“变量'line'在被赋值之前通过引用传递。在运行时可能会产生空引用异常。”
我将c＃转换为VB并收到警告。我在我的c＃代码中得到了结果，但不是我的VB。我假设它是因为InlineAssignHelper函数。如何在Visual Basic中正确读取和写入文件？我从未使用过VB。
static void Main(string[] args)
{
string line;
try
{
using (StreamWriter sw = new StreamWriter("C:\\writetest\\writetest.csv"))
{
string mydirpath = "C:\\chat\\";
string[] txtFileList = Directory.GetFiles(mydirpath, "*.txt");
foreach (string txtName in txtFileList)
{
string spart = ".prt";
string sam = " AM";
string spm = " PM";
string sresult = "TEST RESULT: ";
string svelocity = "MEASURED VELOCITY: ";
string sthickness = "MEASURED THICKNESS: ";
string smaxthickness = "MAX THICKNESS: ";
string sminthickness = "MIN THICKNESS: ";
string part = string.Empty;
string date = string.Empty;
string result = string.Empty;
string velocity = string.Empty;
string thickness = string.Empty;
string maxthickness = string.Empty;
string minthickness = string.Empty;
using (StreamReader sr = new StreamReader(txtName))
{
while ((line = sr.ReadLine()) != null)
{
if (!string.IsNullOrEmpty(line) && line.Trim().Length != 0)
{
if (line.Contains(sam) || line.Contains(spm))
{
// Every new date means a new record. If you already have data for a record, first write it.
if (!string.IsNullOrEmpty(date) && date.Trim().Length != 0 && !string.IsNullOrEmpty(velocity) && velocity.Trim().Length != 0 &&
!string.IsNullOrEmpty(part) && part.Trim().Length != 0 && !string.IsNullOrEmpty(result) && result.Trim().Length != 0 &&
!string.IsNullOrEmpty(thickness) && thickness.Trim().Length != 0 && !string.IsNullOrEmpty(maxthickness) && maxthickness.Trim().Length != 0 &&
!string.IsNullOrEmpty(minthickness) && minthickness.Trim().Length != 0)
{
// Parse DateTime format
DateTime dt = Convert.ToDateTime(date);
DateTime dt1 = Convert.ToDateTime(line);
TimeSpan secondsdiff = dt1.Subtract(dt);
double seconds = secondsdiff.TotalSeconds;
int I = 8;
string ckRes;
if (velocity.Remove(0, 20).Length > 4)
{
ckRes = velocity.Remove(0, 20);
}
else { ckRes = "0"; }
string ckThick;
if (thickness.Remove(0, 20).Length > 4)
{
ckThick = thickness.Remove(0, 20);
}
else { ckThick = "0"; }
string[] x = new string[I];
x[0] = date;
x[1] = ckRes;
x[2] = part.Remove(0, 21);
x[3] = result.Remove(0, 13);
x[4] = ckThick;
x[5] = maxthickness.Remove(0, 15);
x[6] = minthickness.Remove(0, 15);
x[7] = seconds.ToString();
sw.WriteLine(x[0] + "," + x[1] + "," + x[2] + "," + x[3] + "," + x[4] + "," + x[5] + "," + x[6] + "," + x[7]);
}
// Then reset data to prepare it for a new record
part = string.Empty;
result = string.Empty;
velocity = string.Empty;
thickness = string.Empty;
minthickness = string.Empty;
maxthickness = string.Empty;
date = line;
}
if (line.Contains(spart)) { part = line; }
if (line.Contains(sresult)) { result = line; }
if (line.Contains(svelocity)) { velocity = line; }
if (line.Contains(sthickness)) { thickness = line; }
if (line.Contains(smaxthickness)) { maxthickness = line; }
if (line.Contains(sminthickness)) { minthickness = line; }
}
} //end while
}
// After last record you still have some data to write
if (!string.IsNullOrEmpty(date) && date.Trim().Length != 0 && !string.IsNullOrEmpty(velocity) && velocity.Trim().Length != 0 &&
!string.IsNullOrEmpty(part) && part.Trim().Length != 0 && !string.IsNullOrEmpty(result) && result.Trim().Length != 0 &&
!string.IsNullOrEmpty(thickness) && thickness.Trim().Length != 0 && !string.IsNullOrEmpty(maxthickness) && maxthickness.Trim().Length != 0 &&
!string.IsNullOrEmpty(minthickness) && minthickness.Trim().Length != 0)
{
int I = 7;
string ckRes;
if (velocity.Remove(0, 20).Length > 4)
{
ckRes = velocity.Remove(0, 20);
}
else { ckRes = "0"; }
string ckThick;
if (thickness.Remove(0, 20).Length > 4)
{
ckThick = thickness.Remove(0, 20);
}
else { ckThick = "0"; }
string[] x = new string[I];
x[0] = date;
x[1] = ckRes;
x[2] = part.Remove(0, 21);
x[3] = result.Remove(0, 13);
x[4] = ckThick;
x[5] = maxthickness.Remove(0, 15);
x[6] = minthickness.Remove(0, 15);
sw.WriteLine(x[0] + "," + x[1] + "," + x[2] + "," + x[3] + "," + x[4] + "," + x[5] + "," + x[6] + ",9000");
}
}
}
}
catch
{
}
}
Private Shared Sub Main(ByVal args As String())
Dim line As String
Try
Using sw As New StreamWriter("C:\writetest\writetest.csv")
Dim mydirpath As String = "C:\chat\"
Dim txtFileList As String() = Directory.GetFiles(mydirpath, "*.txt")
For Each txtName As String In txtFileList
Dim spart As String = ".prt"
Dim sam As String = " AM"
Dim spm As String = " PM"
Dim sresult As String = "TEST RESULT: "
Dim svelocity As String = "MEASURED VELOCITY: "
Dim sthickness As String = "MEASURED THICKNESS: "
Dim smaxthickness As String = "MAX THICKNESS: "
Dim sminthickness As String = "MIN THICKNESS: "
Dim part As String = String.Empty
Dim [date] As String = String.Empty
Dim result As String = String.Empty
Dim velocity As String = String.Empty
Dim thickness As String = String.Empty
Dim maxthickness As String = String.Empty
Dim minthickness As String = String.Empty
Using sr As New StreamReader(txtName)
While (InlineAssignHelper(line, sr.ReadLine())) IsNot Nothing
If Not String.IsNullOrEmpty(line) AndAlso line.Trim().Length <> 0 Then
If line.Contains(sam) OrElse line.Contains(spm) Then
' Every new date means a new record. If you already have data for a record, first write it.
If Not String.IsNullOrEmpty([date]) AndAlso [date].Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(velocity) AndAlso velocity.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(part) AndAlso part.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(result) AndAlso result.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(thickness) AndAlso thickness.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(maxthickness) AndAlso maxthickness.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(minthickness) AndAlso minthickness.Trim().Length <> 0 Then
' Parse DateTime format
Dim dt As DateTime = Convert.ToDateTime([date])
Dim dt1 As DateTime = Convert.ToDateTime(line)
Dim secondsdiff As TimeSpan = dt1.Subtract(dt)
Dim seconds As Double = secondsdiff.TotalSeconds
Dim I As Integer = 8
Dim ckRes As String
If velocity.Remove(0, 20).Length > 4 Then
ckRes = velocity.Remove(0, 20)
Else
ckRes = "0"
End If
Dim ckThick As String
If thickness.Remove(0, 20).Length > 4 Then
ckThick = thickness.Remove(0, 20)
Else
ckThick = "0"
End If
Dim x As String() = New String(I - 1) {}
x(0) = [date]
x(1) = ckRes
x(2) = part.Remove(0, 21)
x(3) = result.Remove(0, 13)
x(4) = ckThick
x(5) = maxthickness.Remove(0, 15)
x(6) = minthickness.Remove(0, 15)
x(7) = seconds.ToString()
sw.WriteLine(x(0) + "," + x(1) + "," + x(2) + "," + x(3) + "," + x(4) + "," + x(5) + "," + x(6) + "," + x(7))
End If
' Then reset data to prepare it for a new record
part = String.Empty
result = String.Empty
velocity = String.Empty
thickness = String.Empty
minthickness = String.Empty
maxthickness = String.Empty
[date] = line
End If
If line.Contains(spart) Then
part = line
End If
If line.Contains(sresult) Then
result = line
End If
If line.Contains(svelocity) Then
velocity = line
End If
If line.Contains(sthickness) Then
thickness = line
End If
If line.Contains(smaxthickness) Then
maxthickness = line
End If
If line.Contains(sminthickness) Then
minthickness = line
End If
End If
'end while
End While
End Using
' After last record you still have some data to write
If Not String.IsNullOrEmpty([date]) AndAlso [date].Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(velocity) AndAlso velocity.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(part) AndAlso part.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(result) AndAlso result.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(thickness) AndAlso thickness.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(maxthickness) AndAlso maxthickness.Trim().Length <> 0 AndAlso Not String.IsNullOrEmpty(minthickness) AndAlso minthickness.Trim().Length <> 0 Then
Dim I As Integer = 7
Dim ckRes As String
If velocity.Remove(0, 20).Length > 4 Then
ckRes = velocity.Remove(0, 20)
Else
ckRes = "0"
End If
Dim ckThick As String
If thickness.Remove(0, 20).Length > 4 Then
ckThick = thickness.Remove(0, 20)
Else
ckThick = "0"
End If
Dim x As String() = New String(I - 1) {}
x(0) = [date]
x(1) = ckRes
x(2) = part.Remove(0, 21)
x(3) = result.Remove(0, 13)
x(4) = ckThick
x(5) = maxthickness.Remove(0, 15)
x(6) = minthickness.Remove(0, 15)
sw.WriteLine(x(0) + "," + x(1) + "," + x(2) + "," + x(3) + "," + x(4) + "," + x(5) + "," + x(6) + ",9000")
End If
Next
End Using
Catch
End Try
End Sub
Private Shared Function InlineAssignHelper(Of T)(ByRef target As T, ByVal value As T) As T
target = value
Return value
End Function
答案 0 :(得分：1)
你真正应该做的是改用StreamReader.EndOfStream。将您的while循环转换为：
While sr.EndOfStream = false
line = sr.ReadLine()
' rest of code'
End While
这将使代码更易于阅读，您也可以在C＃中使用相同的习惯用法。
答案 1 :(得分：0)
在使用它之前，您似乎正确地检查它是否为空，但只是因此编译器没有抱怨您可以将line设置为占位符值，如""
答案 2 :(得分：0)
While (InlineAssignHelper(line, sr.ReadLine())) IsNot Nothing
这应该更像 -
While(true)
line = sr.ReadLine()
if Not object.Equals(line, nothing) 'continue with the rest of your code...
另外，正如其他人所说，您的line变量应设置为""，您也应该抓住Catch块中的exec。
半相关的MSDN文章 - https://msdn.microsoft.com/en-us/library/system.io.stringreader.readline(v=vs.110).aspx?cs-save-lang=1&cs-lang=vb#code-snippet-1代码在页面底部的snippit有点显示了我所得到的......
编辑：作为一个脚注，这是我最好的猜测，如果没有OP实际在调试器中正确运行代码，并且不知道在catch语句中会抛出什么错误。