如何在运行时创建任意Array类型的实例？

I'm trying to deserialize an array of an type unknown at compile time. At runtime I've discovered the type, but I don't know how to create an instance.

我正在尝试在编译时反序列化未知类型的数组。在运行时我发现了类型,但我不知道如何创建实例。

Something like:

Object o = Activator.CreateInstance(type);

which doesn't work because there is no parameterless constructor, Array doesn't seem to have any constructor.

这是行不通的,因为没有无参数构造函数,Array似乎没有任何构造函数。

4 个解决方案

#1

Use Array.CreateInstance.

#2

You can use one of Array's CreateInstance overloads e.g.:-

您可以使用Array的CreateInstance重载之一,例如:-

object o = Array.CreateInstance(type, 10);

#3

Quite an old post, but while answering a new question, though of posting a related example of creating a multi-dimensional array.

相当古老的帖子,但在回答一个新问题时,虽然发布了创建多维数组的相关示例。

Assuming the type (elementType) as int and a two-dimensional array for example.

假设类型(elementType)为int,例如二维数组。

var size = new[] { 2, 3 };                
var arr = Array.CreateInstance(typeof(int), size);

When it's two dimensional, for example, it can be populated as

例如,当它是二维时,它可以填充为

var value = 1;
for (int i = 0; i < size[0]; i++)
    for (int j = 0; j < size[1]; j++)
        arr.SetValue(value++, new[] { i, j });
//arr = [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]

#4

An alternative is to use expression trees for performance. For e.g. if you have array type, type you could do

另一种方法是使用表达式树来提高性能。对于例如如果您有阵列类型,请键入

var ctor = type.GetConstructors().First(); // or find suitable constructor
var argsExpr = ctor.GetParameters().Select(x => Expression.Constant(0)); 
var func = Expression.Lambda<Func<object>>(Expression.New(ctor, argsExpr)).Compile();

This just returns an empty array. Probably not very useful. MSDN states GetConstructors doesn't guarantee any order, so you might need a logic to find right constructor with right parameters to instantiate with correct size. For e.g. you could do:

这只返回一个空数组。可能不是很有用。 MSDN声明GetConstructors不保证任何顺序,因此您可能需要一个逻辑来查找具有正确参数的正确构造函数,以使用正确的大小进行实例化。对于例如你可以这样做:

static Func<object> ArrayCreateInstance(Type type, params int[] bounds) // can be generic too
{
    var ctor = type
        .GetConstructors()
        .OrderBy(x => x.GetParameters().Length) // find constructor with least parameters
        .First();

    var argsExpr = bounds.Select(x => Expression.Constant(x)); // set size
    return Expression.Lambda<Func<object>>(Expression.New(ctor, argsExpr)).Compile();
}

The same can be achieved much easier with Expression.NewArrayBounds instead of Expression.New, more over it works if all you got is array element type, not array type itself. Demo:

使用Expression.NewArrayBounds而不是Expression.New可以更容易地实现相同的功能,如果您只获得了数组元素类型而不是数组类型本身,则更多。演示:

static Func<object> ArrayCreateInstance(Type type, params int[] bounds) // can be generic too
{
    var argsExpr = bounds.Select(x => Expression.Constant(x)); // set size
    var newExpr = Expression.NewArrayBounds(type.GetElementType(), argsExpr);
    return Expression.Lambda<Func<object>>(newExpr).Compile();
}

// this exercise is pointless if you dont save the compiled delegate, but for demo purpose:

x = string[] {...
y = ArrayCreateInstance(x.GetType(), 10)(); // you get 1-d array with size 10

x = string[,,] {...
y = ArrayCreateInstance(x.GetType(), 10, 2, 3)(); // you get 3-d array like string[10, 2, 3]

x = string[][] {...
y = ArrayCreateInstance(x.GetType(), 10)(); // you get jagged array like string[10][]

Just change type.GetElementType() to simply type if what you're passing is element type itself.

只需更改type.GetElementType()即可输入您传递的内容是元素类型本身。

#1