java.lang.IllegalStateException: Could not find method count(View) in a parent or ancestor Context for android:onClick attribute defined on view class

Question

The app keeps crashing whenever I click the count or reset button I think that the app is not recognizing the onclick methods count and reset I tried the same using java but it was working fine using java so the problem must be with kotlin Is there any solution對於這個問題？ 還是我應該遵循任何替代方法？

package com.example.a39kotlinfun

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.TextView

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


    var textView = findViewById<TextView>(R.id.textView)

    var count = 0

    fun count(view : View){
        count += 1
        textView.text = count.toString()
    }

    fun reset(view : View){
        count = 0
        textView.text = "0"
    }
}

}

XML：

 <?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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=".MainActivity">
<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="50dp"
    android:layout_marginBottom="400dp"
    android:text="Hello World!"
    android:textSize="36sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<Button
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="55dp"
    android:layout_marginLeft="55dp"
    android:layout_marginTop="111dp"
    android:layout_marginBottom="247dp"
    android:onClick="count"
    android:text="count"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/textView" />

<Button
    android:id="@+id/button2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="111dp"
    android:layout_marginEnd="51dp"
    android:layout_marginRight="51dp"
    android:layout_marginBottom="247dp"
    android:onClick="reset"
    android:text="reset"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/textView" />

</androidx.constraintlayout.widget.ConstraintLayout>

日志貓：

java.lang.IllegalStateException: Could not find method count(View) in a parent or ancestor Context for android:onClick attribute defined on view class com.google.android.material.button.MaterialButton with id 'button'
    at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.resolveMethod(AppCompatViewInflater.java:447)
    at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:405)
    at android.view.View.performClick(View.java:7189)
    at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
    at android.view.View.performClickInternal(View.java:7166)
    at android.view.View.access$3500(View.java:819)
    at android.view.View$PerformClick.run(View.java:27682)
    at android.os.Handler.handleCallback(Handler.java:883)
    at android.os.Handler.dispatchMessage(Handler.java:100)
    at android.os.Looper.loop(Looper.java:224)
    at android.app.ActivityThread.main(ActivityThread.java:7592)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)

Answer 1

將count和reset方法移出onCreate方法。

class MainActivity : AppCompatActivity() {

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

       var textView = findViewById<TextView>(R.id.textView)
    }

    var count = 0

    fun count(view : View){
        count += 1
        textView.text = count.toString()
    }

    fun reset(view : View){
        count = 0
        textView.text = "0"
    }
}

在任何情況下都應避免設置android:onClick ，最好的解決方案是使用：

val button = findViewById<Button>(R.id.button)
button.setOnClickListener {
    count += 1
    textView.text = count.toString()
}