Android开发应用案例——简易计算器（附完整源码）

Android开发-AS学习（一）

Android开发-AS学习（二）

使用Android studio开发简易计算器app（完整源码可在博主资源中自行下载）

最终效果：

开发步骤：

1. 创建一个名为calculator的新项目

2. 编写代码

项目目录

MyTextView文件

package com.example.calculator.my_control;import android.content.Context;import android.graphics.canvas;import android.graphics.Color;import android.graphics.Paint;import android.util.AttributeSet;import androidx.annotation.NonNull;import androidx.annotation.Nullable;public class MyTextView extends androidx.appcompat.widget.AppCompatTextView {    Paint paint = new Paint();//创建一个paint对象    public MyTextView(@NonNull Context context, @Nullable AttributeSet attrs) {        super(context, attrs);//构造函数    }    @Override//重写方法    protected void onDraw(Canvas canvas){        super.onDraw(canvas);        paint.setColor(Color.BLACK);//设置paint的颜色        //绘制边框        canvas.drawLine(0,0,this.getWidth(),0,paint);//绘制上方的边框        canvas.drawLine(0,this.getHeight()-1,this.getWidth(),this.getHeight()-1,paint);//绘制下方的边框(因为会被遮挡，所以需要-1）        canvas.drawLine(0,0,0,this.getHeight(),paint);//绘制左边的边框        canvas.drawLine(this.getWidth()-1,0,this.getWidth()-1,this.getHeight(),paint);//绘制右边的边框(因为会被遮挡，所以需要-1）    }}

MainActivity文件

package com.example.calculator;import androidx.appcompat.app.AppCompatActivity;import androidx.databinding.DataBindingUtil;import androidx.lifecycle.Observer;import androidx.lifecycle.ViewModelProvider;import android.database.DatabaseUtils;import android.os.Bundle;import android.view.View;import com.example.calculator.databinding.ActivityMainBinding;public class MainActivity extends AppCompatActivity {    private ActivityMainBinding binding;//组件存储类    private MyViewModel myViewModel;//数据模型    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);//获取所有控件        myViewModel = new ViewModelProvider(this,new ViewModelProvider.NewInstanceFactory()).get(MyViewModel.class);//获取数据模型        //事件监听        myViewModel.getMainNum().observe(this, new Observer() {            @Override            public void onChanged(String s) {//监听 mainNum数据发生改变的监听                binding.myTextView.setText(myViewModel.getMainNum().getValue());//让 myTextView显示mainNum的数值，也就是计算器中的输入框显示数值                if (myViewModel.sign2.equals("")){                    if (myViewModel.sign1.equals("")){                        binding.textView2.setText(myViewModel.getMainNum().getValue());//让 textView显示式子，也就是输入框上面的小框显示计算式                    }                    else {//如果是像a + b这种形式的式子时                        binding.textView2.setText(myViewModel.num[0] + myViewModel.sign1 + myViewModel.getMainNum().getValue());                    }                }                else {//如果是像a+b*c这种形式的式子的时候                    binding.textView2.setText(myViewModel.num[0] + myViewModel.sign1 + myViewModel.num[1] + myViewModel.sign2 + myViewModel.getMainNum().getValue());                }            }        });        binding.button0.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("0");            }        });        binding.button1.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("1");            }        });        binding.button2.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("2");            }        });        binding.button3.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("3");            }        });        binding.button4.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("4");            }        });        binding.button5.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("5");            }        });        binding.button6.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("6");            }        });        binding.button7.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("7");            }        });        binding.button8.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("8");            }        });        binding.button9.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.setMainNum("9");            }        });        //给小数点按钮的监听        binding.button15.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                if (!myViewModel.havePoint){                    myViewModel.getMainNum().setValue(myViewModel.getMainNum().getValue()+".");                    myViewModel.havePoint=true;                }            }        });        //给加号按钮的监听        binding.button11.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                if (myViewModel.sign1.equals("")){                    myViewModel.sign1="+";                    myViewModel.num[0] = myViewModel.getMainNum().getValue();                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint=false;                }                else if (myViewModel.sign2.equals("")){//如果是像a+b这种形式的式子时                    myViewModel.num[0] = myViewModel.mainNumWithNum_0_Tocal();                    myViewModel.sign1="+";                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint = false;                }                else {//如果是像a+b*c这种形式的式子时                    myViewModel.getMainNum().setValue(myViewModel.mainNumWith_Num_1_Tocal());                    myViewModel.sign2="";                    myViewModel.num[1] = "";                    myViewModel.num[0] = myViewModel.mainNumWithNum_0_Tocal();                    myViewModel.sign1 = "+";                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint = false;                }            }        });        //给减号设置监听        binding.button12.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                if (myViewModel.sign1.equals("")){                    myViewModel.sign1="-";                    myViewModel.num[0] = myViewModel.getMainNum().getValue();                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint=false;                }                else if (myViewModel.sign2.equals("")){//如果是像a-b这种形式的式子时                    myViewModel.num[0] = myViewModel.mainNumWithNum_0_Tocal();                    myViewModel.sign1="-";                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint = false;                }                else {//如果是像a-b*c这种形式的式子时                    myViewModel.getMainNum().setValue(myViewModel.mainNumWith_Num_1_Tocal());                    myViewModel.sign2="";                    myViewModel.num[1] = "";                    myViewModel.num[0] = myViewModel.mainNumWithNum_0_Tocal();                    myViewModel.sign1 = "-";                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint = false;                }            }        });        //给乘号设置监听        binding.button13.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                if (myViewModel.sign1.equals("")){                    myViewModel.sign1 = "*";                    myViewModel.num[0] = myViewModel.getMainNum().getValue();                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint = false;                }                else if (myViewModel.sign2.equals("")){                    if (myViewModel.sign1.equals("*") || myViewModel.sign1.equals("/")){//按顺序进行计算                        myViewModel.num[0] = myViewModel.mainNumWithNum_0_Tocal();                        myViewModel.sign1="*";                        myViewModel.getMainNum().setValue("0");                        myViewModel.havePoint = false;                    }                    else {//如果sign1是减号或者加号时                        myViewModel.num[1] = myViewModel.getMainNum().getValue();                        myViewModel.sign2 = "*";                        myViewModel.getMainNum().setValue("0");                        myViewModel.havePoint = false;                    }                }                else {//如果像a+b*c形式的式子时                    myViewModel.num[1] = myViewModel.mainNumWith_Num_1_Tocal();                    myViewModel.sign2 = "*";                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint = false;                }            }        });        //给除号设置监听        binding.button14.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                if (myViewModel.sign1.equals("")){                    myViewModel.sign1 = "/";                    myViewModel.num[0] = myViewModel.getMainNum().getValue();                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint = false;                }                else if (myViewModel.sign2.equals("")){                    if (myViewModel.sign1.equals("*") || myViewModel.sign1.equals("/")){//按顺序进行计算                        myViewModel.num[0] = myViewModel.mainNumWithNum_0_Tocal();                        myViewModel.sign1="/";                        myViewModel.getMainNum().setValue("0");                        myViewModel.havePoint = false;                    }                    else {//如果sign1是减号或者加号时                        myViewModel.num[1] = myViewModel.getMainNum().getValue();                        myViewModel.sign2 = "/";                        myViewModel.getMainNum().setValue("0");                        myViewModel.havePoint = false;                    }                }                else {//如果像a+b/c形式的式子时                    myViewModel.num[1] = myViewModel.mainNumWith_Num_1_Tocal();                    myViewModel.sign2 = "/";                    myViewModel.getMainNum().setValue("0");                    myViewModel.havePoint = false;                }            }        });        //给 清空 设置监听        binding.button17.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                myViewModel.sign2 = "";                myViewModel.num[1] = "";                myViewModel.sign1 = "";                myViewModel.num[0] = "";                myViewModel.getMainNum().setValue("0");                myViewModel.havePoint = false;            }        });        //给 计算按钮 设置监听        binding.button16.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                if (myViewModel.sign2.equals("")){                    if (!myViewModel.sign1.equals("")){                        myViewModel.getMainNum().setValue(myViewModel.mainNumWithNum_0_Tocal());                        if (myViewModel.getMainNum().getValue().contains(".")){//判断是否包含小数点myViewModel.havePoint = true;                        }                        else myViewModel.havePoint = false;                        myViewModel.num[0]="";                        myViewModel.sign1 = "";                    }                }                else {//如果是像 a+b*c 这种形式的式子时                    myViewModel.getMainNum().setValue(myViewModel.mainNumWith_Num_1_Tocal());                    myViewModel.num[1] = "";                    myViewModel.sign2 = "";                    myViewModel.getMainNum().setValue(myViewModel.mainNumWithNum_0_Tocal());                    if (myViewModel.getMainNum().getValue().contains(".")){//判断是否包含小数点                        myViewModel.havePoint = true;                    }                    else myViewModel.havePoint = false;                    myViewModel.num[0]="";                    myViewModel.sign1 = "";                }                binding.textView2.setText(myViewModel.num[0] + myViewModel.sign1 + myViewModel.getMainNum().getValue());            }        });        //给 退格按钮 设置监听        binding.imageButton.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                if (!myViewModel.getMainNum().getValue().equals("0")){                    myViewModel.getMainNum().setValue(myViewModel.getMainNum().getValue().substring(0,myViewModel.getMainNum().getValue().length()-1));//不为空，长度减1                    if (myViewModel.getMainNum().getValue().equals("")){                        myViewModel.getMainNum().setValue("0");//如果为空，将其设为0                    }                }            }        });    }}

MyViewModel

package com.example.calculator;import androidx.lifecycle.MutableLiveData;import androidx.lifecycle.ViewModel;//用来存储一些数据模型public class MyViewModel extends ViewModel {    private MutableLiveData mainNum;//主数值（用户正在操作的数）    public boolean havePoint =false;//用于记录主数值中是否包含小数点    public String sign1 = "",sign2 = "";//用于存储运算符号    public String num[]={"",""};//用于存储参与计算的数值    public MutableLiveData getMainNum(){        if (mainNum == null){            mainNum = new MutableLiveData<>();            mainNum.setValue("0");        }        return mainNum;    }    public void setMainNum(String n ){        if (mainNum.getValue().equals("0")){            mainNum.setValue(n);        }        else {            mainNum.setValue(mainNum.getValue() + n);        }    }    public String mainNumWithNum_0_Tocal(){        String value = "0";        if (mainNum.getValue().contains(".") || num[0].contains(".")) {//如果两个数的其中一个有小数点的运算            switch (sign1){                case "+":                    value = String.valueOf(Double.valueOf(num[0]) + Double.valueOf(mainNum.getValue()));                    break;                case "-":                    value = String.valueOf(Double.valueOf(num[0]) - Double.valueOf(mainNum.getValue()));                    break;                case "*":                    value = String.valueOf(Double.valueOf(num[0]) * Double.valueOf(mainNum.getValue()));                    break;                case "/":                    if (mainNum.getValue().equals("0")){                        mainNum.setValue("1");                    }                    value = String.valueOf(Double.valueOf(num[0]) / Double.valueOf(mainNum.getValue()));            }        }        else {            switch (sign1){//如果没有小数点则为整数运算                case "+":                    value = String.valueOf(Integer.valueOf(num[0]) + Integer.valueOf(mainNum.getValue()));                    break;                case "-":                    value = String.valueOf(Integer.valueOf(num[0]) - Integer.valueOf(mainNum.getValue()));                    break;                case "*":                    value = String.valueOf(Integer.valueOf(num[0]) * Integer.valueOf(mainNum.getValue()));                    break;                case "/"://除号依旧为小数运算方式                    if (mainNum.getValue().equals("0")){                        mainNum.setValue("1");                    }                    value = String.valueOf(Double.valueOf(num[0]) / Double.valueOf(mainNum.getValue()));            }        }        return value;    }    public String mainNumWith_Num_1_Tocal(){        String value = "0";        if (mainNum.getValue().contains(".") || num[0].contains(".")) {//如果两个数的其中一个有小数点的运算            switch (sign2){                case "*":                    value = String.valueOf(Double.valueOf(num[1]) * Double.valueOf(mainNum.getValue()));                    break;                case "/":                    if (mainNum.getValue().equals("0")){                        mainNum.setValue("1");                    }                    value = String.valueOf(Double.valueOf(num[1]) / Double.valueOf(mainNum.getValue()));            }        }        else {            switch (sign2){//如果没有小数点则为整数运算                case "*":                    value = String.valueOf(Integer.valueOf(num[1]) * Integer.valueOf(mainNum.getValue()));                    break;                case "/"://除号依旧为小数运算方式                    if (mainNum.getValue().equals("0")){                        mainNum.setValue("1");                    }                    value = String.valueOf(Double.valueOf(num[1]) / Double.valueOf(mainNum.getValue()));            }        }        return value;    }}

activity_main.xml

补充：

1、在drawable中引入backspace矢量图

2、在build.gradle文件中添加dataBinding{enabled true}代码

来源地址：https://blog.csdn.net/beiye_/article/details/128649689