.net - Casting DataTypes With DirectCast, CType, TryCast?
Apr 24, 2010
Ever since I moved from VB6 to VB.NET somewhere in 2005, I've been using CType to do casting from one data type to another. I do this because it is simply faster to type, used to exist in VB6 and I do not know why I have to be using DirectCast if there is apparently no difference between them.I use TryCast once in a while because I understand that sometimes casting can fail. I however cannot get the difference between CType and DirectCast.
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Aug 28, 2010
Possible Duplicate: Why use TryCast instead of Directcast ? I want to know about the trycast and direct cast in vb.net. What is the difference between them?
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Feb 23, 2010
What is the difference between DirectCast and TryCast? Can someone illustrate it in very simple words along with an example?
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Aug 19, 2010
I find this behavior of TryCast in .NET 4.0 / VS 2010 rather confusing. In my understanding TryCast works like DirectCast, but will return Nothing instead of throwing an exception if a cast is not possible. VS 2010 / .NET 4
[Code]...
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Jun 16, 2010
I am an experienced C/C++/C# programmer who has just gotten into VB.NET. I generally use CType (and CInt, CBool, CStr) for casts because it is less characters and was the first way of casting which I was exposed to, but I am aware of DirectCast and TryCast as well. Simply, are there any differences (effect of cast, performance, etc.) between DirectCast and CType? I understand the idea of TryCast.
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Dec 13, 2009
I turned option strict on, wich gave me some errors. The errors are quite easy to fix, but it seems like there are several ways of doing things. [code] 'previoustime' is declared as a TimeSpan, and the column "sluttid" is defined as a TimeSpan-column.Now, as far as I know, there are two ways of solving this; using CType and using DirectCast, like this: [code]
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Jun 17, 2009
Here is a test program I wrote to explore a facet of object casting ...
Module Module1
Sub Main()
Dim class1 As MyBaseClass = New MyBaseClass()
Dim class2 As MyInheritedClass = New MyInheritedClass()
Dim class3 As MyBaseClass = Nothing
[Code] .....
The problem comes with the TryCast statement on class3. My intention is that class3 remains as a baseclass, but when the TryCast is applied, class3 morphs itself into an Inherited class which is not what I wanted. So is there a gap in my OOP/VB.NET knowledge and this action is legitimate or should class3 still be regarded as a base class?
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Oct 13, 2009
Public Enum Fruit
Red_Apple = 1
Oranges
Ripe_Banana
End Enum
Private Sub InitCombosRegular()
[Code]...
Why does the Ctype work and the Directcast does not with the same syntax? Yet if I cast the selectedValue to an int before I DirectCast, then it works
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Oct 12, 2009
Does DirectCast, ctype, etc., are common function? Why it return type, and how do I used it? Is there others function where I need learn to be dot net expert?
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Jan 14, 2011
in terms of performance (speed), does directcast beat ctype?
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Sep 4, 2009
I usually avoid VB's built-in conversion functions (CStr, CDate, CBool, CInt, etc.) unless I need to do an actual conversion. If I'm just casting, say from an object to a string, I normally use either DirectCast or TryCast, under the assumption that CStr, etc., are doing some extra stuff I don't need. But sometimes the DirectCast syntax is a little cumbersome, as in the following example.[code]SqlDataReader.Item returns an Object, which needs to be cast to a String. CStr is easier to read, type, and explain (IMO). My question is, does it matter which one I use? Should I just go with CStr (and CDate and CBool, etc.) and not worry about the extra work I assume those functions are doing? Is there any other downside to using these functions?
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Oct 15, 2009
How come this is not a valid DirectCast:
Public Sub FB(OF T0 As IGH_Goo, T1 As IGH_Goo) _
(ByVal A As DataTree(Of T0), _
ByVal B As DataTree(Of T1))
Dim val_A As T1 = DirectCast(A.FirstItem, T1)
End Sub
[Code]...
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Feb 25, 2011
[Code]...
What happens when a user wants to alocate "" as Item(DurationColumn) to integer? I get an exception. clean solution to avoid this and set 0 for ""?
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Dec 2, 2011
I am wondering if this is a bug. Can't understand why would CType work this way...!
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Jan 30, 2012
I want to see if try cast can convert user entered answer to the type I have specified. Here's what I have: Dim t as type = GetType(myType) Dim ans = console.readline() If TryCast(ans, t) <> Nothing Then ... 'Doesn't work` In the example above the intelisense doesn't even show t. How to make it work?
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Jun 8, 2009
I was wondering, what are the benefits of having a variety of different data types available to programmers?
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Jan 2, 2011
I am working on a produce inventory database in my VB Express program. I have a form on the bottom and a spreadsheet at the top. I want to enter all the data in the form and have that data automatically transferred as a group to the spreadshet in the upper part of the page when I press a button.
I know that there's an insert function. I set it up correctly. The problem is that I have to convert the textbox, which contain string data, to the datatype used in the database spreadsheet. HOw do I use CAST or do this?
Here's the function I am using:
Me.TableAdapterManager.InventoryTableAdapter.Insert(IDTextBox.Text, fruitName, unitprice, unitsize, unitIn, unitTransit, unitOut)
Evernything is a string cause the data is coming from a textbox, I need to convert it to the datatypes used in the database.
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Aug 31, 2011
I need to call a function that expects a DataType as a paremeter. I fail to get the right syntax to specify a datatype (integer, string, single, boolean, etc):
Public Sub AddSetting(ByVal PropertyName As String, ByVal PropertyType As Type, ByVal DefaultValue As String)
Dim p As New SettingsProperty(PropertyName)
p.PropertyType = PropertyType
p.DefaultValue = DefaultValue
[Code] .....
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Feb 24, 2010
Using VB.Net and C#.Net.
For Example
Am Using More than one form
If am assigning a variables like this.[code]...
This variables cannot be easily understand for everyone(other programmers).
How to assign a Standard Datatype variables,
Standard Variable Means (Everyone can understandable)
And also How to give a standard name for gridview, text boxes, labels etc.
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Jun 18, 2009
Changing datatypes of properties of serialized objects?
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Jan 13, 2012
Anyone have any insight on the Big O notation for comparisons for a LINQ Except query using primitive datatypes? I couldn't find anything on google.
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Oct 5, 2010
I'm looking at the following in the Data Types docs for the Windows API:
#if defined(_WIN64)
typedef __int64 LONG_PTR;
#else
[code]....
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Nov 11, 2010
I defined the following extension of the Date? data type
[Code]...
But when I moved my compiler definition to a separate DLL, I the ToObject method was no longer available from my project even though I had referenced the Class project which now contained the extension. Is this a limitation of the Compiler Extensions? HOw do you get reusability out of them?
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May 26, 2010
It looks like they are converted to regular date types in the generated proxy object.I'd like to optionally pass null values for these dates.Other than switching to WCF (no time to learn it right now), what is the best way to handle this situation. It looks like I also cannot pass NULLABLE date types.
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Apr 21, 2010
Does C# have an equivalent to VB.Net's DirectCast?I am aware that it has () casts and the 'as' keyword, but those line up to CType and TryCast.To be clear, these keywords do the following;CType/() casts: If it is already the correct type, cast it, otherwise look for a type converter and invoke it. If no type converter is found, throw an InvalidCastException.
TryCast/"as" keyword: If it is the correct type, cast it, otherwise return null.DirectCast: If it is the correct type, cast it, otherwise throw an InvalidCastException.
EDIT: After I have spelled out the above, some people have still responded that () is equivalent, so I will expand further upon why this is not true.
DirectCast only allows for either Narrowing or Widening conversions on inheritance tree, it does not support conversions across different branches like () does.ie: C#, this compiles and runs:
//This code uses a type converter to go across an inheritance tree
double d = 10;
int i = (int)d;
[code]....
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Jan 14, 2012
i am using code to the value textbox2.text in the report and using the code like below [code]the textbox2 take various values in run time but when i run the code it display only the final value intermediated values are not displayed the whole situation is as follows.[code]
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Aug 4, 2011
I have a very simple problem where I have a MyList As List(Of MyBaseClass) but and a couple of MySub(ByVal Dummy As MyDerivedClassA)/MySub(ByVal Dummy As MyDerivedClassB). So I want to do the following ...
For Each MyInstance As MyBaseClass In MyList
MySub(DirectCast(MyInstance, MyInstance.GetType())
...
[code].....
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May 8, 2011
I learned how to use DirectCast over the last few days and it's really helped me. However, I have a similar issue, instead of textboxes I am looking at variables that are referenced in the class.To bring you all up to speed, I have four variables, a Boolean that dictates each of the 4 players I have playing my game. [code] I would assume it'd work similar to DirectCast but I am unsure. What I came up with caused errors: [code]
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Dec 1, 2009
I have 15 textboxes named MissionT1-15Is there a simple way to set all of their text to "Mission"?
missionT1.text="Mission"but for all of them with a loop?I saw something with directcast but wasn't able to make it work.
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Jul 25, 2011
PROJECT TYPE: Windows Forms Application
LANGUAGE: Visual Basic
.NET VERSION: 3.5
IDE: Visual Studio 2008
OPTION STRICT: on
OPTION EXPLICIT: ON
I need to populated a ComboBox and a CheckedListBox with a list of the Windows Accounts on the host computer. I also need to the user to be able to apply settings to the users individually. Thirdly, I need to find a way to add a startup registry key in the CURRENT_USER for a different user than the "Current User" (For example: User1 is an Administrator. User2 is a Limited Account [can't modify registry]. User1 needs to add Registry key to User2's "CURRENT_USER". This is a parental control application so the Admin accounts need to be able to access the registry from all users without affecting all users at once. I do not have any code to paste because I still have not the foggiest idea of where to start. I think it probably has something to do with an array (I have no experience with arrays whatsoever) but I am stumped from there. I'm a new, self-taught programmer so I speak idiot at times,
Summary of Questions
1) How do I retrieve a list of Windows Users?
2) How do I populate the objects above with such a list?
3) How do I interact with the items on that list (specific user accounts)?
4) How do I modify another user's CURRENT_USER Registry key?
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