编写一个简易计算器（安卓开发）

编写一个简单的计算器，界面参考课本，实现简单的加减乘除运算。

//activity_main.xml   界面设置





    

    
    

    

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

package com.example.counter;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import java.math.BigDecimal;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    Button btn_0;                   //数字按钮
    Button btn_1;
    Button btn_2;
    Button btn_3;
    Button btn_4;
    Button btn_5;
    Button btn_6;
    Button btn_7;
    Button btn_8;
    Button btn_9;
    Button btn_equal;            //运算符按钮
    Button btn_add;
    Button btn_minus;
    Button btn_mul;
    Button btn_divide;
    Button btn_point;               //小数点按钮
    Button btn_delete;
    Button btn_clear;
    EditText et_input;
    boolean clear_flag;  //清空标识

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn_0 = (Button) findViewById(R.id.btn_0);
        btn_1 = (Button) findViewById(R.id.btn_1);
        btn_2 = (Button) findViewById(R.id.btn_2);
        btn_3 = (Button) findViewById(R.id.btn_3);
        btn_4 = (Button) findViewById(R.id.btn_4);
        btn_5 = (Button) findViewById(R.id.btn_5);
        btn_6 = (Button) findViewById(R.id.btn_6);
        btn_7 = (Button) findViewById(R.id.btn_7);
        btn_8 = (Button) findViewById(R.id.btn_8);
        btn_9 = (Button) findViewById(R.id.btn_9);
        btn_point = (Button) findViewById(R.id.btn_point);
        btn_add = (Button) findViewById(R.id.btn_add);
        btn_clear = (Button) findViewById(R.id.btn_clear);
        btn_delete = (Button) findViewById(R.id.btn_delete);
        btn_divide = (Button) findViewById(R.id.btn_divide);
        btn_equal = (Button) findViewById(R.id.btn_equal);
        btn_minus = (Button) findViewById(R.id.btn_minus);
        btn_mul = (Button) findViewById(R.id.btn_mul);      //实例化按钮
        et_input = (EditText) findViewById(R.id.et_input);          //实例化显示屏

        btn_0.setOnClickListener(this);      //设置按钮的点击事件
        btn_1.setOnClickListener(this);
        btn_2.setOnClickListener(this);
        btn_3.setOnClickListener(this);
        btn_4.setOnClickListener(this);
        btn_5.setOnClickListener(this);
        btn_6.setOnClickListener(this);
        btn_7.setOnClickListener(this);
        btn_8.setOnClickListener(this);
        btn_9.setOnClickListener(this);
        btn_point.setOnClickListener(this);
        btn_add.setOnClickListener(this);
        btn_clear.setOnClickListener(this);
        btn_divide.setOnClickListener(this);
        btn_delete.setOnClickListener(this);
        btn_equal.setOnClickListener(this);
        btn_mul.setOnClickListener(this);
        btn_minus.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {                   //设置触发器
        String str = et_input.getText().toString();
        switch (v.getId()) {
            case R.id.btn_0:
            case R.id.btn_1:
            case R.id.btn_2:
            case R.id.btn_3:
            case R.id.btn_4:
            case R.id.btn_5:
            case R.id.btn_6:
            case R.id.btn_7:
            case R.id.btn_8:
            case R.id.btn_9:
            case R.id.btn_point:
                if (clear_flag) {
                    clear_flag = false;
                    str = "";
                    et_input.setText("");
                }
                et_input.setText(str + ((Button) v).getText());
                break;
            case R.id.btn_add:
            case R.id.btn_minus:
            case R.id.btn_mul:
            case R.id.btn_divide:
                if (clear_flag) {
                    clear_flag = false;
                    str = "";
                    et_input.setText("");
                }
                et_input.setText(str + " " + ((Button) v).getText() + " ");
                break;

            case R.id.btn_delete:
                if (clear_flag) {
                    clear_flag = false;
                    str = "";
                    et_input.setText("");
                } else if (str != null && !str.equals("")) {

                    et_input.setText(str.substring(0, str.length() - 1));
                }
                break;

            case R.id.btn_clear:
                clear_flag = false;
                str = "";
                et_input.setText("");

            case R.id.btn_equal:
                getResult();
                break;
        }
    }

    private void getResult() {
        String exp = et_input.getText().toString();
        if (exp == null || exp.equals("")) {
            return;
        }
        if (!exp.contains(" ")) {
            return;
        }
        if (clear_flag) {
            clear_flag = false;
            return;
        }

        clear_flag = true;
        double result=0;
        String s1 = exp.substring(0, exp.indexOf(" "));  //运算符前面的字符串
        String op = exp.substring(exp.indexOf(" ") + 1, exp.indexOf(" ") + 2);//获取运算符
        String s2 = exp.substring(exp.indexOf(" ") + 3);  //获取运算符后面的字符串
        
        double d1 = Double.parseDouble(s1);     //将字符串转化为双精度数值
        double d2 = Double.parseDouble(s2);

        if (op.equals("+")) {
            result =d1 + d2;
        } else if (op.equals("-")) {
            result = result = d1 - d2;
        } else if (op.equals("×")) {
            result =result = d1 * d2;
        } else if (op.equals("÷")) {
            if (d2 == 0) {
                result = 0;
            } else {
             result = d1 / d2;
            }
        }
        et_input.setText(result+"");
    }
}