30 @@ void main() {
 
     expect(semantics, includesNodeWith(flags: <SemanticsFlags>[SemanticsFlags.isTextField]));
   });
+
+  testWidgets('Caret works when maxLines is null', (WidgetTester tester) async {
+    final TextEditingController controller = new TextEditingController();
+
+    await tester.pumpWidget(
+      overlay(
+        child: new TextField(
+          controller: controller,
+          maxLines: null,
+        ),
+      )
+    );
+
+    final String testValue = 'x';
+    await tester.enterText(find.byType(TextField), testValue);
+    await skipPastScrollingAnimation(tester);
+    expect(controller.selection.baseOffset, -1);
+
+    // Tap the selection handle to bring up the "paste / select all" menu.
+    await tester.tapAt(textOffsetToPosition(tester, 0));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 200)); // skip past the frame where the opacity is
+
+    // Confirm that the selection was updated.
+    expect(controller.selection.baseOffset, 0);
+  });
 }