Trying to Draw a Button: How to Set a Stroke Color and How to "Align" a Gradient to the Bottom Without Knowing the Height

Trying to draw a button: how to set a stroke color and how to align a gradient to the bottom without knowing the height?

In terms of your first question, I struggled with this as well, and it doesn't look like there are any suitable methods within Drawables themselves (I was using ShapeDrawable) or the Paint class. However, I was able to extend ShapeDrawable and override the draw method, as below, to give the same result:

public class CustomBorderDrawable extends ShapeDrawable {
    private Paint fillpaint, strokepaint;
    private static final int WIDTH = 3; 

    public CustomBorderDrawable(Shape s) {
        super(s);
        fillpaint = this.getPaint();
        strokepaint = new Paint(fillpaint);
        strokepaint.setStyle(Paint.Style.STROKE);
        strokepaint.setStrokeWidth(WIDTH);
        strokepaint.setARGB(255, 0, 0, 0);
    }

    @Override
    protected void onDraw(Shape shape, Canvas canvas, Paint fillpaint) {
        shape.draw(canvas, fillpaint);
        shape.draw(canvas, strokepaint);
    }

    public void setFillColour(int c){
        fillpaint.setColor(c);
    }
}

Programmatically create a button with a gradient stroke?

I have tried something for you..
Use mRect.set to set path and mPath.addRoundRectadd rectangle.Use setShader for strock purpose link

Drawable class:

public class CustomDrawable extends Drawable {
Paint mPaint;
int startColor, endColor, mBorderWidth, mBorderRadius;
RectF mRect;
Path mPath;

public CustomDrawable(int startColor, int endColor, int borderWidth, int borderRadius) {
    mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mPaint.setStyle(Paint.Style.FILL);

    mPath = new Path();
    mPath.setFillType(Path.FillType.EVEN_ODD);

    mRect = new RectF();
    this.startColor = startColor;
    this.endColor = endColor;

    mBorderWidth = borderWidth;
    mBorderRadius = borderRadius;
}

@Override
protected void onBoundsChange(Rect bounds) {
    super.onBoundsChange(bounds);
    mPath.reset();

    // out rect
    mRect.set(bounds.left + mBorderWidth, bounds.top + mBorderWidth, bounds.right - mBorderWidth, bounds.bottom - mBorderWidth);
    mPath.addRoundRect(mRect, mBorderRadius, mBorderRadius, Path.Direction.CW);

    // inner rect
    mRect.set(bounds.left + 20, bounds.top + 20, bounds.right - 20, bounds.bottom - 20);
    mPath.addRoundRect(mRect, mBorderRadius, mBorderRadius, Path.Direction.CW);
}

@Override
public void draw(@NonNull Canvas canvas) {
    // kind of strock 
    mPaint.setShader(new LinearGradient(0, 0, 0, 100, startColor, endColor, Shader.TileMode.MIRROR));
    canvas.drawPath(mPath, mPaint);
}
@Override
public void setAlpha(int alpha) { mPaint.setAlpha(alpha);}
@Override
public void setColorFilter(@Nullable ColorFilter colorFilter) {mPaint.setColorFilter(colorFilter);}
@Override
public int getOpacity() {return PixelFormat.TRANSLUCENT;}
}

Main :

Button but = ((Button)findViewById(R.id.but));
but.setBackground(new CustomDrawable(Color.parseColor("#FD659B"),
       Color.parseColor("#F76E63"),
       but.getPaddingLeft(), 100));

layout :

<Button
    android:id="@+id/but"
    android:layout_width="300dp"
    android:layout_height="80dp"
    android:background="@android:color/transparent"
    android:layout_centerInParent="true"
    android:text="Signin"/>

Outlined transparent button with gradient border in flutter

I spent about two hours on it :)

how to use:

import 'package:flutter/material.dart';

void main() => runApp(App());

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: SafeArea(
          child: Center(
            child: Column(
              mainAxisSize: MainAxisSize.min,
              children: <Widget>[
                UnicornOutlineButton(
                  strokeWidth: 2,
                  radius: 24,
                  gradient: LinearGradient(colors: [Colors.black, Colors.redAccent]),
                  child: Text('OMG', style: TextStyle(fontSize: 16)),
                  onPressed: () {},
                ),
                SizedBox(width: 0, height: 24),
                UnicornOutlineButton(
                  strokeWidth: 4,
                  radius: 16,
                  gradient: LinearGradient(
                    colors: [Colors.blue, Colors.yellow],
                    begin: Alignment.topCenter,
                    end: Alignment.bottomCenter,
                  ),
                  child: Text('Wow', style: TextStyle(fontSize: 16)),
                  onPressed: () {},
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

and the class itself:

class UnicornOutlineButton extends StatelessWidget {
  final _GradientPainter _painter;
  final Widget _child;
  final VoidCallback _callback;
  final double _radius;

  UnicornOutlineButton({
    @required double strokeWidth,
    @required double radius,
    @required Gradient gradient,
    @required Widget child,
    @required VoidCallback onPressed,
  })  : this._painter = _GradientPainter(strokeWidth: strokeWidth, radius: radius, gradient: gradient),
        this._child = child,
        this._callback = onPressed,
        this._radius = radius;

  @override
  Widget build(BuildContext context) {
    return CustomPaint(
      painter: _painter,
      child: GestureDetector(
        behavior: HitTestBehavior.translucent,
        onTap: _callback,
        child: InkWell(
          borderRadius: BorderRadius.circular(_radius),
          onTap: _callback,
          child: Container(
            constraints: BoxConstraints(minWidth: 88, minHeight: 48),
            child: Row(
              mainAxisSize: MainAxisSize.min,
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                _child,
              ],
            ),
          ),
        ),
      ),
    );
  }
}

class _GradientPainter extends CustomPainter {
  final Paint _paint = Paint();
  final double radius;
  final double strokeWidth;
  final Gradient gradient;

  _GradientPainter({@required double strokeWidth, @required double radius, @required Gradient gradient})
      : this.strokeWidth = strokeWidth,
        this.radius = radius,
        this.gradient = gradient;

  @override
  void paint(Canvas canvas, Size size) {
    // create outer rectangle equals size
    Rect outerRect = Offset.zero & size;
    var outerRRect = RRect.fromRectAndRadius(outerRect, Radius.circular(radius));

    // create inner rectangle smaller by strokeWidth
    Rect innerRect = Rect.fromLTWH(strokeWidth, strokeWidth, size.width - strokeWidth * 2, size.height - strokeWidth * 2);
    var innerRRect = RRect.fromRectAndRadius(innerRect, Radius.circular(radius - strokeWidth));

    // apply gradient shader
    _paint.shader = gradient.createShader(outerRect);

    // create difference between outer and inner paths and draw it
    Path path1 = Path()..addRRect(outerRRect);
    Path path2 = Path()..addRRect(innerRRect);
    var path = Path.combine(PathOperation.difference, path1, path2);
    canvas.drawPath(path, _paint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => oldDelegate != this;
}

How to add a stroke to ShapeDrawable

It looks like this person struggled with the same issue and the only way they found was to subclass the ShapeDrawable:

Trying to draw a button: how to set a stroke color and how to "align" a gradient to the bottom without knowing the height?

How to make Elevated Button with Gradient background?

Screenshot (Null safe)

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Create this class (customizable)

class MyElevatedButton extends StatelessWidget {
  final BorderRadiusGeometry? borderRadius;
  final double? width;
  final double height;
  final Gradient gradient;
  final VoidCallback? onPressed;
  final Widget child;

  const MyElevatedButton({
    Key? key,
    required this.onPressed,
    required this.child,
    this.borderRadius,
    this.width,
    this.height = 44.0,
    this.gradient = const LinearGradient(colors: [Colors.cyan, Colors.indigo]),
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final borderRadius = this.borderRadius ?? BorderRadius.circular(0);
    return Container(
      width: width,
      height: height,
      decoration: BoxDecoration(
        gradient: gradient,
        borderRadius: borderRadius,
      ),
      child: ElevatedButton(
        onPressed: onPressed,
        style: ElevatedButton.styleFrom(
          backgroundColor: Colors.transparent,
          shadowColor: Colors.transparent,
          shape: RoundedRectangleBorder(borderRadius: borderRadius),
        ),
        child: child,
      ),
    );
  }
}

Usage:

Use it like a regular ElevatedButton:

MyElevatedButton(
  width: double.infinity,
  onPressed: () {},
  borderRadius: BorderRadius.circular(20),
  child: Text('SIGN IN'),
)

Android shape border with gradient

try something like this:

<?xml version="1.0" encoding="UTF-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >

    <item>
        <shape android:shape="rectangle" >
            <gradient
                android:angle="360"
                android:centerColor="#e95a22"
                android:endColor="#ff00b5"
                android:gradientRadius="360"
                android:startColor="#006386"
                android:type="sweep" />

            <stroke
                android:width="2dp"
                android:color="#ff207d94" />
        </shape>
    </item>
    <item
        android:bottom="2dp"
        android:left="2dp"
        android:right="2dp"
        android:top="2dp">
        <shape android:shape="rectangle" >
            <solid android:color="#fff" />
        </shape>
    </item>

</layer-list>

Gradient stroke shape

Shape (rectangle) supports a gradient fill. You can also round the corners to get a nice toolbar button effect.

I don't think that stroke supports a gradient, but if you want a gradient stroke around your button you can create two layered rectangles - the first one using your gradient and the second using a solid or a different gradient sized to be 2 pixels smaller in height and width.

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