add tabbar

lib/base/ui/abs_underline_tabindicator.dart

@@ -0,0 +1,71 @@
+import 'package:flutter/material.dart';
+
+
+///tabbar样式下方横条固定宽度
+class AbsUnderlineTabIndicator extends Decoration {
+  const AbsUnderlineTabIndicator({
+    this.wantWidth,
+    this.borderSide = const BorderSide(width: 2.0, color: Colors.white),
+    this.insets = EdgeInsets.zero,
+  })  : assert(borderSide != null),
+        assert(insets != null);
+
+  final BorderSide? borderSide;
+  final double? wantWidth;
+
+  final EdgeInsetsGeometry? insets;
+
+  @override
+  Decoration? lerpFrom(Decoration? a, double t) {
+    if (a is UnderlineTabIndicator) {
+      return UnderlineTabIndicator(
+        borderSide: BorderSide.lerp(a.borderSide, borderSide!, t),
+        insets: EdgeInsetsGeometry.lerp(a.insets, insets, t)!,
+      );
+    }
+    return super.lerpFrom(a, t);
+  }
+
+  @override
+  Decoration? lerpTo(Decoration? b, double t) {
+    if (b is UnderlineTabIndicator) {
+      return UnderlineTabIndicator(
+        borderSide: BorderSide.lerp(borderSide!, b.borderSide, t),
+        insets: EdgeInsetsGeometry.lerp(insets, b.insets, t)!,
+      );
+    }
+    return super.lerpTo(b, t);
+  }
+
+  @override
+  _UnderlinePainter createBoxPainter([VoidCallback? onChanged]) {
+    return _UnderlinePainter(this, onChanged);
+  }
+}
+
+class _UnderlinePainter extends BoxPainter {
+  _UnderlinePainter(this.decoration, VoidCallback? onChanged) : super(onChanged);
+
+  final AbsUnderlineTabIndicator decoration;
+
+  BorderSide? get borderSide => decoration.borderSide;
+
+  EdgeInsetsGeometry? get insets => decoration.insets;
+
+  Rect _indicatorRectFor(Rect rect, TextDirection textDirection) {
+    final Rect indicator = insets!.resolve(textDirection).deflateRect(rect);
+    //取中间坐标
+    double cw = (indicator.left + indicator.right) / 2;
+    return Rect.fromLTWH(cw - decoration.wantWidth! / 2, indicator.bottom - borderSide!.width, decoration.wantWidth!, borderSide!.width);
+  }
+
+  @override
+  void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {
+    assert(configuration.size != null);
+    final Rect rect = offset & configuration.size!;
+    final TextDirection textDirection = configuration.textDirection!;
+    final Rect indicator = _indicatorRectFor(rect, textDirection).deflate(borderSide!.width / 2.0);
+    final Paint paint = borderSide!.toPaint()..strokeCap = StrokeCap.round;
+    canvas.drawLine(indicator.bottomLeft, indicator.bottomRight, paint);
+  }
+}