Android实现简易计算功能

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="Http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="clip_horizontal"
    android:orientation="vertical"
    android:padding="30dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="操作数:"
            android:textSize="20sp" />

        <EditText
            android:id="@+id/firstNum"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="请输入数值操作数"
            android:textStyle="bold"
            android:inputType="number" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="算术运算:"
            android:textSize="20sp">

        </TextView>

        <Spinner
            android:id="@+id/operator"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:entries="@array/sign" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="操作数:"
            android:textSize="20sp" />

        <EditText
            android:id="@+id/secondNum"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="请输入数值操作数"
            android:textStyle="bold"
            android:inputType="number" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <Button
            android:id="@+id/calc"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="等于：" />

        <TextView
            android:id="@+id/result"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="5"
            android:hint="计算结果"
            android:padding="15dp"
            android:textColor="#F44336"
            android:textSize="25sp"
            android:textStyle="bold" />
    </LinearLayout>
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string-array name="sign">
        <item>请选择运算符</item>
        <item>+</item>
        <item>-</item>
        <item>*</item>
        <item>/</item>
    </string-array>
</resources>

package com.jld.homework;

import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    String op;

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

        Spinner spinner = (Spinner) this.findViewById(R.id.operator);//获取活动布局中的Spinner对象
        //为Spinner注册内部监听器对象
        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                //将Spinner选项的值赋值给成员变量op（保存算术运算符）
                op = ((TextView) view).getText().toString();
            }
            @Override
            public void onNothingSelected(AdapterView<?> parent) {
            }
        });

        //各类组件
        Button calcButton = findViewById(R.id.calc);
        EditText firstNum = findViewById(R.id.firstNum);
        EditText secondNum = findViewById(R.id.secondNum);
        TextView result = findViewById(R.id.result);

        //计算核心
        calcButton.setOnClickListener(v -> {
            switch (op) {
                case "+": {
                    double r = Double.parseDouble(firstNum.getText().toString()) + Double.parseDouble(secondNum.getText().toString());
                    result.setText(String.valueOf(r));
                    break;
                }
                case "-": {
                    double r = Double.parseDouble(firstNum.getText().toString()) - Double.parseDouble(secondNum.getText().toString());
                    result.setText(String.valueOf(r));
                    break;
                }
                case "*": {
                    double r = Double.parseDouble(firstNum.getText().toString()) * Double.parseDouble(secondNum.getText().toString());
                    result.setText(String.valueOf(r));
                    break;
                }
                case "/": {
                    double r = Double.parseDouble(firstNum.getText().toString()) / Double.parseDouble(secondNum.getText().toString());
                    result.setText(String.valueOf(r));
                    break;
                }
                default://非法情况报错
                    result.setText(R.string.ERROR);
                    break;
            }
        });
    }
}