c# DataChanged event does trigger on a windows form (Desktop Application)

Question

I have a form, I select some checkboxes , edit some text field , select from a combobox etc. then I click Exit . Based on the fact that "Data has been changed ??" I wish to perform actions. The problem is I can't get the event work :

private void DataChanged(object sender, EventArgs e)
{
    MessageBox.Show("Data is changed", "debug");
    isDataSaved = false;
}

When is this method called, how do I make it work? Is this supposed to get fired when the form's fields have some data ie filL a text box ?

I dont really get the API: DataChanged event

Note: I'm following Mike Murach C# 5th edition chapter 10 example.

Edit (exact words from book):

Generate an event handler named DataChanged for the SelectedIndexChanged event of the XXXX Name combo box. Then , wire this event handler to the TextChanged event of the YYYYY Method label and add the code to this event handler so it sets the isDataSaved variable to false

When I double click on the commbo box the generated event handler it is not named DataChanged but cboNames_SelectedIndexChanged... (is this a book screw up or me total noob ? PS: There is no .. 'database' in the project)

Answer 1

Personally I mostly use databinding these days to get notified of changes in data.

A data holder class, which implements INotifyPropertyChanged . This interface gives you the possibility to get notified when the value of a property changes.

public class SomeData: INotifyPropertyChanged {
    public event PropertyChangedEventHandler PropertyChanged;

    private void SetProperty<T>(ref T field, T value, [CallerMemberName] string name = "") {
        if (!EqualityComparer<T>.Default.Equals(field, value)) {
            field = value;
            var handler = PropertyChanged;
            if (handler != null) {
              handler(this, new PropertyChangedEventArgs(name));
            }
        }
    }

    private boolean _someBoolean;
    public int SomeBoolean {
        get { return _someBoolean; }
        set { 
            SetProperty(ref _someBoolean, value);
        }
    }

    private string _someString;
    public string SomeString {
        get { return _someString; }
        set { 
            SetProperty(ref _someString, value);
        }
    }

    // etc
}

Now our form, which uses the data class and it's INotifyPropertyChanged implementation to get notified when a change in data occurs.

public partial class SomeForm: Form {
    private SomeData _data;
    private void LoadData() {
        _data = new SomeData();
        _data.PropertyChanged += Data_PropertyChanged;
    }

    private void SaveData() {
        // TODO: Save data
    }

    private void AddDataBindings() {
        checkbox1.DataBindings.Add("Checked", _data, "SomeBoolean");
        textbox1.DataBindings.Add("Text", _data, "SomeString");
        // add other
    }

    private void Data_PropertyChanged(object sender, PropertyChangedEventArgs e) {
        // Here you can add actions that must be triggered when some data changes.
        if (e.PropertyName == "SomeBoolean") {
            // Do something when some-boolean property changes
        }

        // Set is-changed-boolean to true to 'remember' that something has changed.
        _isChanged = true;

        // Give message
        MessageBox.Show(string.Format("Data changed, property {0}", e.PropertyName));
    }

    private bool _isChanged = false;

    protected void Form_Closed(object sender, EventArgs e) {
        // If data is changed, save it
        if (_isChanged) {
            SaveData();
        }           
    }
}

Answer 2

Your problem is not known where the method DataChanged use and how. I have a suggestion for you that is use Focus Activated in properties.Add datachanged printing method Activated good luck.

You must make properties this like