Simple gradient for boxDecoration border

README.md

@@ -14,5 +14,21 @@ InputDecoration(
 
 ![demo](demo.gif)
 
+
+# Gradient Box decoration border
+
+Use it with BoxDecoration
+
+```dart
+BoxDecoration(
+       border: GradientBorder.uniform(
+           width: 3.0,
+           gradient: LinearGradient(
+               colors: <Color>[Colors.deepOrange, Colors.grey],
+               stops: [0.3, 0.5])),
+       borderRadius: BorderRadius.circular(Dimens.buttonRadius))
+```
+
+
 <hr/>
 Created by iteo

lib/gradient_box_border.dart

@@ -0,0 +1,88 @@
+import 'package:flutter/painting.dart';
+import 'package:meta/meta.dart';
+
+class GradientBorder extends Border {
+  final Gradient borderGradient;
+  final double width;
+
+  const GradientBorder({this.width = 0.0, @required this.borderGradient})
+      : assert(borderGradient != null),
+        super();
+
+  @override
+  void paint(Canvas canvas, Rect rect,
+      {TextDirection textDirection,
+        BoxShape shape = BoxShape.rectangle,
+        BorderRadius borderRadius}) {
+    if (isUniform) {
+      switch (shape) {
+        case BoxShape.circle:
+          assert(borderRadius == null,
+          'A borderRadius can only be given for rectangular boxes.');
+          this._paintGradientBorderWithCircle(canvas, rect);
+          break;
+        case BoxShape.rectangle:
+          if (borderRadius != null) {
+            this._paintGradientBorderWithRadius(canvas, rect, borderRadius);
+            return;
+          }
+          this._paintGradientBorderWithRectangle(canvas, rect);
+          break;
+      }
+      return;
+    }
+  }
+
+  void _paintGradientBorderWithRadius(
+      Canvas canvas, Rect rect, BorderRadius borderRadius) {
+    final Paint paint = Paint();
+    final RRect outer = borderRadius.toRRect(rect);
+
+    paint.shader = borderGradient.createShader(outer.outerRect);
+
+    if (width == 0.0) {
+      paint
+        ..style = PaintingStyle.stroke
+        ..strokeWidth = 0.0;
+      canvas.drawRRect(outer, paint);
+    } else {
+      final RRect inner = outer.deflate(width);
+      canvas.drawDRRect(outer, inner, paint);
+    }
+  }
+
+  void _paintGradientBorderWithCircle(Canvas canvas, Rect rect) {
+    final double radius = (rect.shortestSide - width) / 2.0;
+    final Paint paint = Paint();
+    paint
+      ..strokeWidth = width
+      ..style = PaintingStyle.stroke
+      ..shader = borderGradient
+          .createShader(Rect.fromCircle(center: rect.center, radius: radius));
+
+    canvas.drawCircle(rect.center, radius, paint);
+  }
+
+  void _paintGradientBorderWithRectangle(Canvas canvas, Rect rect) {
+    final Paint paint = Paint();
+    paint
+      ..strokeWidth = width
+      ..shader = borderGradient.createShader(rect)
+      ..style = PaintingStyle.stroke;
+
+    canvas.drawRect(rect.deflate(width / 2.0), paint);
+  }
+
+  factory GradientBorder.uniform({
+    Gradient gradient = const LinearGradient(colors: [Color(0x00000000)]),
+    double width = 1.0,
+  }) {
+    return GradientBorder._fromUniform(gradient, width);
+  }
+
+  const GradientBorder._fromUniform(Gradient gradient, double width)
+      : assert(gradient != null),
+        assert(width >= 0.0),
+        borderGradient = gradient,
+        width = width;
+}