Nothing Equals String.Empty, Null Does Not Equal String.Empty?
Jun 28, 2010
This must've have been asked before but I couldn't locate it. In a mixed code project (VB and C#) we were debugging some old Visual Basic code where a statement as follows could be found:
If Request.Params("xxx") <> "" Then
'do something
I considered this a bug as Request.Params could be null, in which case the statement would've become false which wasn't the idea. So I thought. I just found out, -- probably for the tenth time and I will keep forgetting -- that the following two statements are not equal, while Nothing in VB should be equal to null in C# (thought I):
if(String.Empty == null) // always false
If String.Empty = Nothing Then ' always true
Should I dismiss this as a typical Microsoft backward compatibility effort, or should I consider this a huge error in the VB.NET compiler? Does anybody know the Microsoftean opinion on this oddity?
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Apr 13, 2010
Why does the first if statement evaluate to true? I know if I use "is" instead of "=" then it won't evaluate to true. If I replace String.Empty with "Foo" it doesn't evaluate to true. Both String.Empty and "Foo" have the same type of String, so why does one evaluate to true and the other doesn't?
//this evaluates to true
If Nothing = String.Empty Then
[CODE]...
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Jul 28, 2009
I'm using FileHelper to generate object's property. Here is an example of one property:
<FieldOptional(), _
FieldTrim(TrimMode.Both)> _
<FieldNullValue(GetType(String), " ")> _
Public StoreNo As String
As you can see the StoreNo will either have a value or " ", one of the business policy is to check if the StoreNo is empty or nothing if the object's StoreNo is empty or null then the record will not create.
I though about creating an HasValue Function in the class to check the StoreNo and other properties in the object but I feel like it is a hack.
Public Function HasValue() As Boolean
Dim _HasValue As Boolean = True
If StringHelper.IsNullOrBlank(Me.StoreNo) Then
[Code]....
I don't think this approach is an ideal solution. what if the StoreNo is remove or change to something else. What's the best approach to check object's property?
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Jan 4, 2012
I have a couple of textfields in a Windows form. One of these textfields is allowed to be NULL. When I enter a value for every field, it is all inserted, no problem. When I leave the field (txtGewicht) blank, I can't seem to be able to insert NULL in Access Database.
If Double.TryParse(txtGewicht.Text, 0) Then
klant.Gewicht = Double.Parse(txtGewicht.Text)
Else
[Code]....
This is what I get:
"Cannot set column 'Gewicht' to NULL, please use DBNull instead"
So I changed 'Nothing' to DBNull.value, but it then tells me that System.DBNull cannot be converted to type Double.
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Aug 11, 2010
I have a array of strings and I am looping through them, but the string might be empty so I am trying this:
[Code]...
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Feb 7, 2011
I need to sort a DataTable or DataGridView by a column that is a string value, but with null/empty values at the BOTTOM when sorting ASCENDING. The DataTable is NOT populated by a SQL statement, so no order by. If I do
[Code]...
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Dec 9, 2011
I have a property called ReplacementTo and I set a value to it based on the selecteditem from the combobox, like this:
classEquipmentItem.ReplacementTo = cmbReplcmnt.SelectedItem.ToString
Now I can't use cmbReplcmnt.Text because what I actually need is the value of that SelectedItem
So problem is, if the user leaves the combobox as blank, it throws a null exception.I decided to use the IIf function then:classEquipmentItem.ReplacementTo = IIf(IsNothing(cmbReplcmnt.SelectedItem.ToString), classEquipmentItem.ReplacementTo = "", cmbReplcmnt.SelectedItem.ToString)
Unfortunately I still get the error I tried using a Try-Catch for it and it worked, but I don't want to rely on the Try-Catch, so I was wondering is there a another way to work this through?
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Mar 5, 2009
I need to sort a DataTable or DataGridView by a column that is a string value, but with null/empty values at the BOTTOM when sorting ASCENDING.The DataTable is NOT populated by a SQL statement, so no order by.If I doDataGridView1.Sort(New RowComparer(System.ComponentModel.ListSortDirection.Ascending))then it throws an exception, saying that the DataGridView is DataBound, which is correct, but doesn't help me, and I want to keep it databound.
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Feb 4, 2012
I was trying to call a method using Reflection on a method that has a STRING parameter.However a STRING does not have a parameterless constructor.So instead of something like.>>
Option Strict On
Option Explicit On
Option Infer Off
Public Class Form1
[code].....
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Mar 2, 2009
i have a string array that i want to output to a text file. the array size is 10000. i fill the array starting from 0 with some strings. at the end, i only want to show the array from index 256 to the last array that is not empty (for eg. if the array is filled with data from 0 to 2000, i only want the text file to show the data from 256 to 2000 and ignore the remaining strings). Is there any function to do this?t i use is shown below
Dim myArray(10000) as string
Dim strArray As New System.IO.StreamWriter("c:List.txt")
strArray.WriteLine("{0,10}{1,30}", "Index", "Symbol")
[code].....
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Mar 2, 2009
i have a string array that i want to output to a text file. the array size is 10000. i fill the array starting from 0 with some strings. at the end, i only want to show the array from index 256 to the last array that is not empty (for eg. if the array is filled with data from 0 to 2000, i only want the text file to show the data from 256 to 2000 and ignore the remaining strings). Is there any function to do this? i am using visual basic express 2008. The code that i use is shown below
[Code]...
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Feb 24, 2010
I have a nullable database field of type varchar. I am writing a unit test for a service method that retrieves the value of this field. The service method uses a custom DAL that returns a value of String.Empty if the database field is Null (this is desired behaviour).
[Code]...
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Oct 2, 2009
just found out that replace(string does not do the same as string.replace when my string variable was an empty str the first one returns "nothing" and the second returns an empty string (as expected).just sloppy coding anyhow, it was a function that was converted from classic asp and never rewritten properly. [code]
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Jun 8, 2009
I have a webpage that has a Telerik RadComboBox on the page. One of the properties of this ComboBox is EmptyMessage, which fills the combobox with a message when an item is not selected. I am binding my combobox to a datasource at runtime and for some reason, it wipes this EmptyMessage away. Is there a way to keep my data items in tact and have the empty message there too?
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May 19, 2010
I'm using VB's StringBuilder, and I was curious what is considered "best practice" for emptying the builder/setting it to a new string. Would it be something like this:[code]or is there a "Better" way?
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Sep 16, 2010
Possible Duplicate: In C#, should I use string.Empty or String.Empty or "" ? I just don't understand the benefits of using String.Empty over "". Aside it being strongly typed its longer.
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Apr 30, 2012
I am storing value in Double. If that value is 0.0, I dont want to display anything.
means,
If Value = 14.0, I want to display Value = 14.0
If value = 0.0, I want to display Value =
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Nov 26, 2010
I have an attribute class:
[code]...
With that said, shall the Private Property Attributes() As String() not return the values of DirectoryAttribute placed over the interfaces properties as well, since I specify True in the inheritance parameter of the Type.GetCustomAttributes method?
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Jan 5, 2011
In my EF4 EntityModel I have an entity named Users. Users have the common UserName and Password string fields. If I do something like this
Dim u as new USERS
U.UserName = String.Empty
Then U.UserName are still Nothing.
But if I Do Something like this
Dim u as new USERS
u.UserName = "A"
u.UserName = String.Empty
Then U.UserName take String.Empty as value without problem.
The reason is the way that EF4 generate the UserName Property
Public Property UserName() As Global.System.String
Get
Return _UserName
End Get
[Code] .....
I do not want to make two assignations every time I want to set string.empty to a property with a nothing value, and I do not want to remember that I must do it in this way everytime, because I'm pretty sure that I will forget it and then I will introduce bugs in the code. I just want to assign the empty.string value to a property and the property take "" as value.
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Aug 19, 2009
How can i check if a string collection is empty? I tried
VB.NET
My.Settings.IPBank.Count = 0
But it said
Quote:
Object reference not set to an instance of an object.
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Oct 31, 2011
I'm sure this is simple to do but I'm struggling to get this work, I've tried using convert.tostring, decimal.tostring, ctype(object, type) and cstr(object) but without success. I guess I'm trying to change the decial object to a string object and then assign it a value of empty string but always get type mismatch error.[code]
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Jan 31, 2011
How can I create an empty string that is a certain length?
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Jul 27, 2010
In my program i have it send an email and it send the email but after it sends i get this error "The parameter 'addresses' cannot be an empty string. Parameter name: addresses". I don't know why.
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Apr 26, 2011
To make it clear this IS homework, however this is also a method of research. i only ask when i get in binds i can not find answers to in other forums . There are so many i could spend more time[code]...
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Mar 31, 2009
I always initialize my variables with a value when declaring them.I was wondering if using String.Empty to initialize a variable is correct.'Is this OK ?
Dim strValue As String = String.Empty
'I used to do
Dim strValue2 As String = ""
On the same subject.
[code]....
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Jul 9, 2010
Private Declare Function GetPrivateProfileString Lib "kernel32" Alias _
"GetPrivateProfileStringA" (ByVal lpApplicationName As String, _
ByVal lpKeyName As String, _
ByVal lpDefault As String, _
ByVal lpReturnedString As String, _
ByVal nSize As Integer, ByVal lpFileName As String) As Integer
Dim value As String = ""
Dim length As Integer
Dim IniFileName As String
GetPrivateProfileString("Config", "UserName", "None", value, length, IniFileName)
but value contains an empty string I confes to being a VB n00b, less than a week, in fact, but I can't see what's wrong there. The file exists, it contains a section called "Config" which has an entry called "UserName" with a value - but even if not, wouldn't value take the default?
Edit: It's not returning an empty string - it's returning whatever I initialize value to before calling GetPrivateProfileString().
Which is to say that if I Dim value As String = "xxx" then it stil contains "xxx" after the call and not the default value.
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Apr 7, 2009
I've always use String.IsNullOrEmpty to check for a empty string. It recently come to my attention that a " " count as not a empty string. For example,
Dim test As String = " "
If String.IsNullOrEmpty(test) Then
MessageBox.Show("Empty String")
[Code]....
It will show "Not Empty String". So how do we check for " " or " " in a string?
edit: I wasn't aware that " " count as character.
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Apr 26, 2011
My button gets a commandargument of empty string even though the commandargument gets set. I have verified it gets set to the correct ID in debug mode, but then when I go to access this commandargument later in the repeaters ItemCommand event the commandarguments are empty string. And I have no idea why. I end up getting a sq foreign key exception because it is inserting an ID of 0 from the empty string values. There is no other code regarding the repeaters buttons that would be resetting it.
Repeater:
<asp:Repeater ID="repeaterAddresses" ViewStateMode="Enabled" DataSourceID="sqlFacilityAddresses" runat="server">
<ItemTemplate>
<Select:Address ID="AddressControl" runat="server" />
[code]....
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Dec 11, 2009
new with Linq and very excited with this feature. However, I want to see if I can do the following with LINQ:
[code]...
Notice that I have a break in my foreach loop, meaning that I just need to reset the first match row's column value to empty string.
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Jul 20, 2010
I'm trying to do some validation testing in VB.NET. If Entity.WeekEndDate.ToString = String.Empty Then ErrorList.Add(New cValidationError("id", "Incorrect Week End Date"))
Where WeekEndDate is of type Date. When I originally build the object, how can I insert a value into WeekEndDate that will generate an empty string(ie. "") when converted from a Date to a String?
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