在自动加载实现完成后，接着new \flight\Engine()自动加载的方式实例化了下框架的核心类Engine，这个类名翻译过来就是引擎发动机的意思，是flight的引擎发动机，很有想象力吧。

public static function app() {
    static $initialized = false;

    if (!$initialized) {
        require_once __DIR__.'/autoload.php';

        self::$engine = new \flight\Engine();

        $initialized = true;
    }

    return self::$engine;
}

在实例化Engine这个类的时候，当前类的构造方法进行了对框架的初始化工作。

public function __construct() {
    $this->vars = array();

    $this->loader = new Loader();
    $this->dispatcher = new Dispatcher();

    $this->init();
}

接着来看init方法都做了什么，将初始化状态标记为静态变量static $initialized，判断如果为true，将$this->vars以及$this->loader、$this->dispatcher中保存的属性重置为默认状态。

static $initialized = false;
$self = $this;

if ($initialized) {
    $this->vars = array();
    $this->loader->reset();
    $this->dispatcher->reset();
}

接下来将框架的Request、Response、Router、View类的命定空间地址register（设置）到Loader类的classes属性中。

// Register default components
$this->loader->register('request', '\flight\net\Request');
$this->loader->register('response', '\flight\net\Response');
$this->loader->register('router', '\flight\net\Router');
$this->loader->register('view', '\flight\template\View', array(), function($view) use ($self) {
    $view->path = $self->get('flight.views.path');
    $view->extension = $self->get('flight.views.extension');
});  

flight/core/Loader.php

public function register($name, $class, array $params = array(), $callback = null) {
    unset($this->instances[$name]);

    $this->classes[$name] = array($class, $params, $callback);
}

再接下来就是将框架给用户提供的调用方法，设置到调度器Dispatcher类的events属性中。

// Register framework methods
$methods = array(
    'start','stop','route','halt','error','notFound',
    'render','redirect','etag','lastModified','json','jsonp'
);
foreach ($methods as $name) {
    $this->dispatcher->set($name, array($this, '_'.$name));
}

flight/core/Dispatcher.php

/**
 * Assigns a callback to an event.
 *
 * @param string $name Event name
 * @param callback $callback Callback function
 */
public function set($name, $callback) {
    $this->events[$name] = $callback;
}

接下来呢，就是设置框架的一些配置，将这些配置保存在Engine类的vars属性中。

// Default configuration settings
$this->set('flight.base_url', null);
$this->set('flight.case_sensitive', false);
$this->set('flight.handle_errors', true);
$this->set('flight.log_errors', false);
$this->set('flight.views.path', './views');
$this->set('flight.views.extension', '.php');

flight/Engine.php

/**
 * Sets a variable.
 *
 * @param mixed $key Key
 * @param string $value Value
 */
public function set($key, $value = null) {
    if (is_array($key) || is_object($key)) {
        foreach ($key as $k => $v) {
            $this->vars[$k] = $v;
        }
    }
    else {
        $this->vars[$key] = $value;
    }
}

最后一步的操作，当调用框架的start方法时，给其设置一些前置操作，通过set_error_handler()和set_exception_handler()设置用户自定义的错误和异常处理函数，如何使用自定义的错误和异常函数，可以看这两个范例:https://segmentfault.com/n/13…
https://segmentfault.com/n/13…。

// Startup configuration
$this->before('start', function() use ($self) {
    // Enable error handling
    if ($self->get('flight.handle_errors')) {
        set_error_handler(array($self, 'handleError'));
        set_exception_handler(array($self, 'handleException'));
    }

    // Set case-sensitivity
    $self->router()->case_sensitive = $self->get('flight.case_sensitive');
});

$initialized = true;

/**
 * Custom error handler. Converts errors into exceptions.
 *
 * @param int $errno Error number
 * @param int $errstr Error string
 * @param int $errfile Error file name
 * @param int $errline Error file line number
 * @throws \ErrorException
 */
public function handleError($errno, $errstr, $errfile, $errline) {
    if ($errno & error_reporting()) {
        throw new \ErrorException($errstr, $errno, 0, $errfile, $errline);
    }
}

/**
 * Custom exception handler. Logs exceptions.
 *
 * @param \Exception $e Thrown exception
 */
public function handleException($e) {
    if ($this->get('flight.log_errors')) {
        error_log($e->getMessage());
    }

    $this->error($e);
}

当调用$self->router()时，会触发当前类的__call()魔术方法，通过$this->loader->get($name)判断属性$classes中router索引是否存在，不存在抛出异常，存在就通过$this->loader->load($name, $shared)去实例化初始化时设置的'\flight\net\Router'，这里是工厂模式，接下来的路由文章会详细分析。

/**
 * Handles calls to class methods.
 *
 * @param string $name Method name
 * @param array $params Method parameters
 * @return mixed Callback results
 * @throws \Exception
 */
public function __call($name, $params) {
    $callback = $this->dispatcher->get($name);
 
    if (is_callable($callback)) {
        return $this->dispatcher->run($name, $params);
    }

    if (!$this->loader->get($name)) {
        throw new \Exception("{$name} must be a mapped method.");
    }

    $shared = (!empty($params)) ? (bool)$params[0] : true;

    return $this->loader->load($name, $shared);
}

在$this->before()操作中，会将前置操作设置到Dispatcher类的filters属性中。这些操作完成后，将$initialized = true。

/**
 * Adds a pre-filter to a method.
 *
 * @param string $name Method name
 * @param callback $callback Callback function
 */
public function before($name, $callback) {
    $this->dispatcher->hook($name, 'before', $callback);
}

flight/core/Dispatcher.php

/**
 * Hooks a callback to an event.
 *
 * @param string $name Event name
 * @param string $type Filter type
 * @param callback $callback Callback function
 */
public function hook($name, $type, $callback) {
    $this->filters[$name][$type][] = $callback;
}

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