Блог

Я пытаюсь извлечь уроки из этого блога. Другое дело, что я пытаюсь установить его setOnClickListener во фрагменте, а не в основном действии.

Мой основной:

 package com.example.testingapp

import android.graphics.Color
import android.os.Bundle
import com.google.android.material.floatingactionbutton.FloatingActionButton
import com.google.android.material.snackbar.Snackbar
import androidx.appcompat.app.AppCompatActivity
import android.view.Menu
import android.view.MenuItem
import android.view.inputmethod.EditorInfo
import android.webkit.WebView
import android.webkit.WebViewClient
import android.widget.Button
import android.widget.EditText
import android.widget.Toast
class MainActivity : AppCompatActivity() {

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

        // Variable and constants declaration
        val btnShow = findViewById<Button>(R.id.btnShow)
        val editText = findViewById<EditText>(R.id.editText)
        val btnExit = findViewById<Button>(R.id.btnExit)
        val webview = findViewById<WebView>(R.id.webview)
        btnExit.setOnClickListener{
            finish()
        }

        // Function that runs when the showButton is clicked.
        // It takes one argument, which is the text entered by the user.
        // Then it loads a web page, using the text as a part of the url.
        btnShow.setOnClickListener{

            // Declare the text from editText
            val text = editText.text

            // Show the text from the user in a small toast window
            Toast.makeText(this, text, Toast.LENGTH_SHORT).show()

            // Make the webView
            webview.webViewClient = WebViewClient()
            webview.setBackgroundColor(Color.parseColor("#ffffff"))

        }
    }
}
 

Второй фрагмент:

 class SecondFragment : Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_second, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    view.findViewById<Button>(R.id.button_second).setOnClickListener {
        findNavController().navigate(R.id.action_SecondFragment_to_FirstFragment)
    }
}
 

}

fragment_second:

  <?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:id="@ id/btnUpdate"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffffff"
    tools:context=".SecondFragment">

    <Button
        android:id="@ id/btnExit"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginBottom="24dp"
        android:backgroundTint="@color/colorPrimary"
        android:textColor="@android:color/white"
        android:text="Exit"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />

    <Button
        android:id="@ id/btnShow"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginBottom="24dp"
        android:backgroundTint="@color/colorPrimary"
        android:text="show temp"
        android:textColor="@android:color/white"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent" />

    <WebView
        android:id="@ id/webview"
        android:layout_width="337dp"
        android:layout_height="386dp"
        android:layout_marginStart="32dp"
        android:layout_marginLeft="32dp"
        android:layout_marginEnd="32dp"
        android:layout_marginRight="32dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.581"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.213" />

    <EditText
        android:id="@ id/editText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:ems="10"
        android:hint="Enter sensor name"
        android:inputType="textPersonName"
        app:layout_constraintBottom_toTopOf="@ id/btnShow"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />



</androidx.constraintlayout.widget.ConstraintLayout>
 

Однако я застрял в этой ошибке и не смог выяснить, как это исправить:

 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.testingapp, PID: 10308
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testingapp/com.example.testingapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:223)
    at android.app.ActivityThread.main(ActivityThread.java:7656)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at com.example.testingapp.MainActivity.onCreate(MainActivity.kt:59)
    at android.app.Activity.performCreate(Activity.java:8000)
    at android.app.Activity.performCreate(Activity.java:7984)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
 

Заранее благодарю вас!

в вашем button_second fragment_second