一个简易的计算器，边学边写，还有很多不足希望多多指教

先看布局，整体线性布局，上面两个TextView，一个存放计算过程，一个给出结果，然后一个table布局，button没有声明在xml里，用Java写的，好处是比较方便，坏处是我不会怎么让button适应屏幕，看起来有点丑。

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
  

    <LinearLayout
        android:id="@+id/linearLayout"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginTop="8dp"
        android:orientation="vertical"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <TextView
            android:id="@+id/textView1"
            android:layout_width="382dp"
            android:layout_height="67dp"
            android:layout_columnSpan="4"
            android:layout_gravity="right"
            android:layout_marginLeft="4px"
            android:layout_marginRight="4px"
            android:background="#eee"
            android:padding="5px"
            android:textColor="#000" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="382dp"
            android:layout_height="67dp"
            android:layout_columnSpan="4"
            android:layout_gravity="right"
            android:layout_marginLeft="4px"
            android:layout_marginRight="4px"
            android:background="#eee"
            android:padding="5px"
            android:textColor="#000" />

        <Button
            android:id="@+id/buttonclear"
            android:layout_width="match_parent"
            android:layout_height="60dp"
            android:layout_columnSpan="4"
            android:text="clear" />

        <TableLayout
            android:id="@+id/tablelayout"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
        </TableLayout>
    </LinearLayout>

</android.support.constraint.ConstraintLayout>

然后看Java部分，我用数组button建立在TableRow上，再加入TextView，同时监听方式是独立类（外部类）实现事件监听

package com.example.w.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TableLayout;
import android.widget.TableRow;
import android.widget.TextView;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    


    String[] strs = {
    "7", "8", "9", "/",
            "4", "5", "6", "-",
            "1", "2", "3", "+",
            ".", "0", "*", "="
    };
    TextView thequestion;
    TextView theanswer;
    Button butt;
    private StringBuilder sb = new StringBuilder();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }
    
    class mOnClickListener implements View.OnClickListener {
    
        @Override
        public void onClick(View view) {
    
            sb.append(((Button) view).getText().toString());
            thequestion.setText(sb);
        }
    }
    
    public double Count()
    {
    
        Character op='+';
        sb=sb.deleteCharAt(sb.length()-1);
       int j=0;
        for (int i=0;i<sb.length();i++) {
    
            switch (sb.charAt(i)) {
    
                case '+':
                case '-':
                case '*':
                case '/':op=sb.charAt(i);j=i;break;
                default:
                    break;
            }
        }
        String front=sb.substring(0,j);
        String back=sb.substring(j+1,sb.length());
        double res=0;

        switch (op) {
    
            case '+':res= Double.parseDouble(front)+Double.parseDouble(back);break;
            case '-':res= Double.parseDouble(front)-Double.parseDouble(back);break;
            case '*':res= Double.parseDouble(front)*Double.parseDouble(back);break;
            case '/':res= Double.parseDouble(front)/Double.parseDouble(back);break;
            default:
                break;
        }

        return res;
    }
    
    public void initView() {
    
        TableLayout  TableLayout=( TableLayout)findViewById(R.id.tablelayout);
        thequestion=findViewById(R.id.textView1);
        theanswer=findViewById(R.id.textView2);
        butt=findViewById(R.id.buttonclear);
        butt=findViewById(R.id.buttonclear);
        butt.setOnClickListener(new View.OnClickListener()//clear按钮初始化
        {
    
            public void onClick(View view) {
    
                thequestion.setText("");
                theanswer.setText("");
                sb=new StringBuilder();
            }
        });
        Button[] b = new Button[strs.length];
        int k=0;

//        TableRow []row = { findViewById(R.id.tablerow1), findViewById(R.id.tablerow2),findViewById(R.id.tablerow3), findViewById(R.id.tablerow4)
//        };
        for (int i = 0; i < 4; i++) {
    
            TableRow row=new TableRow(getApplicationContext());
//            row.setMinimumHeight(120);
            for (int j = 0; j < 4; j++) {
    
                    b[k] = new Button(getApplicationContext());
                    b[k].setText(strs[k]);
                    if(k==strs.length-1)//“=”单独处理
                    {
    
                        b[k].setOnClickListener(new mOnClickListener() {
    
                            public void onClick(View view) {
    
                                super.onClick(view);
                                theanswer.setText(Count()+"");//结果输出
                            }
                        });
                    }
                    else {
    
                        b[k].setOnClickListener(new mOnClickListener() {
    
                        });
                    }
                    row.addView(b[k]);
                     k++;
            }
            TableLayout.addView(row);
        }
    }

}

计算部分等于是计算StringBuilder里的一串式子，先去掉最后加入的等号，再寻找运算符，将两边的数字分开。
这个计算器没有考虑到带括号的运算和各种非常规使用的情况，后面有时间再完善。