flutter 制作TabBar的圆角

参考
制作TabBar的圆角

前言
最近开始搞flutter，然后想去使用TabBar，遇到了一些坑，记录一下。

分析过程
需求是这样：



需要处理这样几个细节：

下划线固定宽度
下划线圆角
下划线和文字的间距
两个文字之间的间距
然后在使用TabBar过程中：

下划线想固定25，indicatorSize只有两个属性，一是与tab父布局同宽，二是与字同宽
圆角看看能不能用自定义indicator来实现
默认的text和下划线挺大的，看看有什么办法改改
文字间的默认间距也挺大，看看怎么改
看看源码研究一下：那么找到TabBar有一个indicator的属性。

看注释大体是说如果使用自定义的indicator，那么indicatorColor、indicatorWeight、indicatorPadding都将被忽略

默认的indicator是UnderlineTabIndicator，然后indicator的size有两种情况

  

OK，那我们找一找这个indicator是怎么初始化的，在_TabBarState中找到：



然后在UnderlineTabIndicator中找到了答案，我们把UnderlineTabIndicator拷贝出来改个名

修改如下两处就可以固定宽度和修改圆角：



对于下划线和文字的间距问题，找到Tab，看到text是居中显示的，而且tab高度是固定的

如果你的Container的高度比46小，那么indicator就会被截掉一部分，甚至是截没了

我们把tab拷贝出来换个命名，然后把高度改低一些





对于两个tab间距很宽的问题，看了一下发现有默认的padding，然后添加labelPadding属性就OK了

那么最后这样使用：
child: TabBar(
   indicator: RoundUnderlineTabIndicator(
      borderSide: BorderSide(
         width: 3.5,
         color: Color(0xff00cdd7),
      )
   ),
   labelColor: Color(0xff333333),
   labelStyle: TextStyle(fontSize: 17, fontWeight: FontWeight.bold),
   labelPadding: EdgeInsets.only(left: 0, right: 0),
   unselectedLabelColor: Color(0xff333333),
   unselectedLabelStyle: TextStyle(fontSize: 13, fontWeight: FontWeight.normal),
   controller: controller,
   tabs: [VgTab(text:"哈哈哈"), VgTab(text:"呵呵 · 99")],
),
修改后的源码，将以下代码保存到一个新的dart文件里，就可以使用RoundUnderlineTabIndicator和VgTab了：

/**************************** 以下为修改的源码部分 ******************************/
 
// 默认高度从46改为40
const double _kTabHeight = 40.0;
const double _kTextAndIconTabHeight = 72.0;
 
class RoundUnderlineTabIndicator extends Decoration {
  /// Create an underline style selected tab indicator.
  ///
  /// The [borderSide] and [insets] arguments must not be null.
  const RoundUnderlineTabIndicator({
    this.borderSide = const BorderSide(width: 2.0, color: Colors.white),
    this.insets = EdgeInsets.zero,
  }) : assert(borderSide != null),
        assert(insets != null);
 
  /// The color and weight of the horizontal line drawn below the selected tab.
  final BorderSide borderSide;
 
  /// Locates the selected tab's underline relative to the tab's boundary.
  ///
  /// The [TabBar.indicatorSize] property can be used to define the
  /// tab indicator's bounds in terms of its (centered) tab widget with
  /// [TabIndicatorSize.label], or the entire tab with [TabIndicatorSize.tab].
  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)
      : assert(decoration != null),
        super(onChanged);
 
  final RoundUnderlineTabIndicator decoration;
 
  BorderSide get borderSide => decoration.borderSide;
  EdgeInsetsGeometry get insets => decoration.insets;
 
  Rect _indicatorRectFor(Rect rect, TextDirection textDirection) {
    assert(rect != null);
    assert(textDirection != null);
    final Rect indicator = insets.resolve(textDirection).deflateRect(rect);
//    return Rect.fromLTWH(
//      indicator.left,
//      indicator.bottom - borderSide.width,
//      indicator.width,
//      borderSide.width,
//    );
    //希望的宽度
    double wantWidth = 25;
    //取中间坐标
    double cw = (indicator.left + indicator.right) / 2;
    return Rect.fromLTWH(cw - wantWidth / 2,
        indicator.bottom - borderSide.width, wantWidth, borderSide.width);
  }
 
  @override
  void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {
    assert(configuration != null);
    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.square;
    // 改为圆角
    final Paint paint = borderSide.toPaint()..strokeCap = StrokeCap.round;
    canvas.drawLine(indicator.bottomLeft, indicator.bottomRight, paint);
  }
}
 
 
 
 
 
 
class VgTab extends StatelessWidget {
  /// Creates a material design [TabBar] tab.
  ///
  /// At least one of [text], [icon], and [child] must be non-null. The [text]
  /// and [child] arguments must not be used at the same time.
  const VgTab({
    Key key,
    this.text,
    this.icon,
    this.child,
  }) : assert(text != null || child != null || icon != null),
        assert(!(text != null && null != child)), // TODO(goderbauer): https://github.com/dart-lang/sdk/issues/34180
        super(key: key);
 
  /// The text to display as the tab's label.
  ///
  /// Must not be used in combination with [child].
  final String text;
 
  /// The widget to be used as the tab's label.
  ///
  /// Usually a [Text] widget, possibly wrapped in a [Semantics] widget.
  ///
  /// Must not be used in combination with [text].
  final Widget child;
 
  /// An icon to display as the tab's label.
  final Widget icon;
 
  Widget _buildLabelText() {
    return child ?? Text(text, softWrap: false, overflow: TextOverflow.fade);
  }
 
  @override
  Widget build(BuildContext context) {
    assert(debugCheckHasMaterial(context));
 
    double height;
    Widget label;
    if (icon == null) {
      height = _kTabHeight;
      label = _buildLabelText();
    } else if (text == null && child == null) {
      height = _kTabHeight;
      label = icon;
    } else {
      height = _kTextAndIconTabHeight;
      label = Column(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: <Widget>[
          Container(
            child: icon,
            margin: const EdgeInsets.only(bottom: 10.0),
          ),
          _buildLabelText(),
        ],
      );
    }
 
    return SizedBox(
      height: height,
      child: Center(
        child: label,
        widthFactor: 1.0,
      ),
    );
  }
 
  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(StringProperty('text', text, defaultValue: null));
    properties.add(DiagnosticsProperty<Widget>('icon', icon, defaultValue: null));
  }
}
总结
当然这几个宽度和高度属性也可以抽离出去，从外面传进来，更加灵活。
要导入以下
import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
import 'dart:ui' show lerpDouble;
import 'package:flutter/foundation.dart';
import 'package:flutter/rendering.dart';

从源码分析了一遍，终于实现了需求。记录下来，希望能帮到大家。
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版权声明：本文为CSDN博主「pengboboer」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/pengbo6665631/article/details/103645037