CODEWITHSUNDEEP
androidkotlin
Lisa Baron
Lisa Baron

Reputation: 71

onClick & What argument to put inside increment()?

I wish the amount to increase by 1 every time the "+" is clicked.

enter image description here

But now when I click "+", it shows like this

enter image description here

Problem(A): increment is red in android:onClick="increment" /> in activity_main.xml

Problem(B): I know I should write something inside () of increment() and I have tried (1)increment(view: View?)=> red alert: parameter 'view' is never used shows up, but Problem (A) will be solved.

increment(view: View?) is modified from java codes.

    public void submitOrder(View view) {
        display(1);
    }

if I replace (view: View?) with something else then red alert: parameter 'view' is never used disappears. (2)increment(number:Int)(3)increment() None of them works. (2)(3) will result Unfortunately, Order Coffee has stopped.

Here is my MainActivity.kt

class MainActivity : AppCompatActivity() {
    var amount: Int=2
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
    fun increment() {
        amount++
        display(amount)
    }
    //This method is called when the order button is clicked.
    fun submitOrder() {
        var amount: Int=2
        display(amount)
        displayPrice(amount*10)
    }
    fun decrement() {
        amount--
        display(amount)
    }
    //This method displays the given quantity value on the screen.
     private fun display(number: Int) {
        val amountTextView = findViewById<View>(R.id.amount_text_view) as TextView
        amountTextView.text = "" + number
    }
    /**
     * This method displays the given price on the screen.
     */
    private fun displayPrice(number: Int) {
        val priceTextView = findViewById<View>(R.id.price_text_view) as TextView
        priceTextView.setText(NumberFormat.getCurrencyInstance().format(number))
    }
}

Upvotes: 0

Views: 254

Answers (1)

cactustictacs
cactustictacs

Reputation: 19524

It doesn't matter if you don't use the view parameter in your onClick method, you can ignore the warning - it's just a cleanup hint, it should be yellow not red. (It's also wrong in this case, because you know you need that View parameter! The compiler doesn't know about the onClick attribute in the XML though, so it thinks it's unused)

If it says the app has stopped, that's a crash and there should be an error log saying where it crashed and why - the crashes you're getting are probably because you're changing the signature of your onClick function. An onClickListener has a single View parameter, so whatever function you use has to match that.

Because you're saying "look for a function called this and use that as the click listener" in your XML file, it doesn't know what that function's going to be until you run the app and try clicking a thing. If you want to do it in code instead, you can do:

plusButton.setOnClickListener() { increment() }

which technically still has the View passed in, as a variable called it by default, but we're not using it so we can just ignore it! I prefer doing things in code like this personally, setting it in XML is kinda brittle and unhelpful sometimes (like you've discovered) but it's just a personal choice really

Upvotes: 1

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