call_user_func_array传递参数到构造函数 [英] call_user_func_array passing arguments to a constructor

问题描述

我搜索了很多Google结果页面，以及这里的stackoverflow，但找不到一个似乎适合我的情况的解决方案。我似乎只有一个最后一个陷阱在我试图建立的函数，它使用call_user_func_array动态创建对象。

I have searched many a page of Google results as well as here on stackoverflow but cannot find a solution that seems to fit my situation. I appear to have but one last snag in the function I am trying to build, which uses call_user_func_array to dynamically create objects.

我可以得到的致命错误是类Product的对象无法转换为字符串。当错误发生时，在日志中我得到其中的五个（每个参数一个）： PHP警告：缺少参数1 Product :: __ construct（），致命错误。

The catchable fatal error I am getting is Object of class Product could not be converted to string. When the error occurs, in the log I get five of these (one for each argument): PHP Warning: Missing argument 1 for Product::__construct(), before the catchable fatal error.

这是函数的代码：

public static function SelectAll($class, $table, $sort_field, $sort_order = "ASC")
{  
/* First, the function performs a MySQL query using the provided arguments. */

$query = "SELECT * FROM " .$table. " ORDER BY " .$sort_field. " " .$sort_order;
$result = mysql_query($query);

/* Next, the function dynamically gathers the appropriate number and names of properties. */

$num_fields = mysql_num_fields($result);
for($i=0; $i < ($num_fields); $i++)
{
  $fetch = mysql_fetch_field($result, $i);
  $properties[$i] = $fetch->name;
}

/* Finally, the function produces and returns an array of constructed objects.*/

while($row = mysql_fetch_assoc($result))
{
  for($i=0; $i < ($num_fields); $i++)
  {
    $args[$i] = $row[$properties[$i]];
  }
  $array[] = call_user_func_array (new $class, $args);
}

return $array;
}

现在，如果我注释掉call_user_func_array行并将其替换为： / p>

Now, if I comment out the call_user_func_array line and replace it with this:

$array[] = new $class($args[0],$args[1],$args[2],$args[3],$args[4]);

页面按原样加载，并填充我正在构建的表。所以一切都是绝对功能，直到我尝试实际使用 $ args 数组 call_user_func_array 。

The page loads as it should, and populates the table I am building. So everything is absolutely functional until I try to actually use my $args array within call_user_func_array.

有没有一些关于调用该数组的细节？我读了一次call_user_func_array的PHP手册，然后一些，在那个页面的例子似乎显示人们只是建立一个数组，并调用它的第二个参数。

Is there some subtle detail about calling that array that I am missing? I read the PHP manual for call_user_func_array once, and then some, and examples on that page seemed to show people just building an array and calling it for the second argument. What could I be doing wrong?

推荐答案

您不能调用 $ class

You can't call the constructor of $class like this:

call_user_func_array (new $class, $args);

这不是有效回电作为第一个参数。让我们分开选择：

That's no valid callback as first parameter. Let's pick this apart:

call_user_func_array (new $class, $args);

与

$obj = new $class;
call_user_func_array ($obj, $args);

正如你所看到的， $ class 已在调用 call_user_func_array 之前调用。由于没有参数，您将看到此错误消息：

As you can see, the constructor of $class has been already called before call_user_func_array comes into action. As it has no parameters, you see this error message:

Missing argument 1 for Product::__construct()

接下来， $ obj 有效回调必须是字符串或数组（或例外是非常特殊的对象： Closure ，但这里没有讨论，我只是为了完整性而命名）。

Next to that, $obj is of type object. A valid callback must be either a string or an array (or exceptionally a very special object: Closure, but that's out of discussion here, I only name it for completeness).

As $ obj 是一个对象，不是有效的回调，因此您会看到PHP错误消息：

As $obj is an object and not a valid callback, so you see the PHP error message:

Object of class Product could not be converted to string.

PHP尝试将对象转换为字符串，但不允许。

PHP tries to convert the object to string, which it does not allow.

你可以看到，你不能轻易地创建一个构造函数的回调，因为对象不存在。也许这就是为什么你不能在手册中轻松查找它。

So as you can see, you can't easily create a callback for a constructor, as the object yet not exists. Perhaps that's why you were not able to look it up in the manual easily.

构造函数需要一些特殊的处理：如果你需要传递变量参数到一个类构造函数尚未初始化对象，则可以使用 ReflectionClass 执行此操作： / p>

Constructors need some special dealing here: If you need to pass variable arguments to a class constructor of a not-yet initialize object, you can use the ReflectionClass to do this:

  $ref = new ReflectionClass($class);
  $new = $ref->newInstanceArgs($args);

请参阅 ReflectionClass :: newInstanceArgs

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