Add Border and BorderSide objects

@@ -59,13 +59,9 @@ Future<Uint8List> generateReport(PdfPageFormat pageFormat) async {
           ),
           overlay: pw.ChartLegend(
             position: const pw.Alignment(-.7, 1),
-            decoration: const pw.BoxDecoration(
+            decoration: pw.BoxDecoration(
               color: PdfColors.white,
-              border: pw.BoxBorder(
-                bottom: true,
-                top: true,
-                left: true,
-                right: true,
+              border: pw.Border.all(
                 color: PdfColors.black,
                 width: .5,
               ),

@@ -19,6 +19,7 @@
 - Remove dependency to the deprecated utf library
 - Fix RichText.maxLines with multiple TextSpan
 - Fix Exif parsing
+- Add Border and BorderSide objects
 
 ## 1.12.0
 

@@ -162,11 +162,7 @@ abstract class Dataset extends Widget {
     return Container(
       decoration: BoxDecoration(
         color: color,
-        border: const BoxBorder(
-          left: true,
-          top: true,
-          bottom: true,
-          right: true,
+        border: Border.all(
           color: PdfColors.black,
           width: .5,
         ),

@@ -152,6 +152,74 @@ class BoxBorder {
   }
 }
 
+/// A side of a border of a box.
+class BorderSide {
+  /// Creates the side of a border.
+  const BorderSide({
+    this.color = PdfColors.black,
+    this.width = 1.0,
+    this.style = BorderStyle.solid,
+  });
+
+  /// The color of this side of the border.
+  final PdfColor color;
+
+  /// The width of this side of the border.
+  final double width;
+
+  /// The style of this side of the border.
+  final BorderStyle style;
+
+  BorderSide copyWith({
+    PdfColor color,
+    double width,
+    BorderStyle style,
+  }) =>
+      BorderSide(
+        color: color,
+        width: width,
+        style: style,
+      );
+}
+
+/// A border of a box, comprised of four sides: top, right, bottom, left.
+class Border extends BoxBorder {
+  const Border._(bool left, bool top, bool right, bool bottom, PdfColor color,
+      double width, BorderStyle style)
+      : super(
+          left: left,
+          top: top,
+          right: right,
+          bottom: bottom,
+          color: color,
+          width: width,
+          style: style,
+        );
+
+  /// A uniform border with all sides the same color and width.
+  factory Border.all({
+    PdfColor color = PdfColors.black,
+    double width = 1.0,
+    BorderStyle style = BorderStyle.solid,
+  }) =>
+      Border._(
+        true,
+        true,
+        true,
+        true,
+        color,
+        width,
+        style,
+      );
+
+  /// Creates a border whose sides are all the same.
+  factory Border.fromBorderSide(BorderSide side) => Border.all(
+        color: side.color,
+        width: side.width,
+        style: side.style,
+      );
+}
+
 @immutable
 class DecorationImage {
   @Deprecated('Use DecorationImage.provider()')

@@ -42,12 +42,8 @@ class Checkbox extends SingleChildWidget {
                 height: height,
                 margin: const EdgeInsets.all(1),
                 decoration: decoration ??
-                    const BoxDecoration(
-                        border: BoxBorder(
-                      left: true,
-                      top: true,
-                      bottom: true,
-                      right: true,
+                    BoxDecoration(
+                        border: Border.all(
                       color: PdfColors.grey600,
                       width: 2,
                     ))));

@@ -36,15 +36,11 @@ void main() {
         alignment: Alignment.center,
         margin: const EdgeInsets.all(30),
         padding: const EdgeInsets.all(20),
-        decoration: const BoxDecoration(
+        decoration: BoxDecoration(
             color: PdfColors.blue,
-            borderRadiusEx: BorderRadius.all(Radius.circular(20)),
-            border: BoxBorder(
+            borderRadiusEx: const BorderRadius.all(Radius.circular(20)),
+            border: Border.all(
               color: PdfColors.blue800,
-              top: true,
-              left: true,
-              right: true,
-              bottom: true,
               width: 2,
             )),
         width: 200,
@@ -103,30 +99,18 @@ void main() {
             Container(
               height: 200.0,
               width: 200.0,
-              decoration: const BoxDecoration(
+              decoration: BoxDecoration(
                 shape: BoxShape.circle,
-                border: BoxBorder(
-                    bottom: true,
-                    top: true,
-                    left: true,
-                    right: true,
-                    color: PdfColors.blue,
-                    width: 3),
+                border: Border.all(color: PdfColors.blue, width: 3),
               ),
             ),
             Container(
               height: 200.0,
               width: 200.0,
-              decoration: const BoxDecoration(
+              decoration: BoxDecoration(
                 shape: BoxShape.rectangle,
-                borderRadiusEx: BorderRadius.all(Radius.circular(40)),
-                border: BoxBorder(
-                    bottom: true,
-                    top: true,
-                    left: true,
-                    right: true,
-                    color: PdfColors.blue,
-                    width: 3),
+                borderRadiusEx: const BorderRadius.all(Radius.circular(40)),
+                border: Border.all(color: PdfColors.blue, width: 3),
               ),
             ),
           ],
@@ -141,9 +125,9 @@ void main() {
         alignment: Alignment.center,
         margin: const EdgeInsets.all(30),
         padding: const EdgeInsets.all(20),
-        decoration: const BoxDecoration(
-            borderRadiusEx: BorderRadius.all(Radius.circular(20)),
-            gradient: LinearGradient(
+        decoration: BoxDecoration(
+            borderRadiusEx: const BorderRadius.all(Radius.circular(20)),
+            gradient: const LinearGradient(
               colors: <PdfColor>[
                 PdfColors.blue,
                 PdfColors.red,
@@ -154,12 +138,8 @@ void main() {
               stops: <double>[0, .8, 1.0],
               tileMode: TileMode.clamp,
             ),
-            border: BoxBorder(
+            border: Border.all(
               color: PdfColors.blue800,
-              top: true,
-              left: true,
-              right: true,
-              bottom: true,
               width: 2,
             )),
         width: 200,
@@ -174,9 +154,9 @@ void main() {
         alignment: Alignment.center,
         margin: const EdgeInsets.all(30),
         padding: const EdgeInsets.all(20),
-        decoration: const BoxDecoration(
-            borderRadiusEx: BorderRadius.all(Radius.circular(20)),
-            gradient: RadialGradient(
+        decoration: BoxDecoration(
+            borderRadiusEx: const BorderRadius.all(Radius.circular(20)),
+            gradient: const RadialGradient(
               colors: <PdfColor>[
                 PdfColors.blue,
                 PdfColors.red,
@@ -187,12 +167,8 @@ void main() {
               focal: FractionalOffset(.7, .45),
               focalRadius: 1,
             ),
-            border: BoxBorder(
+            border: Border.all(
               color: PdfColors.blue800,
-              top: true,
-              left: true,
-              right: true,
-              bottom: true,
               width: 2,
             )),
         width: 200,

@@ -54,11 +54,7 @@ class Decorated extends StatelessWidget {
       padding: const EdgeInsets.all(2),
       decoration: BoxDecoration(
         color: color ?? PdfColors.yellow100,
-        border: const BoxBorder(
-          left: true,
-          top: true,
-          right: true,
-          bottom: true,
+        border: Border.all(
           color: PdfColors.grey,
           width: .5,
         ),

@@ -54,14 +54,10 @@ void main() {
               Container(
                 padding: const EdgeInsets.all(5),
                 margin: const EdgeInsets.only(bottom: 10),
-                decoration: const BoxDecoration(
-                    color: PdfColors.amber,
-                    border: BoxBorder(
-                        top: true,
-                        bottom: true,
-                        left: true,
-                        right: true,
-                        width: 2)),
+                decoration: BoxDecoration(
+                  color: PdfColors.amber,
+                  border: Border.all(width: 2),
+                ),
                 child: Text(
                   'Hello World',
                   textScaleFactor: 2,