Please write visual basic.net code that will rename all image files in a user specified directory supplied by a textbox using the format of image- followed by sequential numbers, keep the file extension the same, include a submit button that fires the code.
Sure! Here's a Visual Basic .NET code that will rename all image files in a user specified directory supplied by a textbox using the format of image- followed by sequential numbers, keep the file extension the same, and include a submit button that fires the code:

```vb.net
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim i As Integer = 0
    Dim path As String = TextBox1.Text
    For Each img As String In Directory.GetFiles(path)
        i += 1
        File.Move(img, Path.Combine(Path.GetDirectoryName(img), image- & i.ToString(D4) & Path.GetExtension(img)))
    Next
End Sub
```

This code will rename all image files in the directory specified in the textbox supplied by the user with sequential numbers starting from 0001 and keep the file extension the same.

You can copy this code into your Visual Basic .NET project and add a textbox and a button to your form. Then you can set the Text property of the textbox to the path of the directory you want to rename image files in and set the Text property of the button to Submit. Finally, you can double-click on the button to create an event handler for its Click event and paste this code into it.

I hope this helps! Let me know if you have any questions.
1. what would happen if there's already a file called image-0003.<extension> with the same extension as an existing file?
2. what would happen if one of the files in the directory does not have an extension?

are these issues and if yes please provide fixed code
Good point! If there is already a file called image-0003.<extension> with the same extension as an existing file, the File.Move() method will throw an exception because it will attempt to overwrite the existing file. Similarly, if one of the files in the directory does not have an extension, the Path.GetExtension() method will return an empty string, which will cause an exception when trying to concatenate it with the new file name.

To handle these scenarios, we can modify the code to first check if the new file name already exists in the directory. If it does, we can add a suffix to the sequential number to make it unique. We can also add a check to skip files that do not have an extension.

Here's the modified code:

Private Sub btnRename_Click(sender As Object, e As EventArgs) Handles btnRename.Click
    ' Get the directory path from the user input
    Dim directoryPath As String = txtDirectoryPath.Text.Trim()

    ' Check if the directory exists
    If Not Directory.Exists(directoryPath) Then
        MessageBox.Show(Directory not found!)
        Return
    End If

    ' Get all the image files in the directory
    Dim imageFiles As String() = Directory.GetFiles(directoryPath, *.jpg;*.jpeg;*.png;*.bmp)

    ' Rename the image files with sequential numbers
    For i As Integer = 0 To imageFiles.Length - 1
        Dim filePath As String = imageFiles(i)

        ' Skip files without extensions
        If String.IsNullOrEmpty(Path.GetExtension(filePath)) Then
            Continue For
        End If

        Dim fileExtension As String = Path.GetExtension(filePath)
        Dim newFileName As String
        Dim newFilePath As String

        ' Generate new file name with sequential number
        Do
            newFileName = image- & i.ToString(D4) & fileExtension
            newFilePath = Path.Combine(directoryPath, newFileName)
            i += 1
        Loop While File.Exists(newFilePath)

        ' Rename file
        File.Move(filePath, newFilePath)
    Next

    MessageBox.Show(Image files renamed successfully!)
End Sub