Android 作业：简单计算器实现

image.png

思路

1. 首先设计界面，activity_main.xml
   计算器界面，需要：文本框TextView——显示数字；数字、符号按钮Button

<?xml version="1.0" encoding="utf-8"?>
<GridLayout  xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:rowCount="6"
    android:columnCount="4"
    >
    <!--文本标签-->
    <TextView
        android:id="@+id/text"
        android:layout_width="350dp"
        android:layout_height="wrap_content"
        android:layout_columnSpan="4"
        android:layout_marginLeft="4px"
        android:gravity="left"
        android:textSize="50dp" />
 
    <Button
        android:id="@+id/btnClear"
        android:layout_width="353dp"
        android:layout_height="wrap_content"
        android:layout_columnSpan="4"
        android:background="@color/colorAccent"
        android:text="清除"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn1"
        android:text="1"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn2"
        android:text="2"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn3"
        android:text="3"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btnPlus"
        android:background="@color/colorPrimary"
        android:text="+"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn4"
        android:text="4"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn5"
        android:text="5"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn6"
        android:text="6"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btnSubtract"
        android:background="@color/colorPrimary"
        android:text="-"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn7"
        android:text="7"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn8"
        android:text="8"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn9"
        android:text="9"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btnMultiply"
        android:background="@color/colorPrimary"
        android:text="*"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btnPoint"
        android:text="."
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btn0"
        android:text="0"
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btnSum"
        android:text="="
        android:textSize="26sp" />
 
    <Button
        android:id="@+id/btnDivide"
        android:background="@color/colorPrimary"
        android:text="/"
        android:textSize="26sp" />
</GridLayout>

2. 接下来是功能的实现，MainActivity.java
   给各个按钮注册点击事件、对输入内容的判断和计算等。

package com.example.asus.calculator;
 
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;
import android.view.View;
import android.view.View.OnClickListener;
 
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
 
    Button btn0,btn1,btn2,btn3,btn4,btn5,btn6,btn7,btn8,btn9,
            btnClear,btnPlus,btnSubtract,btnMultiply,btnDivide,btnSum,btnPoint;
    TextView text;
    String str = "";
    boolean clr_flag;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        btn0 = (Button) findViewById(R.id.btn0);
        btn1 = (Button) findViewById(R.id.btn1);
        btn2 = (Button) findViewById(R.id.btn2);
        btn3 = (Button) findViewById(R.id.btn3);
        btn4 = (Button) findViewById(R.id.btn4);
        btn5 = (Button) findViewById(R.id.btn5);
        btn6 = (Button) findViewById(R.id.btn6);
        btn7 = (Button) findViewById(R.id.btn7);
        btn8 = (Button) findViewById(R.id.btn8);
        btn9 = (Button) findViewById(R.id.btn9);
        btnClear = (Button) findViewById(R.id.btnClear);
        btnPlus = (Button) findViewById(R.id.btnPlus);
        btnSubtract = (Button) findViewById(R.id.btnSubtract);
        btnMultiply = (Button) findViewById(R.id.btnMultiply);
        btnDivide = (Button) findViewById(R.id.btnDivide);
        btnPoint = (Button) findViewById(R.id.btnPoint);
        btnSum = (Button) findViewById(R.id.btnSum);
 
        text = (TextView) findViewById(R.id.text) ;
 
        btn0.setOnClickListener(this);
        btn1.setOnClickListener(this);
        btn2.setOnClickListener(this);
        btn3.setOnClickListener(this);
        btn4.setOnClickListener(this);
        btn5.setOnClickListener(this);
        btn6.setOnClickListener(this);
        btn7.setOnClickListener(this);
        btn8.setOnClickListener(this);
        btn9.setOnClickListener(this);
        btnClear.setOnClickListener(this);
        btnPlus.setOnClickListener(this);
        btnSubtract.setOnClickListener(this);
        btnMultiply.setOnClickListener(this);
        btnDivide.setOnClickListener(this);
        btnPoint.setOnClickListener(this);
        btnSum.setOnClickListener(new click());
 
    }
 
    public void onClick(View v) {
        String input=text.getText().toString();
        switch (v.getId()){
            case   R.id.btn0:
            case   R.id.btn1:
            case   R.id.btn2:
            case   R.id.btn3:
            case   R.id.btn4:
            case   R.id.btn5:
            case   R.id.btn6:
            case   R.id.btn7:
            case   R.id.btn8:
            case   R.id.btn9:
            case   R.id.btnPoint:
                if(clr_flag){
                    clr_flag=false;
                    str="";
                    text.setText("");
                }
                text.setText(input+((Button)v).getText());
                break;
            case R.id.btnPlus:
            case R.id.btnSubtract:
            case R.id.btnMultiply:
            case R.id.btnDivide:
                if(clr_flag){
                    clr_flag=false;
                    input="";
                    text.setText("");
                }
                text.setText(input + " " + ((Button)v).getText() + " ");
                break;
            case R.id.btnClear:
                text.setText("");
                break;
        }
    }
    class click implements OnClickListener{
        public void onClick (View v) {
            getResult();//调用方法，计算结果
        }
    }
 
    private void getResult () {
        String str1 = text.getText().toString();
        if(str1 == null || str1.equals("")){
            return;
        }
        if(!str1.contains(" ")){
            return ;
        }
        if(clr_flag){
            clr_flag=false;
            return;
        }
        clr_flag=true;
        double result = 0;
//        运算符前的数字
        String s1 = str1.substring(0,str1.indexOf(" "));
//        运算符
        String op = str1.substring(str1.indexOf(" ")+1,str1.indexOf(" ")+2);
//        运算符后的数字
        String s2 = str1.substring(str1.indexOf(" ")+3);
//        判断
//        1. 如果s1、s2都不为空
        if(!s1.equals("")&&!s2.equals("")) {   //包含小数点运算
            double d1 = Double.parseDouble(s1);//则数字都是double类型
            double d2 = Double.parseDouble(s2);
            if (op.equals("+")) {   //如果是 +
                result = d1 + d2;
            } else if (op.equals("-")) {   //如果是 -
                result = d1 - d2;
            } else if (op.equals("*")) {   //如果是 *
                result = d1 * d2;
            } else if (op.equals("/")) {   //如果是 /
                if (d2 == 0) { //如果被除数是0
                    result = 0; //则结果是0
                }
                else {//否则执行正常是除法运算
                    result = d1 / d2;
                }
            }
            if (!s1.contains(".") && !s2.contains(".") && !op.equals("/")) {//如果是整数类型
                int r = (int) result; //都是整形
                text.setText(str1 + " = " + r + "");
            } else{
                text.setText(str1 + " = " + result + "");
            }
        }
//            如果s1不是空，s2是空
        else if(!s1.equals("")&&s2.equals("")){
            double d1 = Double.parseDouble(s1);
            if (op.equals("+")){
                result = d1;
            }
            if (op.equals("-")) {
                result = d1;
            }
            if (op.equals("*")) {
                result = 0;
            }
            if (op.equals("/")) {
                result = 0;
            }
            if(!s1.contains(".")) {
                int res = (int) result;
                text.setText(str1 + " = " + res+"");
            }else {
                text.setText(str1 + " = " + result+"");
            }
        }
//        如果s1是空，s2不是空
        else if(s1.equals("")&& !s2.equals("")){
            double d2 = Double.parseDouble(s2);
            if(op.equals("+")){
                result = 0+d2;
            }else if(op.equals("-")){
                result = 0-d2;
            }else if(op.equals("*")){
                result = 0;
            }else if(op.equals("/")){
                result = 0;
            }
            if(!s1.contains(".") && !s2.contains(".")){
                int res = (int) result;
                text.setText(str1 + " = " + res + "");
            }else{
                text.setText(str1 + " = " + result + "");
            }
        }else{
            text.setText("");
        }
    }
}