Opening Form - Expression Cannot Be Converted To Type TextBox
Mar 13, 2011
A week ago, I encounter an error while doing my project. I failed to open certain form in vb.net. While clicking a button to show the form this will came out.
"[An error occurred creating the form. See Exception.InnerException for details. The error is: Argument 'Expression' cannot be converted to type 'TextBox']".
I'm trying to convert a VB6 project to .NET, but I get problems with some callback functions, and the following message comes up: "AddressOf' expression cannot be converted to 'integer' because integer is not a delegate type" I've seen several solutions to similar problems like this, but I am not able to understand this issue with delegates.
After the conversion, the code look like this:
Declare Function vsmsgwSetDataPackageCB Lib "vsmsgwW.dll" (ByVal PACKAGE As Integer, ByRef arg As Integer) As Integer Dim arginitP As Integer
Which gives the error: Method 'Public Function PackageCB(HisNodeID As Integer, ByRef data() As Byte, ByVal length As Integer, ByRef arg As Integer) As Integer' does not have the same signature as delegate 'Delegate Function DelegatePackageCallback(hwnd As Integer, lparam As Integer) As Integer
How to create an instance of a form if it is not know in advance which formtype has to be opened. If you want to skip the chitchat: the .NET code example is at the end of this post. First the Symantec: when we create a new form, this form has a name. If we refer to that name, we actually refer to the name of the type of object that is just created. When to use of course when reading the subject you might think: why not just pass the form to a parameter that takes a form (or control/object)?
The answer is: you don't when it is not sure, when or if a new instance of the object has to be created or, as mentioned, when the procedure is called it is not known which class has to be created. You could of course hold a bunch of created objects, but that would be a shameless misuse of memory. Imagine the following scenario (seen something like this in a post, but can't find it anymore):
You have a class that is able to trap an event, say the doubleclick of a textbox, and has to open a form when it occurs. If it's always the same form, that's easy, but what if you want it to be determined during runtime? This is a quite common story: doubleclick on article opens the detail form of that article, doubleclick on supllier opens that particular form. If you use a form variable, how do you say to the class which form should be opened? This will not work
Code: Dim FormToOpen as Form 'you don't want to open it right away, you want to know when the time comes what form to openFormToOpen = Form1You could say FormToOpen = new Form1, but then 1. an instance would be immediately created, even if it never will be used: memory leak. 2. you can never close the form, you'll always have to use the same instance created when setting the form. Consequently, you can never open more than 1 instance using this way.
The solution: use the type. If you know the type, the Activator class will enable you to open (and return) an instance of that form at any time and as much times as you like. (The Activotor class exposes the function CreateInstance which returns an instance of the specified object)The following code creates an instance of the type form1 and shows it.
Code: CType(Activator.CreateInstance(GetType(Form1)), Form).Show()Or for better readability, the same code split up: Code: Dim FormToOpen As Type FormToOpen = GetType(Form1) Dim frm As Form = CType(Activator.CreateInstance(FormToOpen), Form) frm.Show()
I'm trying to code a program but this error repeatedly shows up and I can't for the life of me figure it out EValue of type 'String' cannot be converted to 'System.Windows.Forms.TextBox'. It appears in relation to this code
Migrated application from vb6 to vb.net. application calling VC++ method. whoes parameter is int/long which is pointer of method
which is passing from vb6 like
I am getting error ddressOf expression cannot be converted to integer.I know addressof working different in vb6 it givie value in int which is function pointer. Please suggest how can I get value of fuction pointer in vb.net or any other solution in this situation.
Im getting some VB.Net Late binding operations cannot be converted to an expression tree. errors, have search here on the site and can only find solutions to the SQL get data code, not to my problem. The error "Late binding operations cannot be converted to an expression tree." At all my x.NAME) lines !? Im new to this so can anyone say me why i get this error..
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The error I'm getting is Late binding operations cannot be converted to an expression tree.
The particular snippet I'm encountering the error on is:
I have a bunch of Excel files full of research data. Everything is strait forward: rows of research categories and columns of research parameters. I want to create a simple search form that allows opening any of the spread sheets that contains the type of data that I specify. For example, I would choose a parameter
I have a project in VS2008.Net3.5. I have 3 forms in total. The Sub Main() in Module1 first calls the Form1. Then Clicking Button1_Click event in Form1 opens up Form2. In Form2 I have a text box that I will fill out from Form3. But when I am Clicking Button1_Click event in Form1, it can't keep Form2 open but it opens up Form3 directly. I dont want this. I want to open Form2. In Form2 I will press the textbox and then we have Form3 open. But this is not working.==============
Module Module1 Public frm1 As Form1 Public Sub Main()
The Sub Main() in Module1 first calls the Form1. Then Clicking Button1_Click event in Form1 opens up Form2. In Form2 I have a text box that I will fill out from Form3. But when I am Clicking Button1_Click event in Form1, it can't keep Form2 open but it opens up Form3 directly. I dont want this. I want to open Form2. In Form2 I will press the textbox and then we have Form3 open. But this is not working.
I knew that in Form2 the first focus is going to the textbox and it then opening the Form3 for the GotFocus method. How can I move the focus to other control in Form2 instead of the default focus to my textbox. Or is there other event method other than GotFocus?
I am trying to make it so when I use Me.Controls("Timer1") for example I can access specific commands for a timer such as Stop() Start(), I tried CType() and typed in "Timer" as the type but it says the control type can't be converted to the "Timer" type.
I am trying to create a program with vb.net. I am getting the following error in the form1.designer.vb and so I am not able to run the program. Its urgent. Error1Value of type 'String' cannot be converted to 'System.Windows.Forms.TextBox'.C:\Documents and Settings\Srivathsan\Local Settings\Application Data\Temporary Projects\Cyber Cloud\Form1.Designer.vb49119Cyber Cloud And it says that the error is with this line?
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Public Class MortgageCaluclator17 'Write the program in VB.Net (not Web based) and have it accept user input of the amount, term and interest rate. 'Display the mortgage payment amount. Then, list the loan balance and interest paid for each payment over the term
If I remove the datagridview code the 1st part of the program runs fine and works well, it is when I add in the datagridview that the error occers.
I need to take 6 user entered dates and compare them to a date pulled from a database & stored in a variable. If greater than 6 weeks, then some action needs to take place.When writing the code, I get the following message (before compilation). Value of type 'Date' cannot be converted to 'System.TimeSpan'. [code] Within my code the 'dt' in the line above is underlined with the error message appearing on mouseover. I have tried using CType, as in dt = CType(Session("dt_occurence"), DateTime) in the hopes that might work, but it doesn't do it.