无法将整数强制转换为android.support.design.widget.FloatingActionButton _floating

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我试图访问片段内的浮动操作按钮但由于某种原因，我不能。我一直在收到错误。我已经尝试了一切，似乎没有任何工作。这是我片段中的代码：

import android.os.Bundle import android.support.design.widget.FloatingActionButton import android.support.v4.app.Fragment import android.view.LayoutInflater import android.view.View import android.view.ViewGroup import android.widget.Toast import com.google.firebase.database.DatabaseReference import com.google.firebase.database.FirebaseDatabase import com.ntx_deisgns.cyberchatter.cyberchatter.Message import com.ntx_deisgns.cyberchatter.cyberchatter.R import kotlinx.android.synthetic.main.groups.* import kotlinx.android.synthetic.main.groups2.*class groups2 : Fragment() {override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? { //inflater.inflate(R.layout.groups2, container, false) val fab = R.id.fab as FloatingActionButtonfab.setOnClickListener {if (!mainActivityEditText.text.toString().isEmpty()){ sendData() }else{ //Toast.makeText(this, "Please enter a message", Toast.LENGTH_SHORT).show() } } return inflater.inflate(R.layout.groups2, container, false) }private fun sendData(){val editText = groupInput val database = FirebaseDatabase.getInstance() val myRef = database.getReference("message")myRef.setValue(Message(editText.text.toString())) val mDatabase: DatabaseReference? = null mDatabase?. child("messages")?. child(java.lang.String.valueOf(System.currentTimeMillis()))?. setValue(Message(editText.text.toString()))//clear the text editText.setText("") }companion object { fun newInstance(): groups2 = groups2() } }

我究竟做错了什么？为什么在片段中访问setOnClickListener如此困难？
更新：
这是我的groups2.xml：

< ?xml version="1.0" encoding="utf-8"?> < RelativeLayout 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/groups2_relative" android:layout_width="match_parent" android:layout_height="wrap_content" android:paddingBottom="60dp" android:paddingLeft="10dp" android:paddingRight="10dp" android:paddingTop="55dp" tools:context="com.ntx_deisgns.cyberchatter.cyberchatter.MainActivity"> < android.support.design.widget.FloatingActionButton android:id="@+id/myFab" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:layout_alignParentEnd="true" android:clickable="true" android:focusable="true" android:src="https://www.songbingjia.com/android/@drawable/ic_send_black_24dp" android:tint="@android:color/white" app:fabSize="mini"/> < android.support.design.widget.TextInputLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:layout_alignParentStart="true" android:layout_toStartOf="@id/myFab"> < EditText android:id="@+id/groupInput" android:layout_width="match_parent" android:layout_height="57dp" android:hint="Please enter your text here" /> < /android.support.design.widget.TextInputLayout> < ListView android:id="@+id/list_of_messages" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_above="@id/myFab" android:layout_alignParentStart="true" android:layout_alignParentTop="true" android:layout_marginBottom="16dp" android:divider="@android:color/transparent" android:dividerHeight="16dp" /> < /RelativeLayout>

答案【无法将整数强制转换为android.support.design.widget.FloatingActionButton】在调用findViewById之前，您需要对视图进行膨胀。在充气之前访问浮动操作按钮会导致空指针异常。

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? { //inflate and store view val view =inflater.inflate(R.layout.groups2, container, false) val fab = view.findViewById(R.id.fab) as FloatingActionButton //If using kotlinx then above line is not neededfab.setOnClickListener { //do your thing... } return view }