c# how to detect textbox changes?

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I have a form with alot of textboxes i am trying to loop controls in form to detect if textbox,combobox changes befor colsing form but not work!!

C#

 public partial class PatientFiles : Form, ILookup
    {
      bool NeedSaving = false;
      void CheckChanges(Control.ControlCollection cc)
    {
       foreach (Control ctrl in cc)
    {
        MaskedTextBox mtxtBox = ctrl as MaskedTextBox;
        TextBox txtBox = ctrl as TextBox;
        ComboBox cmb = ctrl as ComboBox;

        mtxtBox.TextChanged += new EventHandler(this.TextWasChanged);
        txtBox.TextChanged += new EventHandler(this.TextWasChanged);
        cmb.SelectedIndexChanged += new EventHandler(this.TextWasChanged);
        //CheckChanges(ctrl.Controls);

    }

}
  //formload
  private void frmPatient_Load(object sender, EventArgs e)
{
    EnableNavigation();
    //txtEngName.TextChanged += new EventHandler(TextWasChanged);
    CheckChanges(this.Controls);

}` 

 public void TextWasChanged(object sender, EventArgs e)
{
    NeedSaving = true;
}`

private void PatientFiles_FormClosing(object sender, FormClosingEventArgs e)
{
    //NeedSaving();
    // Disable Navigation On Form closing
    if (NeedSaving)
    {

        DialogResult dt = MessageBox.Show("Save Changes", "information", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Warning);
        if (dt == DialogResult.Yes)
        {
            SaveData();
            //DisableNavigation();
        }

        else if (dt == DialogResult.No)
        {

            DisableNavigation();
            NeedSaving = false;
            this.Close();
        }
        else if (dt == DialogResult.Cancel)

            e.Cancel = true;
    }

}

Posted 10-Aug-15 3:17am

mrimamm

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Kornfeld Eliyahu Peter 10-Aug-15 9:34am

Handle Change event...

1 solution

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Richard Deeming · Answer 1 · 2015-08-10T03:41:00

C#

MaskedTextBox mtxtBox = ctrl as MaskedTextBox;
TextBox txtBox = ctrl as TextBox;
ComboBox cmb = ctrl as ComboBox;

mtxtBox.TextChanged += new EventHandler(this.TextWasChanged);
txtBox.TextChanged += new EventHandler(this.TextWasChanged);
cmb.SelectedIndexChanged += new EventHandler(this.TextWasChanged);

A control will not be both a MaskedTextBox, a TextBox and a ComboBox at the same time. Two of those variables will always be null, so you'll get a NullReferenceException when you try to add a handler to the relevant "changed" event.

Change your code to check for null before trying to add the handler:

C#

MaskedTextBox mtxtBox = ctrl as MaskedTextBox;
if (mtxtBox != null)
{
    mtxtBox.TextChanged += TextWasChanged;
}
else
{
    TextBox txtBox = ctrl as TextBox;
    if (txtBox != null)
    {
        txtBox.TextChanged += TextWasChanged;
    }
    else
    {
        ComboBox cmb = ctrl as ComboBox;
        if (cmb != null)
        {
            cmb.SelectedIndexChanged += TextWasChanged;
        }
    }
}

NB: For future reference, "it doesn't work" is not a good description of the problem. Always include the full details of any exception your code is throwing.