使用flutter搭建一个计算器

以下是使用Flutter搭建计算器的步骤：

1. 创建一个新的Flutter项目并命名为calculator。

2. 在lib目录下创建一个名为calculator.dart的文件，并将其作为应用程序的入口文件。

3. 在calculator.dart中导入所需的库：

import 'package:flutter/material.dart';

4. 创建一个新的StatefulWidget类，名为Calculator。

class Calculator extends StatefulWidget {
  @override
  _CalculatorState createState() => _CalculatorState();
}

5. 创建一个新的State类，名为_CalculatorState，并在其中实现UI。

class _CalculatorState extends State<Calculator> {
  String _output = "0";
  String _outputHistory = "";
  double num1 = 0.0;
  double num2 = 0.0;
  String operand = "";

  buttonPressed(String buttonText) {
    if (buttonText == "CLEAR") {
      _outputHistory = "";
      _output = "0";
      num1 = 0.0;
      num2 = 0.0;
      operand = "";
    } else if (buttonText == "+" ||
        buttonText == "-" ||
        buttonText == "x" ||
        buttonText == "/") {
      num1 = double.parse(_output);
      operand = buttonText;
      _output = "0";
    } else if (buttonText == ".") {
      if (_output.contains(".")) {
        print("Already contains a decimal");
        return;
      } else {
        _output = _output + buttonText;
      }
    } else if (buttonText == "=") {
      num2 = double.parse(_output);

      if (operand == "+") {
        _output = (num1 + num2).toString();
      }

      if (operand == "-") {
        _output = (num1 - num2).toString();
      }

      if (operand == "x") {
        _output = (num1 * num2).toString();
      }

      if (operand == "/") {
        _output = (num1 / num2).toString();
      }

      num1 = 0.0;
      num2 = 0.0;
      operand = "";
    } else {
      _output = _output + buttonText;
    }

    setState(() {
      _output = double.parse(_output).toStringAsFixed(2);
    });
  }

  Widget buildButton(String buttonText) {
    return new Expanded(
      child: new OutlineButton(
        padding: new EdgeInsets.all(24.0),
        child: new Text(
          buttonText,
          style: TextStyle(fontSize: 20.0, fontWeight: FontWeight.bold),
        ),
        onPressed: () => buttonPressed(buttonText),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text("Calculator"),
      ),
      body: new Container(
        child: new Column(
          children: <Widget>[
            new Container(
              alignment: Alignment.centerRight,
              padding: new EdgeInsets.symmetric(
                vertical: 24.0,
                horizontal: 12.0,
              ),
              child: new Text(
                _outputHistory,
                style: new TextStyle(
                  fontSize: 20.0,
                  fontWeight: FontWeight.bold,
                ),
              ),
            ),
            new Container(
              alignment: Alignment.centerRight,
              padding: new EdgeInsets.symmetric(
                vertical: 24.0,
                horizontal: 12.0,
              ),
              child: new Text(
                _output,
                style: new TextStyle(
                  fontSize: 48.0,
                  fontWeight: FontWeight.bold,
                ),
              ),
            ),
            new Expanded(
              child: new Divider(),
            ),
            new Column(
              children: <Widget>[
                new Row(
                  children: [
                    buildButton("7"),
                    buildButton("8"),
                    buildButton("9"),
                    buildButton("/")
                  ],
                ),
                new Row(
                  children: [
                    buildButton("4"),
                    buildButton("5"),
                    buildButton("6"),
                    buildButton("x")
                  ],
                ),
                new Row(
                  children: [
                    buildButton("1"),
                    buildButton("2"),
                    buildButton("3"),
                    buildButton("-")
                  ],
                ),
                new Row(
                  children: [
                    buildButton("."),
                    buildButton("0"),
                    buildButton("00"),
                    buildButton("+")
                  ],
                ),
                new Row(
                  children: [
                    buildButton("CLEAR"),
                    buildButton("="),
                  ],
                ),
              ],
            )
          ],
        ),
      ),
    );
  }
}

在上述代码中，我们定义了一个_CalculatorState类，其中包含了一个字符串变量_output，用于存储计算器的输出结果，以及其他变量，用于存储计算器的状态。我们还定义了一个buttonPressed函数，该函数用于处理按下的按钮并更新输出结果。在buildButton函数中，我们创建了一个新的按钮，并将其与buttonPressed函数关联起来。

6. 在Calculator类中，创建一个build函数，用于返回一个MaterialApp并将其包装在Calculator Widget中。

class Calculator extends StatefulWidget {
  @override
  _CalculatorState createState() => _CalculatorState();
}

class CalculatorApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Calculator',
      home: Calculator(),
    );
  }
}

void main() => runApp(CalculatorApp());

7. 运行应用程序并测试计算器。

完成上述步骤后，您应该能够成功创建一个基本的Flutter计算器应用程序。您可以根据需要对其进行扩展并添加更多的功能。