I have an app with 24 different Forms. They have some security options based on which the 5 different buttons Submit, Approve, 2nd Approve, 3rd Approve, Reject etc get enabled disabled.
Now I designed a MainForm that has all the buttons and the security code for them. I have created eachform as a usercontrol and load them dynamically based on which form the user wants. My loading works perfectly fine. I load the control and Add it to the place holder in the Page load event of the main page.
Now when the user selects the Submit button I want to call the Save method inside the usercontrol of the Form as each form will have a separate Save. So when I try this code snippet I get the Null reference error. Do let me know how to resolve it.
Private UCDynamic As UserControl
Then on Page Load event I use this code
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If not Me.IsPostBack
UCDynamic = LoadControl("Controls/BkCode.ascx")
Me.PlaceHolderForm.Controls.Add(UCDynamic)
End if
Then on the ButtonClick Event for Submit I do this
Protected Sub Save_OnClick(ByVal sender As Object, ByVal e As EventArgs)
Save()
End Sub
Sub Save()
CType(Me.UCDynamic, controls_BkCode).Save()
End Sub
Thats where I get the cast Null reference error. So is it that after post back the control no longer exist on the page. Any ideas will be greatly appreciated.
Thanks.
Http protocol is stateless, so all server variables are nothing after postback.
Have you tried to find it with FindControl, it should be stored in the Viewstate of your Placeholder?
Directcast(Me.PlaceHolderForm.FindControl("the_id_of_your_usercontrol"),
controls_BkCode).Save()
Hi Tim Thanks for your help. But Findcontrol does not work for the placeholder. Though I have the viewstate enabled for the placeholder yet it does not hold the control after post backs.
Finally resolved this issue by moving my LoadControl code out of If not is postback. So I load the control every time and the code inside the control takes care of the logic of post backs and the viewsataes for the control.
Related
A very basic/simple question with I'm sure, an even simpler answer, but I just cannot figure it out. I have two forms that a user can switch between using the corresponding menu link on each form. I want to be able to keep the previous form visible on screen until the new form is displayed. In it's current state, the form disappears off screen for around 3/4 of a second before the new one is shown and from a UI/design perspective, I'd like this to stay on screen.
I'm currently using the below code to close and open the forms:
form1.Show()
Me.Close()
form2.Show()
Me.Close
I have tried experimenting with ShowDialog() which does seem to keep it on screen on first run, but clicking back into the form a second time says an error message:
System.InvalidOperationException: 'Form that is already visible cannot be displayed as a modal dialog box. Set the form's visible property to false before calling showDialog.'
Is there a simple line of code to achieve what I want here?
If there is some time consuming code in the Form.Load event (for example, if data is being retrieved from a database) then the following code might help.
Private Sub Form2_Shown(sender As Object, e As EventArgs) Handles Me.Shown
'Assuming default instances
Form1.Close()
End Sub
Posting an answer incase there's an inherit reason this is not best practice or to avoid doing this, but using the below sped it up:
Private Sub menu1_Click(sender As Object, e As EventArgs) Handles menu1.Click
form1.Show()
form1.Refresh()
Me.Close()
End Sub
This was inspired by adding in a Application.DoEvents working, so adjusted the code to avoid that dreaded line.
I am having trouble figuring out how to run code on application startup. The scenario is, I need to check if a user setting exists, if it does not, then I need to open a company configuration form. I tried creating a module to store application level events, but get an error:
BC31418 Visual Basic AND VB.NET in modules must specify a 'WithEvents' variable qualified with a single identifier.
Module ApplicationEvents
Private Sub MyApplication_Startup(sender As Object, e As Microsoft.VisualBasic.ApplicationServices.StartupEventArgs) Handles Me.Startup
If My.Settings.xmlpath = "" Then
Dim f As New CompanySetup()
f.ShowDialog()
f.Dispose()
End If
End Sub
End Module
I really do not want to put the IF statement into the default form mybase.load handler, since this application is in early stages, and the default form may change, leading me to have to move this code around. Any help on this error, or suggestions of how to get the IF statement to occur on application startup without tying it into a sub on the default form would be greatly appreciated.
Get rid of that module. Open the Application page of the project properties and click the View Application Events button. That will open the proper code file in which to create a Startup event handler. You can do that using the second and third drop-downs in the Navigation Bar at the top of the code window.
How can I show the datagridview after the form loads?? Because after my form loads my datagridview looks like this. I just want to make my data in the datagridview visible after my form loads. The data appears when I type at the searchbar(not automatic).
enter image description here
Welcome to Stackoverflow!
Firstly, please post the code for your DataGridView, as it is much easier if you provide us code to deal with.
So, let's get this issue fixed.
One problem could be, is that you're making a sub or a function, but you're never calling it.
What I mean by that is, if you create a sub or a function but you never call it, then it won't usually do anything, but for your case, since you want the DataGridView to show on startup (Form_Load), you need to call your sub or function in Form_Load.
So, what I suggest you doing is this:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
// your code here which would be your sub or function
End Sub
Since you're now calling your sub or function in Form1_Load, your DataGridView will now show on the form when it first loads.
Edit: Changed some text around to make the answer make more sense.
I am refactoring an existing project that is one large file. All form controls live in a single form, and all event handlers live in the form's code behind.
I am refactoring out a piece of the UI into a User Control. One piece of this UI is an 'Add Contract' button. This goes to my data layer, adds a row to a DataTable, and various grids in other parts of form are updated with the new row.
My question is, where should I put the event handler for the button click in the User Control?
I could leave the event handler code in the parent form, and use AddHandler in the User Control to reference the parent form's sub
I could write all the event handler code in the User Control. In this case, I'd need to access the parent form to get a reference to the data layer.
I come from a web background where I'm used to the 'controller' handling this sort of thing. I suppose my parent form is turning into a kind of controller - but is this a good practice? Should I have a separate class that coordinates user interactions with my model layer, or, once I separate out all the UI into separate user controls, will the main form be a good place for this sort of thing?
Your user control should raise events that the form hosting the user control will handle. If the user control has a reference to the form, then the user control is not reusable in any other context; in other words, the user control is tightly coupled to that one form and form X would break if it tried to use the user control.
Note: If your form is the only thing that will use the user control, then there is not much re-usability value in making it a user control at all. Kind of similar to it is not much use to make an interface if there is only one implementation of said interface. That said from an organization standpoint, user controls can be used to clean up a crowded form. It also has the benefit of allowing for the dynamic loading of content in user controls.
There is nothing wrong with your parent form becoming the controller.
Here is a quick example (in this case the clicking of the button in the user control) of how you can raise events from your user control and subscribe to the event in the form:
Public Class UserControlClass
' Define event that will be raised by user control to anyone interested in handling the event
Public Event UC_Button1Click()
' Mechanism to allow event to be raised by user control
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
RaiseEvent UC_Button1Click()
End Sub
End Class
Now in your form class, you need to add a handler for the event raised by the user control, like this:
AddHandler userControl1.UC_Button1Click, AddressOf Button1_Click
Finally, you would create the method that is referenced in the AddressOf syntax, like this:
Public Sub Button1_Click(ByVal sender As Object, ByVal args As EventArgs)
' Do something here
End Sub
I want to update a database based on the form that is currently activated. I had originally decided to use the GotFocus event. However I now understand that will not work as the form has controls on it. So I then thought I wouls use the activated event. This works but seems to fire multiple times. I put in the following code:
Private Sub frmNewTicket_Activated(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Activated
MsgBox("Form Activated")
End Sub
I select the form and make it activated and the message box appears about 15 times.
Why does it do this? How should I handle this. I only want my code to execute once when the form is activated.
NOTE: There are several forms that the users will be changing between, incuding forms from other applications.
Each time you click OK on the messagebox, the form regains the focus and is activated again.
Put a static Boolean value in your frmNewTicket_Activated like someone has posted here:
Static HasRan As Boolean=False
If Not HasRan Then
HasRan=True
'put code here
End If
It sounds like you are wanting to do something everytime your form gets activated. The Form Activated event will work fine as long as what you are doing doesn't pull focus from the Form which will then trigger another Activation event when the Form gets focus again. Try using something other than a MessageBox for testing like Beep or changing the Form's Color