PHP class not found when using namespace

问题

I am new with this namespace thing.

I have 2 classes(separate files) in my base directory, say class1.php and class2.php inside a directory src/.

class1.php

namespace \src\utility\Timer;

class Timer{
    public static function somefunction(){

    }
}

class2.php

namespace \src\utility\Verification;
use Timer;

class Verification{
     Timer::somefunction();
}

When I execute class2.php, i get the Fatal error that

PHP Fatal error: Class 'Timer' not found in path/to/class2.php at line ***

I read somewhere on SO, that I need to create Autoloaders for this. If so, how do I approach into creating one, and if not, then what else is the issue?

UPDATE

I created an Autoloader which will require all the required files on top of my php script. So, now the class2.php would end up like this.

namespace \src\utility\Verification;
require '/path/to/class1.php'
use Timer;
//or use src\utility\Timer ... both doesn't work.

class Verification{
     Timer::somefunction();
}

This also does not work, and it shows that class not found. But, if I remove all the namespaces, and use's. Everything works fine.

回答1:

We can solve the namespace problem in two ways

1) We can just use namespace and require

2) We can use Composer and work with the autoloading!

The First Way (Namespace and require) way

Class1.php (Timer Class)

namespace Utility;

class Timer
   {
    public static function {}
   }

Class2.php (Verification Class)

namespace Utility;
require "Class1.php";

//Some interesting points to note down!
//We are not using the keyword "use" 
//We need to use the same namespace which is "Utility" 
//Therefore, both Class1.php and Class2.php has "namespace Utility"

//Require is usually the file path!
//We do not mention the class name in the require " ";
//What if the Class1.php file is in another folder?
//Ex:"src/utility/Stopwatch/Class1.php"  

//Then the require will be "Stopwatch/Class1.php"
//Your namespace would be still "namespace Utility;" for Class1.php

class Verification
   {
     Timer::somefunction();
   }

The Second Way (Using Composer and the autoloading way)

Make composer.json file. According to your example "src/Utility" We need to create a composer.json file before the src folder. Example: In a folder called myApp you will have composer.json file and a src folder.

   {
     "autoload": {
     "psr-4": {
        "Utility\\":"src/utility/"
        }
     }   
   }

Now go to that folder open your terminal in the folder location where there is composer.json file. Now type in the terminal!

   composer dump-autoload

This will create a vendor folder. Therefore if you have a folder named "MyApp" you will see vendor folder, src folder and a composer.json file

Timer.php(Timer Class)

namespace Utility;

class Timer
     {
      public static function somefunction(){}
     }

Verification.php (Verification Class)

namespace Utility; 
require "../../vendor/autoload.php"; 
use Utility\Timer; 

class Verification
  {
     Timer::somefunction(); 
  }

This method is more powerful when you have a complex folder structure!!

回答2:

You are going to need to implement an autoloader, as you have already read about it in SO.

You could check the autoloading standard PSR-4 at http://www.php-fig.org/psr/psr-4/ and you can see a sample implementation of PSR-4 autoloading and an example class implementation to handle multiple namespaces here https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader-examples.md.

来源：https://stackoverflow.com/questions/36787079/php-class-not-found-when-using-namespace