The PHP template engine principle is an effective solution to separate the view layer and the model layer, allowing for better division of labor and collaboration between the front and back ends. It comes from the classic MVC model, that is, [model layer-view layer-control [Controller Model], which separates M and V code, so that the same program can use different expressions.
The principle of the php template engine is:
1. The origin of the template engine
The idea of template engine comes from the classic MVC model, that is, model layer - view layer - controller model. MVC originally existed in desktop programs, M refers to the data model, V refers to the user interface, and C refers to the controller. The purpose of using MVC is to separate M and V codes so that the same program can use different presentation forms.
With the popularity of the Web, this model was introduced into Web development. At this time, V (view layer), commonly known as the template, realizes the separation of data generation and data display. Early views usually controlled the interface by HTML elements. With the development of the Internet, some new presentation technologies (such as Flex, etc.) became popular. MVC separated data and presentation, and a set of data can be used in multiple presentation layers. There is no need to modify the code of the logic layer. For example, the data of a blog article list can be generated in the M layer (model layer), and then different presentation layer technologies can be used to display the data in traditional Web pages, RIA applications, and mobile applications without modifying the code of the logic layer. Separation of front-end and back-end.
In addition, the popularity of AJAX technology and the widespread application of the Jquery library have changed the situation of early mixed writing of HTML, Javascript, and PHP codes. The application of AJAX technology separates data request, generation and display, and promotes the separation of presentation layer (V) and code layer.
Template engine is an effective solution to separate the view layer and model layer, allowing for better division of labor and collaboration between the front and back ends. PHP development has gone through several stages of development, from front-end and back-end mixing, to the strong promotion of template engines (represented by Smarty), to today's return to nature, and even questioning the necessity of the existence of PHP template engines.
Is it necessary to use a template engine in PHP? What is the principle of template engine? Why is Smarty so popular and causing so much controversy in the PHP community today? These are issues discussed next.
2 The idea of code layering
As a lightweight and flexible scripting language, PHP is very suitable for Web development, which has short development cycles, rapid changes in requirements, and emphasizes user experience. needs and business. In the early days of PHP development, PHP code and HTML were usually mixed. Database operations, logical judgments, HTML code generation, and even Javascript code can be seen everywhere in the code. For small projects, this coding method can quickly complete the requirements. However, once the project expands, the front-end logic will become more and more complex. This completely mixed writing method will inevitably cause problems such as poor code readability and difficulty in later maintenance.
In the early days of PHP development, we might write like this:
<html>
<head>
<meta http-equiv="content-type"content="text/html;charset=utf-8">
<title>最原始的PHP编码风格 - 李苦李</title>
</head>
<body>
<table>
<tr>
<td>ID</td>
<td>姓名</td>
</tr>
<?php
mysql_connect("localhost","admin","password")or
die("Could not connect:".mysql_error());
mysql_select_db("user_db");
$result= mysql_query("select id,username from user");
while($row= mysql_fetch_array($result)) {
echo"<tr><td>".$row['id']."</td><td>"
.$row['username']."</td></tr>";
}
mysql_free_result($result);
?>
</table>
<?php
//其他功能模块
?>
</body>
</html> Obviously, the above code is extremely poor in terms of readability, maintainability and code reusability. of. You need to find a way to separate data generation and display. Usually the easiest way to think of is to put the code that interacts with the database in a separate file, and the part that displays the data in another file. Create a new file data.php and obtain the data, as shown in the following code:
<?php
mysql_connect("localhost","admin","password")or
die("Could not connect:".mysql_error());
mysql_select_db("user_db");
$result= mysql_query("select id,username from user");
while($row= mysql_fetch_array($result)) {
$data[] =$row;
}
mysql_free_result($result);
?>Neither of these two methods achieves the separation of PHP code and HTML code, but compared with the second method The first approach achieves the separation of data acquisition and data display. In the second processing method, one of the files is specifically responsible for interacting with the database, obtaining and processing data. Then it is handed over to another file to display the data. This file responsible for display only performs some simple logical operations, such as looping, judgment, output, etc. Obviously, the second processing method is easier to maintain than the first processing method.
For the second processing method, we can also use HereDoc syntax to make it more concise. The code is as follows:
<?php
foreach($dataas$value) {
echo<<< TM
<tr><td>$value[id]</td><td>$value[username]</td></tr>;
TM;
}
?>The second processing method is the original PHP template mechanism, which is The template mechanism currently used by some PHP programs is characterized by its simplicity, flexibility, compliance with PHP's syntax and usage habits, and low learning cost. The disadvantage is that it cannot implement some advanced functions, such as configurability, caching, making template files independent of PHP syntax, etc. I will write this here today, and we will solve these problems one after another in the following articles.
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