似乎Flutter不支持动态更改 Controller 值，或者我遗漏了一些东西。我在Google上搜索了很多，但是找不到这个具体案例。
我要在这里实现的是在PageView中双击图像时将其放大2倍。
我尝试使用Transform和图像本身的缩放比例，它可以工作，但视口不能很好地使用它，即图像被缩放，但是当左右滑动图像时，PageView可以更改页面。
为简单起见，这只是我的build方法，除此之外，除了_viewportScale最初设置为1.0外，没有什么其他的。
@override
Widget build(BuildContext context) {
this.controller = PageController(
initialPage: 0,
viewportFraction: _viewportScale,
);
return PageView(
controller: controller,
onPageChanged: (int pageIndex) {
setState(() {
_viewportScale = 1.0;
});
},
children: this.urls.map((String url) {
return Container(
child: GestureDetector(
child: Image.network(url),
onTap: () => Navigator.pop(context),
onDoubleTap: () {
setState(() {
_viewportScale = _viewportScale == 1.0 ? 2.0 : 1.0;
});
},
),
);
}).toList(),
);
}
这里的问题是
onDoubleTap失败，并带有异常:I/flutter ( 6492): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 6492): The following assertion was thrown building NotificationListener<ScrollNotification>:
I/flutter ( 6492): Unexpected call to replaceSemanticsActions() method of RawGestureDetectorState.
I/flutter ( 6492): The replaceSemanticsActions() method can only be called outside of the build phase.
I/flutter ( 6492):
I/flutter ( 6492): When the exception was thrown, this was the stack:
I/flutter ( 6492): #0 RawGestureDetectorState.replaceSemanticsActions.<anonymous closure> (package:flutter/src/widgets/gesture_detector.dart:737:9)
I/flutter ( 6492): #1 RawGestureDetectorState.replaceSemanticsActions (package:flutter/src/widgets/gesture_detector.dart:743:6)
I/flutter ( 6492): #2 ScrollableState.setSemanticsActions (package:flutter/src/widgets/scrollable.dart:379:40)
I/flutter ( 6492): #3 ScrollPosition._updateSemanticActions (package:flutter/src/widgets/scroll_position.dart:445:13)
I/flutter ( 6492): #4 ScrollPosition.notifyListeners (package:flutter/src/widgets/scroll_position.dart:695:5)
I/flutter ( 6492): #5 ScrollPosition.forcePixels (package:flutter/src/widgets/scroll_position.dart:318:5)
I/flutter ( 6492): #6 _PagePosition.viewportFraction= (package:flutter/src/widgets/page_view.dart:263:7)
I/flutter ( 6492): #7 PageController.attach (package:flutter/src/widgets/page_view.dart:173:18)
I/flutter ( 6492): #8 ScrollableState.didUpdateWidget (package:flutter/src/widgets/scrollable.dart:356:26)
I/flutter ( 6492): #9 StatefulElement.update (package:flutter/src/widgets/framework.dart:3884:58)
I/flutter ( 6492): #10 Element.updateChild (package:flutter/src/widgets/framework.dart:2752:15)
I/flutter ( 6492): #11 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3752:16)
I/flutter ( 6492): #12 Element.rebuild (package:flutter/src/widgets/framework.dart:3564:5)
I/flutter ( 6492): #13 StatelessElement.update (package:flutter/src/widgets/framework.dart:3801:5)
I/flutter ( 6492): #14 Element.updateChild (package:flutter/src/widgets/framework.dart:2752:15)
I/flutter ( 6492): #15 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3752:16)
I/flutter ( 6492): #16 Element.rebuild (package:flutter/src/widgets/framework.dart:3564:5)
I/flutter ( 6492): #17 StatefulElement.update (package:flutter/src/widgets/framework.dart:3899:5)
I/flutter ( 6492): #18 Element.updateChild (package:flutter/src/widgets/framework.dart:2752:15)
I/flutter ( 6492): #19 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3752:16)
I/flutter ( 6492): #20 Element.rebuild (package:flutter/src/widgets/framework.dart:3564:5)
I/flutter ( 6492): #21 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2277:33)
I/flutter ( 6492): #22 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:700:20)
I/flutter ( 6492): #23 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:275:5)
I/flutter ( 6492): #24 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter ( 6492): #25 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter ( 6492): #26 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter ( 6492): #30 _invoke (dart:ui/hooks.dart:209:10)
I/flutter ( 6492): #31 _drawFrame (dart:ui/hooks.dart:168:3)
I/flutter ( 6492): (elided 3 frames from package dart:async)
I/flutter ( 6492): ════════════════════════════════════════════════════════════════════════════════════════════════════
手指交叉以便轻松解决... :)
最佳答案
临时解决方案将在page的结束位置添加额外的无用PageView。
关于dart - 在PageController中动态更改viewportFraction，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/55317171/