目录前言屏幕适配的一些基础概念Flutter 移动端开发的通用做法存在的问题桌面端解决方案一、需求分析二、实现原理写在最后前言 通过此篇文章,你将了解到: Flutter wind
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编程网其它相关文章!
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