C# StartIndex 不能小于零。- 尝试更改字符串时出错
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/17282058/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
StartIndex cannot be less than zero. - Error when trying to change a string
提问by Nave Tseva
I have the following C# code:
我有以下 C# 代码：
ArticleContent = ds1.Tables[0].Rows[i]["ArticleContent"].ToString();
if (ArticleContent.Length > 260)
{
ArticleContent = ArticleContent.Remove(ArticleContent.IndexOf('.', 250)) + "...";
}
The problem here is that I get this error message:
这里的问题是我收到此错误消息：
StartIndex cannot be less than zero.
StartIndex 不能小于零。
Why and how can I fix it?
为什么以及如何修复它？
采纳答案by D Stanley
You are getting that error because there is no '.'character on or after index 250, so IndexOfreturns -1. You then try to remove the character at position -1which gives you the error you are seeing.
您收到该错误是因为'.'索引 250 上或之后没有字符，因此IndexOf返回-1. 然后，您尝试删除位置处的字符，-1这会给您带来您所看到的错误。
Also realize that Removeonly removes one character at that position, not everything after that position. What I suspectyou want is:
还要意识到Remove只删除该位置的一个字符，而不是该位置之后的所有字符。我怀疑你想要的是：
if (ArticleContent.Length > 260)
{
int lastPeriod = ArticleContent.LastIndexOf('.');
if(lastPeriod < 0)
lastPeriod = 257; // just replace the last three characters
ArticleContent = ArticleContent.Substring(0,lastPeriod) + "...";
}
That will add ellipses to the string, making sure it is no longer that 260 characters and breaking at a sentence if possible.
这将在字符串中添加省略号，确保它不再是 260 个字符，并在可能的情况下断句。
回答by Crab Bucket
If the below can't find the '.' it will return -1 which will not be valid for the RemoveAt
如果下面找不到'.' 它将返回 -1，这对 RemoveAt 无效
ArticleContent.IndexOf('.', 250)
回答by Kamil
As others wrote - when your ArticleContenthas no '.' character - method .Remove()will return -1.
正如其他人所写-当您ArticleContent没有 '.' 时 字符 - 方法.Remove()将返回 -1。
I suggest to add one more condition in your if:
我建议在您的if:
if (ArticleContent.Length > 260 && ArticleContent.Contains('.'))
{
ArticleContent = ArticleContent.Remove(ArticleContent.IndexOf('.', 250)) + "...";
}
回答by armen.shimoon
There's a chance that there is no . after position 250. You need to check first:
有可能没有。在位置 250 之后。您需要先检查：
ArticleContent = ds1.Tables[0].Rows[i]["ArticleContent"].ToString();
var periodPosition = ArticleContent.IndexOf('.', 250);
if (ArticleContent.Length > 260 && periodPosition >= 0)
{
ArticleContent = ArticleContent.Remove(ArticleContent.IndexOf('.', 250)) + "...";
}
回答by Derek W
Source of error:'.'does not appear after index 250. The IndexOfmethod returns -1 in this case.
错误来源：'.'不会出现在索引 250 之后IndexOf。在这种情况下，该方法返回 -1。
While others have just identified the source of the error, I will also post a fix to your problem.
虽然其他人刚刚确定了错误的来源，但我也会发布解决您的问题的方法。
Solution:Use the LastIndexOfmethod:
解决LastIndexOf方法：使用方法：
if (ArticleContent.Length > 260)
{
if (ArticleContent.Remove(ArticleContent.LastIndexOf('.') != -1)
{
ArticleContent = String.Concat(ArticleContent.Remove(ArticleContent.LastIndexOf('.')), "...");
}
else
{
ArticleContent = String.Concat(ArticleContent.Substring(0, 257), "...")
}
}
回答by Meredith Poor
ArticleContent = ds1.Tables[0].Rows[i]["ArticleContent"].ToString();
if (ArticleContent.Length > 260)
{
if (ArticleContent.Substring(250).Contains("."))
{
ArticleContent = ArticleContent.Remove(ArticleContent.IndexOf('.', 250)) + "...";
}
else
{
ArticleContent = ArticleContent.Remove(ArticleContent.Substring(0, 250)) + "...";
}
}
回答by AdmiralSnackbar
It's clear why it's failing, but what exactly are you trying to do? If it's simply to truncate a string to a particular length and indicating the truncation, I might suggest the extension method listed below. It's usage is simply:
很明显它失败的原因，但你到底想做什么？如果只是将字符串截断为特定长度并指示截断，我可能会建议使用下面列出的扩展方法。它的用法很简单：
ArticleContent = ArticleContent.Truncate(250);
Truncate extension method:
截断扩展方法：
public static string Truncate(this string pThis, int pLength)
{
if (string.IsNullOrEmpty(pThis))
return pThis;
if (0 >= pLength)
return string.Empty;
var lTruncatedString = pThis;
const string lEllipses = @"…";
if (pThis.Length > pLength)
{
var lSubstringLength = Math.Max(pLength - lEllipses.Length, 0);
lTruncatedString = pThis.Substring(0, lSubstringLength) + lEllipses;
if (lTruncatedString.Length > pLength)
lTruncatedString = lTruncatedString.Substring(0, pLength);
}
return lTruncatedString;
}
I hope this helps.
我希望这有帮助。
