Flutter异常 NoSuchMethodError The getter focusScopeNode was called on null

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在启动新页面是出现异常：

 [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: NoSuchMethodError: The 
getter 'focusScopeNode' was called on null.
E/flutter (26425): Receiver: null    
E/flutter (26425): Tried calling: focusScopeNode
E/flutter (26425): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
E/flutter (26425): #1      Route.didPush.<anonymous closure> (package:flutter/src/widgets/navigator.dart:139:17)  

错误代码：

 void _onPass(){Navigator.push(context, MaterialPageRoute(builder: (context){return DetailPage();}));Navigator.pop(context);}

出现异常的原因是在刚push界面之后，不能立即调用Navigator.pop(context)，

Navigator.pop方法看源码声明：

/// Pop the top-most route off the navigator.////// {@macro flutter.widgets.navigator.pop}////// {@tool sample}////// Typical usage for closing a route is as follows:////// ```dart/// void _handleClose() {///   navigator.pop();/// }/// ```/// {@end-tool}/// {@tool sample}////// A dialog box might be closed with a result:////// ```dart/// void _handleAccept() {///   navigator.pop(true); // dialog returns true/// }/// ```/// {@end-tool}@optionalTypeArgsbool pop<T extends Object>([ T result ]) {assert(!_debugLocked);assert(() {_debugLocked = true;return true;}());

可以将页面路由当做一个栈，在刚push进去一个页面时，

立即调用Navigator.pop(context)会将栈顶的页面删除，此时push的页面就不能正常启动，会报上述异常

看源码，官方给的推荐用法：

/// The state from the closest instance of this class that encloses the given context.////// Typical usage is as follows:////// ```dart/// Navigator.of(context)///   ..pop()///   ..pop()///   ..pushNamed('/settings');/// ```////// If `rootNavigator` is set to true, the state from the furthest instance of/// this class is given instead. Useful for pushing contents above all subsequent/// instances of [Navigator].

修改之后代码：

void _onPass(){Navigator.of(context)..pop()..push(MaterialPageRoute(builder: (context){return DetailPage();}));}

或者

 void _onPass(){Navigator.pop(context);Navigator.push(context, MaterialPageRoute(builder: (context){return DetailPage();}));}

 

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