| // 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:ui' as ui show PlaceholderAlignment; |
| |
| import 'package:flutter/foundation.dart'; |
| |
| import 'basic_types.dart'; |
| import 'inline_span.dart'; |
| import 'text_painter.dart'; |
| import 'text_span.dart'; |
| import 'text_style.dart'; |
| |
| /// An immutable placeholder that is embedded inline within text. |
| /// |
| /// [PlaceholderSpan] represents a placeholder that acts as a stand-in for other |
| /// content. A [PlaceholderSpan] by itself does not contain useful |
| /// information to change a [TextSpan]. Instead, this class must be extended |
| /// to define contents. |
| /// |
| /// [WidgetSpan] from the widgets library extends [PlaceholderSpan] and may be |
| /// used instead to specify a widget as the contents of the placeholder. |
| /// |
| /// See also: |
| /// |
| /// * [WidgetSpan], a leaf node that represents an embedded inline widget. |
| /// * [TextSpan], a node that represents text in a [TextSpan] tree. |
| /// * [Text], a widget for showing uniformly-styled text. |
| /// * [RichText], a widget for finer control of text rendering. |
| /// * [TextPainter], a class for painting [TextSpan] objects on a [Canvas]. |
| abstract class PlaceholderSpan extends InlineSpan { |
| /// Creates a [PlaceholderSpan] with the given values. |
| /// |
| /// A [TextStyle] may be provided with the [style] property, but only the |
| /// decoration, foreground, background, and spacing options will be used. |
| const PlaceholderSpan({ |
| this.alignment = ui.PlaceholderAlignment.bottom, |
| this.baseline, |
| super.style, |
| }); |
| |
| /// The unicode character to represent a placeholder. |
| static const int placeholderCodeUnit = 0xFFFC; |
| |
| /// How the placeholder aligns vertically with the text. |
| /// |
| /// See [ui.PlaceholderAlignment] for details on each mode. |
| final ui.PlaceholderAlignment alignment; |
| |
| /// The [TextBaseline] to align against when using [ui.PlaceholderAlignment.baseline], |
| /// [ui.PlaceholderAlignment.aboveBaseline], and [ui.PlaceholderAlignment.belowBaseline]. |
| /// |
| /// This is ignored when using other alignment modes. |
| final TextBaseline? baseline; |
| |
| /// [PlaceholderSpan]s are flattened to a `0xFFFC` object replacement character in the |
| /// plain text representation when `includePlaceholders` is true. |
| @override |
| void computeToPlainText(StringBuffer buffer, {bool includeSemanticsLabels = true, bool includePlaceholders = true}) { |
| if (includePlaceholders) { |
| buffer.writeCharCode(placeholderCodeUnit); |
| } |
| } |
| |
| @override |
| void computeSemanticsInformation(List<InlineSpanSemanticsInformation> collector) { |
| collector.add(InlineSpanSemanticsInformation.placeholder); |
| } |
| |
| /// Populates the `semanticsOffsets` and `semanticsElements` with the appropriate data |
| /// to be able to construct a [SemanticsNode]. |
| /// |
| /// [PlaceholderSpan]s have a text length of 1, which corresponds to the object |
| /// replacement character (0xFFFC) that is inserted to represent it. |
| /// |
| /// Null is added to `semanticsElements` for [PlaceholderSpan]s. |
| void describeSemantics(Accumulator offset, List<int> semanticsOffsets, List<dynamic> semanticsElements) { |
| semanticsOffsets.add(offset.value); |
| semanticsOffsets.add(offset.value + 1); |
| semanticsElements.add(null); // null indicates this is a placeholder. |
| offset.increment(1); |
| } |
| |
| @override |
| void debugFillProperties(DiagnosticPropertiesBuilder properties) { |
| super.debugFillProperties(properties); |
| |
| properties.add(EnumProperty<ui.PlaceholderAlignment>('alignment', alignment, defaultValue: null)); |
| properties.add(EnumProperty<TextBaseline>('baseline', baseline, defaultValue: null)); |
| } |
| } |