java - 在我的计算器应用程序中使用运算符时出现 "NaN"错误

Question

所以我一直在根据网上的教程开发计算器应用程序。到目前为止一切都很好，但每次我尝试使用运算符(operator)按钮时，我似乎无法找出导致应用程序中出现“NaN”错误的原因。我将附上代码和应用程​​序的屏幕截图。抱歉，如果我含糊不清，我是编码新手，只是想学习。

我的MainActivity.java

package com.example.calculator_prjct;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import android.app.Activity;
import com.example.calculator_prjct.databinding.ActivityMainBinding;
import android.os.Bundle;
import android.view.View;
import java.text.DecimalFormat;

public class MainActivity extends AppCompatActivity {

  private ActivityMainBinding binding;
  private static final char ADDITION = '+';
  private static final char SUBTRACTION = '-';
  private static final char MULTIPLICATION = '*';
  private static final char DIVISION = '/';

  private char CURRENT_ACTION;

  private double valueOne = Double.NaN;
  private double valueTwo;

  private DecimalFormat decimalFormat;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    decimalFormat = new DecimalFormat("#.##########");

    final ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);

    binding.buttonDot.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + ".");
        }
    });

    binding.buttonZero.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "0");
        }
    });

    binding.buttonOne.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "1");
        }
    });

    binding.buttonTwo.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "2");
        }
    });

    binding.buttonThree.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "3");
        }
    });

    binding.buttonFour.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "4");
        }
    });

    binding.buttonFive.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "5");
        }
    });

    binding.buttonSix.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "6");
        }
    });

    binding.buttonSeven.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "7");
        }
    });

    binding.buttonEight.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "8");
        }
    });

    binding.buttonNine.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "9");
        }
    });


    binding.buttonAdd.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            computeCalculation();
            CURRENT_ACTION = ADDITION;
            binding.infoTextView.setText(decimalFormat.format(valueOne) + "+");
            binding.editText.setText(null);
        }
    });

    binding.buttonSubtract.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            computeCalculation();
            CURRENT_ACTION = SUBTRACTION;
            binding.infoTextView.setText(decimalFormat.format(valueOne) + "-");
            binding.editText.setText(null);
        }
    });

    binding.buttonMultiply.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            computeCalculation();
            CURRENT_ACTION = MULTIPLICATION;
            binding.infoTextView.setText(decimalFormat.format(valueOne) + "*");
            binding.editText.setText(null);
        }
    });

    binding.buttonDivide.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            computeCalculation();
            CURRENT_ACTION = DIVISION;
            binding.infoTextView.setText(decimalFormat.format(valueOne) + "/");
            binding.editText.setText(null);
        }
    });

    binding.buttonEquals.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            computeCalculation();
            binding.infoTextView.setText(binding.infoTextView.getText().toString() +
                    decimalFormat.format(valueTwo) + " = " + decimalFormat.format(valueOne));
            valueOne = Double.NaN;
            CURRENT_ACTION = '0';
        }
    });

    binding.buttonClear.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (binding.editText.getText().length() > 0) {
                CharSequence currentText = binding.editText.getText();
                binding.editText.setText(currentText.subSequence(0, currentText.length() - 1));
            } else {
                valueOne = Double.NaN;
                valueTwo = Double.NaN;
                binding.editText.setText("");
                binding.infoTextView.setText("");
            }
        }
    });
}

private void computeCalculation() {
    if (!Double.isNaN(valueOne)) {
        valueTwo = Double.parseDouble(binding.editText.getText().toString());
        binding.editText.setText(null);

        if (CURRENT_ACTION == ADDITION)
            valueOne = this.valueOne + valueTwo;
        else if (CURRENT_ACTION == SUBTRACTION)
            valueOne = this.valueOne - valueTwo;
        else if (CURRENT_ACTION == MULTIPLICATION)
            valueOne = this.valueOne * valueTwo;
        else if (CURRENT_ACTION == DIVISION)
            valueOne = this.valueOne / valueTwo;
    } else {
        try {
            valueOne = Double.parseDouble(binding.editText.getText().toString());
        } catch (Exception e) {
        }
    }

}

}

我的activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<layout>
<RelativeLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<TextView
    android:id="@+id/infoTextView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginBottom="30dp"
    android:textSize="30sp" />

<EditText
    android:id="@+id/editText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@id/infoTextView"
    android:enabled="false"
    android:gravity="bottom"
    android:lines="2"
    android:maxLines="2"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonSeven"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:text="7"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonFour"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_alignParentStart="true"
    android:layout_marginStart="1dp"
    android:layout_marginLeft="-87dp"
    android:layout_marginTop="47dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="4"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonFive"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_marginLeft="1dp"
    android:layout_marginTop="47dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="5"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonSix"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_marginLeft="89dp"
    android:layout_marginTop="46dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="6"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonOne"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_alignParentStart="true"
    android:layout_marginStart="-1dp"
    android:layout_marginLeft="-89dp"
    android:layout_marginTop="96dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="1"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonTwo"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_marginLeft="-1dp"
    android:layout_marginTop="95dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="2"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonThree"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_marginLeft="88dp"
    android:layout_marginTop="97dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="3"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonDot"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_alignParentStart="true"
    android:layout_marginStart="2dp"
    android:layout_marginLeft="-86dp"
    android:layout_marginTop="144dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="."
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonZero"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_alignParentStart="true"
    android:layout_marginStart="90dp"
    android:layout_marginLeft="2dp"
    android:layout_marginTop="144dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="0"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonEquals"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_alignParentStart="true"
    android:layout_marginStart="179dp"
    android:layout_marginLeft="91dp"
    android:layout_marginTop="145dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="="
    android:textSize="20sp" />


<Button
    android:id="@+id/buttonClear"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_alignParentStart="true"
    android:layout_centerVertical="true"
    android:layout_marginStart="265dp"
    android:layout_marginLeft="177dp"
    android:layout_marginTop="197dp"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="C"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonEight"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_toRightOf="@id/buttonSeven"
    android:text="8"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonNine"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/editText"
    android:layout_toRightOf="@id/buttonEight"
    android:text="9"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonDivide"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@id/buttonNine"
    android:layout_toRightOf="@id/buttonNine"
    android:text="/"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonMultiply"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@id/buttonDivide"
    android:layout_marginLeft="-88dp"
    android:layout_marginTop="48dp"
    android:layout_toRightOf="@id/buttonDivide"
    android:text="*"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonSubtract"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@id/buttonMultiply"
    android:layout_marginLeft="-86dp"
    android:layout_marginTop="53dp"
    android:layout_toRightOf="@id/buttonMultiply"
    android:text="-"
    android:textSize="20sp" />

<Button
    android:id="@+id/buttonAdd"
    style="@style/Widget.AppCompat.Button.Borderless"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@id/buttonSubtract"
    android:layout_marginLeft="-89dp"
    android:layout_marginTop="49dp"
    android:layout_toRightOf="@id/buttonSubtract"
    android:text="+"
    android:textSize="20sp" />

</RelativeLayout>
</layout>

实际错误的屏幕截图 "NaN Error on all operator buttons"

Answer 1

这是因为您没有检查所有操作按钮各自的onClick方法中的EditText是否为空。将这样的代码添加到所有操作符按钮:

binding.buttonAdd.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(binding.editText.getText().toString().isEmpty()) {
                Toast.makeText(MainActivity.this, "Enter number before performing operation", Toast.LENGTH_LONG).show();
                return;
            }
            computeCalculation();
            CURRENT_ACTION = ADDITION;

            //if editText was empty then valueOne would still be NaN
            //and infoTextView will show NaN+ with this line of code

            binding.infoTextView.setText(decimalFormat.format(valueOne) + "+");
            binding.editText.setText(null);
        }
    });

完整 Activity 代码:

public class MainActivity extends AppCompatActivity {

private ActivityMainBinding binding;
private static final char ADDITION = '+';
private static final char SUBTRACTION = '-';
private static final char MULTIPLICATION = '*';
private static final char DIVISION = '/';

private char CURRENT_ACTION;

private double valueOne = Double.NaN;
private double valueTwo;

private DecimalFormat decimalFormat;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    binding = ActivityMainBinding.inflate(getLayoutInflater());
    View view = binding.getRoot();
    setContentView(view);


    decimalFormat = new DecimalFormat("#.##########");

    binding.buttonDot.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + ".");
        }
    });

    binding.buttonZero.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "0");
        }
    });

    binding.buttonOne.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "1");
        }
    });

    binding.buttonTwo.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "2");
        }
    });

    binding.buttonThree.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "3");
        }
    });

    binding.buttonFour.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "4");
        }
    });

    binding.buttonFive.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "5");
        }
    });

    binding.buttonSix.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "6");
        }
    });

    binding.buttonSeven.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "7");
        }
    });

    binding.buttonEight.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "8");
        }
    });

    binding.buttonNine.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            binding.editText.setText(binding.editText.getText() + "9");
        }
    });


    binding.buttonAdd.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(binding.editText.getText().toString().isEmpty()) {
                Toast.makeText(MainActivity.this, "Enter number before performing operation", Toast.LENGTH_LONG).show();
                return;
            }
            computeCalculation();
            CURRENT_ACTION = ADDITION;
            binding.infoTextView.setText(decimalFormat.format(valueOne) + "+");
            binding.editText.setText(null);
        }
    });

    binding.buttonSubtract.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(binding.editText.getText().toString().isEmpty()) {
                Toast.makeText(MainActivity.this, "Enter number before performing operation", Toast.LENGTH_LONG).show();
                return;
            }
            computeCalculation();
            CURRENT_ACTION = SUBTRACTION;
            binding.infoTextView.setText(decimalFormat.format(valueOne) + "-");
            binding.editText.setText(null);
        }
    });

    binding.buttonMultiply.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(binding.editText.getText().toString().isEmpty()) {
                Toast.makeText(MainActivity.this, "Enter number before performing operation", Toast.LENGTH_LONG).show();
                return;
            }
            computeCalculation();
            CURRENT_ACTION = MULTIPLICATION;
            binding.infoTextView.setText(decimalFormat.format(valueOne) + "*");
            binding.editText.setText(null);
        }
    });

    binding.buttonDivide.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(binding.editText.getText().toString().isEmpty()) {
                Toast.makeText(MainActivity.this, "Enter number before performing operation", Toast.LENGTH_LONG).show();
                return;
            }
            computeCalculation();
            CURRENT_ACTION = DIVISION;
            binding.infoTextView.setText(decimalFormat.format(valueOne) + "/");
            binding.editText.setText(null);
        }
    });

    binding.buttonEquals.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(binding.editText.getText().toString().isEmpty()) {
                Toast.makeText(MainActivity.this, "Enter number before performing operation", Toast.LENGTH_LONG).show();
                return;
            }
            computeCalculation();
            binding.infoTextView.setText(binding.infoTextView.getText().toString() +
                    decimalFormat.format(valueTwo) + " = " + decimalFormat.format(valueOne));
            valueOne = Double.NaN;
            CURRENT_ACTION = '0';
        }
    });

    binding.buttonClear.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (binding.editText.getText().length() > 0) {
                CharSequence currentText = binding.editText.getText();
                binding.editText.setText(currentText.subSequence(0, currentText.length() - 1));
            } else {
                valueOne = Double.NaN;
                valueTwo = Double.NaN;
                binding.editText.setText("");
                binding.infoTextView.setText("");
            }
        }
    });
}

private void computeCalculation() {
    if (!Double.isNaN(valueOne)) {
        valueTwo = Double.parseDouble(binding.editText.getText().toString());
        binding.editText.setText(null);

        if (CURRENT_ACTION == ADDITION)
            valueOne = this.valueOne + valueTwo;
        else if (CURRENT_ACTION == SUBTRACTION)
            valueOne = this.valueOne - valueTwo;
        else if (CURRENT_ACTION == MULTIPLICATION)
            valueOne = this.valueOne * valueTwo;
        else if (CURRENT_ACTION == DIVISION)
            valueOne = this.valueOne / valueTwo;
    } else {
        try {
            valueOne = Double.parseDouble(binding.editText.getText().toString());
        } catch (Exception e) {
        }
    }

}
}