How do I validate more than one textfields in VB

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VB

I have been given an assignment which says that i am supposed to

Write an Input validation, such that, the number of units for each package entered by the user will be only Numeric, and is not negative

Write a code to clear spaces before and after a text. (Hint: applying trimming)

At runtime, we cannot afford to allow the software to crash. You are to write appropriate error messages for the following:
a.When the user enters non-numeric value in any of the packages.
b.When the user enters negative value in any of the packages.
c.When the application suffers critical runtime error.

What I have tried:

Try
    packageA = CInt(CDec(txtPackageA.Text))
    packageB = CInt(CDec(txtPackageB.Text))
    packageC = CInt(CDec(txtPackageC.Text))
Catch ex As Exception
    MessageBox.Show("Numbers only and not Negative", "Input Error")
    Return
End Try
If (packageA < 1) Then
    MessageBox.Show("Numbers only and not Negative", " Input Error")
    Return
End If
If (packageB < 1) Then
    MessageBox.Show("Numbers only and not Negative", " Input Error")
    Return
End If
If (packageC < 1) Then
    MessageBox.Show(" Numbers only and not Negative", " Input Error")
    Return
End If

lblAmountA.Text = " GHc" & packA.ToString
lblAmountB.Text += " GHc" & packB.ToString
lblAmountC.Text += " GHc" & packC.ToString

GrandTotal = CInt(packA + packB + packC)
lblTotal.Text += " GHc" & GrandTotal.ToString

Catch ex As Exception
End Try


End Sub


Private Sub txtPackageA_TextChanged(sender As Object, e As EventArgs) Handles txtPackageA.TextChanged
If (Not IsNumeric(txtPackageA.Text)) Then

ErrorProvider1.SetError(txtPackageA, "Only Numeric")

Else
ErrorProvider1.SetError(txtPackageA, "")
End If
End Sub

Private Sub txtPackageB_TextChanged(sender As Object, e As EventArgs) Handles txtPackageB.TextChanged
If (Not IsNumeric(txtPackageB.Text)) Then

ErrorProvider1.SetError(txtPackageB, "Only Numeric")

Else
ErrorProvider1.SetError(txtPackageB, "")
End If
End Sub

Private Sub txtPackageC_TextChanged(sender As Object, e As EventArgs) Handles txtPackageC.TextChanged
If (Not IsNumeric(txtPackageC.Text)) Then

ErrorProvider1.SetError(txtPackageC, "Only Numeric")

Else
ErrorProvider1.SetError(txtPackageC, "")
End If
End Sub

Private Sub txtPackageA_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles txtPackageA.Validating

If (String.IsNullOrEmpty(txtPackageA.Text)) Then
e.Cancel = True

ErrorProvider1.SetError(txtPackageA, "Please enter a Unit here!!!")

Else
e.Cancel = False
ErrorProvider1.SetError(txtPackageA, "")
End If
End Sub

Private Sub txtPackageB_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles txtPackageB.Validating
If (String.IsNullOrEmpty(txtPackageB.Text)) Then
e.Cancel = True

ErrorProvider1.SetError(txtPackageB, "Please enter a Unit here!!!")

Else
e.Cancel = False
ErrorProvider1.SetError(txtPackageB, "")
End If
End Sub
End Class