What I'm trying to do is put buttons I have already created into an array, however, whenever I look into the array it says that there is nothing in there? I was wondering if I'm doing something wrong.
Dim buttons As System.Windows.Forms.Button() = {Button1, Button2, Button3, Button4, Button5, Button6, Button7, Button8, Button9, Button10, Button11, Button12, Button13, Button14, Button15, Button16, Button17, Button18, Button19, Button20, Button21, Button22, Button23, Button24, Button25, Button26, Button27, Button28, Button29, Button30, Button31, Button32, Button33, Button34, Button35, Button36, Button37, Button38, Button39, Button40}
Private Sub ClearBtn_Click(sender As Object, e As EventArgs) Handles ClearBtn.Click
For i = 1 To 40
buttons(i).BackgroundImage = System.Drawing.Image.FromFile("leaf.png")
Next
End Sub
When the Clearbtn is clicked I get System.NullReferenceException: 'Object reference not set to an instance of an object.' And the array is empty. I've set the array to a global variable so it should work?
The problem is that the code that creates your array is executed before the form constructor, so before all the child controls are created. Of course those fields are Nothing at that point. The solution is to declare the field where you are but to create the array and assign it to that field in the Load event handler.
I would store the background image at form level, and build the list in the Load() event like this:
Dim buttons As New List(Of Button)
Dim imgClear As Image = System.Drawing.Image.FromFile("leaf.png")
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
For i As Integer = 1 To 40
Dim ctl As Control = Me.Controls.Find("Button" & i, True).FirstOrDefault
If Not IsNothing(ctl) AndAlso TypeOf ctl Is Button Then
buttons.Add(DirectCast(ctl, Button))
End If
Next
End Sub
Private Sub ClearBtn_Click(sender As Object, e As EventArgs) Handles ClearBtn.Click
For Each btn As Button In buttons
btn.BackgroundImage = imgClear
Next
End Sub
Note that searching for the buttons in this manner will find them no matter where they are. They don't have to be directly contained by the form, or even in the same containers.
Related
i want to add a tabcontrol tab by pressing on a button:
Dim inp As String
inp = TextBox6.Text
TabControl2.TabPages.Add(inp)
and when i open this tabpage some object should be already created like a button and a textbox, etc.
i havent found any type of onload events for a tabpage so i tried to add this with:
TabPage8.Controls.Add(New Button())
tabpage8 would be the name of the new created tabpage but like vb already told me, i cant add objects to a tabpage which doesnt exist at that time.
is there any way i can do that or have you any other ideas which could help me?
Your code is close. Try the following:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
TabControl2.TabPages.Add("Test")
Dim tp = TabControl2.TabPages(TabControl2.TabPages.Count - 1)
Dim b = New Button()
b.Text = "My Button"
tp.Controls.Add(b)
AddHandler b.Click, AddressOf MyButton_Click
End Sub
Private Sub MyButton_Click(sender As Object, e As EventArgs)
MessageBox.Show("MyButton clicked")
End Sub
This code grabs the last page added and adds a button to it. It also configures the button as needed and adds an event handler.
I have a bit of code where i have a dynamically created array or buttons with staff pictures on them, as well as the staff's name. I've added one handler to handle any button click from any of the buttons. where i am stuck is, if you look at the code below, it all works fine, and if you click any of the buttons you get the "aha" test message. but i want the name of the staff clicked on (so btnArray(i).Text) to be passed to the handler for further processing. I tried adding a ByVal parameter to the handler but that caused an error. what's the correct way to do this? As i said, the code below works for me, i just am at a loss as to how to add the extra functionality.
Dim btnArray(staffcount) As System.Windows.Forms.Button
For i As Integer = 1 To staffcount - 1
btnArray(i) = New System.Windows.Forms.Button
btnArray(i).Visible = True
btnArray(i).Width = 80
btnArray(i).Height = 101
btnArray(i).BackgroundImage = Image.FromFile(picloc(i))
btnArray(i).BackgroundImageLayout = ImageLayout.Stretch
btnArray(i).Text = staffname(i)
Dim who As String
who = btnArray(i).Text
AddHandler btnArray(i).Click, AddressOf Me.theButton_Click
btnArray(i).ForeColor = Color.White
btnArray(i).TextAlign = ContentAlignment.BottomCenter
Dim fnt As Font
fnt = btnArray(i).Font
btnArray(i).Font = New Font(fnt.Name, 10, FontStyle.Bold)
FlowLayoutPanel1.Controls.Add(btnArray(i))
Next i
End Sub
Private Sub theButton_Click()
MsgBox("aha")
End Sub
First, correct the signature of your shared handler.
Private Sub theButton_Click(sender As Object, e As EventArgs)
End Sub
Once that is done getting the text of the button clicked is a simple matter.
Private Sub theButton_Click(sender As Object, e As EventArgs)
Dim textOfButtonClicked As String = DirectCast(sender, Button).Text
MessageBox.Show(textOfButtonClicked)
End Sub
The sender is the button that was clicked. Since signatures use objects for the sender the DirectCast 'changes' it to button and you then can access the .Text property of the button.
If there are more manipulations you want to perform on the clicked button you could do it this way
Private Sub theButton_Click(sender As Object, e As EventArgs)
Dim whBtn As Button = DirectCast(sender, Button) ' get reference to button clicked
Dim textOfButtonClicked As String = whBtn.Text
MessageBox.Show(textOfButtonClicked)
'e.g. change the color
whBtn.BackColor = Color.LightYellow
End Sub
I'm working on a proof of concept type situation that will eventually be tied to a scheduling database. As a Test I created this:
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
'AddButton("test")
addLots()
End Sub
Private Sub AddLots()
Dim x As Integer
For x = 0 To 10
Dim b As New Button
Dim newLabel As New Label
newLabel.Location = New Point(100, x * 20)
newLabel.Name = x
newLabel.BorderStyle = BorderStyle.Fixed3D
newLabel.Text = newLabel.Name
Me.Controls.Add(newLabel)
Me.Controls.Add(b)
b.Location = New Point(20, x * 20)
b.Text = x
b.Tag = x
b.Name = x
AddHandler b.Click, AddressOf Button_Click
Next
End Sub
Private Sub Button_Click(ByVal sender As Object, ByVal e As System.EventArgs)
Dim B As Button = sender
MsgBox(B.Name)
End Sub
For this proof of concept, I simply want label 1 text to be updated when I press button 1 seems like a simple process but it's kicking my butt.
As for any object, to affect a Label you will need a reference to it. As it stands, the only reference you have is via the Controls collection of the parent control you added the Label to, i.e. the form itself. You could loop through the Controls of the form and as soon as you find a Label then you know you have the first one, or you could call OfType and First or FirstOrDefault. That assumes that there are no other Label controls on the form.
You might also consider using a dedicated parent control so that you know it will only contain the Label controls you created at run time. The obvious choice would be a TableLayoutPanel because it will handle the layout for you too.
If accessing the dynamic controls via a Controls collection is an issue then keep your own collection. Declare a member variable of type List(Of Label) and add each Label you create to it. You can then access your control from that collection and know that there are no other controls in there to get mixed up with.
By the way, if you're creating those controls at run time then they won't be automatically disposed when the form is. Make sure that you dispose them yourself and also use RemoveHandler for each AddHandler you used.
Actually, looking closer at your code, I just realised that there's a 1:1 correspondence between the Button and Label controls. It would make sense to use that. Two options are to assign the corresponding Label to the Tag of each Button or else use a Dictionary(Of Button, Label) assigned to a member variable to store the relationships. That way, you can then use the sender in the event handler, which will be the Button that was clicked, to get the corresponding Label.
Option 1.
Creating the Label:
Dim btn As New Button
Dim lbl As New Label
btn.Tag = lbl
In the event handler:
Dim btn = DirectCast(sender, Button)
Dim lbl = DirectCast(btn.Tag, Label)
Option 2.
At class level:
Private labelsByButton As New Dictionary(Of Button, Label)
Creating the Label:
Dim btn As New Button
Dim lbl As New Label
Me.labelsByButton.Add(btn, lbl)
In the event handler:
Dim btn = DirectCast(sender, Button)
Dim lbl = Me.labelsByButton(btn)
I added this to the button click event. Doesn't seem very efficient as I will eventually have 30-40 buttons and controls on the form but it works.
Private Sub Button_Click(ByVal sender As Object, ByVal e As System.EventArgs)
Dim B As Button = sender
Dim lblToChange As Integer = B.Name
For Each objCtrl As Control In Me.Controls
If TypeOf objCtrl Is Label Then
Dim Lbl As Label = DirectCast(objCtrl, Label)
If Lbl.Name = lblToChange Then
Lbl.Text = "This ONe"
End If
End If
Next
End Sub
I've ported a large VB6 to VB.NET project and while it will compile correctly, I've had to comment out most of the event handlers as to get around there being no array collection for winform objects and so putting the various objects that were in at the collection array into a List object.
For example, in VB6 you could have an array of Buttons. In my code I've got
Dim WithEvents cmdButtons As New List(Of Button)
(and in the Load event, the List is propagated)
Obviously, you can't fire an event on a container. Is there though a way to fire the events from the contents of the container (which will have different names)?
In the Button creation code, the event name is there, but from what I understand the handler won't intercept as the Handles part of the code is not there (commented out).
I'm not exactly sure what you're after, but if you want to be able to add event handlers to some buttons in a container and also have those buttons referenced in a List, you can do something like
Public Class Form1
Dim myButtons As List(Of Button)
Private Sub AddButtonsToList(targetContainer As Control)
myButtons = New List(Of Button)
For Each c In targetContainer.Controls
If TypeOf c Is Button Then
Dim bn = DirectCast(c, Button)
AddHandler bn.Click, AddressOf SomeButton_Click
myButtons.Add(bn)
End If
Next
End Sub
Private Sub SomeButton_Click(sender As Object, e As EventArgs)
Dim bn = DirectCast(sender, Button)
MsgBox("You clicked " & bn.Name)
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
' GroupBox1 has some Buttons in it
AddButtonsToList(GroupBox1)
End Sub
End Class
In VB6 there is a feature called Control Arrays, where you name controls the same name and provide them an index value. This allows you to set a value by looping through the controls and setting each value. In VB .NET I can't create a control array could someone provide me with a similar solution.
Here is a sample I wrote for something else that shows how to do something similar and shows how to do the handler as well. This makes a 10x10 grid of buttons that turn red when you click them.
Dim IsCreated(99) As Boolean
Dim Buttons As New Dictionary(Of String, Button)
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
For i As Integer = 0 To 99
Dim B As New Button
Me.Controls.Add(B)
B.Height = 30
B.Width = 40
B.Left = (i Mod 10) * 41
B.Top = (i \ 10) * 31
B.Text = Chr((i \ 10) + Asc("A")) & i Mod 10 + 1
Buttons.Add(B.Text, B)
B.Tag = i
AddHandler B.Click, AddressOf Button_Click
Next
End Sub
Private Sub Button_Click(ByVal sender As Object, ByVal e As System.EventArgs)
Dim B As Button = sender
IsCreated(B.Tag) = True
B.BackColor = Color.Red
End Sub
Avoid using the proposed iteration approaches, you'll get a fairly random collection of controls unless your form is very simple. Simply declare the control array in your code and initialize it in the form constructor. Like this:
Public Class Form1
Private OrderNumbers() As TextBox
Public Sub New()
InitializeComponent()
OrderNumbers = New TextBox() {TextBox1, TextBox2}
End Sub
End Class
You can now treat OrderNumbers just like you could in VB6.
Maybe this is simpler. To create a control array, I put the control array declaration in a module. For example, if I have a Form with three TextBoxes and I want the TextBoxes to be part of a control array called 'mytext', I declare my control array in a module as follows:
Module Module1
Public mytext() As TextBox = {Form1.TextBox1, Form1.TextBox2, Form1.TextBox3}
End Module
And, I use the TextBoxes from the control array as follows:
Public Class Form1
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
mytext(0).Text = "Hello"
mytext(1).Text = "Hi"
mytext(2).Text = "There"
End Sub
End Class
You can even loop through the control array, like you could in VB6:
Public Class Form1
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
For i As Integer = 0 To 2
mytext(i).Text = i + 1
Next
End Sub
End Class
The beauty of using a module is that the TextBoxes do not even need to be in the same form.
With Winforms, you could do this:
myForm.Controls _
.OfType(Of TextBox) _
.OrderBy(Function(c) c.Name) _
.Where(Function(c) c.Name.StartsWith("somePrefix")) _
.ToArray()
On your form you would name your textboxes somePrefix1, somePrefix2, etc.
Here is an old article but it could give you more information. The top method is super easy.
Your Form, or PanelControl, or anything else that can contain child controls will have a Property called Controls.
You can loop through all of the text boxes in a control by using
'Create a List of TextBoxes, like an Array but better
Dim myTextBoxControls As New List
For Each uxControl As UserControl in MyFormName.Controls
If TypeOf(uControl) is TextBox
myTextBoxControls.Add(uControl)
End IF
Next
Now you have your iterate-able collection you can work with.
You can access a TextBoxes value with the EditValue property.
After looking at what you're trying to do a little further.
You probably want to name all of your controls with a Prefix, let's say abc for now.
For Each uxControl As UserControl in MyFormName.Controls
If TypeOf(uControl) is TextBox Then
Dim tbControl As TextBox = DirectCast(uControl, TextBox)
If tbControl.Name.StartsWith("abc") Then
tbControl.EditValue = "the Value you want to initialize"
End If
End If
Next
So this is one of the features that did not make the transition to VB.NET -- exactly :-( However, you can accomplish much of what you would have done in VB6 with two different mechanisms in .NET: Looping through the controls collection and handling control events.
Looping Through the Controls Collection
In VB.NET every form and control container has a controls collection. This is a collection that you can loop through and then do an operation on the control like set the value.
Dim myTxt As TextBox
For Each ctl As Control In Me.Controls
If TypeOf ctl Is TextBox Then
myTxt = CType(ctl, TextBox)
myTxt.Text = "something"
End If
Next
In this code sample you iterate over the controls collection testing the type of the returned object. If you find a textbox, cast it to a textbox and then do something with it.
Handling Control Events
You can also handle events over multiple controls with one event handler like you would have using the control array in VB6. To do this you will use the Handles keyword.
Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged, TextBox2.TextChanged, TextBox3.TextChanged
Dim myTxt As TextBox = CType(sender, TextBox)
MessageBox.Show(myTxt.Text)
End Sub
The key here is the Handles keyword on the end of the event handler. You separate out the various controls that you want to handle and the event by using a comma. Make sure that you are handling controls that have the same event declaration. If you ever wondered what sender was for on every event well here's one of the uses for it. Cast the sender argument to the type of control that you are working with and assign it to a local variable. You will then be able to access and manipulate the control that fired the event just like you would have in VB6 if you specified and index to the array.
Using these two techniques you can replicate the functionality of control arrays in VB6. Good luck.
Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click
Dim a() As Control = GetControls("textbox")
For Each c As TextBox In a
c.Text = c.Name
Next
End Sub
Private Function GetControls(typeOfControl As String) As Control()
Dim allControls As New List(Of Control)
'this loop will get all the controls on the form
'no matter what the level of container nesting
'thanks to jmcilhinney at vbforums
Dim ctl As Control = Me.GetNextControl(Me, True)
Do Until ctl Is Nothing
allControls.Add(ctl)
ctl = Me.GetNextControl(ctl, True)
Loop
'now return the controls you want
Return allControls.OrderBy(Function(c) c.Name). _
Where( _
Function(c) (c.GetType.ToString.ToLower.Contains(typeOfControl.ToLower) AndAlso _
c.Name.Contains("Box")) _
).ToArray()
End Function