如何区分用户输入，但允许应用程序本身更改文本

Question

I've got a textbox, which does not allow users to enter "[" and "]" characters. However, I would like to set the text to be a value containing both "[" and "]" by default. How can I go about this? This is my code:

TextBox txtEdit = new TextBox();
txtEdit.TextChanged += txtEdit_TextChanged;
txtEdit.Text = "[Test]";

private void txtEdit_TextChanged(object sender, TextChangedEventArgs e)
{
    if ((sender as TextBox).Text.Contains("[") || (sender as TextBox).Text.Contains("]"))
    {
        MessageBox.Show("Cannot enter '[' or ']' characters!", "", MessageBoxButton.OK, MessageBoxImage.Information);
        (sender as TextBox).Text = "";
    }
}

Answer 1

Put the TextChanged Event after you change the Text property

TextBox txtEdit = new TextBox();
txtEdit.TextChanged += txtEdit_TextChanged;

private void txtEdit_TextChanged(object sender, TextChangedEventArgs e)
{
    if (comboBoxYou.Text == txtEdit.Text) 
    {
        return;
    }
    else if ((sender as TextBox).Text.Contains("[") || (sender as TextBox).Text.Contains("]"))
    {
        MessageBox.Show("Cannot enter '[' or ']' characters!", "", MessageBoxButton.OK, MessageBoxImage.Information);
        (sender as TextBox).Text = "";
    }
}

Answer 2

I'd set a keydown event for the Textbox.

If you don't want users enetering the '[' and ']' characters, then read in the key character and set e.Handled = true if it matches the character you don't want.

Answer 3

The answer of Toon Casteele is a good solution. Otherwise try adding a boolean to your form and when the user selects a value set it to true and check for the value in the TextChanged event if it is true.

private bool IsSelectedItemText; //set it to true when an item is selected

And then do following check:

if(!IsSelectedItemText)
    //Check for square brackets
else
    //Add text from item

Also, and this is not directly related to the question but I strongly suggest that you cast the 'sender' object only once. Complete, the code would look like:

private void txtEdit_TextChanged(object sender, TextChangedEventArgs e)
{
    TextBox tb = sender as TextBox;

    if(!IsSelectedItemText)
    {            
        if (tb.Text.Contains("[") || tb.Text.Contains("]"))
        {
            MessageBox.Show("Cannot enter '[' or ']' characters!", "", MessageBoxButton.OK, MessageBoxImage.Information);
            tb.Text = "";
        }
    }
    else
    {
        //Set text from selected item
    }

    IsSelectedItemText = false;
}

Remember to set the boolean-variable to 'true' when an item is selected.

Answer 4

If thats what you wanted.

private void txtEdit_TextChanged(object sender, TextChangedEventArgs e)
{
string a = (sender as TextBox).Text.substing(0,1).subsctring;
a = a.Remove(0, 1);
            a = a.Remove(a.Length - 1, 1);
            if (a.Contains('[') || a.Contains(']') )
            {
                MessageBox.Show("Cannot enter '[' or ']' characters!", "", MessageBoxButton.OK, MessageBoxImage.Information);
            }
            (sender as TextBox).Text = "[" + a.Replace("[", "").Replace("]", "") + "]";

}