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Utility methods for measuring text #111493

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Sep 13, 2022
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Utility methods for measuring text #111493

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Utility methods for measuring text
dnfield Sep 13, 2022
aee23da
ws
dnfield Sep 13, 2022
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12 changes: 1 addition & 11 deletions packages/flutter/lib/src/cupertino/date_picker.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -470,23 +470,13 @@ class CupertinoDatePicker extends StatefulWidget {

assert(longestText != '', 'column type is not appropriate');

final TextPainter painter = TextPainter(
return TextPainter.computeMaxIntrinsicWidth(
text: TextSpan(
style: _themeTextStyle(context),
text: longestText,
),
textDirection: Directionality.of(context),
);

// This operation is expensive and should be avoided. It is called here only
// because there's no other way to get the information we want without
// laying out the text.
painter.layout();
try {
return painter.maxIntrinsicWidth;
} finally {
painter.dispose();
}
}
}

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80 changes: 80 additions & 0 deletions packages/flutter/lib/src/painting/text_painter.dart
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Expand Up @@ -217,6 +217,86 @@ class TextPainter {
_textWidthBasis = textWidthBasis,
_textHeightBehavior = textHeightBehavior;

/// Computes the width of a configured [TextPainter].
///
/// This is a convenience method that creates a text painter with the supplied
/// parameters, lays it out with the supplied [minWidth] and [maxWidth], and
/// returns its [TextPainter.width] making sure to dispose the underlying
/// resources.
static double computeWidth({
required InlineSpan text,
TextAlign textAlign = TextAlign.start,
TextDirection? textDirection,
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@LongCatIsLooong LongCatIsLooong Sep 13, 2022

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TextDirection must be non null I think?

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@dnfield dnfield Sep 13, 2022

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This was copied from the TextPainter ctor. I'd like to keep the types the same for ease of migration.

If we want to update this we should update the ctor as well.

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@dnfield dnfield Sep 13, 2022

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Ahh but I see what you're saying, on the regular object we can set this to some value later, whereas we can't with this method. Ok. In that case, I'll file a follow upt o make it non-nullable.

double textScaleFactor = 1.0,
int? maxLines,
String? ellipsis,
Locale? locale,
StrutStyle? strutStyle,
TextWidthBasis textWidthBasis = TextWidthBasis.parent,
ui.TextHeightBehavior? textHeightBehavior,
double minWidth = 0.0,
double maxWidth = double.infinity,
}) {
final TextPainter painter = TextPainter(
text: text,
textAlign: textAlign,
textDirection: textDirection,
textScaleFactor: textScaleFactor,
maxLines: maxLines,
ellipsis: ellipsis,
locale: locale,
strutStyle: strutStyle,
textWidthBasis: textWidthBasis,
textHeightBehavior: textHeightBehavior,
)..layout(minWidth: minWidth, maxWidth: maxWidth);

try {
return painter.width;
} finally {
painter.dispose();
}
}

/// Computes the max intrinsic width of a configured [TextPainter].
///
/// This is a convenience method that creates a text painter with the supplied
/// parameters, lays it out with the supplied [minWidth] and [maxWidth], and
/// returns its [TextPainter.maxIntrinsicWidth] making sure to dispose the
/// underlying resources.
static double computeMaxIntrinsicWidth({
required InlineSpan text,
TextAlign textAlign = TextAlign.start,
TextDirection? textDirection,
double textScaleFactor = 1.0,
int? maxLines,
String? ellipsis,
Locale? locale,
StrutStyle? strutStyle,
TextWidthBasis textWidthBasis = TextWidthBasis.parent,
ui.TextHeightBehavior? textHeightBehavior,
double minWidth = 0.0,
double maxWidth = double.infinity,
}) {
final TextPainter painter = TextPainter(
text: text,
textAlign: textAlign,
textDirection: textDirection,
textScaleFactor: textScaleFactor,
maxLines: maxLines,
ellipsis: ellipsis,
locale: locale,
strutStyle: strutStyle,
textWidthBasis: textWidthBasis,
textHeightBehavior: textHeightBehavior,
)..layout(minWidth: minWidth, maxWidth: maxWidth);

try {
return painter.maxIntrinsicWidth;
} finally {
painter.dispose();
}
}

// _paragraph being null means the text needs layout because of style changes.
// Setting _paragraph to null invalidates all the layout cache.
//
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24 changes: 24 additions & 0 deletions packages/flutter/test/painting/text_painter_test.dart
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Expand Up @@ -1184,6 +1184,30 @@ void main() {
painter.dispose();
expect(painter.debugDisposed, true);
});

test('TextPainter computeWidth', () {
const InlineSpan text = TextSpan(text: 'foobar');
final TextPainter painter = TextPainter(text: text, textDirection: TextDirection.ltr);
painter.layout();
expect(painter.width, TextPainter.computeWidth(text: text, textDirection: TextDirection.ltr));

painter.layout(minWidth: 500);
expect(painter.width, TextPainter.computeWidth(text: text, textDirection: TextDirection.ltr, minWidth: 500));

painter.dispose();
});

test('TextPainter computeMaxIntrinsicWidth', () {
const InlineSpan text = TextSpan(text: 'foobar');
final TextPainter painter = TextPainter(text: text, textDirection: TextDirection.ltr);
painter.layout();
expect(painter.maxIntrinsicWidth, TextPainter.computeMaxIntrinsicWidth(text: text, textDirection: TextDirection.ltr));

painter.layout(minWidth: 500);
expect(painter.maxIntrinsicWidth, TextPainter.computeMaxIntrinsicWidth(text: text, textDirection: TextDirection.ltr, minWidth: 500));

painter.dispose();
});
}

class MockCanvas extends Fake implements Canvas {
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