Unresolved reference: fabというエラーが直せないです。

Question

解決したいこと

todoアプリを作っています。
デザインを始めたのですがエラーが出てしまいました。

発生している問題・エラー

Unresolved reference: fab

fabというのはidです。

それとfabボタンに警告マークがありました。
Missing contentDescription attribute on image Non-textual widgets like ImageViews and ImageButtons should use the contentDescription attribute to specify a textual description of the widget such that screen readers and other accessibility tools can adequately describe the user interface. Note that elements in application screens that are purely decorative and do not provide any content or enable a user action should not have accessibility content descriptions. In this case, just suppress the lint warning with a tools:ignore="ContentDescription" attribute. Note that for text fields, you should not set both the hint and the contentDescription attributes since the hint will never be shown. Just set the hint. See https://developer.android.com/guide/topics/ui/accessibility/apps#special-cases

該当するソースコード

package com.example.todo

import android.os.Bundle
import android.view.View
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentContainer
import androidx.fragment.app.viewModels
import androidx.navigation.Navigation.findNavController
import androidx.navigation.fragment.findNavController
import com.example.todo.databinding.MainFragmentBinding
import dagger.hilt.android.AndroidEntryPoint


@AndroidEntryPoint
class MainFragment: Fragment(R.layout.activity_main) {
    private val vm: MainViewMotel by viewModels()

    // ここから下を追加
    private var _binding: MainFragmentBinding? = null
    private val binding: MainFragmentBinding get() = _binding!!

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        this._binding = MainFragmentBinding.bind(view)

        binding.fab.setOnClickListener {
            findNavController().navigate(R.id.action_mainFragment2_to_createtodoFragment3)
        }

    }

    override fun onDestroyView() {
        super.onDestroyView()
        this._binding = null
    }
}

<?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">

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="342dp"
        android:layout_marginLeft="342dp"
        android:layout_marginTop="658dp"
        android:layout_marginEnd="13dp"
        android:layout_marginRight="13dp"
        android:layout_marginBottom="13dp"
        android:clickable="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_baseline_add_24" />
</androidx.constraintlayout.widget.ConstraintLayout>

plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-kapt'
    id 'dagger.hilt.android.plugin'

}



android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.example.todo"
        minSdkVersion 16
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

        vectorDrawables.useSupportLibrary = true
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }

    buildFeatures {
        viewBinding  true
    }

}

dependencies {


    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    implementation 'androidx.core:core-ktx:1.5.0'
    implementation 'androidx.appcompat:appcompat:1.3.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    implementation 'androidx.navigation:navigation-fragment-ktx:2.3.5'
    implementation 'androidx.navigation:navigation-ui-ktx:2.3.5'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'


    //Navigation
    implementation("androidx.navigation:navigation-fragment-ktx:2.3.5")
    implementation("androidx.navigation:navigation-ui-ktx:2.3.5")

    //Room
    def room_version = "2.3.0"
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"
    kapt "androidx.room:room-compiler:$room_version"
    implementation "androidx.room:room-runtime:$room_version"
    implementation "androidx.room:room-ktx:$room_version"

    //Hilt
    implementation "com.google.dagger:hilt-android:2.28-alpha"
    kapt "com.google.dagger:hilt-android-compiler:2.28-alpha"

    //activity
    implementation "androidx.activity:activity-ktx:1.1.0"

}

自分で試したこと

このサイト（https://stackoverflow.com/questions/41407811/android-vectordrawables-usesupportlibrary-true-is-stopping-app） を見てbuild.gradleファイルに追加

 vectorDrawables.useSupportLibrary = true

Comments

[1T2R3M4]

https://qiita.com/minto01/questions/6b15b5062a4a7bb54241

以下ご対応ください。
https://teratail.com/help#posted-otherservice

[hoshi-takanori]

MainFragment なのに R.layout.activity_main なのが謎だし、さらに MainFragmentBinding に bind してるのがもっと謎ですね…。