通过此篇文章,你将了解到:
Flutter windows和Android桌面应用屏幕适配的解决方案;
屏幕适配的相关知识和原理;
flutter_screenutil的实现原理和缺陷。
Flutter桌面应用的开发过程中,势必需要适配不同尺寸的屏幕。我们的预期是在不同尺寸的设备上,用户的使用感观基本一致。 如:在个人pc上,应用与屏幕的高度比是2/3;那么到60寸的大设备上,应用的尺寸依然需要2/3比例。
假设我们需要展示一张800×800的图片,那么在160dpi的手机屏幕上,我们只要设置800×800px的宽高;
但在320dpi的屏幕上,由于每英寸的像素点翻倍了,为了用户的视觉感受一致,就需要将图片设置的宽高设为1600×1600px。这就是屏幕适配最基本的原理,我们开发中所用到的适配库,最基础的能力就是提供这层转换。
Flutter移动端的生态已经很完备,我们一般在开发过程中会使用flutter_screenutil这个插件。这是一个纯Dart的pub,阅读源码发现其做法也很简单粗暴。
extension SizeExtension on num { ///[ScreenUtil.setWidth] double get w => ScreenUtil().setWidth(this); ///[ScreenUtil.setHeight] double get h => ScreenUtil().setHeight(this); ...... )
double get screenHeight => _context != null ? MediaQuery.of(_context!).size.height : _screenHeight; double setHeight(num height) => height * scaleHeight; // 高度的缩放比:设备的逻辑像素的高度/设计稿的高度 double get scaleHeight => (_splitScreenMode ? max(screenHeight, 700) : screenHeight) / _uiSize.height;
逻辑像素screenHeight从哪来?
获取MediaQueryData的size,即应用窗口的分辨率。
extension on MediaQueryData? { MediaQueryData? nonEmptySizeOrNull() { if (this?.size.isEmpty ?? true) return null; else return this; } }
/// The size of the media in logical pixels (e.g, the size of the screen). /// /// Logical pixels are roughly the same visual size across devices. Physical /// pixels are the size of the actual hardware pixels on the device. The /// number of physical pixels per logical pixel is described by the /// [devicePixelRatio]. final Size size;
flutter_screenutil 这个库在移动端使用是完全没有问题的。手机尺寸虽说层出不穷,但是也遵循瘦长的长方形规则,最重要的是应用默认都是全屏的,那么上面第3点获取到的应用窗口高度screenHeight和设备的大小刚好是完全吻合的。从而计算出的缩放比(设计稿尺寸/设备的尺寸 = 缩放比值)是偏差不大的。
我们在Android的桌面应用中,这个库也可以支持各种设备。
然而在windows等桌面端却没那么简单:
通过实践我们也验证了flutter_screenutil在桌面端的适配基本不起作用,且还会造成不少问题,比如:第一次运行字体都会偏大;当有多个扩展屏的时候,主副屏切换有bug。
我们希望flutter开发出来的应用,在不同的设备中:
分析以上预期效果,可以提炼出一个原则:应用的尺寸必须跟屏幕的物理大小占比一致,与分辨率、像素密度、缩放比都没关系。
由于Android端用了flutter_screenutil这个库,Flutter又是跨平台的。为了降低开发成本,我试着fork源码下来更改,并且做了以下的操作:
// 文件路径:flutter_screenutil/lib/src/screenutil_init.dart class ScreenUtilInit extends StatefulWidget { /// A helper widget that initializes [ScreenUtil] const ScreenUtilInit({ Key? key, required this.builder, this.child, this.rebuildFactor = RebuildFactors.size, this.designSize = ScreenUtil.defaultSize, this.app2screenWithWidth = 1, this.splitScreenMode = false, this.minTextAdapt = false, this.useInheritedMediaQuery = false, }) : super(key: key); final ScreenUtilInitBuilder builder; final Widget? child; final bool splitScreenMode; final bool minTextAdapt; final bool useInheritedMediaQuery; final RebuildFactor rebuildFactor; /// The [Size] of the device in the design draft, in dp final Size designSize; /// 适用于桌面应用,应用窗口宽度与设备屏幕宽度的比例 final double app2screenWithWidth; @override State<ScreenUtilInit> createState() => _ScreenUtilInitState(); }
dependencies: flutter: sdk: flutter # 获取屏幕物理参数 screen_retriever: ^0.1.2
// 文件路径:flutter_screenutil/lib/src/screen_util.dart /// Initializing the library. static Future<void> init( BuildContext context, { Size designSize = defaultSize, double app2screenWithWidth = 1, bool splitScreenMode = false, bool minTextAdapt = false, }) async { final navigatorContext = Navigator.maybeOf(context)?.context as Element?; final mediaQueryContext = navigatorContext?.getElementForInheritedWidgetOfExactType<MediaQuery>(); final initCompleter = Completer<void>(); WidgetsFlutterBinding.ensureInitialized().addPostFrameCallback((_) { mediaQueryContext?.visitChildElements((el) => _instance._context = el); if (_instance._context != null) initCompleter.complete(); }); // ** 我修改的代码 ** Orientation orientation = Orientation.landscape; Size deviceSize = Size.zero; if (isDesktop) { Display primaryDisplay = await screenRetriever.getPrimaryDisplay(); deviceSize = primaryDisplay.size; orientation = deviceSize.width > deviceSize.height ? Orientation.landscape : Orientation.portrait; } else { final deviceData = MediaQuery.maybeOf(context).nonEmptySizeOrNull(); deviceSize = deviceData?.size ?? designSize; orientation = deviceData?.orientation ?? (deviceSize.width > deviceSize.height ? Orientation.landscape : Orientation.portrait); } _instance .._context = context .._uiSize = designSize .._splitScreenMode = splitScreenMode .._minTextAdapt = minTextAdapt .._orientation = orientation .._screenWidth = deviceSize.width .._screenHeight = deviceSize.height; // 桌面区分设置下窗口大小 if (isDesktop) { double appWidth = deviceSize.width * app2screenWithWidth; double appHeight = appWidth / (designSize.width / designSize.height); _instance._uiSize = Size(appWidth, appHeight); } _instance._elementsToRebuild?.forEach((el) => el.markNeedsBuild()); return initCompleter.future; }
extension SizeExtension on num { ///[ScreenUtil.setWidth] double get w => ScreenUtil().setWidth(this); ///[ScreenUtil.setHeight] double get h => ScreenUtil().setHeight(this); ///[ScreenUtil.radius] double get r => ScreenUtil().radius(this); ///[ScreenUtil.setSp] double get sp => ScreenUtil().setSp(this); ///smart size : it check your value - if it is bigger than your value it will set your value ///for example, you have set 16.sm() , if for your screen 16.sp() is bigger than 16 , then it will set 16 not 16.sp() ///I think that it is good for save size balance on big sizes of screen double get sm => min(toDouble(), sp); ///屏幕宽度的倍数 ///Multiple of screen width double get sw => ScreenUtil().screenWidth * this; ///屏幕高度的倍数 ///Multiple of screen height double get sh => ScreenUtil().screenHeight * this; ///[ScreenUtil.setHeight] Widget get verticalSpace => ScreenUtil().setVerticalSpacing(this); ///[ScreenUtil.setVerticalSpacingFromWidth] Widget get verticalSpaceFromWidth => ScreenUtil().setVerticalSpacingFromWidth(this); ///[ScreenUtil.setWidth] Widget get horizontalSpace => ScreenUtil().setHorizontalSpacing(this); ///[ScreenUtil.radius] Widget get horizontalSpaceRadius => ScreenUtil().setHorizontalSpacingRadius(this); ///[ScreenUtil.radius] Widget get verticalSpacingRadius => ScreenUtil().setVerticalSpacingRadius(this); }
以上方案,我在demo项目中验证过是没有问题的。接下来我希望能跟作者沟通下这个方案,看能否提pr合并进去。不然以后就没办法很轻松的享受到flutter_screenutil的更新迭代了。
期待Flutter桌面社区越来越丰富!更多关于Flutter桌面应用多分辨率适配的资料请关注其它相关文章!