[游戏开发]flutter关于TabBar的使用（一）

由于目前的了解，在Flutter中TabBar要结合AppBar一起使用。

/*考勤查询*/
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:frametrim/utility/sq_color.dart';
import 'package:frametrim/views/tabSizeIndicator.dart';
import 'attendanceQueryCurrentPage.dart';
import 'attendanceQueryExitPage.dart';

class AttendanceQueryPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => AttendanceQueryState();
}

class AttendanceQueryState extends State<AttendanceQueryPage>
    with SingleTickerProviderStateMixin {
  var tabs = ['当前在场', '已退场'];
  late TabController _tabController;
  var _currentIndex = 0;

  @override
  void initState() {
    super.initState();
    _tabController = new TabController(vsync: this, length: tabs.length);
    //添加监听，记录当前切换到的页面索引
    _tabController.addListener(() {
      setState(() => _currentIndex = _tabController.index);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white,
      appBar: AppBar(
        backgroundColor: Colors.white,
        title: Text('考勤查询',style: TextStyle(fontSize: 18,color: Colors.black),),
        bottom: TabBar(
            onTap: (index) {
              setState(() {
                _currentIndex=index;
              });
            },
            //设置下划线的宽度
            indicator: MyUnderlineTabIndicator(borderSide:  BorderSide(width: 3.0, color: SQColor.color_237BFC)),
            //选中下划线颜色
            indicatorColor: SQColor.color_237BFC,
            //选中下划线的高度，值越大高度越高，默认为2
            indicatorWeight: 1,
            //选中下划线的长度，label时跟文字内容长度一样，tab时跟一个Tab的长度一样
            // indicatorSize: TabBarIndicatorSize.tab,
            //设置选中时的字体颜色，tabs里面的字体样式优先级最高
            labelColor: SQColor.color_237BFC,
            //设置未选中时的字体颜色
            unselectedLabelColor: SQColor.black,
            indicatorPadding: EdgeInsets.symmetric(horizontal: 40),
            controller: _tabController, tabs: <Widget>[
          Container(
            height: 40,
            child: Center(
              child: Text(
                tabs[0],
                style: TextStyle(
                  fontSize: 16,
                ),
              ),
            ),
          ),
          Container(
            height: 40,
            child: Center(
              child: Text(
                tabs[1],
                style: TextStyle(fontSize: 16),
              ),
            ),
          ),
        ]),
        centerTitle: true,
        leading: IconButton(
          // icon: Icon(Icons.menu,color: Colors.black,),
          icon: Image.asset('image/imv_back.png',width: 10,height: 15,),
          onPressed: (){
            Navigator.pop(context);
          },
        ),
        // leadingWidth: 10,
      ),
      body: _getTabBarView(),
    );
  }


  Widget _getTabBarView() {
    return TabBarView(controller: _tabController, children: <Widget>[
      AttendanceQueryCurrentPage(),
      AttendanceQueryExitPage()
    ]);
  }
}

tabSizeIndicator.dart
自定义Tabbar下划线的样式（宽度）

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';

/// Used with [TabBar.indicator] to draw a horizontal line below the
/// selected tab.
///
/// The selected tab underline is inset from the tab's boundary by [insets].
/// The [borderSide] defines the line's color and weight.
///
/// The [TabBar.indicatorSize] property can be used to define the indicator's
/// bounds in terms of its (centered) widget with [TabIndicatorSize.label],
/// or the entire tab with [TabIndicatorSize.tab].
class MyUnderlineTabIndicator extends Decoration {
  /// Create an underline style selected tab indicator.
  ///
  /// The [borderSide] and [insets] arguments must not be null.
  const MyUnderlineTabIndicator({
    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 MyUnderlineTabIndicator) {
      return MyUnderlineTabIndicator(
        borderSide: BorderSide.lerp(borderSide, b.borderSide, t),
        insets: EdgeInsetsGeometry.lerp(insets, b.insets, t)!,
      );
    }
    return super.lerpTo(b, t);
  }

/*  @override
  Decoration lerpTo(Decoration b, double t) {
    if (b is MyUnderlineTabIndicator) {
      return MyUnderlineTabIndicator(
        borderSide: BorderSide.lerp(borderSide, b.borderSide, t),
        insets: EdgeInsetsGeometry.lerp(insets, b.insets, t),
      );
    }
    return super.lerpTo(b, t);
  }*/

  @override
  _MyUnderlinePainter createBoxPainter([ VoidCallback? onChanged ]) {
    return _MyUnderlinePainter(this, onChanged!);
  }
}

class _MyUnderlinePainter extends BoxPainter {
  _MyUnderlinePainter(this.decoration, VoidCallback onChanged)
      : assert(decoration != null),
        super(onChanged);

  final MyUnderlineTabIndicator 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);

    //希望的宽度
    double wantWidth = 50;
    //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;
    canvas.drawLine(indicator.bottomLeft, indicator.bottomRight, paint);
  }
}