I copy pasted a code in android studio. Which is as follows
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
// creating variables for our text view and button
lateinit var tvsec: TextView
lateinit var tvMain: TextView
lateinit var bac: Button
lateinit var bc: Button
lateinit var bbrac1: Button
lateinit var bbrac2: Button
lateinit var bsin: Button
lateinit var bcos: Button
lateinit var btan: Button
lateinit var blog: Button
lateinit var bln: Button
lateinit var bfact: Button
lateinit var bsquare: Button
lateinit var bsqrt: Button
lateinit var binv: Button
lateinit var b0: Button
lateinit var b9: Button
lateinit var b8: Button
lateinit var b7: Button
lateinit var b6: Button
lateinit var b5: Button
lateinit var b4: Button
lateinit var b3: Button
lateinit var b2: Button
lateinit var b1: Button
lateinit var bpi: Button
lateinit var bmul: Button
lateinit var bminus: Button
lateinit var bplus: Button
lateinit var bequal: Button
lateinit var bdot: Button
lateinit var bdiv: Button
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// initializing all our variables.
tvsec = findViewById(R.id.idTVSecondary)
tvMain = findViewById(R.id.idTVprimary)
bac = findViewById(R.id.bac)
bc = findViewById(R.id.bc)
bbrac1 = findViewById(R.id.bbrac1)
bbrac2 = findViewById(R.id.bbrac2)
bsin = findViewById(R.id.bsin)
bcos = findViewById(R.id.bcos)
btan = findViewById(R.id.btan)
blog = findViewById(R.id.blog)
bln = findViewById(R.id.bln)
bfact = findViewById(R.id.bfact)
bsquare = findViewById(R.id.bsquare)
bsqrt = findViewById(R.id.bsqrt)
binv = findViewById(R.id.binv)
b0 = findViewById(R.id.b0)
b9 = findViewById(R.id.b9)
b8 = findViewById(R.id.b8)
b7 = findViewById(R.id.b7)
b6 = findViewById(R.id.b6)
b5 = findViewById(R.id.b5)
b4 = findViewById(R.id.b4)
b3 = findViewById(R.id.b3)
b2 = findViewById(R.id.b2)
b1 = findViewById(R.id.b1)
bpi = findViewById(R.id.bpi)
bmul = findViewById(R.id.bmul)
bminus = findViewById(R.id.bminus)
bplus = findViewById(R.id.bplus)
bequal = findViewById(R.id.bequal)
bdot = findViewById(R.id.bdot)
bdiv = findViewById(R.id.bdiv)
// adding on click listener to our all buttons.
b1.setOnClickListener {
// on below line we are appending
// the expression to our text view.
tvMain.text = (tvMain.text.toString() "1")
}
b2.setOnClickListener {
// on below line we are appending
// the expression to our text view.
tvMain.text = (tvMain.text.toString() "2")
}
b3.setOnClickListener {
// on below line we are appending
// the expression to our text view.
tvMain.text = (tvMain.text.toString() "3")
}
b4.setOnClickListener {
tvMain.text = (tvMain.text.toString() "4")
}
b5.setOnClickListener {
tvMain.text = (tvMain.text.toString() "5")
}
b6.setOnClickListener {
tvMain.text = (tvMain.text.toString() "6")
}
b7.setOnClickListener {
tvMain.text = (tvMain.text.toString() "7")
}
b8.setOnClickListener {
tvMain.text = (tvMain.text.toString() "8")
}
b9.setOnClickListener {
tvMain.text = (tvMain.text.toString() "9")
}
b0.setOnClickListener {
tvMain.text = (tvMain.text.toString() "0")
}
bdot.setOnClickListener {
tvMain.text = (tvMain.text.toString() ".")
}
bplus.setOnClickListener {
tvMain.text = (tvMain.text.toString() " ")
}
bdiv.setOnClickListener {
tvMain.text = (tvMain.text.toString() "/")
}
bbrac1.setOnClickListener {
tvMain.text = (tvMain.text.toString() "(")
}
bbrac2.setOnClickListener {
tvMain.text = (tvMain.text.toString() ")")
}
bpi.setOnClickListener {
// on clicking on pi button we are adding
// pi value as 3.142 to our current value.
tvMain.text = (tvMain.text.toString() "3.142")
tvsec.text = (bpi.text.toString())
}
bsin.setOnClickListener {
tvMain.text = (tvMain.text.toString() "sin")
}
bcos.setOnClickListener {
tvMain.text = (tvMain.text.toString() "cos")
}
btan.setOnClickListener {
tvMain.text = (tvMain.text.toString() "tan")
}
binv.setOnClickListener {
tvMain.text = (tvMain.text.toString() "^" "(-1)")
}
bln.setOnClickListener {
tvMain.text = (tvMain.text.toString() "ln")
}
blog.setOnClickListener {
tvMain.text = (tvMain.text.toString() "log")
}
bminus.setOnClickListener {
// on clicking on minus we are checking if
// the user has already a minus operation on screen.
// if minus operation is already present
// then we will not do anything.
val str: String = tvMain.text.toString()
if (!str.get(index = str.length - 1).equals("-")) {
tvMain.text = (tvMain.text.toString() "-")
}
}
bmul.setOnClickListener {
// if mul sign is not present in our
// text view then only we are adding
// the multiplication operator to it.
val str: String = tvMain.text.toString()
if (!str.get(index = str.length - 1).equals("*")) {
tvMain.text = (tvMain.text.toString() "*")
}
}
bsqrt.setOnClickListener {
if (tvMain.text.toString().isEmpty()) {
// if the entered number is empty we are displaying an error message.
Toast.makeText(this, "Please enter a valid number..", Toast.LENGTH_SHORT).show()
} else {
val str: String = tvMain.text.toString()
// on below line we are calculation
// square root of the given number.
val r = Math.sqrt(str.toDouble())
// on below line we are converting our double
// to string and then setting it to text view.
val result = r.toString()
tvMain.setText(result)
}
}
bequal.setOnClickListener {
val str: String = tvMain.text.toString()
// on below line we are calling an evaluate
// method to calculate the value of expressions.
val result: Double = evaluate(str)
// on below line we are getting result
// and setting it to text view.
val r = result.toString()
tvMain.setText(r)
tvsec.text = str
}
bac.setOnClickListener {
// on clicking on ac button we are clearing
// our primary and secondary text view.
tvMain.setText("")
tvsec.setText("")
}
bc.setOnClickListener {
// on clicking on c button we are clearing
// the last character by checking the length.
var str: String = tvMain.text.toString()
if (!str.equals("")) {
str = str.substring(0, str.length - 1)
tvMain.text = str
}
}
bsquare.setOnClickListener {
if (tvMain.text.toString().isEmpty()) {
// if the entered number is empty we are displaying an error message.
Toast.makeText(this, "Please enter a valid number..", Toast.LENGTH_SHORT).show()
} else {
// on below line we are getting the expression and then calculating the square of the number
val d: Double = tvMain.getText().toString().toDouble()
// on below line we are calculating the square.
val square = d * d
// after calculating the square we
// are setting it to text view.
tvMain.setText(square.toString())
// on below line we are setting
// the d to secondary text view.
tvsec.text = "$d²"
}
}
bfact.setOnClickListener {
if (tvMain.text.toString().isEmpty()) {
// if the entered number is empty we are displaying an error message.
Toast.makeText(this, "Please enter a valid number..", Toast.LENGTH_SHORT).show()
} else {
// on below line we are getting int value
// and calculating the factorial value of the entered number.
val value: Int = tvMain.text.toString().toInt()
val fact: Int = factorial(value)
tvMain.setText(fact.toString())
tvsec.text = "$value`!"
}
}
}
fun factorial(n: Int): Int {
// this method is use to find factorial
return if (n == 1 || n == 0) 1 else n * factorial(n - 1)
}
fun evaluate(str: String): Double {
return object : Any() {
// on below line we ar creating variable
// for tracking the position and char pos.
var pos = -1
var ch = 0
// below method is for moving to next character.
fun nextChar() {
// on below line we are incrementing our position
// and moving it to next position.
ch = if ( pos < str.length) str[pos].toInt() else -1
}
// this method is use to check the extra space
// present int the expression and removing it.
fun eat(charToEat: Int): Boolean {
while (ch == ' '.toInt()) nextChar()
// on below line we are checking the char pos
// if both is equal then we are returning it to true.
if (ch == charToEat) {
nextChar()
return true
}
return false
}
// below method is to parse our
// expression and to get the ans
// in this we are calling a parse
// expression method to calculate the value.
fun parse(): Double {
nextChar()
val x = parseExpression()
if (pos < str.length) throw RuntimeException("Unexpected: " ch.toChar())
return x
}
// in this method we will only perform addition and
// subtraction operation on the expression.
fun parseExpression(): Double {
var x = parseTerm()
while (true) {
if (eat(' '.toInt())) x = parseTerm() // addition
else if (eat('-'.toInt())) x -= parseTerm() // subtraction
else return x
}
}
// in below method we will perform
// only multiplication and division operation.
fun parseTerm(): Double {
var x = parseFactor()
while (true) {
if (eat('*'.toInt())) x *= parseFactor() // multiplication
else if (eat('/'.toInt())) x /= parseFactor() // division
else return x
}
}
// below method is use to parse the factor
fun parseFactor(): Double {
//on below line we are checking for addition
// and subtraction and performing unary operations.
if (eat(' '.toInt())) return parseFactor() // unary plus
if (eat('-'.toInt())) return -parseFactor() // unary minus
// creating a double variable for ans.
var x: Double
// on below line we are creating
// a variable for position.
val startPos = pos
// on below line we are checking
// for opening and closing parenthesis.
if (eat('('.toInt())) { // parentheses
x = parseExpression()
eat(')'.toInt())
} else if (ch >= '0'.toInt() && ch <= '9'.toInt() || ch == '.'.toInt()) {
// numbers
while (ch >= '0'.toInt() && ch <= '9'.toInt() || ch == '.'.toInt()) nextChar()
// on below line we are getting sub string from our string using start and pos.
x = str.substring(startPos, pos).toDouble()
} else if (ch >= 'a'.toInt() && ch <= 'z'.toInt()) {
// on below function we are checking for the operator in our expression.
while (ch >= 'a'.toInt() && ch <= 'z'.toInt()) nextChar()
val func = str.substring(startPos, pos)
// calling a method to parse our factor.
x = parseFactor()
// on below line we are checking for square root.
x =
if (func == "sqrt") Math.sqrt(x)
// on below line we are checking for sin function
// and calculating sin function using Math class.
else if (func == "sin") Math.sin(
Math.toRadians(x)
// on below line we are calculating the cos value
) else if (func == "cos") Math.cos(
Math.toRadians(x)
// on below line we are calculating
// the tan value of our expression.
) else if (func == "tan")
Math.tan(Math.toRadians(x))
// on below line we are calculating
// log value of the expression.
else if (func == "log")
Math.log10(x)
// on below line we are calculating
// ln value of expression.
else if (func == "ln") Math.log(x)
// f we get any error then
// we simply return the exception.
else throw RuntimeException(
"Unknown function: $func"
)
} else {
// if the condition not satisfy then we are returning the exception
throw RuntimeException("Unexpected: " ch.toChar())
}
// on below line we are calculating the power of the expression.
if (eat('^'.toInt())) x = Math.pow(x, parseFactor()) // exponentiation
return x
}
// at last calling a parse for our expression.
}.parse()
}
}
I am getting 33 errors saying same thing as "Unresolved reference: R". I am new to programming and android studio so please help me with the code. i tried running the code but the app does not open in the emulator. It simply gives the error.
CodePudding user response：
It could be due to many possible causes. R is a generated reference to your application's resources, and it is mainly created by Gradle.
Things you should check are Gradle (And dependencies) and also imports of your class/file at the top, maybe even resources couldn't be recognized as well so the automatic import didn't happen, if so you you can see Res folder to check XML attributes or other stuff. Sometimes a Build -> Rebuild or File -> Invalidate Catches / Restart could resolve certain things as well
But there could be other reasons as well, like for example your package and application id as mentioned below:
"As such, the name in the package attribute should always match your project's base package name where you keep your activities and other app code. Of course, you can have sub-packages in your project, but then those files must import the R.java class using the namespace from the package attribute, and any app components declared in the manifest must add the missing sub-package names (or use fully-qualified package names).
If you want to refactor your package name completely, be sure you update the package attribute as well. As long as you use Android Studio's tools to rename and refactor your packages, then these automatically stay in sync. (If they don't stay in sync, your app code can't resolve the R class because it's no longer in the same package, and the manifest won't identify your activities or other components.)"
https://developer.android.com/studio/build/configure-app-module#set_the_application_id
Or afterall, it's a common topic, a Google search gave me these, if non worked, you might wanna check these or look up more in-depth queries:
- Android Studio 3.1.3 - Unresolved reference: R - Kotlin
- Unresolved reference in kotlin with id and activity_main
- Unresolved Reference R after Androidx Migration
CodePudding user response：
Short Answer: R.java didn't generate correctly due to error in your XML files. Fix the errors in XML and then sync with gradle.
Long Answer: The answer of @poorix is quite right. I would like to add something to it that mostly, R.java doesn't generate due to errors in XML, when you fix your errors, then only build your project, that would solve the problem. The links provided are also very useful, so go through them.
CodePudding user response：
You have not imported Resources class, i.e., R class.
it should look something like this,
import com.example.xxxxx.R
You can also achieve this by simply right-clicking on the R and the import option will be there.
Update- You can also enable auto-import of classes, by doing the following:
- Goto File
- New Projects Settings
- Settings for New Project...
- In "Auto Import", enable the following:
- Xml - "Show import popup"
- C/C - "Show import popup" && "auto import on completion"
- Java - "Add unambiguous imports on the fly" && "optimize imports on the fly"
- Kotlin - "Add unambiguous imports on the fly" && "optimize imports on the fly"