在计算文本文件中字符串的长度之前检查文件是否存在(Check if file exist before counting the length of the string in text file)

在计算文本文件中字符串的长度之前检查文件是否存在(Check if file exist before counting the length of the string in text file)

我很难弄清楚为什么我的这段代码给了我一个未处理的异常错误，实际上它是一个if语句..

If (Not System.IO.File.Exists("C:\file.txt") And System.IO.File.ReadAllText("C:\file.txt").Length <> "20") Then MessageBox.Show("Code executed!") Else MessageBox.Show("Failed to execute!") End If

你能告诉我我错过了什么吗？

I am having a hard time figuring up why this code of mine gives me an unhandled exception error where in fact it is an if statement..

If (Not System.IO.File.Exists("C:\file.txt") And System.IO.File.ReadAllText("C:\file.txt").Length <> "20") Then MessageBox.Show("Code executed!") Else MessageBox.Show("Failed to execute!") End If

Can you please tell me what have I missed?

最满意答案

如下所示，最好分解代码，这使得检测和调试变得更加容易。 最好写一些额外的行，这样发生的事情根本不会发生。

Dim fileName As String = "C:\file.txt" Dim FileText As String = "" If IO.File.Exists(fileName) Then FileText = IO.File.ReadAllText(fileName) If FileText.Length <> 20 Then MessageBox.Show("Code executed!") Else ' recover End If Else MessageBox.Show("Failed to execute!") End If

It is better to break down code as shown below which makes detecting and debugging a whole lot easier. Better to write a few extra lines so what happen here does not happen at all.

Dim fileName As String = "C:\file.txt" Dim FileText As String = "" If IO.File.Exists(fileName) Then FileText = IO.File.ReadAllText(fileName) If FileText.Length <> 20 Then MessageBox.Show("Code executed!") Else ' recover End If Else MessageBox.Show("Failed to execute!") End If