将数据插入 Cloud Firestore Flutter 时出错？

Question

i'm working on an admin page i have three fields in a particular page where i was facing problems while displaying error messages in textfields before that my insertion was working fine but when i fixed that error and started running my app im ran into a new error.can someone please help me in it.

Here's my code:

class _AddPromoState extends State<AddPromo> {
  final databaseReference = Firestore.instance;

  var priceReductionController = TextEditingController();
  var perReductionController = TextEditingController();
  var promocodeController = TextEditingController();

  bool _validate = false;
  bool _validatePrice = false;
  bool _validatePerReduction = false;
  bool _validatePromoCode = false;


  @override
  void dispose() {
    priceReductionController.dispose();
    perReductionController.dispose();
    promocodeController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Add promo"),backgroundColor: Colors.indigo,),
      body: Column(
        children : <Widget>[
          Padding(
            padding: const EdgeInsets.all(8.0),
            child: TextField(
              keyboardType: TextInputType.number,
            controller: priceReductionController,
              decoration: InputDecoration(labelText: "Price Reduction",
                  errorText: _validatePrice ? 'value cant be empty' : null,
                  border: new OutlineInputBorder(
                borderRadius: const BorderRadius.all(
                  const Radius.circular(0.0),
                ),
                borderSide: new BorderSide(
                  color: Colors.indigo,
                  width: 1.0,
                ),
              )),
            ),
          ),
         Padding(
           padding: const EdgeInsets.all(8.0),
           child: TextField(
             keyboardType: TextInputType.number,


             controller: perReductionController,
             decoration: new InputDecoration(labelText: "Percentage Reduction",
                 errorText: _validatePerReduction ? 'value cant be empty' : null,
                 border: new  OutlineInputBorder(
               borderSide: new BorderSide(color: Colors.indigo)

             )),


            ),
         ),
         Padding(
           padding: const EdgeInsets.all(8.0),
           child: TextField(

             controller: promocodeController,
             decoration: InputDecoration(labelText: "Promo code",
                 errorText: _validatePromoCode ? 'value cant be empty' : null,
                 border: OutlineInputBorder(

             )),

            ),
         ),
          Spacer(flex:2),
        Container(
          width: 350,

          child: RaisedButton(
            color: Colors.indigo,
            onPressed: () async {

              //perform the validation first
              setState(() {
                priceReductionController.text.isEmpty
                    ? _validatePrice = true
                    : _validatePrice = false;
                perReductionController.text.isEmpty
                    ? _validatePerReduction = true
                    : _validatePerReduction = false;
                promocodeController.text.isEmpty
                    ? _validatePromoCode = true
                    : _validatePromoCode = false;
              });

              //verify that all are fine
              if (_validatePrice || _validatePromoCode || _validatePerReduction) {
                return;
              }

              //store the values into the database
              DocumentReference ref = await databaseReference.collection("promo_codes")
                  .add({
                'percentage_reduction': perReductionController.text,
                'price_reduction': priceReductionController.text,
                'promo_code': promocodeController.text,
              });

              Scaffold.of(context)
                  .showSnackBar(SnackBar(content: Text("Promo saved.")))
                  .closed
                  .then((reason) {
                // snackbar is now closed
              });

              //print(ref.documentID);
            }, child: Text("Add Promo", style: TextStyle(color:Colors.white),)
        ) ]
      ),
    );
  }
}

My error message looks like this:

E/flutter (13616): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: Scaffold.of() called with a context that does not contain a Scaffold.
E/flutter (13616): No Scaffold ancestor could be found starting from the context that was passed to Scaffold.of(). This usually happens when the context provided is from the same StatefulWidget as that whose build function actually creates the Scaffold widget being sought.
E/flutter (13616): There are several ways to avoid this problem. The simplest is to use a Builder to get a context that is "under" the Scaffold. For an example of this, please see the documentation for Scaffold.of():
E/flutter (13616):   https://api.flutter.dev/flutter/material/Scaffold/of.html
E/flutter (13616): A more efficient solution is to split your build function into several widgets. This introduces a new context from which you can obtain the Scaffold. In this solution, you would have an outer widget that creates the Scaffold populated by instances of your new inner widgets, and then in these inner widgets you would use Scaffold.of().
E/flutter (13616): A less elegant but more expedient solution is assign a GlobalKey to the Scaffold, then use the key.currentState property to obtain the ScaffoldState rather than using the Scaffold.of() function.
E/flutter (13616): The context used was:
E/flutter (13616):   AddPromo
E/flutter (13616): #0      Scaffold.of (package:flutter/src/material/scaffold.dart:1316:5)
E/flutter (13616): #1      _AddPromoState.build.<anonymous closure> (package:adminbookingpage/screens/addPromo.dart:119:24)
E/flutter (13616): <asynchronous suspension>
E/flutter (13616): #2      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:706:14)
E/flutter (13616): #3      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:789:36)
E/flutter (13616): #4      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
E/flutter (13616): #5      TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:486:11)
E/flutter (13616): #6      BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:264:5)
E/flutter (13616): #7      BaseTapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:199:7)
E/flutter (13616): #8      PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:467:9)
E/flutter (13616): #9      PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:76:12)
E/flutter (13616): #10     PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:117:9)
E/flutter (13616): #11     _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:379:8)
E/flutter (13616): #12     PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:115:18)
E/flutter (13616): #13     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:7)
E/flutter (13616): #14     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:218:19)
E/flutter (13616): #15     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22)
E/flutter (13616): #16     GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7)
E/flutter (13616): #17     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7)
E/flutter (13616): #18     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7)
E/flutter (13616): #19     _rootRunUnary (dart:async/zone.dart:1138:13)
E/flutter (13616): #20     _CustomZone.runUnary (dart:async/zone.dart:1031:19)
E/flutter (13616): #21     _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7)
E/flutter (13616): #22     _invoke1 (dart:ui/hooks.dart:273:10)
E/flutter (13616): #23     _dispatchPointerDataPacket (dart:ui/hooks.dart:182:5)

Answer 1

from your error logs

E/flutter (13616): No Scaffold ancestor could be found starting from the context that was passed to Scaffold.of(). This usually happens when the context provided is from the same StatefulWidget as that whose build function actually creates the Scaffold widget being sought. E/flutter (13616): There are several ways to avoid this problem. The simplest is to use a Builder to get a context that is "under" the Scaffold. For an example of this, please see the documentation for Scaffold.of(): E/flutter (13616): https://api.flutter.dev/flutter/material/Scaffold/of.html E/flutter (13616): A more efficient solution is to split your build function into several widgets. This introduces a new context from which you can obtain the Scaffold. In this solution, you would have an outer widget that creates the Scaffold populated by instances of your new inner widgets, and then in these inner widgets you would use Scaffold.of(). E/flutter (13616): A less elegant but more expedient solution is assign a GlobalKey to the Scaffold, then use the key.currentState property to obtain the ScaffoldState rather than using the Scaffold.of() function. E/flutter (13616): The context used was: E/flutter (13616): AddPromo E/flutter (13616): #0 Scaffold.of (package:flutter/src/material/scaffold.dart:1316:5) E/flutter (13616): #1 _AddPromoState.build. (package:adminbookingpage/screens/addPromo.dart:119:24) E/flutter (13616):

if you follow the link provided you will see that When the Scaffold is actually created in the same build function, the context argument to the build function can't be used to find the Scaffold (since it's "above" the widget being returned in the widget tree). In such cases, the following technique with a Builder can be used to provide a new scope with a BuildContext that is "under" the Scaffold:

example

        Widget build(BuildContext context) {
      return Scaffold(
        appBar: AppBar(
          title: Text('Demo')
        ),
        body: Builder(
          // Create an inner BuildContext so that the onPressed methods
          // can refer to the Scaffold with Scaffold.of().
          builder: (BuildContext context) {
            return  Column(
        children : <Widget>[
          Padding(
            padding: const EdgeInsets.all(8.0),
            child: TextField(
              keyboardType: TextInputType.number,
            controller: priceReductionController,
              decoration: InputDecoration(labelText: "Price Reduction",
                  errorText: _validatePrice ? 'value cant be empty' : null,
                  border: new OutlineInputBorder(
                borderRadius: const BorderRadius.all(
                  const Radius.circular(0.0),
                ),
                borderSide: new BorderSide(
                  color: Colors.indigo,
                  width: 1.0,
                ),
              )),
            ),
          ),
...


      );
    }

A more efficient solution is to split your build function into several widgets.you can read more about it from flutter docs

Answer 2

make (b) 字母小 buildContext 不是 BuildContext 就可以了