[Android] 간단한 계산기 어플 만들기

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/tvInput"
        android:layout_width="match_parent"
        android:layout_height="250dp"
        android:background="@color/light_gray"
        android:padding="10dp"
        android:textSize="40dp"
        android:text=""
        android:gravity="right|bottom"
        />
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:layout_margin="0dp">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:orientation="horizontal">

            <Button
                android:id="@+id/btnOne"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_margin="2dp"
                android:layout_weight="1"
                android:onClick="onDigit"
                android:text="@string/_1" />

            <Button
                android:id="@+id/btnTwo"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_margin="2dp"
                android:layout_weight="1"
                android:onClick="onDigit"
                android:text="@string/_2" />

            <Button
                android:id="@+id/btnThree"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_margin="2dp"
                android:layout_weight="1"
                android:onClick="onDigit"
                android:text="@string/_3" />

            <Button
                android:id="@+id/btnSubtract"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_margin="2dp"
                android:layout_weight="1"
                android:onClick="onOperator"
                android:text="@string/minus" />
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:layout_weight="1"
            >
            <Button
                android:id="@+id/btnFour"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_4"/>
            <Button
                android:id="@+id/btnFive"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_5"/>
            <Button
                android:id="@+id/btnSix"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_6"/>
            <Button
                android:id="@+id/btnMultiply"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onOperator"
                android:text="@string/multiply"/>
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:layout_weight="1"
            >
            <Button
                android:id="@+id/btnSeven"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_7"/>
            <Button
                android:id="@+id/btnEight"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_8"/>
            <Button
                android:id="@+id/btnNine"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_9"/>
            <Button
                android:id="@+id/btnDivide"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onOperator"
                android:text="@string/div"/>
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:layout_weight="1"
            >
            <Button
                android:id="@+id/btnDot"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDecimalPoint"
                android:text="."/>
            <Button
                android:id="@+id/btnZero"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="0"/>
            <Button
                android:id="@+id/btnClr"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onClear"
                android:text="CLR"/>
            <Button
                android:id="@+id/btnAdd"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onOperator"
                android:text="+"/>
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:layout_weight="1"
            >
            <Button
                android:id="@+id/btnEqaul"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="2"
                android:layout_margin="2dp"
                android:onClick="onEqaul"
                android:text="="/>
        </LinearLayout>

    </LinearLayout>


</LinearLayout>

 

MainActivity.kt

package com.example.mycalculator

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.TextView
import android.widget.Toast
import java.lang.ArithmeticException

class MainActivity : AppCompatActivity() {

    private var tvInput: TextView? = null
    var lastNumeric : Boolean = false
    var lastDot : Boolean = false

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        tvInput = findViewById(R.id.tvInput)
    }

    fun onDigit(view:View){
        tvInput?.append((view as Button).text)
        lastNumeric = true
        Toast.makeText(this, "Button clicked", Toast.LENGTH_LONG).show()
    }

    fun onDecimalPoint(view:View){
        if(lastNumeric && !lastDot){
            tvInput?.append(".")
            lastNumeric = false
            lastDot = true
        }
    }

    fun onClear(view: View){
        tvInput?.text = ""
    }

    fun onOperator(view: View){
        tvInput?.text?.let {
            if (lastNumeric && !isOperatorAdded(it.toString())){
                tvInput?.append((view as Button).text)
                lastNumeric = false
                lastDot = false
            }
        }
    }

    fun onEqaul(view : View){
        if(lastNumeric){
            var tvValue = tvInput?.text.toString()
            var prefix = ""
            try{
                if(tvValue.startsWith("-")){
                    prefix = "-"
                    tvValue = tvValue.substring(1)
                }
                if(tvValue.contains("-")){
                    val splitValue = tvValue.split("-")
                    var one = splitValue[0]
                    var two = splitValue[1]

                    if(prefix.isNotEmpty()){
                        one = prefix + one
                    }

                    tvInput?.text = removeZeroAfterDot((one.toDouble() - two.toDouble()).toString())
                } else if(tvValue.contains("+")){
                    val splitValue = tvValue.split("+")
                    var one = splitValue[0]
                    var two = splitValue[1]

                    if(prefix.isNotEmpty()){
                        one = prefix + one
                    }

                    tvInput?.text = removeZeroAfterDot((one.toDouble() + two.toDouble()).toString())
                }else if(tvValue.contains("*")){
                    val splitValue = tvValue.split("*")
                    var one = splitValue[0]
                    var two = splitValue[1]

                    if(prefix.isNotEmpty()){
                        one = prefix + one
                    }

                    tvInput?.text = removeZeroAfterDot((one.toDouble() * two.toDouble()).toString())
                }else if(tvValue.contains("/")){
                    val splitValue = tvValue.split("/")
                    var one = splitValue[0]
                    var two = splitValue[1]

                    if(prefix.isNotEmpty()){
                        one = prefix + one
                    }

                    tvInput?.text = removeZeroAfterDot((one.toDouble() / two.toDouble()).toString())
                }
            }catch(e: ArithmeticException){
                e.printStackTrace()
            }
        }
    }

    private fun removeZeroAfterDot(result: String) : String{
        var value = result
        if(result.contains(".0"))
            value = result.substring(0, result.length-2)

        return value
    }


    private fun isOperatorAdded(value : String) : Boolean{
        return if(value.startsWith("-")){
            false
        }else{
            value.contains("/") || value.contains("*") || value.contains("+") || value.contains("-")
        }
    }

}