一、来源
今天在研究 flutter 相册库 wechat_assets_picker 遇到一个问题:(我需要在第三方库基础上封装一个组件,供项目内部调用,组件
一、来源
今天在研究 flutter 相册库 wechat_assets_picker 遇到一个问题:(我需要在第三方库基础上封装一个组件,供项目内部调用,组件内封装一些公共逻辑。)但是 AssetPicker.pickAssets 的属性太多了,一个个传递实在太麻烦,就想是否有 vue 中那种数据透传的解决方法呢(已知 flutter 中目前不支持这种属性透传)?苦苦思索5分钟之后,灵光一闪:
函数透传
/// pickAssets 方法源码: static Future<List<AssetEntity>?> pickAssets( BuildContext context, { List<AssetEntity>? selectedAssets, int maxAssets = 9, int pageSize = 80, int gridThumbSize = Constants.defaultGridThumbSize, int pathThumbSize = 80, int gridCount = 4, RequestType requestType = RequestType.image, List<int>? previewThumbSize, SpecialPickerType? specialPickerType, Color? themeColor, ThemeData? pickerTheme, SortPathDelegate<AssetPathEntity>? sortPathDelegate, AssetsPickerTextDelegate? textDelegate, FilterOptionGroup? filterOptions, WidgetBuilder? specialItemBuilder, IndicatorBuilder? loadingIndicatorBuilder, SpecialItemPosition specialItemPosition = SpecialItemPosition.none, bool allowSpecialItemWhenEmpty = false, AssetSelectPredicate<AssetEntity>? selectPredicate, bool? shouldRevertGrid, bool useRootNavigator = true, Curve routeCurve = Curves.easeIn, Duration routeDuration = const Duration(milliseconds: 300), }) async { ...
二、 WechatPhotoPicker 使用示例
class WechatPhotoPickerDemo extends StatefulWidget { WechatPhotoPickerDemo({ Key? key, this.title}) : super(key: key); final String? title; @override _WechatPhotoPickerDemoState createState() => _WechatPhotoPickerDemoState(); } class _WechatPhotoPickerDemoState extends State<WechatPhotoPickerDemo> { int maxCount = 9; List<AssetEntity> entitys = []; GlobalKey<WechatPhotoPickerState> _globalKey = GlobalKey(); @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(widget.title ?? "$widget"), actions: ['选择',].map((e) => TextButton( child: Text(e, style: TextStyle(color: Colors.white), ), onPressed: onPicker, )).toList(), ), body: Column( children: [ WechatPhotoPicker( key: _globalKey, selectedAssets: entitys, onChanged: (List<AssetEntity> selectedAssets) { print("selectedAssets: ${selectedAssets.length}"); }, onPicker: () => AssetPicker.pickAssets( context, maxAssets: 8, selectedAssets: entitys, ), ) ], ) ); } onPicker() async { _globalKey.currentState?.onPicker(); print(entitys.length); } }
二、 WechatPhotoPicker 组件源码
/// 基于 wechat_assets_picker 的图片选择组件 class WechatPhotoPicker extends StatefulWidget { WechatPhotoPicker({ Key? key, this.selectedAssets = const [], this.maxCount = 9, this.rowCount = 3, this.spacing = 10, this.decoration, this.addBuilder, required this.onChanged, this.onPicker, }) : super(key: key); /// 媒体对象数组 List<AssetEntity> selectedAssets; /// 最大个数 int maxCount; /// 每行元素个数 int rowCount; /// 元素间距 double spacing; /// 元素修饰器 BoxDecoration? decoration; /// 添加图片 Widget Function(BuildContext context, double itemWidth)? addBuilder; /// 确认选择回调函数 void Function(List<AssetEntity> selectedAssets) onChanged; /// 解决flutter数据无法透传的问题(透传 AssetPicker.pickAssets 方法) Future<List<AssetEntity>?> Function()? onPicker; @override WechatPhotoPickerState createState() => WechatPhotoPickerState(); } class WechatPhotoPickerState extends State<WechatPhotoPicker> { @override Widget build(BuildContext context) { return photoSection( selectedAssets: widget.selectedAssets, maxCount: widget.maxCount, rowCount: widget.rowCount, spacing: widget.spacing, ); } photoSection({ List<AssetEntity> selectedAssets = const [], int maxCount = 9, int rowCount = 3, double spacing = 10, }) { return LayoutBuilder( builder: (BuildContext context, BoxConstraints constraints){ double itemWidth = ((constraints.maxWidth - spacing * (rowCount - 1))/rowCount).truncateToDouble(); // print("itemWidth: $itemWidth"); return Wrap( spacing: spacing, runSpacing: spacing, children: [ ...selectedAssets.map((e) => Container( clipBehavior: Clip.antiAlias, decoration: widget.decoration ?? BoxDecoration( // border: Border.all(width: 2), borderRadius: BorderRadius.all(Radius.circular(4)), ), child: FadeInImage( width: itemWidth, height: itemWidth, placeholder: AssetImage('images/img_placeholder.png'), image: AssetEntityImageProvider(e, isOriginal: false), fit: BoxFit.cover, ), )).toList(), if (selectedAssets.length < maxCount) InkWell( onTap: () { onPicker(); }, child: Container( width: itemWidth, height: itemWidth, decoration: BoxDecoration( color: Colors.black.withOpacity(0.1), // border: Border.all(width: 1), borderRadius: BorderRadius.all(Radius.circular(4)), ), child: widget.addBuilder != null ? widget.addBuilder!(context, itemWidth) : Icon( Icons.add, size: itemWidth/3, color: Colors.black.withOpacity(0.3), ), ), ) ] ); } ); } onPicker() async { List<AssetEntity>? result = widget.onPicker != null ? await widget.onPicker!() : await AssetPicker.pickAssets( context, maxAssets: widget.maxCount, selectedAssets: widget.selectedAssets, ); widget.selectedAssets = result ?? []; widget.onChanged(widget.selectedAssets); setState(() { }); } }
总结
1、onPicker 参数需要和调用方法搭配使用,即实现了函数透传,函数里的参数直接暴露给外部使用者,做二次定制开发;如果默认参数(可以适量添加)能够满足通用需求,则无需使用 onPicker 可选参数;
onPicker: () => AssetPicker.pickAssets( context, maxAssets: 8, selectedAssets: entitys, ),
List<AssetEntity>? result = widget.onPicker != null ? await widget.onPicker!() : await AssetPicker.pickAssets( context, maxAssets: widget.maxCount, selectedAssets: widget.selectedAssets, );
2、WechatPhotoPickerState,没有使用下换线(私有)实现是为了向外部暴露 State, 可以通过 GlobalKey 获取 State 实例对象,进而调用一些封装方法;达到更高的代码复用;
声明 GlobalKey:
GlobalKey:<WechatPhotoPickerState> _globalKey = GlobalKey();
调用 State 方法:
_globalKey.currentState?.onPicker();
3、所有自定义组件原则上都要支持 key 属性,才是一个完整的组件 Widget;
无论是移动原生、前端 h5 或者 flutter 跨平台,各种数据透传的思想是相近,在一端取得突破之后,其他端基本都是平移实现,这些可以减少代码量又不损失功能,而且维护性和扩展性更优的实现方式就是代码重构的本质。
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