I know that a null reference exception generally occurs when accessing an item in a collection that doesn't exist. However, in this case, one is being thrown despite me explicitly creating this item mere lines beforehand. I have scoured my code and cannot find the source of this error (the code is very basic ATM as I have just begun the process of restructuring a solution made for a client.
Background info:
PhotoJobs is a custom class that holds all of the properties of a specific manufacturing Job
These are all held in a Public Dictionary(of string, PhotoJob) which is held in the MainForm class.
A ("temp") photojob is created within this dictionary to handle the addition of new jobs as data is added (this appears to be the source of the error.
Code:
Private Sub AddJob_Load(sender As Object, e As EventArgs) Handles MyBase.Load
MainForm.photoJobs.Add("temp", New PhotoJob())
pctBox.AllowDrop = True
End Sub
Public Sub pctbox_drop(sender As Object, e As DragEventArgs) Handles pctBox.DragDrop
Dim pics As String() = CType(e.Data.GetData(DataFormats.FileDrop), String()) 'Gets the data from the file drop
If MainForm.photoJobs("temp").imageList.Count = 0 Then
MainForm.photoJobs("temp").imageList = pics.ToList 'Gets the data from the file drop
Else
For i = 0 To MainForm.photoJobs("temp").imageList.Count - 1
If Not MainForm.photoJobs("temp").imageList.Contains(pics(i)) Then
MainForm.photoJobs("temp").imageList.Add(pics(i))
End If
Next
End If
MainForm.photoJobs("temp").photoID = CType(formatID(MainForm.photoJobs("temp").imageList(0)), String)
txtPhotoID.Text = MainForm.photoJobs("temp").photoID
Select Case MainForm.photoJobs("temp").imageList.Count
Case 0
MsgBox("Please ensure that you are dropping image files")
Case 1
lblImageNumber.Text = txtPhotoID.Text
checkBoxes(0)
Case 2
txtPhotoID.Text = txtPhotoID.Text & "(2)"
lblImageNumber.Text = txtPhotoID.Text
checkBoxes(1)
Case 3
txtPhotoID.Text = txtPhotoID.Text & "(3)"
lblImageNumber.Text = txtPhotoID.Text
checkBoxes(2)
Case 4
txtPhotoID.Text = txtPhotoID.Text & "(4)"
lblImageNumber.Text = txtPhotoID.Text
checkBoxes(3)
End Select
spinCounter.Value = 1
spinCounter.Minimum = 1
spinCounter.Maximum = MainForm.photoJobs("temp").imageList.Count
pctBox.ImageLocation = MainForm.photoJobs("temp").imageList(0)
End Sub
The error gets called on the If MainForm.photoJobs("temp").imageList.Count = 0 Then line.
On a second, minor note, is it fairly typical for clients to ask for "just one more little thing" that results in you having to make a major overhaul to an application, or have I just got unlucky? (slightly rhetorical)
Ensure that imageList is not null, as you declare a new PhotoJob but don't set any values in it.
When dealing with a NullReferenceException, you're not looking at something missing from a collection, it means you tried to access a member of a object which is null. This can sometimes be a side effect of an item not in a collection, if that collection returns null, but if a value does not exist in a Dictionary, you get a KeyNotFoundException
Please make sure that 'imageList' has 'count' property more than 0. Means just check that the list does have elements in it by executing theses lines before executing loop.
Dim pics As String() =CType(e.Data.GetData(DataFormats.FileDrop),String())
If MainForm.photoJobs("temp").imageList.Count > 0 Then
For i = 0 To MainForm.photoJobs("temp").imageList.Count - 1
If Not MainForm.photoJobs("temp").imageList.Contains(pics(i)) Then
MainForm.photoJobs("temp").imageList.Add(pics(i))
End If
Next
'Gets the data from the file drop
Else
MainForm.photoJobs("temp").imageList = pics.ToList
End If
Well this is embarrassing...
The solution was simply that I was missing new when I declared the list it used to read Public Property imageList as list(of string) can't believe I did that... Hey ho, thanks for all of your help guys.
Related
This should be easy but I am having a headbanging of a time trying to get this to work! I have done a search and tried all most EVERY SINGLE ONE. Nothing works. I have a datagrid with a binding source. A user will type text into a textbox and the grid is SUPPOSED to change to only show records that contain what user typed in the name. Simple right? NOPE! Not for me! What am I doing wrong? Code below.
Private Sub SearchButton_Click(sender As Object, e As EventArgs) Handles SearchButton.Click
Dim Found As Boolean = False
Dim StringToSearch As String = ""
Dim ValueToSearchFor As String = "%" & SearchTextBox.Text.Trim.ToLower & "%"
Dim CurrentRowIndex As Integer = 0
Try
If ReferencesGrid.Rows.Count = 0 Then
CurrentRowIndex = 0
Else
CurrentRowIndex = ReferencesGrid.CurrentRow.Index + 1
End If
If CurrentRowIndex > ReferencesGrid.Rows.Count Then
CurrentRowIndex = ReferencesGrid.Rows.Count - 1
End If
If ReferencesGrid.Rows.Count > 0 Then
For Each gRow As DataGridViewRow In ReferencesGrid.Rows
StringToSearch = gRow.Cells(1).Value.ToString.Trim.ToLower
If InStr(1, StringToSearch, LCase(Trim(SearchTextBox.Text)), vbTextCompare) Then
TrainingItemBindingSource.Filter = String.Format("Name LIKE '{0}'", ValueToSearchFor)
Exit For
End If
Next
End If
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End Sub
You should get rid of pretty much all that code. If you want to filter the data then just filter the data. There's no conditional statements required and loops required. Just set the Filter property and any records that don't match the filter will be hidden:
Private Sub SearchButton_Click(sender As Object, e As EventArgs) Handles SearchButton.Click
TrainingItemBindingSource.Filter = $"Name LIKE '%{SearchTextBox.Text.Trim()}%'"
End Sub
As you can see, it is simple. I've no real idea what you were actually trying to achieve with the rest of that code. That will exclude any records where the Name column does not contain the search text.
Note that there is no need to try to force case-insensitivity by using ToLower or the like. Just like in real SQL, comparisons done this way in a DataTable are case-insensitive by default. You have to explicitly set the CaseSensitive property of the DataTable or its parent DataSet to True to make such comparisons case-sensitive.
I should also point out that the ability to filter is predicated on the data source implementing certain interfaces. If the data source is a DataTable then you have those interfaces for free. If you have actually bound to something else, e.g. a List(Of T), then you won't be able to filter this way because the required members do not exist.
Apologies if this has already been asked. If so, I am unable to find a simple solution. I am trying to allow a user to copy/paste multiple records in a DataGridView (the in memory copy of the data, to be saved later when the user clicks the save button) and cannot find anything that works. It probably is because there is something I do not understand about all of this.
I set up a standard edit form with Visual Studio's drag/table into a form, so it's using a BindingSource control and all the other controls that come with doing that. It works just fine when manually entering something in the new row one by one, so it seems to be set up correctly, but when it comes to adding a record (or multiples) using code, nothing seems to work.
I tried a few things as outline in the code below. Could someone please at least steer me in the right direction? It cannot be that difficult to paste multiple records.
I run this when the user presses Control-V (the clipboard correctly holds the delimited strings):
Private Sub PasteClipboard()
If Clipboard.ContainsText Then
Dim sLines() As String = Clipboard.GetText.Split(vbCrLf)
For Each sLine As String In sLines
Dim Items() As String = sLine.Split(vbTab)
Dim drv As DataRowView = AdjustmentsBindingSource.AddNew()
drv.Item(1) = Items(0)
drv.Item(2) = Items(1)
drv.Item(3) = Items(2)
drv.Item(4) = Items(3)
'Error on next line : Cannot add external objects to this list.
AdjustmentsBindingSource.Add(drv)
Next
End If
End Sub
EDIT
(the bindingsource is bound to a dataadapter, which is bound to a table in an mdb file, if that helps understand)
I adjusted the inner part of the code to this:
If (RowHasData(Items)) Then
Dim drv As DataRowView = AdjustmentsBindingSource.AddNew()
drv.Item("FontName") = Items(0)
drv.Item("FontSize") = Items(1)
drv.Item("LetterCombo") = Items(2)
drv.Item("Adjustment") = Items(3)
drv.Item("HorV") = Items(4)
End If
It kinda works, but it also adds a blank row before the 2 new rows. Not sure where that is coming from, as I have even included your RowHasData() routine...
I would think that “attemp3” SHOULD work, however, it is unclear “what” the AdjustmentsBindingSource’s DataSource is. Is it a List<T> or DataTable?
If I set the BinngSource.DataSource to a DataTable, then attempt 3 appears to work. Below is an example that worked.
Private Sub PasteClipboard2()
If Clipboard.ContainsText Then
Dim sLines() As String = Clipboard.GetText.Split(vbCrLf)
For Each sLine As String In sLines
Dim Items() As String = sLine.Split(vbTab)
If (RowHasData(Items)) Then
Dim drv As DataRowView = AdjustmentsBindingSource.AddNew()
drv.Item("FontName") = Items(0)
drv.Item("FontSize") = Items(1)
drv.Item("LetterCombo") = Items(2)
drv.Item("Adjustment") = Items(3)
drv.Item("HorV") = Items(4)
End If
Next
End If
End Sub
This appears to work in my tests. I added a small function (RowHasData) to avoid malformed strings causing problems. It simply checks the size (at least 5 items) and also checks to make sure a row actually has “some” data. If a row is just empty strings, then it is ignored.
Private Function RowHasData(items As String())
If (items.Count >= 5) Then
For Each item In items
If (item <> "") Then Return True
Next
End If
Return False
End Function
I am guessing it would be just as easy to add the new rows “directly” to the BindingSource’s DataSource. In the example below, the code is adding the row “directly” to the DataTable that is used as a DataSource to the BindingSource. I am confident you could do the same thing with a List<T> by simply adding a new object to the list. Below is a complete example using a BindingSource and a DataTable. This simply adds the rows to the bottom of the table.
Dim gridTable1 As DataTable
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
PasteClipboard()
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
gridTable1 = GetTable()
FillTable(gridTable1)
AdjustmentsBindingSource.DataSource = gridTable1
AdjustmentsDataGridView.DataSource = AdjustmentsBindingSource
End Sub
Private Function GetTable() As DataTable
Dim dt = New DataTable()
dt.Columns.Add("FontName", GetType(String))
dt.Columns.Add("FontSize", GetType(String))
dt.Columns.Add("LetterCombo", GetType(String))
dt.Columns.Add("Adjustment", GetType(String))
dt.Columns.Add("HorV", GetType(String))
Return dt
End Function
Private Sub FillTable(dt As DataTable)
For index = 1 To 10
dt.Rows.Add("Name_" + index.ToString(), "Size_" + index.ToString(), "Combo_" + index.ToString(), "Adjust_" + index.ToString(), "HorV_" + index.ToString())
Next
End Sub
Private Sub PasteClipboard()
If Clipboard.ContainsText Then
Dim sLines() As String = Clipboard.GetText.Split(vbCrLf)
Try
Dim dataRow As DataRow
For Each sLine As String In sLines
Dim Items() As String = sLine.Split(vbTab)
If (RowHasData(Items)) Then
dataRow = gridTable1.NewRow()
dataRow("FontName") = Items(0)
dataRow("FontSize") = Items(1)
dataRow("LetterCombo") = Items(2)
dataRow("Adjustment") = Items(3)
dataRow("HorV") = Items(4)
gridTable1.Rows.Add(dataRow)
End If
Next
Catch ex As Exception
MessageBox.Show("Error: " + ex.Message)
End Try
End If
End Sub
Private Function RowHasData(items As String())
If (items.Count >= 5) Then
For Each item In items
If (item <> "") Then Return True
Next
End If
Return False
End Function
Hope the code helps…
Last but important, I am only guessing that you may have not “TESTED” the different ways users can “SELECT” data and “how” other applications “copy” that selected data. My previous tests using the WIN-OS “Clipboard” can sometimes give unexpected results. Example, if the user selects multiple items using the ”Ctrl” key to “ADD” to the selection, extra rows appeared in the Clipboard if the selection was not contiguous. My important point is that using the OS clipboard is quirky IMHO. I recommend LOTS of testing on the “different” ways the user can select the data. If this is not an issue then the code above should work.
I'm writing a program that has two forms. One form gets the user to enter multiple values, and then does some calculations. Then it passes that information to another form However I can't figure out how to do it. Here is a relevant part of my code. To head some confusion, I am trying to pass 11 values, also initially, form 2 is not shown, and then when the values are passed from form 1 to form 2, then form 1 goes away and form 2 is the only one that shown
NOTE: This is not all my code, I don't believe all my code is required (I have 1000 lines right now) However this is the code with the information I want to be passed to the other form.
A lot of people are apparently saying that this is a duplicate of another question, however that question, he seems to already know how to pass the variables, but is just having issues with it (and even with looking at his, i cant figure it out)
Private Sub btnSubmit_Click(sender As Object, e As EventArgs) Handles btnSubmit.Click
'declarations
Dim intNormal As Integer
Dim intChildren As Integer
Dim intBonanza As Integer
Dim intDiamond As Integer
Dim intPictureFrame As Integer
Dim intKite As Integer
Dim intCrazyT As Integer
Dim intLetterX As Integer
Dim int2PostageStamp As Integer
Dim intPick7 As Integer
Dim intJackpot As Integer
Validate()
If txtNormal1.Enabled = False Then
intNormal = intNormInput
Else
intNormal = CalcNormalBooks()
End If
If txtChildren1.Enabled = False Then
intChildren = intChildInput
Else
intChildren = calcChildrensBooks()
End If
If txtBonanza1.Enabled = False Then
intBonanza = intBonInput
Else
intBonanza = calcBonanza()
End If
If txtSpecial1.Enabled = False Then
intSpecial = intSpeInput
Else
intSpecial = calcSpecialBooks(intSpecial)
End If
If txtDiamond1.Enabled = False Then
intDiamond = intDiaInput
Else
intDiamond = calcDiamond(intSpecial)
End If
If txtPictureFrame1.Enabled = False Then
intPictureFrame = intPicInput
Else
intPictureFrame = calcPictureFrame(intSpecial)
End If
If txtKite1.Enabled = False Then
intKite = intKiteInput
Else
intKite = calcKite(intSpecial)
End If
If txtCrazyT1.Enabled = False Then
intCrazyT = intCrazyInput
Else
intCrazyT = calcCrazyT(intSpecial)
End If
If txtLetterX1.Enabled = False Then
intLetterX = intLettInput
Else
intLetterX = calcLetterX(intSpecial)
End If
If txt2PostageStamp1.Enabled = False Then
int2PostageStamp = intPostInput
Else
int2PostageStamp = CalcPostageStamp(intSpecial)
End If
If txtPick71.Enabled = False Then
intPick7 = intPickInput
Else
intPick7 = calcPick7(intSpecial)
End If
If txtJackpot1.Enabled = False Then
intJackpot = intJackInput
Else
intJackpot = calcJackpot()
End If
End Sub
Since I had almost the same requiremnt lately here is my solution:
Custom Event which fires when your 2nd Form is closing
Public Event HotKeyFormClosed As EventHandler(Of HotKeyFormClosedEventArgs)
Custom EventArgs class where you store your values you want to pass to Main Form
Public Class HotKeyFormClosedEventArgs
Inherits EventArgs
'Your properties here
Public Sub New(...) 'your params here
MyBase.New()
'set your properties here
End Sub
End Class
On 2nd Form handle FormClosed event and pass your values to EventArgs
Private Sub HotKey_FormClosed(sender As Object, e As System.Windows.Forms.FormClosedEventArgs)
RaiseEvent HotKeyFormClosed(Me, New HotKeyFormClosedEventArgs(...)) 'your params here
End Sub
On Main Form handle your custom event (here HotKeyFormClosed) and extract its values
AddHandler frmHotKey.HotKeyFormClosed, AddressOf HotKey_FormClosed;
...
Private Sub HotKey_FormClosed(sender As Object, e As HotKeyFormClosedEventArgs)
'Do stuff with values from e
End If
I have chosen the Event approach since it decouples the two forms from another.
One could easily duplicate the information on both forms, make them public and access it directly thru an object instance.
But I like the observable approach from the events more due to it gives mor flexibility (additonal forms using the same events etc.)
P.S.: I wrote my code in c# and blind entered the VB code here so be gracious.
The values/variables that a method expects to receive (specified in the method's signature) are called Parameters.
The values sent to a method when the method is called are called Arguments.
As long as the arguments used when calling a method match the parameters for that method, those values can be passed.
For example (and I'll try to apply this to your context), if you want to create an instance of a form that takes certain values, you can specify those parameters in the form's New event, like so:
Public Sub New(someInt As Integer)
'do something with someInt here
End Sub
Then when you call this method you'd pass it the arguments, like so:
Dim myInt As Integer = 10
Dim newForm As myForm = New myForm(myInt)
When I say the arguments need to match the parameters, that means the number of values, the order of those values, and the value types must be the same (or in the case of numbers the parameter's type must be the same or larger than the argument's type).
As long as that is true, then it shouldn't really matter how you pass these - you could pass 11 individual arguments, you just have to make sure you are matching the argument to the parameter.
Hope that helps!
I am making a dvd database system in windows form and trying to display the dvd's entered by a user. Then display the Title, Director and Genre in 3 separate listBoxes.
When the user enters the information through 3 separate text boxes, the information is stored in a structure I made called TDvd. This means I can call for example dvd.Title or dvd.Director. I also use the variable index to add this information to an array I made called Dvd(100) (just a random number I used to test).
Here is the code I currently have for adding the items to the ListBox:
For i = 1 To noOfAddedDvds
lstTitle.Items.Add(dvd(i).Title)
lstDirector.Items.Add(dvd(i).Director)
lstGenre.Items.Add(dvd(i).Genre)
Next
The variable NoOfDvdsAdded is just a way of keeping track of the number of dvd's the user has already entered.
I run this and enter the Title, Director and Genre, but when I try and display this information across the 3 listboxes, I get the error:
An unhandled exception of type 'System.ArgumentNullException' occurred in System.Windows.Forms.dll
Public Class Form1
Structure TDvd
Dim Title As String
Dim Director As String
Dim Genre As String
End Structure
Dim dvd(100) As TDvd
Dim index As Integer = 0
Dim noOfAddedDvds As Integer
Private Sub btnAddToDatabase_Click(sender As Object, e As EventArgs) Handles btnAddToDatabase.Click
If txtDirector.Text <> "" Or txtGenre.Text <> "" Or txtTitle.Text <> "" Then
txtTitle.Text = dvd(index).Title
txtDirector.Text = dvd(index).Director
txtGenre.Text = dvd(index).Genre
index += 1
noOfAddedDvds += 1
End If
End Sub
Private Sub btnDisplayDatabase_Click(sender As Object, e As EventArgs) Handles btnDisplayDatabase.Click
Dim i As Integer
For i = 0 To noOfAddedDvds
MessageBox.Show(index & ", " & i)
lstTitle.Items.Add(dvd(i).Title)
lstDirector.Items.Add(dvd(i).Director)
lstGenre.Items.Add(dvd(i).Genre)
MessageBox.Show(index & ", " & i)
Next
End Sub
End Class
According to the documentation, an ArgumentNullException is thrown by the Add() method if the argument passed to it is null. (Or Nothing in VB.) So one of these is Nothing at runtime:
dvd(i).Title
dvd(i).Director
dvd(i).Genre
You'll have to debug to determine which. It would seem that the error is because you're starting your iteration at 1 instead of 0, I would think it should be:
For i = 0 To noOfAddedDvds - 1
So when you get to the index of noOfAddedDvds in your collection, that element will be an uninitialized struct with Nothing strings.
You'll definitely want to fix the iteration (indexes start at 0). Additionally, you may also benefit from initializing the String properties in your struct to String.Empty internally. Depends on whether you want similar errors to manifest as an exception or as an empty record. Sometimes the latter makes the problem more obvious since at runtime you'd see that your output started on the second record.
Just a few pointers...
The Items collection on the ListBox is actually 0 indexed, by which I mean that instead of going "1,2,3", it actually goes (0,1,2).
That's what your problem is.
Hint - think about perhaps using a List instead of an array as well... (for dvd)
Your thing cries out for being rewritten in OO form:
Friend DVDGenres
Undefined
Comedy
Action
Adventure
Sci-Fi
End Enum
Friend Class DVD
Public Property Title As String
Public Property Director As String
Public Property Genre As DVDGenres
Public Sub New
Title = ""
Director = ""
Genre = DVDGenres.Undefined
' other stuff too
End Sub
Public Overrides Function ToString As String
Return Title
End Sub
End Class
Now something to store them in. Arrays went out with Rubik's Cubes, so a List:
Private myDVDs As New List(of DVD)
A list and a class can do what arrays and structures can without the headaches. Add a DVD:
Dim d As New DVD
d.Name = TextBoxName.Text
d.Director = TextBoxDir.Text
d.Genre = comboboxGenre.SelectedItem
' add to the container:
myDVDs.Add(d)
Display all the DVDs in a ListBox to pick from:
AllDVDsLB.DataSource = myDVDs
AllDVDsLB.DisplayMember = "Title"
This will set your list as the datasource for the listbox. Whatever is in the List is automatically displayed without copying data into the Items collection. Then, say from selectedindex changed event, display the selected item details to some labels:
Label1.Text = Ctype(AllDVDsLB.SelectedItem, DVD).Title
Label2.Text = Ctype(AllDVDsLB.SelectedItem, DVD).Director
Label3.Text = Ctype(AllDVDsLB.SelectedItem, DVD).Genre.ToString
Iterate to do something like what is in the Question:
For Each d As DVD in myDVDs ' CANT run out of data
lstTitle.Items.Add(d.Title)
lstDirector.Items.Add(d.Director)
lstGenre.Items.Add(d.Genre.ToString)
Next
Or iterate and reference with an Int32:
For n As Integer = 0 To myDVDs.Count - 1
lstTitle.Items.Add(myDVDs(n).Title)
' etc
Next n
HTH
The program is a booking system (amongst other things) for a holiday letting company. I am working on the screen where you can see properties and ammend them or add more (etc)
Okay so It works fine in my other cases, but this one it just doesn't want to accept...I expect it's something stupid. Basically In the initial loading of the entire program I filled the Data Tables with the relevant info and then accessed them when needs be, in this case I am in the Form Properties and want to access Bookings (Which were made in FrmBookings) to see when the property is next booked to have guests in.
Dim Intcounter As Integer = 0
Dim NumberBookingRecords As Integer = BookingsNumRecs
Dim PropertyName As String
Dim PropertyFromBookings As String
Do
PropertyName = DTProperties(Intcounter)("Property Name").ToString
PropertyFromBookings = (DTBookings(NumberBookingRecords)("Property").ToString)
If PropertyName = PropertyFromBookings Then
lblDateOfArrival.Text = (DTBookings(NumberBookingRecords)("Arrival").ToString)
Intcounter = Intcounter + 1
Else
If Not NumberBookingRecords = 0 Then
NumberBookingRecords = NumberBookingRecords - 1
Else
End If
End If
Loop Until Intcounter >= intNumPropertyRecs
However when I get to PropertyFromBookings = (DTBookings(NumberBookingRecords)("Property").ToString)
it tells me that it could not be set to an instance of an object...no matter what I try an access from DTBookings I get the same response.
This is in the initial load form at the opening of the program
Dim FSBookings As New FileStream(strFileNameBookings, FileMode.OpenOrCreate, FileAccess.Read)
Application.DoEvents()
If FileLen(strFileNameBookings) > 0 Then
DTBookings.ReadXmlSchema(strFileNameBookings)
DTBookings.ReadXml(strFileNameBookings)
BookingsNumRecs = DTBookings.Rows.Count
intCurrRec = 1
Else
End If
FSBookings.Close()
blnStopAuto = True
blnStopAuto = False
Based on your code sample, DTBookings() is a function call. There are two possibilties here. Either:
The result of that function is Nothing, and when you try to use a Nothing as if there were an actual object there, (in this case, when trying to look up the ("Property") indexer) you'll get that exception, or ...
The result of the ("Property") index returns Nothing, in which case you'll get that exception when you try to call the .ToString() method.