protected $_countryFactory;
    public function __construct(
        \Magento\Directory\Model\ResourceModel\Country\CollectionFactory $countryFactory
    ) {
        $this->_countryFactory= $countryFactory;
    }

Then in your class you can do:

 public function getAllOptions()
    {
        return $options = $this->getCountryCollection()->toOptionArray();
    }
    public function getCountryCollection()
    {
        $collection = $this->_countryFactory->create()->loadByStore();
        return $collection;
    }

Full Code:

protected $_countryFactory;
public function __construct(
     \Magento\Directory\Model\ResourceModel\Country\CollectionFactory $countryFactory
) {
     $this->_countryFactory= $countryFactory;
}
public function getAllOptions()
{
    return $options = $this->getCountryCollection()->toOptionArray();
}
public function getCountryCollection()
{
    $collection = $this->_countryFactory->create()->loadByStore();
    return $collection;
}
public function getOptionValue($value) 
{ 
    foreach ($this->getAllOptions() as $option) {
        if ($option['value'] == $value) {
            return $option['label'];
        }
    }
    return false;
}

Run php bin/magento setup:di:compile when you add any dependency injection.Because without php bin/magento setup:di:compile it throws error in code.

By Dependency Injection

First you need to inject a \Magento\Quote\Model\QuoteFactory in your class constructor:

namespace Awa\Demo\Controller\Adminhtml\Quote;

use Magento\Backend\App\Action;
use Magento\Backend\App\Action\Context;

class Demo extends \Magento\Backend\App\Action
{
     protected $quoteFactory;

     public function __construct(
          Context $context,
          \ \Magento\Quote\Model\QuoteFactory $quoteFactory
     ) {
         $this->quoteFactory = $quoteFactory;
         parent::__construct($context);
    }
   public function execute()
   {
      $quoteId=12;
      $quote = $this->quoteFactory->create()->load($quoteId);
   }
}

By ObjectManager

Try to Avoid this Method.

$quoteId = 12;
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$objectManager ->create('Magento\Quote\Model\Quote')->loadByIdWithoutStor‌​e($quoteId);

Run php bin/magento setup:di:compile when you add any dependency injection.Because without php bin/magento setup:di:compile it throws error in code.

Hope this will helps you!

The below things are done in the below code:

• Initialize the object manager.
• Set the area code as adminhtml as we are editing the product.
• Define the logger to log information about the delete process. Zend Logger is used.

<?php
error_reporting(1);
set_time_limit(0);
ini_set('memory_limit', '2056M');
use Magento\Framework\App\Bootstrap;
/**
 * If your external file is in root folder
 */
require __DIR__ . '/app/bootstrap.php';
 
/**
 * If your external file is NOT in root folder
 * Let's suppose, your file is inside a folder named 'xyz'
 *
 * And, let's suppose, your root directory path is
 * /var/www/html/magento2
 */
// $rootDirectoryPath = '/var/www/html/magento2';
// require $rootDirectoryPath . '/app/bootstrap.php';
 
$params = $_SERVER; 
$bootstrap = Bootstrap::create(BP, $params); 
$objectManager = $bootstrap->getObjectManager();
 
// Set Area Code
$state = $objectManager->get('Magento\Framework\App\State');
$state->setAreaCode(\Magento\Framework\App\Area::AREA_ADMINHTML); // or \Magento\Framework\App\Area::AREA_FRONTEND, depending on your need
 
// Define Zend Logger
$writer = new \Zend\Log\Writer\Stream(BP . '/var/log/assign-remove-product-to-category.log');
$logger = new \Zend\Log\Logger();
$logger->addWriter($writer);

Here we need product SKU for this operation, if you have product ID then follow below instruction to get product SKU
Get Product SKU from Product ID:

$productId = 897; // product ID
$productRepository = $objectManager->get('Magento\Catalog\Api\ProductRepositoryInterface');
$product = $productRepository->getById($productId);
$sku = $product->getSku(); // product SKU

Assign a Product to Multiple Categories:

/**
 * Assign product to categories
 */ 
$categoryIds = ['10', '18', '38'];
$categoryLinkRepository = $objectManager->get('\Magento\Catalog\Api\CategoryLinkManagementInterface'); 
$categoryLinkRepository->assignProductToCategories($sku, $categoryIds);

Remove a Product from a Category:

/**
 * Remove product from category
 */ 
$categoryId = 10;
$categoryLinkRepository = $objectManager->get('\Magento\Catalog\Model\CategoryLinkRepository');
$categoryLinkRepository->deleteByIds($categoryId, $sku);

Hope this will helps you!

Create/Add new stores and websites from Magento admin:

1. Login to Magento admin panel
2. Go to STORES -> All Stores
3. Create Website
4. Create Store
5. And, then Create Store View

Assume that we have created the following Website/Store/Store view:

Website: base
Store: main_website_store
Store View: default

Website: base
Store: main_website_store
Store View: new

Website: wholesale_website
Store: wholesale_store
Store View: wholesale


This means that we have created 2 websites.

– One website is the base or main website which has two store views with code `default` and `new`.
– The other website is the wholesale website which has a single store view with code wholesale.


Here are the URLs that I want to use for my stores and website:

Default Store: example.com
New Store: new.example.com
Wholesale Website: wholesale.example.com


Link the URLs to the stores and website
To link the URLs to their respective stores and website, we can either add the code in the index.php file or in the .htaccess file.


Please note:
– You don’t need to update both files.
– You can either update .htaccess file or index.php file.
– Updating .htaccess file is recommended.


Adding code in .htaccess file
Add the following code at the end of the .htaccess file:

SetEnvIf Host .*new.example.com.* MAGE_RUN_CODE=new
SetEnvIf Host .*new.example.com.* MAGE_RUN_TYPE=store
 
SetEnvIf Host .*wholesale.example.com.* MAGE_RUN_CODE=wholesale_site
SetEnvIf Host .*wholesale.example.com.* MAGE_RUN_TYPE=website

Adding code in index.php file
By default, at the end of your index.php file, you will have the code something like this:

$bootstrap = \Magento\Framework\App\Bootstrap::create(BP, $_SERVER);
/** @var \Magento\Framework\App\Http $app */
$app = $bootstrap->createApplication(\Magento\Framework\App\Http::class);
$bootstrap->run($app);

We will update it like this:

switch($_SERVER['HTTP_HOST']) {
    case 'new.example.com':
        $mageRunCode = 'new';
        $mageRunType = 'store';
    break;
    case 'wholesale.example.com':
        $mageRunCode = 'wholesale_site';
        $mageRunType = 'website';
    break;
    default:
        $mageRunCode = 'base';
        $mageRunType = 'website';
}
$params = $_SERVER;
$params[\Magento\Store\Model\StoreManager::PARAM_RUN_CODE] = $mageRunCode;
$params[\Magento\Store\Model\StoreManager::PARAM_RUN_TYPE] = $mageRunType;
$bootstrap = \Magento\Framework\App\Bootstrap::create(BP, $params);
 
/** @var \Magento\Framework\App\Http $app */
$app = $bootstrap->createApplication(\Magento\Framework\App\Http::class);
$bootstrap->run($app);

Hope this will helps you!

Using Dependency Injection (DI)
Below is a block class of my custom module (Mtutorials_HelloWorld). I have injected object of \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory class in the constructor of my module’s block class.

app/code/Mtutorials/HelloWorld/Block/HelloWorld.php

<?php
namespace Mtutorials\HelloWorld\Block;
class HelloWorld extends \Magento\Framework\View\Element\Template
{    
    protected $_productCollectionFactory;
 
    public function __construct(
        \Magento\Backend\Block\Template\Context $context,        
        \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory $productCollectionFactory,        
        array $data = []
    )
    {    
        $this->_productCollectionFactory = $productCollectionFactory;    
        parent::__construct($context, $data);
    }
 
    public function getProductCollection()
    {
        $collection = $this->_productCollectionFactory->create();
        $collection->addAttributeToSelect('*');
        $collection->setPageSize(3); // fetching only 3 products
        return $collection;
    }
}
?>

As you can see in above code, I have addded limit to the product collection. I have selected only 3 products.
Now, we print the product collection in our template (.phtml) file.

$productCollection = $block->getProductCollection();
foreach ($productCollection as $product) {
    print_r($product->getData());     
    echo "<br>";
}

Using Object Manager

$objectManager =  \Magento\Framework\App\ObjectManager::getInstance();        
 
$appState = $objectManager->get('\Magento\Framework\App\State');
$appState->setAreaCode('frontend');
 
$productCollectionFactory = $objectManager->get('\Magento\Catalog\Model\ResourceModel\Product\CollectionFactory');
$collection = $productCollectionFactory->create();
$collection->addAttributeToSelect('*');
$collection->setPageSize(3); // selecting only 3 products
 
foreach ($collection as $product) {
    print_r($product->getData());     
    echo "<br>";
}

Hope this will helps you!

1. As a user with root privileges, open your Vanish configuration file:
CentOS 6: /etc/sysconfig/varnish
CentOS 7: /etc/varnish/varnish.params
Debian: /etc/default/varnish
Ubuntu: /etc/default/varnish

2. Edit varnish config file and search for http_resp_hdr_len parameter in this file and change this by following line:

-p http_resp_hdr_len=67000

And if you not found above parameter then add it after thread_pool_max.

See Below:

DAEMON_OPTS="-a ${VARNISH_LISTEN_ADDRESS}:${VARNISH_LISTEN_PORT} \
     -f ${VARNISH_VCL_CONF} \
     -T ${VARNISH_ADMIN_LISTEN_ADDRESS}:${VARNISH_ADMIN_LISTEN_PORT} \
     -p thread_pool_min=${VARNISH_MIN_THREADS} \
     -p thread_pool_max=${VARNISH_MAX_THREADS} \
     -p http_resp_hdr_len=67000\
     -p http_resp_size=98500 \
 -p workspace_backend=98500 \
     -S ${VARNISH_SECRET_FILE} \
     -s ${VARNISH_STORAGE}"

After this changes save file and restart server.

Hope this will helps you!

1). First you need to Create below file in your custom theme:

app/design/frontend/Select_theme_folder/Magento_Customer/layout/customer_account_create.xml

2). Now put below code in this xml file.

<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <body>
        <referenceBlock name="customer_form_register">
            <action method="setShowAddressFields">
                <argument name="show.address.fields" xsi:type="boolean">true</argument>
            </action>
        </referenceBlock>
    </body>
</page>

Now save this file. and run below commands:
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy -f
php bin/magento cache:clean

Hope this will helps you!

By Dependency Injection

protected $CurrencySymbol;
 
public function __construct(
    \Magento\Framework\Locale\CurrencyInterface $CurrencySymbol
)
{
    $this->CurrencySymbol= $CurrencySymbol;
}
Now you can use below code in your function to get currency symbol.
$CurrencyCode='USD';
$this->CurrencySymbol->getCurrency($CurrencyCode)->CurrencyCode();

By ObjectManager

$ObjectManager = \Magento\Framework\App\ObjectManager::getInstance();
$CurrencyCode='USD';
$Symbol = $ObjectManager ->create('Magento\Directory\Model\CurrencyFactory')->create()->load($CurrencyCode);
echo $Symbol ->getCurrencySymbol();

By ObjectManager, you can get currency symbol in phtml file also.
Run php bin/magento setup:di:compile when you add any dependency injection. Because without php bin/magento setup:di:compile it throws error in code.

Hope this will helps you!

Case 1:
This kind of error comes when some white space is present in your code.
Solution:
Remove white space from your code.

Case 2:
When you copy code from other source.
Solution:
When you copy code from some source, it includes special character and white space in the lines you have to remove these invisible special characters and white space from lines at beginning or ending.

Hope this will helps you!