Laravel is a popular PHP framework. Its elegant syntax and versatility make it one of the frameworks loved by developers. In Laravel, there is a method called "window" that is used to decide whether to perform some operations based on certain conditions. A common example of a window method is the when method, which allows you to execute a specified closure function under given conditions.

In this article, we will take a deep dive into the when method in Laravel, including how it works, how to use it, and some sample code.

1. How the when method works

The when method can be used in two different situations, that is, the closure function is executed when the condition is true or false. The following is the basic syntax of the when method:

when($value,?$callback,?$default?=?null)

The first parameter $value is the value used as the condition. If $value is true, the closure function specified by the second parameter $callback will be executed; if $value is false, it will not be executed.

The third parameter$default is optional, and the default value is null. If $value is false and a $default value exists, the closure function specified by $default will be executed. The following is an example:

when($value,?function?()?{
????//?do?something
},?function?()?{
????//?do?something?else
});

In this example, if $value is true, the first closure function will be executed; if $value is false , the second closure function will be executed.

2. How to use the when method

When you need to execute a code block based on certain conditions, you can use the when method. For example, when you need to display date-related information, you need to execute the code block only when the date is not empty. Here is an example of using the when method:

$date?=?$request->date;

when($date,?function?()?use?($date)?{
????echo?"日期為："?.?$date;
});

In this example, if $date is not empty, the date will be displayed on the page.

3. Sample code

The following are some sample codes that demonstrate how to use the when method.

1. The link is only displayed when the user name is equal to "admin"

$user?=?Auth::user();

when($user->name?==?'admin',?function?()?{
????echo?"<a href=&#39;/admin&#39;>管理頁面</a>";
});

In this example, if the currently authenticated user is "admin", the link will be displayed on the page Displays a link to the admin page.

2. The search will only be performed when the input value meets the search conditions

$searchTerm?=?$request->input('searchTerm');

when($searchTerm,?function?()?use?($searchTerm)?{
????$results?=?Search::find($searchTerm);
????//?do?something?with?search?results
});

In this example, the search will only be performed after the user enters the search conditions in the search box. operate. If the search criteria is empty, the search operation will not be performed.

3. Perform the default operation when the condition is false

$result?=?null;

when($result,?function?()?use?($result)?{
????//?do?something
},?function?()?{
????$result?=?"默認值";
});

echo?$result;

In this example, when $result is empty, the second closure function and set a default value. The value of the $result variable finally output is "default value".

4. Summary

The when method in Laravel is a very useful tool that can help you execute specified code blocks based on conditions. It improves application performance and efficiency by avoiding unnecessary code execution. In actual development, using the when method can help you better organize your code and improve code readability.

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