0

I am struggling with the code when I run it I get this error.

Dim CheckedItems(clbfiles.CheckedItems.Count) As Object clbfiles.CheckedItems.CopyTo(CheckedItems, 0) For Each CheckedItem As Object In CheckedItems Dim FileToDelete As String If Not CheckedItem.ToString = "" Then <---- error 'creates path to delete FileToDelete = appdata + "\" + CheckedItem.ToString If System.IO.File.Exists(FileToDelete) = True Then 'deletes System.IO.File.Delete(FileToDelete) MsgBox("File Deleted") End If 'removes from list clbfiles.Items.Remove(CheckedItem) End If Next End Sub

ERROR CODE

System.NullReferenceException was unhandled Message=Object reference not set to an instance of an object. Source=ScreenShotCraft StackTrace: at ScreenShotCraft.frmindex.btndeleteselected_Click(Object sender, EventArgs e) at System.Windows.Forms.Control.OnClick(EventArgs e) at System.Windows.Forms.Button.OnClick(EventArgs e) at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent) at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.ButtonBase.WndProc(Message& m) at System.Windows.Forms.Button.WndProc(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg) at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData) at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun() at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel() at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine) at ScreenShotCraft.My.MyApplication.Main(String[] Args) at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args) at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException:
Improve this question

5 Answers 5

Reset to default
4

You made your array too long by 1, so when you get to the last item in the array it bombs. Do this instead: Dim CheckedItems(clbfiles.CheckedItems.Count - 1) As Object.

Improve this answer
Sign up to request clarification or add additional context in comments.

Comments

2

Weird, for some reason from that error, seems like you need to insert this:

IF (CheckedItem Is Nothing) Then Next 'Or the VB version of the C# continue keyword (my VB is rusty)

Right above this:

If Not CheckedItem.ToString = "" Then

HTH.

Improve this answer

1 Comment

This is also an important safety check. While my answer is why you had today's bug, this is the answer to prevent future ones.
2

try checking for the item existance:

If Not CheckedItem is Nothing End If

instead of 

CheckedItem.ToString() = ""

Becuase if CheckedItem is nothing then the ToString method will fail. Or you could use:

If Not String.IsNullOrEmpty(CheckedItem.ToString()) End IF
Improve this answer

Comments

2

Both mattmc3 and BigOrangeSU are correct.

Counterintuitive as it may be, array dimensions in VB.NET are zero-based, meaning if you run the following statement, you'll initialize a new array with 2 slots:

Dim myArray(1) as Integer

So in this case, as mattmc3 describes, reducing the dimension of CheckedItems by one will likely solve your problem. (There is no need to use the New keyword here: the answer given by Anuraj won't even compile!)

But what if the string you're looking at isn't initialized for some reason? As BigOrangeSU has said, you want to verify the string has a value before you examine it, otherwise you could end up throwing an exception.

I prefer the following syntax:

If CheckedItem IsNot Nothing Then End If
Improve this answer

Comments

0

You need to create the instance of CheckedItems like

Dim CheckedItems(clbfiles.CheckedItems.Count) As new Object

Hope it helps.

Improve this answer

Comments

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.