Flutter: Dotted Underline & Solid Strikethrough Text
Hey there, Flutter developers! Ever wanted to add some extra flair to your text by combining a dotted underline with a solid strikethrough? It's a cool effect, but Flutter's decorationStyle can make it seem a bit tricky since it applies to both decorations. But don't worry, we've got you covered! This guide will walk you through creating this stylish text effect step-by-step.
Understanding the Challenge
In Flutter, the Text widget offers powerful styling options, including text decorations like underlines and strikethroughs. The TextDecoration enum lets you specify the type of decoration (underline, overline, lineThrough), and the decorationStyle attribute lets you choose the style (solid, dotted, dashed, wavy, double). The challenge arises when you want different styles for different decorations – for example, a dotted underline and a solid strikethrough. Applying decorationStyle directly to the Text widget affects all decorations, leaving you with either both dotted or both solid. So, how do we achieve this mixed style effect?
The key to achieving this effect lies in layering and custom painting. We'll essentially break down the problem into smaller parts: first, we'll render the text with a solid strikethrough. Then, we'll overlay a custom-painted dotted underline. This gives us the fine-grained control we need to style each decoration independently. We will use a Stack widget to layer these effects, placing the text and strikethrough at the bottom and the dotted underline on top. Custom painting allows us to draw the dotted underline exactly where we need it, ensuring it aligns perfectly with the text. This approach leverages Flutter's flexibility and its powerful custom drawing capabilities to create a visually appealing and unique text style.
This article will dive deep into the practical implementation of this technique, providing you with code snippets and explanations to guide you through the process. We'll explore the necessary Flutter widgets, such as Stack, Text, and CustomPaint. We'll also discuss how to use Canvas and Paint to draw the dotted underline, focusing on the calculations required to position it accurately beneath the text. By the end of this guide, you'll not only know how to create this specific effect but also gain a broader understanding of how to combine different Flutter widgets and custom painting to achieve complex visual designs.
Method 1: Using a Stack and CustomPaint
This is the most flexible approach, giving you complete control over the styling of each decoration. We'll use a Stack to layer the text with a solid strikethrough and a custom-painted dotted underline.
Step 1: Create a Custom Painter
First, let's create a custom painter that will draw the dotted underline. This painter will receive the text size and baseline offset, allowing it to position the underline correctly.
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
class DottedUnderlinePainter extends CustomPainter {
final Size textSize;
final double baselineOffset;
final Color color;
DottedUnderlinePainter({
required this.textSize,
required this.baselineOffset,
required this.color,
});
@override
void paint(Canvas canvas, Size size) {
final paint = Paint()
..color = color
..strokeWidth = 1.0
..strokeCap = StrokeCap.round
..style = PaintingStyle.stroke;
final dashWidth = 3.0;
final dashSpace = 2.0;
double startX = 0.0;
while (startX < textSize.width) {
canvas.drawLine(
Offset(startX, baselineOffset + 2), // Adjust vertical position as needed
Offset(startX + dashWidth, baselineOffset + 2), // Adjust vertical position as needed
paint,
);
startX += dashWidth + dashSpace;
}
}
@override
bool shouldRepaint(DottedUnderlinePainter oldDelegate) {
return oldDelegate.textSize != textSize ||
oldDelegate.baselineOffset != baselineOffset ||
oldDelegate.color != color;
}
}
In this code, the DottedUnderlinePainter class extends CustomPainter and is responsible for drawing the dotted underline. The constructor takes the textSize, baselineOffset, and color as parameters. The paint method uses a Paint object to define the style of the line, including its color, width, cap, and style. The dotted line is drawn by repeatedly drawing short line segments (dashWidth) separated by spaces (dashSpace). The shouldRepaint method optimizes performance by preventing unnecessary repaints.
Step 2: Create a Widget to Measure Text
We need to measure the text to get its size and baseline offset. We'll use a CustomSingleChildLayout widget for this.
class MeasureSize extends SingleChildRenderObjectWidget {
const MeasureSize({Key? key, required Widget child, required this.onChange}) : super(key: key, child: child);
final ValueChanged<Size> onChange;
@override
RenderObject createRenderObject(BuildContext context) {
return MeasureSizeRenderObject(onChange);
}
}
class MeasureSizeRenderObject extends RenderProxyBox {
MeasureSizeRenderObject(this.onChange);
final ValueChanged<Size> onChange;
Size? _size;
@override
void performLayout(Size constraints) {
super.performLayout(constraints);
Size newSize = child!.size;
if (_size == newSize) return;
_size = newSize;
onChange(newSize);
}
}
This code defines two widgets: MeasureSize and MeasureSizeRenderObject. The MeasureSize widget is a SingleChildRenderObjectWidget that takes a child and an onChange callback. The createRenderObject method creates a MeasureSizeRenderObject, which is responsible for measuring the size of the child. The MeasureSizeRenderObject extends RenderProxyBox and overrides the performLayout method. In performLayout, it measures the child's size and calls the onChange callback if the size has changed. This allows us to get the size of the text after it has been laid out.
Step 3: Combine Everything in a Stack
Now, let's put it all together using a Stack. We'll wrap the Text widget in a Stack and overlay the CustomPaint with our DottedUnderlinePainter.
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
class DottedUnderlineText extends StatefulWidget {
final String text;
final TextStyle style;
final Color dottedLineColor;
const DottedUnderlineText({
Key? key,
required this.text,
required this.style,
required this.dottedLineColor,
}) : super(key: key);
@override
_DottedUnderlineTextState createState() => _DottedUnderlineTextState();
}
class _DottedUnderlineTextState extends State<DottedUnderlineText> {
Size _textSize = Size.zero;
double _baselineOffset = 0.0;
@override
Widget build(BuildContext context) {
final TextStyle textStyle = widget.style.copyWith(
decoration: TextDecoration.lineThrough,
decorationColor: widget.style.color, // Inherit text color
);
return Stack(
children: [
MeasureSize(
onChange: (size) {
setState(() {
_textSize = size;
final TextPainter textPainter = TextPainter(
text: TextSpan(text: widget.text, style: textStyle),
textDirection: TextDirection.ltr,
);
textPainter.layout();
_baselineOffset = textPainter.computeLineMetrics().first.baseline;
});
},
child: Text(
widget.text,
style: textStyle,
),
),
Positioned(
left: 0,
bottom: 0,
child: CustomPaint(
size: _textSize,
painter: DottedUnderlinePainter(
textSize: _textSize,
baselineOffset: _baselineOffset,
color: widget.dottedLineColor,
),
),
),
],
);
}
}
This code defines a DottedUnderlineText widget, which is a StatefulWidget that combines the Text widget, MeasureSize, and CustomPaint to create the desired effect. The build method first creates a TextStyle with a solid strikethrough. Then, it uses a Stack to layer the Text widget and the CustomPaint. The MeasureSize widget is used to measure the size of the text and calculate the baseline offset. The CustomPaint widget uses the DottedUnderlinePainter to draw the dotted underline. The Positioned widget is used to position the CustomPaint at the bottom of the text.
Step 4: Usage
Finally, you can use the DottedUnderlineText widget in your app like this:
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Dotted Underline Text Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Scaffold(
appBar: AppBar(
title: Text('Dotted Underline Text Demo'),
),
body: Center(
child: DottedUnderlineText(
text: 'Hello, Flutter!',
style: TextStyle(
fontSize: 24,
color: Colors.black,
),
dottedLineColor: Colors.red,
),
),
),
);
}
}
In this example, we create a simple Flutter app that uses the DottedUnderlineText widget to display the text "Hello, Flutter!" with a solid strikethrough and a red dotted underline. The style property is used to set the font size and color of the text, and the dottedLineColor property is used to set the color of the dotted underline.
Method 2: Alternative approach
While the custom paint method is the most flexible, you could explore other options, though they might be less precise:
- Using multiple Text widgets: You could split the text into parts, apply the strikethrough to the main text, and then use a separate
Textwidget with a dotted underline positioned below it. This approach can be cumbersome for dynamic text. - Third-party packages: Some Flutter packages offer advanced text styling capabilities. Explore options like
styled_textor similar packages, but be mindful of adding external dependencies.
The multiple Text widgets approach involves breaking the text into smaller segments and applying different styles to each segment. For example, you could have one Text widget for the part with the strikethrough and another Text widget for the dotted underline. This method can be useful for simple cases where you have a fixed text string, but it becomes more complex when you need to handle dynamic text or adjust the positioning of the underline. The main challenge with this approach is ensuring that the underline aligns correctly with the text, especially if the text size or font changes.
Third-party packages, such as styled_text, provide a more comprehensive solution for text styling. These packages often include features for applying multiple styles to different parts of the text, making it easier to create complex text effects. However, using third-party packages comes with a trade-off. While they can simplify the implementation, they also add external dependencies to your project, which can increase the app size and introduce potential compatibility issues. Therefore, it's essential to evaluate the benefits and drawbacks before incorporating a third-party package into your Flutter app.
Conclusion
And there you have it! Combining a dotted underline and a solid strikethrough in Flutter might seem tricky at first, but by using a Stack and custom painting, you can achieve this stylish effect with full control over the appearance. Remember, Flutter's flexibility allows for creative solutions like this, so don't be afraid to experiment and push the boundaries of what's possible!
This guide has shown you how to create a custom text style by layering text decorations using Flutter's Stack widget and CustomPaint. The custom painter approach offers the most flexibility and control, allowing you to precisely style each decoration element. While alternative methods exist, such as using multiple Text widgets or third-party packages, they often come with limitations or trade-offs. By mastering custom painting techniques, you can create a wide range of unique text effects and enhance the visual appeal of your Flutter applications.
So, go ahead and try implementing this effect in your Flutter projects. You can customize the colors, line thicknesses, and dash patterns to create your own unique styles. The possibilities are endless when you combine Flutter's powerful widgets with custom painting. Keep exploring and experimenting, and you'll discover even more ways to make your text stand out in your Flutter apps.