Cannot find symbol error in android studio

Issue

I'm trying to add fragments to a navigation drawer. But I have the error: cannot find symbol class Fragment.

I added: import android.support.v4.app.Fragment

Also add the fragment object(Fragment fragment)

Where is the mistake? What should I do?

Home.java

package com.example.eatit;

import android.os.Bundle;

import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;

import android.view.View;

import androidx.core.view.GravityCompat;
import androidx.appcompat.app.ActionBarDrawerToggle;

import android.view.MenuItem;

import com.google.android.material.navigation.NavigationView;

import androidx.drawerlayout.widget.DrawerLayout;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import android.view.Menu;
import android.support.v4.app.Fragment;

public class Home extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {
    Fragment fragment = null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();
        navigationView.setNavigationItemSelectedListener(this);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.home, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        /* Handle navigation view item clicks here. */
        int id = item.getItemId();

        if (id == R.id.nav_home) {
            // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_tools) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

build.grandle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.0"
    defaultConfig {
        applicationId "com.example.eatit"
        minSdkVersion 16
        targetSdkVersion 29
        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'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'com.google.firebase:firebase-database:16.0.4'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    implementation 'com.google.android.material:material:1.0.0'
    testİmplementation 'junit:junit:4.12'
    androidTestİmplementation 'androidx.test:runner:1.2.0'
    androidTestİmplementation 'androidx.test.espresso:espresso-core:3.2.0'
    implementation 'com.google.firebase:firebase-core:17.0.0'
    implementation 'com.google.firebase:firebase-core:10.2.0'
    implementation 'com.google.firebase:firebase-database:17.0.0'
    implementation 'info.hoang8f:fbutton:1.0.5'
    implementation 'com.rengwuxian.materialedittext:library:2.1.4'

    implementation 'androidx.cardview:cardview:1.0.0'
    implementation 'androidx.recyclerview:recyclerview:1.0.0'
    implementation 'com.squareup.picasso:picasso:2.5.2'
    implementation 'com.firebaseui:firebase-ui-database:1.2.0'
    //noinspection GradleCompatible
    implementation 'com.android.support:design:26.+'

    def nav_version = "2.1.0-alpha06"

    // Java
    implementation "androidx.navigation:navigation-fragment:$nav_version"
    implementation "androidx.navigation:navigation-ui:$nav_version"
}
apply plugin: 'com.google.gms.google-services'
apply plugin: "androidx.navigation.safeargs"

I've tried to search the web and forums but so far I didn't find anything helpful.

Thank You so much.

Solution

You are importing Fragment from the old Android Support library (android.support.v<x>) while you’ve configured your project to use AndroidX, so make sure you are importing and using the correct library.

Please visit this link to find the correct import for Fragment.

Replace android.support.v4.app.Fragment with androidx.fragment.app.Fragment.

Answered By - Faiizii Awan