什么是“索引超出范围”异常，我该如何解决？ [重复]

This question already has an answer here:

这个问题在这里已有答案：

• What is an IndexOutOfRangeException / ArgumentOutOfRangeException and how do I fix it? 3 answers
• 什么是IndexOutOfRangeException / ArgumentOutOfRangeException以及如何解决它？ 3个答案

I'm getting one of the following errors:

我收到以下错误之一：

• "Index was out of range. Must be non-negative and less than the size of the collection"
• “指数超出范围。必须是非负数且小于集合的大小”
• "Insertion index was out of range. Must be non-negative and less than or equal to size."
• “插入指数超出范围。必须是非负数且小于或等于大小。”
• "Index was outside the bounds of the array."
• “指数数组的边界之外。”

What does it mean, and how do I fix it?

它是什么意思，我该如何解决？

See Also
IndexOutOfRangeException
ArgumentOutOfRangeException

另请参见IndexOutOfRangeException ArgumentOutOfRangeException

1 个解决方案

#1

Why does this error occur?

Because you tried to access an element in a collection, using a numeric index that exceeds the collection's boundaries.

因为您尝试使用超出集合边界的数字索引来访问集合中的元素。

The first element in a collection is generally located at index 0. The last element is at index n-1, where n is the Size of the collection (the number of elements it contains). If you attempt to use a negative number as an index, or a number that is larger than Size-1, you're going to get an error.

集合中的第一个元素通常位于索引0处。最后一个元素位于索引n-1处，其中n是集合的大小（它包含的元素数）。如果您尝试使用负数作为索引，或者使用大于Size-1的数字，则会出现错误。

How indexing arrays works

When you declare an array like this:

当您声明这样的数组时：

var array = new int[6]

The first and last elements in the array are

数组中的第一个和最后一个元素是

var firstElement = array[0];
var lastElement = array[5];

So when you write:

所以当你写：

var element = array[5];

you are retrieving the sixth element in the array, not the fifth one.

您正在检索数组中的第六个元素，而不是第五个元素。

Typically, you would loop over an array like this:

通常，您将循环遍历数组，如下所示：

for (int index = 0; index < array.Length; index++)
{
    Console.WriteLine(array[index]);
}

This works, because the loop starts at zero, and ends at Length-1 because index is no longer less than Length.

这是有效的，因为循环从零开始，并以Length-1结束，因为索引不再小于Length。

This, however, will throw an exception:

但是，这将抛出异常：

for (int index = 0; index <= array.Length; index++)
{
    Console.WriteLine(array[index]);
}

Notice the <= there? index will now be out of range in the last loop iteration, because the loop thinks that Length is a valid index, but it is not.

注意<=那里？ index现在将在最后一个循环迭代中超出范围，因为循环认为Length是一个有效索引，但事实并非如此。

How other collections work

Lists work the same way, except that you generally use Count instead of Length. They still start at zero, and end at Count - 1.

列表以相同的方式工作，除了您通常使用Count而不是Length。它们仍然从0开始，以Count-1结束。

for (int index = 0; i < list.Count; index++)
{
    Console.WriteLine(list[index]);
} 

However, you can also iterate through a list using foreach, avoiding the whole problem of indexing entirely:

但是，您也可以使用foreach迭代列表，完全避免索引的整个问题：

foreach (var element in list)
{
    Console.WriteLine(element.ToString());
}

You cannot index an element that hasn't been added to a collection yet.

您无法索引尚未添加到集合中的元素。

var list = new List<string>();
list.Add("Zero");
list.Add("One");
list.Add("Two");
Console.WriteLine(list[3]);  // Throws exception.