flutter開發(fā)技巧自定頁面指示器PageIndicator詳解

更新時間：2023年01月15日 11:43:42 作者：SoaringHeart

這篇文章主要為大家介紹了flutter開發(fā)技巧自定頁面指示器PageIndicator詳解,有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進(jìn)步，早日升職加薪

一、來源

項目中遇到多個需要自定義輪播圖指示器的需求，封裝成基礎(chǔ)組件方便復(fù)用；

原理是通過 ValueListenableBuilder 實時監(jiān)聽輪播圖的當(dāng)前索引，然后更新指示器組件，達(dá)到最終效果；

二、效果

三、源碼實現(xiàn)

1、flutter_swiper_null_safety 使用示例：

import 'package:flutter/material.dart';
import 'package:flutter_swiper_null_safety/flutter_swiper_null_safety.dart';
import 'package:flutter_templet_project/R.dart';
import 'package:flutter_templet_project/basicWidget/page_indicator_widget.dart';
import 'package:flutter_templet_project/extension/buildContext_extension.dart';
class FlutterSwiperIndicatorDemo extends StatefulWidget {
  FlutterSwiperIndicatorDemo({ Key? key, this.title}) : super(key: key);
  final String? title;
  @override
  _FlutterSwiperIndicatorDemoState createState() => _FlutterSwiperIndicatorDemoState();
}
class _FlutterSwiperIndicatorDemoState extends State<FlutterSwiperIndicatorDemo> {
  ValueNotifier<int> currentIndex = ValueNotifier(0);
  BorderRadius borderRadius = BorderRadius.all(Radius.circular(8));
  final items = R.imgUrls;//圖片鏈接數(shù)組
  @override
  Widget build(BuildContext context) {
    dynamic arguments = ModalRoute.of(context)!.settings.arguments;
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title ?? "$widget"),
        ),
        body: _buildSwiper()
    );
  }
  ///創(chuàng)建子項
  _buildItem(context, index) {
    final imgUrl = items[index];
    return InkWell(
      onTap: () => print(index),
      child: Container(
        padding: EdgeInsets.only(bottom: 0), //為了顯示陰影
        child: ClipRRect(
          borderRadius: this.borderRadius,
          child: Stack(
            alignment: Alignment.center,
            fit: StackFit.expand,
            children: [
              FadeInImage(
                placeholder: AssetImage('images/img_placeholder.png',),
                image: NetworkImage(imgUrl),
                fit: BoxFit.cover,
              ),
            ],
          ),
        ),
      ),
    );
  }
  _buildSwiper() {
    return Container(
      height: 200,
      child: ClipRRect(
          borderRadius: this.borderRadius,
          child: Stack(
            children: [
              Swiper(
                itemBuilder: (context, index) => _buildItem(context, index),
                // indicatorLayout: PageIndicatorLayout.COLOR,
                autoplay: this.items.length > 1,
                loop: this.items.length > 1,
                itemCount: this.items.length,
                // pagination: this.items.length <= 1 ? null : SwiperPagination(),
                // control: SwiperControl(),
                // itemWidth: 200,
                // viewportFraction: 0.6,
                onIndexChanged: (index){
                  currentIndex.value = index;
                }
              ),
              // if (this.items.length > 1) buildPageIndicator(),
              if (this.items.length > 1) PageIndicatorWidget(
                currentIndex: currentIndex,
                itemCount: this.items.length,
                itemSize: Size(context.screenSize.width/ 4 / this.items.length, 2),
                // itemBuilder: (isSelected, itemSize) {
                //   return Container(
                //     width: itemSize.width,
                //     height: itemSize.height,
                //     color: isSelected ? Colors.red : Colors.green,
                //   );
                // },
              )
            ],
          )
      ),
    );
  }

2、PageIndicatorWidget 指示器源碼：

import 'package:flutter/material.dart';
typedef PageIndicatorItemWidgetBuilder = Widget Function(bool isSelected, Size itemSize);
/// 輪播圖指示器
class PageIndicatorWidget extends StatelessWidget {
  PageIndicatorWidget({ 
    Key? key, 
    this.margin = const EdgeInsets.only(bottom: 10),
    required this.currentPage,
    required this.itemCount,
    this.normalColor = const Color(0x25ffffff), 
    this.selectedColor = Colors.white,
    this.itemSize = const Size(8, 2),
    this.itemBuilder,
    this.hidesForSinglePage = true
  }) : super(key: key);
  /// 當(dāng)前頁面索引
  ValueNotifier<int> currentPage;
  EdgeInsetsGeometry? margin;
  /// item數(shù)量
  int itemCount;
  /// 每個item尺寸(最好用固定寬度除以個數(shù),避免總寬度溢出)
  Size itemSize;
  /// 自定義每個item
  PageIndicatorItemWidgetBuilder? itemBuilder;
  /// 默認(rèn)顏色
  Color? normalColor;
  /// 選中顏色
  Color? selectedColor;
  /// 單頁隱藏
  bool hidesForSinglePage;
  @override
  Widget build(BuildContext context) {
    if (this.hidesForSinglePage && this.itemCount == 1) {
      return SizedBox();
    }
    return buildPageIndicator();
  }
  Widget buildPageIndicator() {
    return Container(
      margin: this.margin,
      child: Align(
        alignment: Alignment.bottomCenter,
        child: ValueListenableBuilder(
          valueListenable: this.currentPage,
          builder: (BuildContext context, dynamic value, Widget? child) {
            return Row(
              mainAxisSize: MainAxisSize.min,
              mainAxisAlignment: MainAxisAlignment.start,
              children: buildPageIndicatorItem(
                currentIndex: this.currentPage.value,
                normalColor: this.normalColor,
                selectedColor: this.selectedColor,
              ),
            );
          },
        ),
      ),
    );
  }
  List<Widget> buildPageIndicatorItem({
    currentIndex: 0,
    normalColor: const Color(0x25ffffff), 
    selectedColor: Colors.white,
  }) {
    List<Widget> list = List.generate(this.itemCount, (index) {
      return this.itemBuilder != null ? this.itemBuilder!(currentIndex == index, this.itemSize) : ClipRRect(
        borderRadius: BorderRadius.all(Radius.circular(1)),
        child: Container(
          width: this.itemSize.width,
          height: this.itemSize.height,
          color: currentIndex == index ? selectedColor : normalColor,
        ),
      );
    });
    return list;
  }
}