It is important to have a rich collection of tools to make development easier in displaying some useful information about requests and responses.

For this purpose, Yii2 provides a toolbar that displays several types of info.

A common way to activate the debug toolbar is to set in config/web.php:

'bootstrap' => ['debug'],
'modules' => [
  'debug' => 'yii\debug\Module',
]

Now you can set the following values:

The default installation of the Yii2 basic template already enables the debug toolbar, as we can see at the bottom of the config/web.php configuration file. The Gii module is also enabled as well, but we will work with it later.

if (YII_ENV_DEV) {
    // configuration adjustments for 'dev' environment
    $config['bootstrap'][] = 'debug';
    $config['modules']['debug'] = 'yii\debug\Module';
    $config['bootstrap'][] = 'gii';
    $config['modules']['gii'] = 'yii\gii\Module';
}

This config entry is only valid in the YII_ENV_DEV mode. So, we must check whether the web/index.php YII_ENV variable has the dev value (as shown in the default installation).

Debug toolbar closed

If we try to reload the web page at basic/web/index.php after these checks, we should see the following screenshot:

Debug toolbar opened

The right arrow reports that the debug toolbar is active but closed. If we click on it, the complete toolbar will open. Now, click on any item, the debug panel will be displayed.

By default, the debug toolbar can be used only in localhost. However, if we are using Yii2 in the remote hosting environment, we set the allowedIPs property of the debug module.

$config['modules']['debug'] = [
    'class' => 'yii\debug\Module',
    'allowedIPs' => [ '127.0.0.1', '::1']
];

In allowedIPs there is only localhost (in the IPv4 and IPv6 forms). We need to put our Internet connection and IP source address here, which can be easily found using any my IP service on the Internet, such as http://www.whatismyip.com/.

If our IP source is, for example, 1.2.3.4, we must add this entry to allowedIPs, in this way:

$config['modules']['debug'] = [
    'class' => 'yii\debug\Module',
    'allowedIPs' => [ '127.0.0.1', '::1', '1.2.3.4']
];

Remember that if we do not have an Internet connection with a static IP, this IP might change. So we need to check whether allowedIPs contains our current IP.

You could also use an asterisk * to allow all IP addresses, so you do not have to deal with dynamic IP issues. If you do this, you need to remember to remove the asterisk before deployment. Finally, at the bottom of our current configuration config/web.php, you will see the following code:

if (YII_ENV_DEV) {
    // configuration adjustments for 'dev' environment
    $config['bootstrap'][] = 'debug';
    $config['modules']['debug'] = [
        'class' => 'yii\debug\Module',
            'allowedIPs' => [ '127.0.0.1', '::1', '1.2.3.4']
    ];
    $config['bootstrap'][] = 'gii';
    $config['modules']['gii'] = 'yii\gii\Module';
}

Let's return to the basic/web/index.php webpage and take a look at the debug info panel.

The debug information is distributed in the menu:

It is possible to filter all data using internal grid filter or to filter for all, latest or selecting among the last 10 rows of the log on top of the content pane.

In the Yii2 application, the debug info is stored using the log component. We can use this tool both in the development and production environment, but for reasons of performance and security in production, we should log only the important messages.

The default configuration file of the Yii2 basic template provides log entry in the components property of config/web.php:

'log' => [
  'traceLevel' => YII_DEBUG ? 3 : 0,
      'targets' => [
      [
             'class' => 'yii\log\FileTarget',
             'levels' => ['error', 'warning'],
      ],
    ],
],

It is now time to code our first project using Yii2.

If we have not installed Yii2 yet, we will to do it now using Composer as follows:

Now, we need a fresh installation of Yii2 in the basic folder of the web server document root. Point the browser to http:/hostname/basic/web and we should see Yii2's congratulations page:

An example of the Hello world page

We will create our first action to display a memorable hello world on the screen.

We know from the Application properties section, in the defaultRoute entry, that the SiteController controller will be called when no route is specified in request.

So, we enter basic/controllers and open SiteController.php, which is the default controller.

In the SiteController class definition, we add a new method at the top, called actionHelloWorld, without parameters.

public function actionHelloWorld()
{
    echo 'hello world'
}

Let's save the file and point to http://hostname/basic/web/index.php?r=site/hello-world.

You should see a blank page with hello world.

This is fantastic, but now we just want to put hello world within the page template.

We must now create a view with the content of response hello world!. In order to do this, we need to create a file named helloWorld.php as the name of the action under views/site. The naming convention need not necessarily be the same here because the view file is not automatically called from the framework.

This file only contains the hello world text.

We update SiteController with the following code:

public function actionHelloWorld()
{
    return $this->render('helloWorld');
}

In the actionHelloWorld() method, $this refers to the SiteController's instance, and render() will insert the views/helloWorld.php file content in the main content layout page.

The extension of the view file, .php, is automatically added from the framework to view the name parameter passed to the render method.

What if we want to pass a parameter, such as name, to actionHelloWorld()? Formally, we need to add just one parameter to actionHelloWorld() in SiteController as follows:

public function actionHelloWorld($nameToDisplay)
{
    return $this->render('helloWorld',
  [ 'nameToDisplay' => $nameToDisplay ]
    );
}

Then, under view/site/helloWorld.php add the following code:

Hello World <?php echo $nameToDisplay ?>

With the update of actionHelloWorld(), we will pass as a second parameter, an array of variables, that will be visible and used in View.

When we use parameters in the action function, we must remember that they will be mandatory and we must respect the order when passing it to the request.

To avoid this obligation, we can use the old method, parsing parameters into the function:

public function actionHelloWorld()
{
    $nameToDisplay = Yii::$app->request->get('nameToDisplay');
    // Equivalent to
// $nameToDisplay = isset($_GET['nameToDisplay'])?$_GET['nameToDisplay']:null;

    return $this->render('helloWorld',
    [ 'nameToDisplay' => $nameToDisplay ]
    );
}

With this solution, we can decide whether to pass the nameToDisplay parameter to request. The default value of the nameToDisplay parameter will be null, but we can decide to assign a different value.

The following is a URL example passing the nameToDisplay parameter Foo:

http://hostname/basic/web/index.php?r=site/hello-world&nameToDisplay=Foo