How to add +/- functionality to a butting in kotli

问题:

I need to add new button with functionality of +/-. If user clicks the button for the first time the value should return -> "-" (ex => -123), if the user clicks again value "-" should be removed (ex => 123). The functionality is similar as +/- button in the calculator.

Here is my code

Activity.kt file

 package com.tripbegins.calculator
 import android.support.v7.app.AppCompatActivity
 import android.os.Bundle
 import android.view.View
 import android.widget.Button
 import com.tripbegins.calculator.R.id.*
 import kotlinx.android.synthetic.main.activity_main.*

 class MainActivity : AppCompatActivity() {

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

var emptyText = true
fun numberEvents(view: View) {
var checkButton:Boolean = false
if(emptyText){
    viewResult.setText("")
}
emptyText = false

var button = view as Button
var isClicked = viewResult.text.toString()
when (button.id) {
    buttonOne.id -> isClicked += "1"
    buttonTwo.id -> isClicked += "2"
    buttonThree.id -> isClicked += "3"
    dotButton.id-> isClicked+="."
}

viewResult.setText(isClicked)
 }

var operation ="+"
var oldValues:String? = null

fun mathOperation(view: View){
var mathButton = view as Button
var isClicked = viewResult.text.toString()

when(mathButton.id){
    plusButton.id-> {
        operation = "+"
    }
    minusButton.id->{
        operation="-"
    }
    mulButton.id->{
        operation="*"
    }

}
oldValues = viewResult.text.toString()
emptyText = true
 }

 fun Calculate(view: View){

var newValues = viewResult.text.toString()
var calulateButton:Double? = null
when(operation){
    "+"-> { calulateButton = oldValues!!.toDouble() + 
newValues.toDouble() }
    "-"-> { calulateButton = oldValues!!.toDouble() - 
newValues.toDouble() }
    "*"-> { calulateButton = oldValues!!.toDouble() * 
newValues.toDouble() }

}
viewResult.setText(calulateButton.toString())
emptyText=true
 }
 fun clearFunction(view: View){
viewResult.setText("")
 }
 }

activity.xml file

<?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="com.tripbegins.calculator.MainActivity">

<EditText
android:id="@+id/viewResult"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="42dp"
android:ems="10"
android:gravity="bottom|right"
android:inputType="textPersonName"
android:text="0"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />

<Button
android:id="@+id/buttonTwo"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="76dp"
android:onClick="numberEvents"
android:text="2"
app:layout_constraintStart_toEndOf="@+id/buttonOne"
app:layout_constraintTop_toBottomOf="@+id/viewResult" />

<Button
android:id="@+id/plusButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="38dp"
android:onClick="mathOperation"
android:text="+"
app:layout_constraintBaseline_toBaselineOf="@+id/minusButton"
app:layout_constraintStart_toStartOf="parent" />

<Button
android:id="@+id/minusButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="12dp"
android:layout_marginTop="33dp"
android:onClick="mathOperation"
android:text="-"
app:layout_constraintStart_toEndOf="@+id/plusButton"
app:layout_constraintTop_toBottomOf="@+id/buttonTwo" />

<Button
android:id="@+id/mulButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="26dp"
android:onClick="mathOperation"
android:text="*"
app:layout_constraintBaseline_toBaselineOf="@+id/minusButton"
app:layout_constraintStart_toEndOf="@+id/minusButton" />

<Button
android:id="@+id/calButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="44dp"
android:onClick="Calculate"
android:text="Calculate"
app:layout_constraintStart_toStartOf="@+id/minusButton"
app:layout_constraintTop_toBottomOf="@+id/minusButton" />

<Button
android:id="@+id/buttonThree"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="26dp"
android:onClick="numberEvents"
android:text="3"
app:layout_constraintBaseline_toBaselineOf="@+id/buttonTwo"
app:layout_constraintStart_toEndOf="@+id/buttonTwo" />

<Button
android:id="@+id/buttonOne"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="34dp"
android:onClick="numberEvents"
android:text="1"
app:layout_constraintBaseline_toBaselineOf="@+id/buttonTwo"
app:layout_constraintStart_toStartOf="parent" />

<Button
android:id="@+id/dotButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="22dp"
android:onClick="numberEvents"
android:text="."
app:layout_constraintBaseline_toBaselineOf="@+id/calButton"
app:layout_constraintEnd_toStartOf="@+id/calButton" />

<Button
android:id="@+id/clearButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="11dp"
android:onClick="clearFunction"
android:text="Clear"
app:layout_constraintBaseline_toBaselineOf="@+id/calButton"
app:layout_constraintStart_toEndOf="@+id/calButton" />
</android.support.constraint.ConstraintLayout>

Updated Activity.kt file I have updated the code for the =/-. Added the var outside the function

  var emptyText = true
  var isMinusPrinted=false
  fun numberEvents(view: View)

**Current result**

If button clicked for the first time value => -123
If button clicked for the second time value => -123
If button clicked for the third time value => --123

**Expected Result**
If button clicked for the first time value => -123
If button clicked for the second time value => 123
If button clicked for the third time value => -123

Updated activity.kt file

package com.tripbegins.calculator
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import com.tripbegins.calculator.R.id.*
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.android.synthetic.main.activity_main.view.*

class MainActivity : AppCompatActivity() {

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

    var emptyText = true
    var isMinusPrinted=false
    fun numberEvents(view: View) { 
        if(emptyText){
            viewResult.setText("")
        }
        emptyText = false
        var button = view as Button
        var plusMinusCheck =""
        var isClicked = viewResult.text.toString()

        when (button.id) {


            buttonOne.id -> isClicked += "1"
            buttonTwo.id -> isClicked += "2"
            buttonThree.id -> isClicked += "3"

            dotButton.id -> {
                isClicked += "."
                dotButton.isClickable = false //**add this line here**
            }
            plusMinusBtn.id->{

                var resultWithoutMinus=isClicked//ex: 123
                if(!isMinusPrinted){

                    isClicked = "-" + resultWithoutMinus//this line for 
    example give result like: -123
                    isMinusPrinted=true
                }
                else{
                    isClicked=resultWithoutMinus //result became : 123
                    isMinusPrinted=false
                }

            }



        }

            viewResult.setText(isClicked)
    }



    var operation ="+"
    var oldValues:String? = null

    fun mathOperation(view: View){
        var mathButton = view as Button
        var isClicked = viewResult.text.toString()

        when(mathButton.id){
            plusButton.id-> {
                operation = "+"
            }
            minusButton.id->{
                operation="-"
            }
            mulButton.id->{
                operation="*"
            }

        }
        oldValues = viewResult.text.toString()
        emptyText = true
        dotButton.isClickable=true//**add this line here**

    }

    fun Calculate(view: View){

        var newValues = viewResult.text.toString()
        var calulateButton:Double? = null

        when(operation){
            "+"-> { calulateButton = oldValues!!.toDouble() + 
newValues.toDouble() }
            "-"-> { calulateButton = oldValues!!.toDouble() - 
newValues.toDouble() }
            "*"-> { calulateButton = oldValues!!.toDouble() * 
newValues.toDouble() }

        }
        viewResult.setText(calulateButton.toString())
        emptyText=true
        dotButton.isClickable=true //**add this line here**
    }
    fun clearFunction(view: View){
        viewResult.setText("")
        dotButton.isClickable=true //**add this line here**
    }
}

Updated the xml file for the button -> +/-

<Button
android:id="@+id/plusMinusBtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="52dp"
android:layout_marginStart="38dp"
android:onClick="numberEvents"
android:text="+/-"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent" />

回答1:

Edit:

    var emptyText = true
    var isMinusPrinted=false//add this line here
    fun numberEvents(view: View) {
    var checkButton:Boolean = false
    if(emptyText){
        viewResult.setText("")
    }
    emptyText = false

    var button = view as Button
    var isClicked = viewResult.text.toString()
    when (button.id) {
        buttonOne.id -> isClicked += "1"
        buttonTwo.id -> isClicked += "2"
        buttonThree.id -> isClicked += "3"
        dotButton.id-> isClicked+="."
        plusMinusBtn.id->{//add this block of code from here

        var resultWithoutMinus=Math.abs(isClicked.toInt()) //ex: 123


        if(!isMinusPrinted){

            isClicked = "-" + resultWithoutMinus//this line for example give result like: -123
            isMinusPrinted=true
        }
        else{
            isClicked=resultWithoutMinus //result became : 123
            isMinusPrinted=false
        }

}//to here

    }

    viewResult.setText(isClicked)
     }