php教程

ArrayAccess::offsetExists

(PHP 5, PHP 7)

ArrayAccess::offsetExists检查一个偏移位置是否存在

说明

abstract public ArrayAccess::offsetExists ( mixed $offset ) : boolean

检查一个偏移位置是否存在。

对一个实现了 ArrayAccess 接口的对象使用 isset()empty() 时,此方法将执行。

Note:

当使用 empty() 并且仅当 ArrayAccess::offsetExists() 返回 TRUE 时,ArrayAccess::offsetGet() 将被调用以检查是为否空。

参数

offset

需要检查的偏移位置。

返回值

成功时返回 TRUE, 或者在失败时返回 FALSE

Note:

如果一个非布尔型返回值被返回,将被转换为布尔型

范例

Example #1 ArrayAccess::offsetExists() 范例

<?php
class obj implements arrayaccess {
    public function 
offsetSet($offset$value) {
        
var_dump(__METHOD__);
    }
    public function 
offsetExists($var) {
        
var_dump(__METHOD__);
        if (
$var == "foobar") {
            return 
true;
        }
        return 
false;
    }
    public function 
offsetUnset($var) {
        
var_dump(__METHOD__);
    }
    public function 
offsetGet($var) {
        
var_dump(__METHOD__);
        return 
"value";
    }
}

$obj = new obj;

echo 
"Runs obj::offsetExists()\n";
var_dump(isset($obj["foobar"]));

echo 
"\nRuns obj::offsetExists() and obj::offsetGet()\n";
var_dump(empty($obj["foobar"]));

echo 
"\nRuns obj::offsetExists(), *not* obj:offsetGet() as there is nothing to get\n";
var_dump(empty($obj["foobaz"]));
?>

以上例程的输出类似于:

Runs obj::offsetExists()
string(17) "obj::offsetExists"
bool(true)

Runs obj::offsetExists() and obj::offsetGet()
string(17) "obj::offsetExists"
string(14) "obj::offsetGet"
bool(false)

Runs obj::offsetExists(), *not* obj:offsetGet() as there is nothing to get
string(17) "obj::offsetExists"
bool(true)

User Contributed Notes

kgun ! mail ! com 08-Feb-2019 11:41
If you care about key-strictness, you may need to use an alternative solution (maybe overriding offsetExists() in subclass(es)). So, offsetExists() acts like array_key_exists() and does not handle the key types. Here;

<?php
$array
= ['one', 'two', 3.=>'boom!'];
$arrayObject = new ArrayObject($array);
$key = '3';
var_dump(array_key_exists($key, $array)); // bool(true)
var_dump(in_array($key, array_keys($array), true)); // bool(false)
var_dump($arrayObject->offsetExists($key)); // bool(true)
var_dump(in_array($key, array_keys($arrayObject->getArrayCopy()), true)); // bool(false)

// @override;
public function offsetExists($key)
{
   
// make a strict check
   
return in_array($key, array_keys($this->getArrayCopy()), true);
}
?>
driezasson at icloud dot com 02-Mar-2015 07:10
Note that even though isset/empty works on classes implementing ArrayAccess, array_key_exists does not. At least not in PHP 5.3.

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