Cannot be negative and avoid letter inputs on textbox

Question

here is my whole code fro the txtProductQuantity_TextChange:

protected void txtProductQuantity_TextChanged(object sender, EventArgs e)
    {
        TextBox txtQuantity = (sender as TextBox);

        //int tempForTryParse = 0;
        //if (!int.TryParse(txtQuantity.Text, out tempForTryParse))
        //{
        //    txtQuantity.Text = txtQuantity.Text.Substring(0, txtQuantity.Text.Length - 1);
        //}

        DataListItem currentItem = (sender as TextBox).NamingContainer as DataListItem; // getting current item on where user wants to add or remove
        HiddenField ProductID = currentItem.FindControl("hfProductID") as HiddenField;
        Label lblAvailableStock = currentItem.FindControl("lblAvailableStock") as Label;

        int tempInt = 0;
        if (txtQuantity.Text == string.Empty || txtQuantity.Text == "0" || txtQuantity.Text == "1" || double.Parse(txtQuantity.Text) < 0 || !int.TryParse(txtQuantity.Text, out tempInt))
        {
            txtQuantity.Text = "1"; //default value is 1, no action 
        }
        else
        {
            if (Session["MyCart"] != null) // not null means user has added a product in the shopping cart
            {
                if (Convert.ToInt32(txtQuantity.Text) <= Convert.ToInt32(lblAvailableStock.Text)) // check if quantity is greater than available stock
                {
                    DataTable dt = (DataTable)Session["MyCart"]; // if quantity is less than the available stock, go inside the code

                    DataRow[] rows = dt.Select("ProductID = '" + ProductID.Value + "'"); // select specific row depending on the product id

                    int index = dt.Rows.IndexOf(rows[0]);

                    dt.Rows[index]["ProductQuantity"] = txtQuantity.Text; // putting the value in the txtQuantityTextbox. changing the product quantity in the data table

                    Session["MyCart"] = dt; // add updated value to datatable
                }
                else // error if quntity is greater than available stock
                {
                    lblAvailableStockAlert.Text = " Alert: product buyout should not be more than the available stock!";
                    txtQuantity.Text = "1"; // automatically change the quantity back to 1.
                }

            }
        }
        UpdateTotalBill();
    }

what i want to happen is to avoid letters being an input from the user. or something like it will be defaulted to "1" if they do.

Alfie Goodacre · Accepted Answer · 2016-04-20T13:32:41.620

3

Use an if statement to check

if(txtQuantity.Text.StartsWith("-")
{
    //Code if negative
}

You could also parse the string as a number and then check if it is negative

if(int.Parse(txtQuantity.Text) < 0)
{
    //Code if negative
}

So in the context of your code you could use it like this

if (txtQuantity.Text == string.Empty || txtQuantity.Text == "0" || txtQuantity.Text == "1" || txtQuantity.Text.StartsWith("-"))
   {
        txtQuantity.Text = "1"; //default value is 1, no action 
   }

or

if (txtQuantity.Text == string.Empty || txtQuantity.Text == "0" || txtQuantity.Text == "1" || int.Parse(txtQuantity.Text) < 0)
   {
        txtQuantity.Text = "1"; //default value is 1, no action 
   }

To avoid text being entered into the field, on the Text Changed event for the textBox you should add another criteria into this if statement, as well as an integer variable to act as an out

int tempInt = 0;
bool parsed = int.TryParse(txtQuantity.Text, out tempInt);
if (txtQuantity.Text == string.Empty || txtQuantity.Text == "0" || txtQuantity.Text == "1" || tempInt < 0 || !parsed)
   {
        txtQuantity.Text = "1"; //default value is 1, no action 
   }

edited Apr 20 '16 at 13:32

answered Apr 20 '16 at 12:54

Alfie Goodacre

2,753
1
13
26

thanks mate. any idea on how to avoid inputting letters on it? because it gives me an error when i do. – Paolo Duhaylungsod Apr 20 '16 at 12:57
@PaoloDuhaylungsod edited for that situation – Alfie Goodacre Apr 20 '16 at 13:02
i have shown my whole code. or can it be like it will be defaulted to the value of 1 if they entered a letter? thank you – Paolo Duhaylungsod Apr 20 '16 at 13:07
@PaoloDuhaylungsod in that case, just after you set sender to be `txtQuantity` you can put that validation, and if there is a letter you can either return so that nothing happens or just let it run anyway – Alfie Goodacre Apr 20 '16 at 13:08
worked perfectly fine. bravo, thank you :) – Paolo Duhaylungsod Apr 20 '16 at 13:14
oh wait, it gives me an error when i input two letters? one letter is fine, it defaults to 1. – Paolo Duhaylungsod Apr 20 '16 at 13:15
If you would prefer that it just defaults to one, I will replace my code, try again once I have edited – Alfie Goodacre Apr 20 '16 at 13:17
yes i prefer to be defaulted to 1. thank you – Paolo Duhaylungsod Apr 20 '16 at 13:18
The last code snippet should now replace the original if, it also creates a new variable for the `TryParse` – Alfie Goodacre Apr 20 '16 at 13:19
same error Input string was not in a correct format. – Paolo Duhaylungsod Apr 20 '16 at 13:22
That does not seem correct, do you still have the original version of that snippet in there? It should have been removed – Alfie Goodacre Apr 20 '16 at 13:24
i removed these codes: int tempForTryParse = 0; if (!int.TryParse(txtQuantity.Text, out tempForTryParse)) { txtQuantity.Text = txtQuantity.Text.Substring(0, txtQuantity.Text.Length - 1); } – Paolo Duhaylungsod Apr 20 '16 at 13:26
i have edited my updated codes sir – Paolo Duhaylungsod Apr 20 '16 at 13:28
1

@PaoloDuhaylungsod Try the updated code – Alfie Goodacre Apr 20 '16 at 13:31
do you have a facebook account? i think i need you for my project. hehe – Paolo Duhaylungsod Apr 20 '16 at 13:36
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/109693/discussion-between-alfie-goodacre-and-paolo-duhaylungsod). – Alfie Goodacre Apr 20 '16 at 13:38

score 1 · Answer 2 · answered Apr 20 '16 at 12:56

1

managed to solve it.i added

int.Parse(txtQuantity.Text)<1)

to the first line of my code.

answered Apr 20 '16 at 12:56

Paolo Duhaylungsod

487
1
7
25

Cannot be negative and avoid letter inputs on textbox

2 Answers2