my task is that, ask the user to write a number in a textbox between 1 and 5. I have to handle the bad cases, like the user write a wrong number or write character instead number and this have to run as long as the program get a correct number. This is what I have right now.

        int right_number = int.Parse(number.Text); 
        try
        {
            if (right_number > 5 || right_number < 1)
            {
                MessageBox.Show("Warning");
            }
        }
        catch (NotFiniteNumberException)
        {
            MessageBox.Show("Warning");
        }

CodePudding user response：

This would be the cleanest way to validate your input:

bool IsInputValid(string input, out string warningMessage)
{
    if (!int.TryParse(input, out var integerValue))
    {
        warningMessage = "input could not be parsed to an integer";
        return false;
    }

    if (integerValue < 1 || integerValue > 5)
    {
        warningMessage = "input is not between one and five";
        return false;
    }

    warningMessage = string.Empty;
    return true;
}

The calling code would look something like this:

void TextChanged(string newText)
{
    if (!IsInputValid(newText, out var warningMessage))
    {
        MessageBox.Show(warningMessage);
    }

    //handle valid input here
}

CodePudding user response：

The cleanest way to solve this is to use a NumericUpDown control with the following properties:

• MinValue = 1
• MaxValue = 5
• Value = (a good starting default)
• DecimalPlaces = 0
• Increment = 1

NumericUpDown doesn't accept non numeric input, or anything outside its ranges, so all those cases you are worried about just.. disappear. The user can also use up/down keys to adjust the value

CodePudding user response：

If user is supposed to enter 1, 2, 3, 4, 5 we can just prevent incorrect input (without annoying MessageBoxes etc.) with a help of KeyPress event handler:

private void myTextBox_KeyPress(object sender, KeyPressEventArgs e) {
  // We allow commands like BackSpace, Shift   Tab etc.
  e.Handled = e.KeyChar >= ' ';

  if (sender is Control control) {
    // If user press 1..5 we put it into the TextBox
    if (e.KeyChar >= '1' && e.KeyChar <= '5')
      control.Text = e.KeyChar.ToString();
  }
}

To prevent user pasting something from ClipBoard we can add TextChanged event handler:

private void myTextBox_TextChanged(object sender, EventArgs e) {
  if (sender is Control control) {
    string text = control.Text.Trim();

    if (text.Length == 1 && text[0] >= '0' && text[0] <= '5')
      control.Text = text;
    else
      control.Text = "";
  }
}

Now user can only do legal actions:

1. Press digit in 1..5 range (incorrect value is ignored)
2. Delete
3. Paste digit in 1..5 range (incorrect paste clears the text box)

CodePudding user response：

HTML supports regex patterns for validating inputs using the "pattern" attribute. You can then add an event listener to run when a user enters a value. The validity of the input can be checked with checkValidity()

HTML

<input  pattern="[0-5]">

JS

var input = document.querySelector("input");
input.addEventListener('change', (event) => 
{
    var valid = event.target.checkValidity();
    //do something
});

CodePudding user response：

        if (int.TryParse(number, out right_number))
        {
            if (right_number > 5 || right_number < 1)
            {
                MessageBox.Show("Warning");
            }
        }
        else
        {
            MessageBox.Show("Warning");
        }