I need to do some refactoring (actually it's A LOT, but this small step will be very helpful for the whole process). So, let's say I've got this code snippet:
If xmlDoc.SelectSingleNode("/dang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/dang")
Type = "dang"
ElseIf xmlDoc.SelectSingleNode("/nang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/nang")
Type = "nang"
ElseIf xmlDoc.SelectSingleNode("/lang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/lang")
Type = "lang"
ElseIf xmlDoc.SelectSingleNode("/tang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/tang")
Type = "tang"
ElseIf xmlDoc.SelectSingleNode("/xtang") IsNot Nothing Then
universalNode = xmlDoc.SelectSingleNode("/xtang")
Type = "xtang"
End If
It's in the body of a big function and I want to take it out to a separate function. So, what I was wondering is whether it will be better to pass both universalNode and Type by value and just assign to them the values, without the need of returning anything? Is that going to work well or it is risky?
If it was just the Type that I'm working on, i.e., then I would just return it, but it's more than 1 variable that is being changed, and both are local variables for the big function, from which I am taking out this code snippet.
Any other suggestions maybe?
You can pass the variables by reference (not by value) to the function, it's not a bad practice and should work:
Public Sub MyFunc(ByRef node As MyNode, ByRef typ As String)
node = ...
typ = ...
End Sub
Or you can return some complex data holder:
Public Class MyParams
Public node As MyNode
Public typ As String
End Class
Public MyParams MyFunc()
Dim result As New MyParams()
result.node = ...
result.typ = ...
Return result
End Sub
Related
So I'm reading through my source code looking for places to improve the code when I come across this unholy chunk of code.
Public Function ReadPDFFile(filePath As String,
Optional maxLength As Integer = 0) As List(Of String)
Dim sbContents As New Text.StringBuilder
Dim cArrayType As Type = GetType(PdfSharp.Pdf.Content.Objects.CArray)
Dim cCommentType As Type = GetType(PdfSharp.Pdf.Content.Objects.CComment)
Dim cIntegerType As Type = GetType(PdfSharp.Pdf.Content.Objects.CInteger)
Dim cNameType As Type = GetType(PdfSharp.Pdf.Content.Objects.CName)
Dim cNumberType As Type = GetType(PdfSharp.Pdf.Content.Objects.CNumber)
Dim cOperatorType As Type = GetType(PdfSharp.Pdf.Content.Objects.COperator)
Dim cRealType As Type = GetType(PdfSharp.Pdf.Content.Objects.CReal)
Dim cSequenceType As Type = GetType(PdfSharp.Pdf.Content.Objects.CSequence)
Dim cStringType As Type = GetType(PdfSharp.Pdf.Content.Objects.CString)
Dim opCodeNameType As Type = GetType(PdfSharp.Pdf.Content.Objects.OpCodeName)
Dim ReadObject As Action(Of PdfSharp.Pdf.Content.Objects.CObject) = Sub(obj As PdfSharp.Pdf.Content.Objects.CObject)
Dim objType As Type = obj.GetType
Select Case objType
Case cArrayType
Dim arrObj As PdfSharp.Pdf.Content.Objects.CArray = DirectCast(obj, PdfSharp.Pdf.Content.Objects.CArray)
For Each member As PdfSharp.Pdf.Content.Objects.CObject In arrObj
ReadObject(member)
Next
Case cOperatorType
Dim opObj As PdfSharp.Pdf.Content.Objects.COperator = DirectCast(obj, PdfSharp.Pdf.Content.Objects.COperator)
Select Case System.Enum.GetName(opCodeNameType, opObj.OpCode.OpCodeName)
Case "ET", "Tx"
sbContents.Append(vbNewLine)
Case "Tj", "TJ"
For Each operand As PdfSharp.Pdf.Content.Objects.CObject In opObj.Operands
ReadObject(operand)
Next
Case "QuoteSingle", "QuoteDbl"
sbContents.Append(vbNewLine)
For Each operand As PdfSharp.Pdf.Content.Objects.CObject In opObj.Operands
ReadObject(operand)
Next
Case Else
'Do Nothing
End Select
Case cSequenceType
Dim seqObj As PdfSharp.Pdf.Content.Objects.CSequence = DirectCast(obj, PdfSharp.Pdf.Content.Objects.CSequence)
For Each member As PdfSharp.Pdf.Content.Objects.CObject In seqObj
ReadObject(member)
Next
Case cStringType
sbContents.Append(DirectCast(obj, PdfSharp.Pdf.Content.Objects.CString).Value)
Case cCommentType, cIntegerType, cNameType, cNumberType, cRealType
'Do Nothing
Case Else
Throw New NotImplementedException(obj.GetType().AssemblyQualifiedName)
End Select
End Sub
Using pd As PdfSharp.Pdf.PdfDocument = PdfSharp.Pdf.IO.PdfReader.Open(filePath, PdfSharp.Pdf.IO.PdfDocumentOpenMode.ReadOnly)
For Each page As PdfSharp.Pdf.PdfPage In pd.Pages
ReadObject(PdfSharp.Pdf.Content.ContentReader.ReadContent(page))
If maxLength > 0 And sbContents.Length >= maxLength Then
If sbContents.Length > maxLength Then
sbContents.Remove(maxLength - 1, sbContents.Length - maxLength)
End If
Exit For
End If
sbContents.Append(vbNewLine)
Next
End Using
'Return sbContents.ToString
Dim ReturnList As New List(Of String)
For Each Line In sbContents.ToString.Split(vbNewLine)
If String.IsNullOrWhiteSpace(Line.Trim) Then
Else
ReturnList.Add(Line.Trim)
End If
Next
Return ReturnList
End Function
All this does is read the text parts of a PDF using PDFSharp. What caught my eye however was line 17. Is that a Sub inside of the function?
So, what exactly is this Sub inside of a function? I didn't write this code so I've never seen anything like this before.
How does this work exactly and why wouldn't I use a function to do the processing and then return the results?
In short, my question is, what is this, how does it work, and why would I want to use something like this?
That's a so-called Lambda expression. They're used to create inline (or more correctly: in-method) methods, which makes them more dynamic than normal methods.
In your example a lambda expression is not necessary and only makes the code harder to understand. I suppose the author of that code wrote a lambda expression instead of a separate method in order to not expose ReadObject to any outside code.
One of the best uses for a lambda expression IMO is when you want to make thread-safe calls to the UI thread, for instance:
If Me.InvokeRequired = True Then
Me.Invoke(Sub() TextBox1.Text = "Process complete!")
Else
TextBox1.Text = "Process complete!"
End If
...where the same code without a lambda would look like this:
Delegate Sub UpdateStatusTextDelegate(ByVal Text As String)
...somewhere else...
If Me.InvokeRequired = True Then
Me.Invoke(New UpdateStatusTextDelegate(AddressOf UpdateStatusText), "Process complete!")
Else
UpdateStatusText("Process complete!")
End If
...end of somewhere else...
Private Sub UpdateStatusText(ByVal Text As String)
TextBox1.Text = Text
End Sub
There are also other examples where lambda expressions are useful, for instance if you want to initialize a variable but do some processing at first:
Public Class Globals
Public Shared ReadOnly Value As Integer = _
Function()
DoSomething()
Dim i As Double = CalculateSomething(3)
Return Math.Floor(3.45 * i)
End Function.Invoke()
...
End Class
Yet another usage example is for creating partially dynamic event handlers, like this answer of mine.
While CommitReader.Read()
Yield New Commit() With {
.FirstValue = CommitReader.GetInt32(CommitReader.GetOrdinal("FirstValue")),
.SecondValue = CommitReader.GetString(CommitReader.GetOrdinal("SecondValue")).Trim(),
'Lots of values
End While
I know I can do something like this; however there are 24 properties and I would like to make this part as clean as possible
While CommitReader.Read()
new Commit (){
Dim index As Integer = reader.GetOrdinal("FirstValue")
If reader.IsDBNull(index) Then
FirstValue = String.Empty
Else
FirstValue = reader(index)
End If
index = reader.GetOrdinal("SecondValue")
If reader.IsDBNull(index) Then
SecondValue = String.Empty
Else
SecondValue = reader(index)
End If
}
End While
Is there a better way to handle this type of thing? I am mainly a C# developer so if the syntax is off a little sorry, I am winging it in VB.
It's a shame that SqlDataReader doesn't have the generic Field extension method like DataRow does, but you could define your own extension method (has to be in a module in VB.NET) to help with the null checks, perhaps something like this:
<Extension>
Function GetValue(Of T)(rdr As SqlDataReader, i As Integer) As T
If rdr.IsDBNull(i) Then
Return Nothing
End If
Return DirectCast(rdr.GetValue(i), T)
End Function
And use it something like this:
While CommitReader.Read()
Yield New Commit() With {
.FirstValue = CommitReader.GetValue(Of Integer?)(CommitReader.GetOrdinal("FirstValue")),
.SecondValue = CommitReader.GetValue(Of String)(CommitReader.GetOrdinal("SecondValue")),
'Lots of values
End While
I haven't tested this fully to make sure it handles all data types appropriately (may be worth looking at DataRowExtensions.Field to see how it does it).
Note that you are using String.Empty as the "null" value for strings, while this will use Nothing/null (I also had to remove the .Trim call to avoid NREs). If you want empty string instead, you could use (adding the Trim back in):
.SecondValue = If(CommitReader.GetValue(Of String)(CommitReader.GetOrdinal("SecondValue")), String.Empty).Trim()
You may also want to move the GetOrdinal calls out of the loop to improve performance.
Obviously you have repetition in your code if ... else ... condition.
So you can extract it in another method.
For your case generic extension method seems good candidate.
Public Module Extensions
<Extension>
Public Function GetValueOrDefault(Of T)(originalValue As object,
defaultValue As T) As T
If originalValue = DbNull.Value Then
Return defaultValue
End If
return DirectCast(originalValue, T)
End Function
End Module
Then use it:
While CommitReader.Read() = True
Dim temp = new Commit With
{
Dim index As Integer = reader.GetOrdinal("FirstValue")
FirstValue = reader(index).GetValueOrDefault(String.Empty)
Dim index As Integer = reader.GetOrdinal("SecondValue")
FirstValue = reader(index).GetValueOrDefault(String.Empty)
}
End While
You can create another overload which return "default" value for given type if it is DbNull
<Extension>
Public Function GetValueOrDefault(Of T)(originalValue As object) As T
Return originalValue.GetValueOrDefault(Nothing)
End Function
Nothing in vb.net is default value, for reference types it is null for Integer it is 0 for example.
For using this overload you need provide type parameter explicitly
While CommitReader.Read() = True
Dim temp = new Commit With
{
Dim index As Integer = reader.GetOrdinal("FirstValue")
FirstValue = reader(index).GetValueOrDefault(Of String)()
Dim index As Integer = reader.GetOrdinal("SecondValue")
FirstValue = reader(index).GetValueOrDefault(Of String)()
}
End While
Notice that your solution executing reader twice, for checking is it null and for reading value. This can cause "tiny" performance issue.
So in extension method above we read value only once and then check value for DbNull.
If you concatenate a string with a Null you get the string:
FirstValue = reader(index) & ""
Kind of "unprofessional" but saves a lot of coding time if all you are doing is converting a possible Null to an empty string. Easy to forget however, so later data dependent errors may pop up.
The codes:
Private m_log_dataTable As System.Data.DataTable = Nothing
Private m_freq As String = Nothing
Private m_r As Single = Nothing
Private m_l As Single = Nothing
Private m_c As Single = Nothing
Private m_rp As Single = Nothing
Private m_rs As Single = Nothing
Private m_z As Single = Nothing
Private m_esr As Single = Nothing
Private m_dcr As Single = Nothing
Private m_q As Single = Nothing
Private m_d As Single = Nothing
...
Private Sub LOG()
Try
m_freq = Nothing
m_r = Nothing
m_l = Nothing
m_c = Nothing
m_rp = Nothing
m_rs = Nothing
m_z = Nothing
m_esr = Nothing
m_dcr = Nothing
m_q = Nothing
m_d = Nothing
m_value = Nothing
m_unit = Nothing
m_log_dataTable.Rows.Add(DateTime.Now, getDUT(), getMode(), m_freq, m_r, m_l, m_c, m_r, m_rs, m_z, m_esr, m_dcr, m_q, m_d)'Line1
m_log_dataTable.Rows.Add(DateTime.Now, getDUT(), getMode(), Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing)'Line2
Catch ex As Exception
MsgBox("Exception when logging:" + ex.Message)
End Try
End Sub
Output:
Why line1 (in the above codes) write 0 to the datatable instead of Nothing?
What should I do?
Thanks
You need to use a Nullable type. Change all of your single types to single? and try it again.
Private m_r As Single? = Nothing
Private m_l As Single? = Nothing
// etc
As Gabor commented, you'll need to access the Value property or one of the other methods that are available to Nullable(Of T).
m_r.Value ' Access the underlying value
m_r.GetValueOrDefault() ' Underlying value or, if none, default for the underlying type
m_r.GetValueOrDefault(3) ' Underlying value or, if none, some default value you decide
Nothing in VB.NET equals to default(T) in C# (instead of null). Value types cannot be null therefore in db they are represented in columns with not null constraint.
You indeed should use Nullable(Of Single) (which is the same as Single?) for your fields.
But of course this is not enough. You should modify the columns in the database so that they will have null constraint instead of not null and the System.Data.DataTable should be configured the same way.
Coz The default value of Single is 0.You can use string column or you can define target datagridview's columns.
DataGridViewCellStyle1.Format = "N"
Column1.DefaultCellStyle = DataGridViewCellStyle1
I am trying to run through all the controls in a panel and find which properties the user has changed for each control.
So I have this code:
Private Sub WriteProperties(ByVal cntrl As Control)
Try
Dim oType As Type = cntrl.GetType
'Create a new control the same type as cntrl to use it as the default control
Dim newCnt As New Control
newCnt = Activator.CreateInstance(oType)
For Each prop As PropertyInfo In newCnt.GetType().GetProperties
Dim val = cntrl.GetType().GetProperty(prop.Name).GetValue(cntrl, Nothing)
Dim defVal = newCnt.GetType().GetProperty(prop.Name).GetValue(newCnt, Nothing)
If val.Equals(defVal) = False Then
'So if something is different....
End If
Next
Catch ex As Exception
MsgBox("WriteProperties : " & ex.Message)
End Try
End Sub
Now I face three problems:
When the property refers to image (BackGround Image) I have an error :
ImageObject reference not set to an instance of an object.
The second problem is that the code:
If val.Equals(defVal) = False Then
'So if something is different....
End If
is executes sometimes when the val and defVal are the same.
This is happening in cases that the property is a "parentProperty" like FlatAppearance (which has more child properties)
My loop doesn't look into basic properties like Size, or Location which I want
Re: Not set to an instance of an object, do something like ...
If val IsNot Nothing AndAlso defVal IsNot Nothing AndAlso Not val.Equals(defVal) Then
Which will only do the comparison if neither value is Nothing (aka Null).
Unfortunately, #2 is a fundamental problem - .Equals by default checks if the 2 object references point at the same object in memory - eg if You did
Dim A As New SomeClass
Dim B As New SomeClass
If A.Equals(B) Then
...
End If
Would return False unless SomeClass has an overridden equality comparer, which many classes do not.
You could check if the value in question is a type you know you can compare (Integer, String, Double, etc). If not, you could iterate through its properties and perform the same check again. This would allow you to compare the public properties of any type for equality but wouldn't guarantee the internal state of the classes is the same.
Something Like (Untested/Pseudo)...
Function Compare (PropA, PropB) As Boolean
Dim Match = True
If PropA.Value Is Nothing Or PropB.Value Is Nothing
Match = False
Else
If PropA.Value.GetType.IsAssignableFrom(GetType(String)) Or
PropA.Value.GetType.IsAssignableFrom(GetType(Integer)) Or ... Then
Match = PropB.Value.Equals(PropB.Value)
Else
For Each Prop In PropA.Value.GetType.GetProperties()
Match = Compare(Prop, PropB.Value.GetType.GetProperty(Prop.Name))
If Not Match Then Exit For
Next
End If
End If
Return Match
End Function
This is still not ideal as the internal states of the values may differ.
Rather than giving the very specific case (which I did earlier), let me give a general example. Let's say that I have a function, called callingFunction. It has one parameter, called parameter. Parameter is of an unknown type. Let us then say that I wish to copy this parameter, and return it as a new object. For example, in pseudo code, something along the lines of...
Function callingFunction(ByVal parameter As Object) As Object
Dim newObj As New Object
'newObj has the same value as parameter, but is a distinctly different object
'with a different reference
newObj = parameter
return newObj
End Function
EDIT: Additional Information
The first time I posted this question, I received only one response - I felt that perhaps I made the question too specific. I guess I will explain more, perhaps that will help. I have an ASP page with 10 tables on it. I am trying, using the VB code behind, to come up with a single solution to add new rows to any table. When the user clicks a button, a generic "add row" function should be called.
The difficulty lies in the fact that I have no guarantee of the contents of any table. A new row will have the same contents as the row above it, but given that there are 10 tables, 1 row could contain any number of objects - text boxes, check boxes, etc. So I want to create a generic object, make it of the same type as the row above it, then add it to a new cell, then to a new row, then to the table.
I've tested it thoroughly, and the only part my code is failing on lies in this dynamic generation of an object type. Hence why I asked about copying objects. Neither of the solutions posted so far work correctly, by the way. Thank you for your help so far, perhaps this additional information will make it easier to provide advice?
You can't do this in general. And it won't be a good idea, for example, if parameter is of a type which implements the singleton pattern. If parameter is of a type which supports copying, it should implement the ICloneable interface. So, your function could look like this:
Function MyFunc(ByVal parameter As Object) As Object
Dim cloneableObject As ICloneable = TryCast(parameter, ICloneable)
If Not cloneableObject Is Nothing Then
Return cloneableObject.Clone()
Else
Return Nothing
End If
End Function
You could implement something like this:
Dim p1 As Person = New Person("Tim")
Dim p2 As Object = CloneObject(p1)
Dim sameRef As Boolean = p2 Is p1 'false'
Private Function CloneObject(ByVal o As Object) As Object
Dim retObject As Object
Try
Dim objType As Type = o.GetType
Dim properties() As Reflection.PropertyInfo = objType.GetProperties
retObject = objType.InvokeMember("", System.Reflection.BindingFlags.CreateInstance, Nothing, o, Nothing)
For Each propertyInfo As PropertyInfo In properties
If (propertyInfo.CanWrite) Then
propertyInfo.SetValue(retObject, propertyInfo.GetValue(o, Nothing), Nothing)
End If
Next
Catch ex As Exception
retObject = o
End Try
Return retObject
End Function
Class Person
Private _name As String
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Public Sub New()
End Sub
Public Sub New(ByVal name As String)
Me.Name = name
End Sub
End Class
Here's a simple class that will work for most objects (assumes at least .Net 2.0):
Public Class ObjectCloner
Public Shared Function Clone(Of T)(ByVal obj As T) As T
Using buffer As MemoryStream = New MemoryStream
Dim formatter As New BinaryFormatter
formatter.Serialize(buffer, obj)
buffer.Position = 0
Return DirectCast(formatter.Deserialize(buffer), T)
End Using
End Function
End Class