Checking whether textboxes have data

Question

I always end up creating a quick return statement above a code block if the simple condition of textbox null fields are found. Naturally, these tend to build up the more controls are added. Now I'm staring at this mess of code, and I'm looking for advice as to avoid this very common mistake in the future.

This is the spaghetti code of a small winform C# project that I'm sure will trigger more than a few people:

   if (txtFirst.Text == "" || txtLast.Text == "" || txtGross.Text == "" ||
        txtLessTNT.Text == "" || txtTCI.Text == "" || txtADDTI.Text == "" || txtGTI.Text == "" ||
        txtLessTE.Text == "" || txtLessPPH.Text == "" || txtLessNTI.Text == "" || txtTD.Text == "" ||
        txtTWCE.Text == "" || txtTWPE.Text == "" || txtTATW.Text == "" ||
        txtFirst.Text == " " || txtLast.Text == " " || txtGross.Text == " " ||
        txtLessTNT.Text == " " || txtTCI.Text == " " || txtADDTI.Text == " " || txtGTI.Text == " " ||
        txtLessTE.Text == " " || txtLessPPH.Text == " " || txtLessNTI.Text == " " || txtTD.Text == " " ||
        txtTWCE.Text == " " || txtTWPE.Text == " " || txtTATW.Text == " " || txtID.Text == "" ||
        txtID.Text == " " || txtTIN.Text == "" || txtTIN.Text == " " || txtFrom.Text == " " || txtFrom.Text == "" || txtTo.Text == " " || txtTo.Text == "" || txtCTC.Text == " " || txtCTC.Text == "" || txtCTC.Text == " " || txtPOI.Text == "" || txtPOI.Text == " " || txtDOI.Text == "" || txtDOI.Text == " " || txtDOI.Text == "" || txtAMT.Text == " " || txtAMT.Text == ""
    )


    { 
        MessageBox.Show("Cannot enter null values!");
        return;
    }

Surely, there is an easier way to do this that allows the code to be modular and concise that permits the addition of new textbox controls. This happens more often than I'd like to admit and I wish to get rid of this habit once and for all.

Note that, I do have another solution, it's a linq block that iterates through ALL textbox controls in a given form. But what I'm looking for is as I mentioned, code that allows for selection of the controls involved.

Answer 1

Why so complicated?

One possible approach is:

var f = new Form();
if (f.Controls.OfType<TextBox>().Any(x => string.IsNullOrWhiteSpace(x.Text)))
{
    /*your stuff*/
}

A second approach is:

var TextBox1 = new TextBox();
var TextBox2 = new TextBox();

var textboxes = new[] { TextBox1, TextBox2 };
if (textboxes.Any(x => string.IsNullOrWhiteSpace(x.Text)))
{
    /*your stuff*/
}

Answer 2

While the suggested approach with enumerating and checking all text-boxes works as an easy workaround, it's a horrible solution from the user point of view because he either gets noticed about some missing inputs when he hits submit or he will constantly be notified with annoying message-boxes when he leaves a text-box. He also won't know which field he left empty.

The right thing to do is to use the Validating event connected with the ErrorProvider that will give instant hints about what's wrong.

---

Here's a small example.

You create an error-provider by dropping it to the form/user-control from the toolbox.

ErrorProvider errorProvider = new ErrorProvider();

Then you create a method to validate the text and to set the error message.

bool ValidateIsNotNullOrWhitespace(TextBox textBox)
{
    if (string.IsNullOrWhiteSpace(textBox.Text))
    {
        // textBox.Tag - use this to get a custom message for this text-box
        var message = "Please provide your Name."
        errorProvider.SetError(textBox, message);
        return true;
    }
    errorProvider.SetError(textBox, string.Empty); // clears error message
    return false;
}

If you don't want to use a generic message like This field must not be empty. then you can use the Tag property to specify the key for the string:

textBox.Tag = "age"; // this can be an enum, string, int or anything

Finally you wire each text-box'es Validating event with a call to the validation method above. Setting Cancel to true will prevent the user from changing the focus to another control until he enters a valid value.

textBox.Validating += (sender, e) => 
{
    e.Cancel = ValidateIsNotNullOrWhitespace((TextBox)sender);
};

When a text-box contains an invalid value an exclamation mark will be shown and hovering over it will display the message.

Answer 3

I was going to add this as a comment to @tym32167's answer, but I am brand new and don't have enough rep to do that.

What you can do, building on @tym32167's answer, is filter the controls by another property. Each of the controls has a Tag property that you can set any string value to, such as "Required". From there, you can find all text boxes whose Tag property matches that value, like so:

var f = new Form();
if (f.Controls.OfType<TextBox>().Where(x => (string)x.Tag == "Required").Any(x => string.IsNullOrWhiteSpace(x.Text)))
{
    /*your stuff*/
}