C# 中的 Redim 保留？
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Redim Preserve in C#?
提问by JL.
I was shocked to find out today that C# does not support dynamic sized arrays. How then does a VB.NETdeveloper used to using ReDim Preservedeal with this in C#?
今天我震惊地发现 C# 不支持动态大小的数组。那么习惯于使用ReDim Preserve的VB.NET开发人员如何在 C# 中处理这个问题？
At the beginning of the function I am not sure of the upper bound of the array. This depends on the rows returned from the database.
在函数开始时，我不确定数组的上限。这取决于从数据库返回的行。
采纳答案by Michael L
Use ArrayLists or Generics instead
改用 ArrayLists 或泛型
回答by driis
Use a List<T>. It will dynamically size as needed.
使用 List<T>。它将根据需要动态调整大小。
回答by Jonathan Allen
You really shouldn't be using ReDim, it can be every expensive. I prefer List(Of T), but there are many options in this area.
你真的不应该使用 ReDim，它可能非常昂贵。我更喜欢 List(Of T)，但在这方面有很多选择。
That said, you had a question and here is your answer.
也就是说，你有一个问题，这是你的答案。
x = (int[]) Utils.CopyArray((Array) x, new int[10]);
回答by Jon Skeet
VB.NET doesn't have the idea of dynamically sized arrays, either - the CLR doesn't support it.
VB.NET 也没有动态大小数组的想法——CLR 不支持它。
The equivalent of "Redim Preserve" is Array.Resize<T>- but you mustbe aware that if there are other references to the original array, they won't be changed at all. For example:
“Redim Preserve”的等价物是Array.Resize<T>- 但您必须注意，如果有其他对原始数组的引用，它们根本不会被更改。例如：
using System;
class Foo
{
static void Main()
{
string[] x = new string[10];
string[] y = x;
Array.Resize(ref x, 20);
Console.WriteLine(x.Length); // Prints out 20
Console.WriteLine(y.Length); // Still prints out 10
}
}
Proof that this is the equivalent of Redim Preserve:
证明这相当于 Redim Preserve：
Imports System
Class Foo
Shared Sub Main()
Dim x(9) as String
Dim y as String() = x
Redim Preserve x(19)
Console.WriteLine(x.Length)
Console.WriteLine(y.Length)
End Sub
End Class
The two programs are equivalent.
这两个程序是等价的。
If you truly want a dynamically sized collection, you should use List<T>(or something similar). There are various issues with using arrays directly - see Eric Lippert's blog postfor details. That's not to say you should always avoid them, by any means - but you need to know what you're dealing with.
如果你真的想要一个动态大小的集合，你应该使用List<T>（或类似的东西）。直接使用数组存在各种问题 -有关详细信息，请参阅Eric Lippert 的博客文章。这并不是说你应该总是避免它们，无论如何——但你需要知道你在处理什么。
回答by Hameer Abbasi
I couldn't help but notice that noneof the above answers approach the concept of multidimensional arrays. That being said, here's an example. The array in question is predefined as x.
我不禁注意到上述答案都没有接近多维数组的概念。话虽如此，这是一个例子。有问题的数组被预定义为x。
int[,] temp = new int[newRows, newCols];
int minRows = Math.Min(newRows, x.GetUpperBound(0) + 1);
int minCols = Math.Min(newCols, x.GetUpperBound(1) + 1);
for (int i = 0; i < minRows ; ++i)
for (int j = 0; j < minCols; ++j)
temp[i, j] = x[i, j];
x = temp;
回答by Tete1805
Just for fun, here's one way to use generics in order to redim/extend a unidimensional array (add one more "row") :
只是为了好玩，这里有一种使用泛型来重新定义/扩展一维数组（再添加一个“行”）的方法：
static T[] Redim<T>(T[] arr, bool preserved)
{
int arrLength = arr.Length;
T[] arrRedimed = new T[arrLength + 1];
if (preserved)
{
for (int i = 0; i < arrLength; i++)
{
arrRedimed[i] = arr[i];
}
}
return arrRedimed;
}
And one to add n rows (though this doesn't prevent user from undersizing the array, which will throw an error in the for loop) :
还有一个添加 n 行（尽管这不会阻止用户缩小数组的大小，这会在 for 循环中引发错误）：
static T[] Redim<T>(T[] arr, bool preserved, int nbRows)
{
T[] arrRedimed = new T[nbRows];
if (preserved)
{
for (int i = 0; i < arr.Length; i++)
{
arrRedimed[i] = arr[i];
}
}
return arrRedimed;
}
I'm sure you get the idea.
我相信你明白了。
For a multidimensional array (two dimensions), here's one possibility:
对于多维数组（二维），这是一种可能性：
static T[,] Redim<T>(T[,] arr, bool preserved)
{
int Ubound0 = arr.GetUpperBound(0);
int Ubound1 = arr.GetUpperBound(1);
T[,] arrRedimed = new T[Ubound0 + 1, Ubound1];
if (preserved)
{
for (int j = 0; j < Ubound1; j++)
{
for (int i = 0; i < Ubound0; i++)
{
arrRedimed[i, j] = arr[i, j];
}
}
}
return arrRedimed;
}
In your program, use this with or even without the type specified, the compiler will recognize it :
在您的程序中，无论是否指定类型都可以使用它，编译器会识别它：
int[] myArr = new int[10];
myArr = Redim<int>(myArr, true);
or
或者
int[] myArr = new int[10];
myArr = Redim(myArr, true);
Not sure if all this is really relevant though. =D Please feel free to correct me or improve my code. ;)
不确定所有这些是否真的相关。=D 请随时纠正我或改进我的代码。;)
回答by AllDayPiano
Even though it's a long time ago it might help someone looking for a simple solution - I found something great in another forum:
即使是很久以前，它也可能会帮助寻找简单解决方案的人 - 我在另一个论坛中发现了一些很棒的东西：
//from Applied Microsoft.NET framework Programming - Jeffrey Richter
public static Array RedimPreserve(Array origArray, Int32 desiredSize)
{
System.Type t = origArray.GetType().GetElementType();
Array newArray = Array.CreateInstance(t, desiredSize);
Array.Copy(origArray, 0, newArray, 0, Math.Min(origArray.Length, desiredSize));
return newArray;
}
来源：https: //social.msdn.microsoft.com/Forums/en-US/6759816b-d525-4752-a3c8-9eb5f4a5b194/redim-in-c?forum=csharplanguage
