计算器应用修改

Question

我是android的新手，我创建了一个calculator app。如果我提供像7+8-2这样的输入，该应用程序可以完美地完成工作，这意味着只有ADDITION和SUBTRACTION可以完美地工作。但是，如果我给出4+2*3之类的输入，那么它会计算出错误的结果。我知道原因，但我无法解决这个问题。

问题描述（我的代码是这样的）：假设我按 4 ，然后按 + ，然后按 2 < /strong> ....当我按 2 然后立即计算4+2，结果(6)存储在名为result的变量中。然后假设我按*，然后按 3 。然后立即将数字 3 与存储在变量结果(6)中的值相乘，意味着变量结果现在为6*3 = 18。这就是为什么我创建的应用会打印4+2*3 = 18的结果，但实际结果应为10

  

activity_simple_calculator.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/infoText"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:paddingLeft="5dp"
            android:paddingBottom="15dp"
            android:paddingTop="15dp"
            android:layout_marginTop="5dp"
            android:layout_marginBottom="10dp"
            android:textSize="30sp"
            android:textColor="@color/textColor"/>

        <EditText
            android:id="@+id/digit"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:paddingTop="15dp"
            android:paddingBottom="15dp"
            android:layout_marginTop="5dp"
            android:layout_marginBottom="5dp"
            android:textSize="25sp"/>

        <GridLayout
            android:id="@+id/calculatorBtns"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:columnCount="4"
            android:orientation="horizontal"
            android:layout_gravity="center">

            <Button android:id="@+id/btnSeven" android:text="7" />
            <Button android:id="@+id/btnEight" android:text="8" />
            <Button android:id="@+id/btnNine" android:text="9" />
            <Button android:id="@+id/btnDivision" android:text="/" />

            <Button android:id="@+id/btnFour" android:text="4" />
            <Button android:id="@+id/btnFive" android:text="5" />
            <Button android:id="@+id/btnSix" android:text="6" />
            <Button android:id="@+id/btnMuliplication" android:text="X" />

            <Button android:id="@+id/btnOne" android:text="1" />
            <Button android:id="@+id/btnTwo" android:text="2" />
            <Button android:id="@+id/btnThree" android:text="3" />
            <Button android:id="@+id/btnAddition" android:text="+" />

            <Button android:id="@+id/btnZero" android:text="0" />
            <Button android:id="@+id/btnDot" android:text="." />
            <Button android:id="@+id/btnEqual" android:text="=" />
            <Button android:id="@+id/btnSubstraction" android:text="-" />

            <Button android:id="@+id/btnClear" android:text="C" />

        </GridLayout>

    </LinearLayout>

</layout>

  

SimpleCalculator.java

package com.example.borntoflirt.calculator;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.databinding.DataBindingUtil;
import android.view.View;
import android.widget.Toast;

import java.text.DecimalFormat;

import com.example.borntoflirt.calculator.databinding.ActivitySimpleCalculatorBinding;

public class SimpleCalculator extends AppCompatActivity {

    private ActivitySimpleCalculatorBinding binding;

    // Declare Operators
    // This simple calculator can only perform operations of either addition, subtraction, multiplication or division.
    // So we define four static chars to represent these operations
    private static final char ADDITION = '+';
    private static final char SUBTRACTION = '-';
    private static final char MULTIPLICATION = '*';
    private static final char DIVISION = '/';

    // current action
    private char CURRENT_ACTION;

    // Declare variables for calculation
    private String digitString = "";
    private double digit;
    private double total = Double.NaN;

    private DecimalFormat decimalFormat;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this, R.layout.activity_simple_calculator);

        // Handle Number Clicks
        binding.btnZero.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("0");
                binding.digit.setText(binding.digit.getText() + "0");
            }
        });
        binding.btnOne.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("1");
                binding.digit.setText(binding.digit.getText() + "1");
            }
        });
        binding.btnTwo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("2");
                binding.digit.setText(binding.digit.getText() + "2");
            }
        });
        binding.btnThree.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("3");
                binding.digit.setText(binding.digit.getText() + "3");
            }
        });
        binding.btnFour.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("4");
                binding.digit.setText(binding.digit.getText() + "4");
            }
        });
        binding.btnFive.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("5");
                binding.digit.setText(binding.digit.getText() + "5");
            }
        });
        binding.btnSix.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("6");
                binding.digit.setText(binding.digit.getText() + "6");
            }
        });
        binding.btnSeven.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("7");
                binding.digit.setText(binding.digit.getText() + "7");
            }
        });
        binding.btnEight.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("8");
                binding.digit.setText(binding.digit.getText() + "8");
            }
        });
        binding.btnNine.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit("9");
                binding.digit.setText(binding.digit.getText() + "9");
            }
        });
        binding.btnDot.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                catchDigit(".");
                binding.digit.setText(binding.digit.getText() + ".");
            }
        });

        // Handle Operator Clicks
        binding.btnAddition.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                computeCalculation();
                CURRENT_ACTION = ADDITION;
                binding.digit.setText(binding.digit.getText() + "+");
            }
        });
        binding.btnSubstraction.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                computeCalculation();
                CURRENT_ACTION = SUBTRACTION;
                binding.digit.setText(binding.digit.getText() + "-");
            }
        });
        binding.btnMuliplication.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                computeCalculation();
                CURRENT_ACTION = MULTIPLICATION;
                binding.digit.setText(binding.digit.getText() + "*");
            }
        });
        binding.btnDivision.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                computeCalculation();
                CURRENT_ACTION = DIVISION;
                binding.digit.setText(binding.digit.getText() + "/");
            }
        });
        binding.btnEqual.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                computeCalculation();
                binding.infoText.setText(binding.digit.getText());
                binding.digit.setText(Double.toString(total));
                CURRENT_ACTION = '0';
                total = Double.NaN;
                digitString = "";
            }
        });
        binding.btnClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                binding.digit.setText(null);
                binding.infoText.setText(null);
                CURRENT_ACTION = '0';
                digitString = "";
                total = Double.NaN;
            }
        });
    }

    private void catchDigit(String dgt) {
        digitString = digitString + dgt;
    }

    private void computeCalculation() {
        if (Double.isNaN(total)) {
            total = Double.parseDouble(digitString);
            digitString = "";
        }
        else {
            digit = Double.parseDouble(digitString);

            if (CURRENT_ACTION == ADDITION) {
                total = this.total + digit;
            }
            else if (CURRENT_ACTION == SUBTRACTION) {
                total = this.total - digit;
            }
            else if (CURRENT_ACTION == MULTIPLICATION) {
                total = this.total * digit;
            }
            else if (CURRENT_ACTION == DIVISION) {
                total = this.total / digit;
            }

            digitString = "";
        }
    }
}

是否可以从ex: 4+2*3字段获取字符串（Edittext），然后计算数学运算.. ??

Answer 1

鉴于目前的限制， 特别是你不需要支持括号， 一个简单的解决方案可能是跟踪最后一个小计， 和最后一个动作， 并在执行更高优先级的操作时将它们考虑在内， 比如乘法和除法。

添加字段以跟踪上一个操作和子总计：

private char lastAction;
private int lastSubTotal;

然后处理这样的动作：

switch (CURRENT_ACTION) {
    case ADDITION:
        total += digit;
        lastAction = CURRENT_ACTION;
        lastSubTotal = digit;
        break;
    case SUBTRACTION:
        total -= digit;
        lastAction = CURRENT_ACTION;
        lastSubTotal = digit;
        break;
    case MULTIPLICATION:
        if (lastAction == ADDITION) {
            total -= lastSubTotal;
            lastSubTotal *= digit;
            total += lastSubTotal;
        } else if (lastAction == SUBTRACTION) {
            total += lastSubTotal;
            lastSubTotal *= digit;
            total -= lastSubTotal;
        } else {
            total *= digit;
            lastAction = CURRENT_ACTION;
            lastSubTotal = digit;
        }
        break;
    case DIVISION:
        // TODO: similar to MULTIPLICATION
        break;
}

即，在添加的情况下， 如果最后一个动作是+或 - ， 撤消该动作， 更新最后一个小计， 并重做+或 - 。 此外，在这种情况下不要更新最后一个动作， 我们仍然希望保留+或 - 如果下一个动作将是另一个乘法或除法。