要显示Toast消息，您可以使用FlutterToast插件。要使用这个插件，你必须:

将此依赖项添加到您的pubspec中。Yaml文件:fluttertoast: ^8.0.8 要获取包，必须运行以下命令:$ flutter packages get 导入包:导入'package:fluttertoast/fluttertoast.dart';

像这样使用它:

Fluttertoast.showToast(
    msg: "your message",
    toastLength: Toast.LENGTH_SHORT,
    gravity: ToastGravity.BOTTOM // Also possible "TOP" and "CENTER"
    backgroundColor: "#e74c3c",
    textColor: '#ffffff');

要了解更多信息，请查看这个。

Importcupertino_icons: ^0.1.2并编写以下代码:

showToast(BuildContext context, String message) {
  showDialog(
    context: context,
    builder: (BuildContext context) {
      return CupertinoAlertDialog(
        title: Text(
          "Name of App",
        ),
        content: Text(
          message,
        ),
        actions: [
          CupertinoButton(
            child: Text("OK"),
            onPressed: () {
              Navigator.of(context).pop();
            },
          )
        ],
      );
    },
  );
});

答案Scaffold.of(context). showsnackbar(…)在大多数情况下都不起作用。

我建议最佳的方法是在类中声明一个Scaffold state键，并将其分配给Scaffold，如下所示:

GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();

然后

Scaffold(
  key: _scaffoldKey,
  ...
)

当你想要显示零食栏时，这样做:

_scaffoldKey.currentState.showSnackBar(SnackBar(
  content: Text("This works!"),
));

您可以使用此链接在Flutter中显示Toast。

可以这样使用:

void method1(){

    Fluttertoast.showToast(
        msg: "This is Add Button",
        toastLength: Toast.LENGTH_SHORT,
        gravity: ToastGravity.CENTER,
        timeInSecForIosWeb: 1,
        backgroundColor: Colors.blueGrey,
        textColor: Colors.white,
        fontSize: 14.0
    );
}

对于Android原始图形吐司，你可以使用这个:

它在Android和iOS上运行良好。

正如Darky指出的那样，SnackBar绝对是正确的类。

关于showSnackBar的一个棘手的事情是到达Scaffold state，如果你试图在构建方法中调用showSnackBar。

您可能会看到这样的错误，其中包括一些解释如何解决问题的文本。

══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
The following assertion was thrown while handling a gesture:
Scaffold.of() called with a context that does not contain a Scaffold.
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.
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():
  https://docs.flutter.io/flutter/material/Scaffold/of.html
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().
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.
The context used was:
  MyHomePage
When the exception was thrown, this was the stack:
#0      Scaffold.of (package:flutter/src/material/scaffold.dart:444:5)
#1      MyHomePage.build.<anonymous closure> (/Users/jackson/Library/Developer/CoreSimulator/Devices/7072C907-DBAD-44FE-8F40-0257442C51D9/data/Containers/Data/Application/77FEC1A4-1453-442C-8208-96E0323DEFB2/tmp/so_scratch2Tkq9Jb/so_scratch2/lib/main.dart:23:24)
#2      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:323:14)
#3      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:375:30)
#4      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:102:24)
#5      TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:149:9)
#6      TapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:119:7)
#7      GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:156:27)
#8      BindingBase&SchedulerBinding&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:147:20)
#9      BindingBase&SchedulerBinding&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:121:22)
#10     BindingBase&SchedulerBinding&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:101:7)
#11     BindingBase&SchedulerBinding&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:64:7)
#12     BindingBase&SchedulerBinding&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:48:7)
#13     _invoke1 (file:///b/build/slave/Mac_Engine/build/src/flutter/lib/ui/hooks.dart:100)
#14     _dispatchPointerDataPacket (file:///b/build/slave/Mac_Engine/build/src/flutter/lib/ui/hooks.dart:58)
Handler: onTap
Recognizer:
  TapGestureRecognizer#69dbc(debugOwner: GestureDetector, state: ready)
════════════════════════════════════════════════════════════════════════════════════════════════════

你可以将GlobalKey传递给你的Scaffold构造函数:

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final key = new GlobalKey<ScaffoldState>();
    return new Scaffold(
      key: key,
      floatingActionButton: new Builder(
        builder: (BuildContext context) {
          return new FloatingActionButton(
            onPressed: () {
              key.currentState.showSnackBar(new SnackBar(
                content: new Text("Sending Message"),
              ));
            },
            tooltip: 'Increment',
            child: new Icon(Icons.add),
          );
        }
      ),
    );
  }
}

或者你可以使用一个Builder来创建一个BuildContext，它是Scaffold的子对象。

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      floatingActionButton: new Builder(
        builder: (BuildContext context) {
          return new FloatingActionButton(
            onPressed: () {
              Scaffold.of(context).showSnackBar(new SnackBar(
                content: new Text("Sending Message"),
              ));
            },
            tooltip: 'Increment',
            child: new Icon(Icons.add),
          );
        }
      ),
    );
  }
}

最后，您可以将小部件分成多个类，这是最佳的长期方法。