我试图从 Fragment 向我的按钮添加一个监听器，但它总是给我这个错误:
Process: com.example.projectdrivemark, PID: 27776
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.projectdrivemark/com.example.MainActivity}: kotlin.UninitializedPropertyAccessException: lateinit property binding has not been initialized
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3341)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3485)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2045)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7478)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:549)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:941)
Caused by: kotlin.UninitializedPropertyAccessException: lateinit property binding has not been initialized
at com.example.tempConverter.TempConverterFragment.<init>(TempConverterFragment.kt:16)
at com.example.MainActivity.onCreate(MainActivity.kt:28)
at android.app.Activity.performCreate(Activity.java:7989)
at android.app.Activity.performCreate(Activity.java:7978)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3316
这是 MainActivity 代码:
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import androidx.fragment.app.Fragment
import androidx.recyclerview.widget.LinearLayoutManager
import com.example.projectdrivemark.R
import com.example.projectdrivemark.databinding.ActivityMainBinding
import com.example.recyclerView.MockDatabase.Companion.createMockData
import com.example.recyclerView.PostAdapter
import com.example.recyclerView.RecyclerViewFragment
import com.example.tempConverter.TempConverterFragment
import com.example.uploaderView.UploaderFragment
class MainActivity : AppCompatActivity(), PostAdapter.OnPostClickListener {
private lateinit var binding: ActivityMainBinding
val dummyList = createMockData()
val adapter = PostAdapter(dummyList, this)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
title = "First Kotlin App"
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
val recyclerView = RecyclerViewFragment()
val tempConverterView = TempConverterFragment()
val uploaderView = UploaderFragment(this)
setFragmentView(recyclerView)
binding.bottomNavBar.setOnNavigationItemSelectedListener {
when(it.itemId){
R.id.listView -> setFragmentView(recyclerView)
R.id.tempConverterView -> setFragmentView(tempConverterView)
R.id.videoUploaderView -> setFragmentView(uploaderView)
}
true
}
}
private fun setFragmentView(fragment: Fragment){
supportFragmentManager.beginTransaction().apply {
replace(R.id.main_fragment_view, fragment)
//Will return to previous page when tap "Back Button" on the phone
addToBackStack(null)
commit()
}
}
override fun onEditPost(position: Int){
val clickedPost = dummyList[position]
clickedPost.title = "Updated title"
clickedPost.body = "Updated body"
adapter.notifyItemChanged(position)
}
override fun onDeletePost(position: Int) {
dummyList.removeAt(position)
adapter.notifyItemRemoved(position)
}
这是我的 TempConverterFragment 的样子:
import android.content.Intent
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Toast
import androidx.fragment.app.Fragment
import com.example.MainActivity
import com.example.projectdrivemark.R
import com.example.projectdrivemark.databinding.FragmentTempConverterBinding
class TempConverterFragment: Fragment(){
private lateinit var binding: FragmentTempConverterBinding
val celsiusButton = binding.celsiusButton
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val binding = inflater.inflate(R.layout.fragment_temp_converter, container, false)
celsiusButton.setOnClickListener {
celsiusFunction(celsiusButton)
}
return binding.rootView
}
fun celsiusFunction(view: View){
val fahrenheitView = binding!!.userTemp
val fahrenheitValue = fahrenheitView.text.toString()
if(!fahrenheitValue.isBlank()){
val celsiusCovertedValue = (fahrenheitValue.toDouble() - 32) * 5/9
val celsiusValue = String.format("%.2f", celsiusCovertedValue)
Toast.makeText(activity,
"$fahrenheitValue fahrenheit is $celsiusValue degrees celsius",
Toast.LENGTH_LONG).show()
}else {
Toast.makeText(activity, "You must enter a value to convert", Toast.LENGTH_LONG).show()
}
}
fun farenheitFunction(view: View){
val celsiusView = binding.userTemp
val celsiusValue = celsiusView.text.toString()
if(!celsiusValue.isBlank()){
val farenheitConvertedValue = celsiusValue.toDouble() * 9/5 + 32
val farenheitValue = String.format("%.2f", farenheitConvertedValue)
Toast.makeText(activity,
"$celsiusValue degrees celsius is $farenheitValue farenheit",
Toast.LENGTH_LONG).show()
}else{
Toast.makeText(activity, "You must enter a value to convert", Toast.LENGTH_LONG).show()
}
}
}
下面是我的 Xml Fragment 的样子:
<?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="com.example.MainActivity">
<ImageView
android:id="@+id/imageView"
android:layout_width="487dp"
android:layout_height="320dp"
android:layout_marginBottom="16dp"
android:adjustViewBounds="true"
android:cropToPadding="false"
android:scaleType="fitXY"
app:layout_constraintBottom_toTopOf="@+id/textView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:srcCompat="@drawable/termometer" />
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="62dp"
android:layout_marginLeft="62dp"
android:layout_marginTop="24dp"
android:layout_marginEnd="76dp"
android:layout_marginRight="76dp"
android:text="Enter desired temperature to convert"
android:textAppearance="@style/TextAppearance.AppCompat.Large"
android:textSize="18sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/imageView" />
<EditText
android:id="@+id/userTemp"
style="@android:style/Widget.DeviceDefault.EditText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="140dp"
android:layout_marginLeft="140dp"
android:layout_marginTop="24dp"
android:layout_marginEnd="140dp"
android:layout_marginRight="140dp"
android:ems="10"
android:hint="Enter Temperature Here"
android:inputType="numberDecimal"
android:selectAllOnFocus="false"
android:singleLine="true"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView" />
<Button
android:id="@+id/celsiusButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="70dp"
android:layout_marginLeft="70dp"
android:layout_marginTop="32dp"
android:onClick="celsiusFunction"
android:text="to Celsius"
app:backgroundTint="@color/purple_200"
app:layout_constraintEnd_toStartOf="@+id/farenheitButton"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/userTemp" />
<Button
android:id="@+id/farenheitButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="41dp"
android:layout_marginLeft="41dp"
android:layout_marginTop="32dp"
android:layout_marginEnd="72dp"
android:layout_marginRight="72dp"
android:onClick="farenheitFunction"
android:text="to Farenheit"
app:backgroundTint="@color/teal_200"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/celsiusButton"
app:layout_constraintTop_toBottomOf="@+id/userTemp" />
</androidx.constraintlayout.widget.ConstraintLayout>
如何初始化一个 lateinit 绑定(bind)？还是只使用 view.findViewById 更好？
最佳答案
在我们 fragment 中的 onCreateView 中绑定(bind)之前删除“val”。您已经声明它并像下面这样初始化它
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View?
{
binding = FragmentTempConverterBinding.inflate(inflater, container, false)
return binding.root
}
关于android - 如何在 fragment 中初始化 "lateinit binding"？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/66256875/