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public class MainActivity extends AppCompatActivity { 
  ...
  Button shareButton;
  private ShareDialog shareDialog;
  
  ...
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      ...
      shareButton = (Button) findViewById(R.id.share_button);

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loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {

                shareButton.setVisibility(View.VISIBLE);
                
                ...
                
            }
});

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if (AccessToken.getCurrentAccessToken() != null) {

    shareButton.setVisibility(View.VISIBLE);
    
    ...
}

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@Override
protected void onCreate(Bundle savedInstanceState) {

    ...

    shareButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            share();

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<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout ...
    <LinearLayout ...
    
        <Button
            android:id="@+id/posts_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:text="Get posts" />

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public class MainActivity extends AppCompatActivity { 
  ...
  Button postsButton;
  
  ...
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      ...
      postsButton = (Button) findViewById(R.id.posts_button);
      postsButton.setVisibility(View.GONE);

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@Override
protected void onCreate(Bundle savedInstanceState) {

    ...

    postsButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getPosts();
            }

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<?xml version="1.0" encoding="utf-8"?>
<menu 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"
    tools:context=".MainActivity">

    <item
        android:id="@+id/menu_add"
        android:icon="@drawable/ic_new"
        android:title="Add"

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<?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/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="io.github.ziginsider.firebasedemo.MainActivity">

    <android.support.v7.widget.Toolbar

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package io.github.ziginsider.firebasedemo;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;


public class MainActivity extends AppCompatActivity {

    @Override