How to resolve the inability to assign a value to a static variable in PHP?

In PHP, static variables can be directly assigned initial values during declaration, or be assigned values using the self:: keyword within a class method. If a static variable cannot be assigned a value, it may be due to several reasons.

1. Error in variable declaration: ensure correct syntax is used when declaring static variables, such as static $variable = value;.
2. Variable scope issue: Inside a method, static variables cannot be directly assigned, the self:: keyword needs to be used to reference static variables.
3. Class name error: Make sure to use the class name instead of an object instance to reference static variables.

Here is an example code that demonstrates how to solve the issue of not being able to assign a value to a static variable.

class MyClass {
    static $staticVariable;

    public function setStaticVariable($value) {
        self::$staticVariable = $value;
    }
}

MyClass::setStaticVariable('Hello World');
echo MyClass::$staticVariable; // 输出 Hello World

By correctly using the self:: syntax and method to reference static variables, the issue of not being able to assign values to PHP static variables can be solved.