Validation using Validating event and ErrorProvider - Show Error Summary

Question

How to show Messagebox "Data is invalid" when there is errors left in my WinForms. Tried something like but it does not work.

if (errorprovider1 == !null)
{
 MessageBox.Show("Data is invalid");
}

Maybe i have to use bool for this solution.

My full code:

private void Form1_Load(object sender, EventArgs e)
{
    this.Text = "Formas elementu validācija";
}

    private void textBox1_Validating(object sender, CancelEventArgs e)
    {
        Regex regex1 = new Regex(@"^[a-zA-Z]+$");
        if (!regex1.IsMatch(textBox1.Text))
        {
            errorProvider1.SetError(textBox1, "Nosaukums nedrīskt saturēt ciparus!");
        }
        else
        {
            errorProvider1.Clear();
        }
    }

    private void textBox2_Validating(object sender, CancelEventArgs e)
    {
        Regex regex1 = new Regex(@"^[0-9]+$");
        if (!regex1.IsMatch(textBox2.Text))
        {
            errorProvider2.SetError(textBox2, "Reģ.nur drīkst saturēt TIKAI ciparus!");
        }
        else
        {
            errorProvider2.Clear();
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {
        // if errorProvider1 is empty (no errors) , show messagebox with text: All data correct.
        // else Data is incorrect.
    }

Let me know if you have any question about the solution. Also when you find an answer helpful, you can kindly click the check mark near the question to accept it. You can only accept one answer while you can vote up as many answer as you find helpful including accepted one by click on up arrow. This way you make the answers more helpful. You can also vote up for good questions. :) — Reza Aghaei, Oct 13 '15 at 16:23

Reza Aghaei · Accepted Answer · 2021-02-24T04:42:22.927

You should first correct your validating events this way:

private void textBox1_Validating(object sender, CancelEventArgs e)
{
    Regex regex1 = new Regex(@"^[a-zA-Z]+$");
    if (!regex1.IsMatch(textBox1.Text))
    {
        //To set validation error
        errorProvider1.SetError(textBox1, "Nosaukums nedrīskt saturēt ciparus!");
        //To say the state of control in invalid
        e.Cancel = true;
    }
    else
    {
        //To clear the validation error
        this.errorProvider1.SetError(this.textBox1, "");
    }
}

Then you should use ValidateChildren method to check if there is a validation error or not, then you can get a list of all errors and show to user this way:

private void button1_Click(object sender, EventArgs e)
{
    if (this.ValidateChildren())
    {
        //Here the form is in valid state
        //Do what you need when the form is valid
    }
    else
    {
        var listOfErrors = this.errorProvider1.ContainerControl.Controls.Cast<Control>()
                               .Select(c => this.errorProvider1.GetError(c))
                               .Where(s => !string.IsNullOrEmpty(s))
                               .ToList();
        MessageBox.Show("Please correct validation errors:\n - " +
            string.Join("\n - ", listOfErrors.ToArray()),
            "Error",  
            MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}

A Sample screenshot:

Note:

You should not use Clear method of error provider to set valid state to control, you should use SetError, for example this.errorProvider1.SetError(textBox2, "");
You should call e.Cancel=true when there is a validation error.
In sample codes I assume that all your controls including the error provider placed directly on your form and not in a container control.
I also recommend to change validation behavior of form by setting AutoValidate property of form to EnableAllowFocusChange in design time or by code in Load event of form this way:

To change validation behavior of form:

this.AutoValidate = System.Windows.Forms.AutoValidate.EnableAllowFocusChange;

Validation using Validating event and ErrorProvider - Show Error Summary

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