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// Copyright 2015 The Chromium 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 ParagraphBuilder;
import 'package:flutter/gestures.dart';
import 'package:flutter/foundation.dart';
import 'basic_types.dart';
import 'text_editing.dart';
import 'text_style.dart';
// TODO(abarth): Should this be somewhere more general?
bool _deepEquals(List<Object> a, List<Object> b) {
if (a == null)
return b == null;
if (b == null || a.length != b.length)
return false;
for (int i = 0; i < a.length; ++i) {
if (a[i] != b[i])
return false;
}
return true;
}
/// An immutable span of text.
///
/// A [TextSpan] object can be styled using its [style] property.
/// The style will be applied to the [text] and the [children].
///
/// A [TextSpan] object can just have plain text, or it can have
/// children [TextSpan] objects with their own styles that (possibly
/// only partially) override the [style] of this object. If a
/// [TextSpan] has both [text] and [children], then the [text] is
/// treated as if it was an unstyled [TextSpan] at the start of the
/// [children] list.
///
/// To paint a [TextSpan] on a [Canvas], use a [TextPainter]. To display a text
/// span in a widget, use a [RichText]. For text with a single style, consider
/// using the [Text] widget.
///
/// See also:
///
/// * [Text]
/// * [RichText]
/// * [TextPainter]
class TextSpan {
/// Creates a [TextSpan] with the given values.
///
/// For the object to be useful, at least one of [text] or
/// [children] should be set.
const TextSpan({
this.style,
this.text,
this.children,
this.recognizer
});
/// The style to apply to the [text] and the [children].
final TextStyle style;
/// The text contained in the span.
///
/// If both [text] and [children] are non-null, the text will preceed the
/// children.
final String text;
/// Additional spans to include as children.
///
/// If both [text] and [children] are non-null, the text will preceed the
/// children.
///
/// Modifying the list after the [TextSpan] has been created is not
/// supported and may have unexpected results.
///
/// The list must not contain any nulls.
final List<TextSpan> children;
/// A gesture recognizer that will receive events that hit this text span.
///
/// [TextSpan] itself does not implement hit testing or event
/// dispatch. The owner of the [TextSpan] tree to which the object
/// belongs is responsible for dispatching events.
///
/// For an example, see [RenderParagraph] in the Flutter rendering library.
final GestureRecognizer recognizer;
/// Apply the [style], [text], and [children] of this object to the
/// given [ParagraphBuilder], from which a [Paragraph] can be obtained.
/// [Paragraph] objects can be drawn on [Canvas] objects.
///
/// Rather than using this directly, it's simpler to use the
/// [TextPainter] class to paint [TextSpan] objects onto [Canvas]
/// objects.
void build(ui.ParagraphBuilder builder) {
assert(debugAssertValid());
final bool hasStyle = style != null;
if (hasStyle)
builder.pushStyle(style.textStyle);
if (text != null)
builder.addText(text);
if (children != null) {
for (TextSpan child in children) {
assert(child != null);
child.build(builder);
}
}
if (hasStyle)
builder.pop();
}
/// Walks this text span and its decendants in pre-order and calls [visitor] for each span that has text.
bool visitTextSpan(bool visitor(TextSpan span)) {
if (text != null) {
if (!visitor(this))
return false;
}
if (children != null) {
for (TextSpan child in children) {
if (!child.visitTextSpan(visitor))
return false;
}
}
return true;
}
/// Returns the text span that contains the given position in the text.
TextSpan getSpanForPosition(TextPosition position) {
assert(debugAssertValid());
TextAffinity affinity = position.affinity;
int targetOffset = position.offset;
int offset = 0;
TextSpan result;
visitTextSpan((TextSpan span) {
assert(result == null);
int endOffset = offset + span.text.length;
if (targetOffset == offset && affinity == TextAffinity.downstream ||
targetOffset > offset && targetOffset < endOffset ||
targetOffset == endOffset && affinity == TextAffinity.upstream) {
result = span;
return false;
}
offset = endOffset;
return true;
});
return result;
}
/// Flattens the [TextSpan] tree into a single string.
///
/// Styles are not honored in this process.
String toPlainText() {
assert(debugAssertValid());
StringBuffer buffer = new StringBuffer();
visitTextSpan((TextSpan span) {
buffer.write(span.text);
return true;
});
return buffer.toString();
}
@override
String toString([String prefix = '']) {
StringBuffer buffer = new StringBuffer();
buffer.writeln('$prefix$runtimeType:');
String indent = '$prefix ';
if (style != null)
buffer.writeln(style.toString(indent));
if (text != null)
buffer.writeln('$indent"$text"');
if (children != null) {
for (TextSpan child in children) {
if (child != null) {
buffer.write(child.toString(indent));
} else {
buffer.writeln('$indent<null>');
}
}
}
if (style == null && text == null && children == null)
buffer.writeln('$indent(empty)');
return buffer.toString();
}
/// In checked mode, throws an exception if the object is not in a
/// valid configuration. Otherwise, returns true.
///
/// This is intended to be used as follows:
/// ```dart
/// assert(myTextSpan.debugAssertValid());
/// ```
bool debugAssertValid() {
assert(() {
if (!visitTextSpan((TextSpan span) {
if (span.children != null) {
for (TextSpan child in span.children) {
if (child == null)
return false;
}
}
return true;
})) {
throw new FlutterError(
'TextSpan contains a null child.\n'
'A TextSpan object with a non-null child list should not have any nulls in its child list.\n'
'The full text in question was:\n'
'${toString(" ")}'
);
}
return true;
});
return true;
}
@override
bool operator ==(dynamic other) {
if (identical(this, other))
return true;
if (other is! TextSpan)
return false;
final TextSpan typedOther = other;
return typedOther.text == text
&& typedOther.style == style
&& typedOther.recognizer == recognizer
&& _deepEquals(typedOther.children, children);
}
@override
int get hashCode => hashValues(style, text, recognizer, hashList(children));
}