Android Java简易计算器问题：等于按钮始终禁用且空值易崩溃

你的代码存在两个核心问题：

• 等于按钮初始设为false后，没有正确的启用逻辑（原本的TextWatcher被注释，且仅计划监听单个输入框）
• 点击等于按钮时未检查输入框内容，直接调用Integer.parseInt会导致空输入/非数字输入时崩溃，且空判断逻辑完全错误（误判按钮文本而非输入框内容）

修复后的完整代码 #

package com.codecademy.simplecalculator;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    EditText firstNumber;
    EditText secondNumber;
    RadioGroup operators;
    RadioButton add;
    RadioButton subtract;
    RadioButton divide;
    RadioButton multiply;
    Button equals;
    TextView result;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        firstNumber = findViewById(R.id.number1);
        secondNumber = findViewById(R.id.number2);
        operators = findViewById(R.id.Radio_Groupoperators);
        add = findViewById(R.id.add);
        subtract = findViewById(R.id.subtract);
        multiply = findViewById(R.id.multiply);
        divide = findViewById(R.id.divide);
        equals = findViewById(R.id.equals);
        result = findViewById(R.id.result);

        equals.setEnabled(false);

        // 共用输入监听，双输入框都不为空时才启用等于按钮
        TextWatcher inputWatcher = new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {}

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {}

            @Override
            public void afterTextChanged(Editable s) {
                String firstInput = firstNumber.getText().toString().trim();
                String secondInput = secondNumber.getText().toString().trim();
                equals.setEnabled(!firstInput.isEmpty() && !secondInput.isEmpty());
            }
        };

        firstNumber.addTextChangedListener(inputWatcher);
        secondNumber.addTextChangedListener(inputWatcher);

        equals.setOnClickListener(v -> {
            String firstStr = firstNumber.getText().toString().trim();
            String secondStr = secondNumber.getText().toString().trim();

            // 双重校验输入完整性
            if (firstStr.isEmpty() || secondStr.isEmpty()) {
                Toast.makeText(this, "请输入完整数字", Toast.LENGTH_SHORT).show();
                return;
            }

            int firstNum, secondNum;
            try {
                // 捕获非数字输入异常
                firstNum = Integer.parseInt(firstStr);
                secondNum = Integer.parseInt(secondStr);
            } catch (NumberFormatException e) {
                Toast.makeText(this, "请输入有效数字", Toast.LENGTH_SHORT).show();
                return;
            }

            int selectedOpId = operators.getCheckedRadioButtonId();
            Integer answer = null;

            if (selectedOpId == add.getId()) {
                answer = firstNum + secondNum;
            } else if (selectedOpId == subtract.getId()) {
                answer = firstNum - secondNum;
            } else if (selectedOpId == multiply.getId()) {
                answer = firstNum * secondNum;
            } else if (selectedOpId == divide.getId()) {
                // 处理除零错误
                if (secondNum == 0) {
                    Toast.makeText(this, "除数不能为0", Toast.LENGTH_SHORT).show();
                    return;
                }
                answer = firstNum / secondNum;
            } else {
                Toast.makeText(this, "请选择运算符", Toast.LENGTH_SHORT).show();
                return;
            }

            if (answer != null) {
                result.setText(answer.toString());
            }
        });
    }
}

关键修改说明 #

• 完善输入监听：创建共用的TextWatcher绑定到两个输入框，只有双输入框都非空时才启用等于按钮
• 修复输入校验：点击按钮时先检查输入完整性，为空则直接提示并终止执行
• 添加异常处理：捕获NumberFormatException，处理用户输入非数字的场景
• 新增除零判断：除法运算前校验除数，避免因除零导致崩溃
• 移除无效逻辑：删除原代码中判断等于按钮文本的错误逻辑

内容的提问来源于stack exchange，提问作者angélique copérée