Question

I want to cancel an event from within that function scope.

Eg. I pressed button click event and on false validation, I want to cancel this event. Likewise i want to cancel other events also.

How can i do this in C#

Answer 1

It depends on the scenario; in most cases: rather than cancel the event, just do nothing, for example:

private void SaveDataClicked(object sender, EventArgs args) {
    if(!ValidateData()) return;
    // [snip: code that does stuff]
}

or:

private void SaveDataClicked(object sender, EventArgs args) {
    if(ValidateData()) {
        // [snip: code that does stuff]
    }
}

There are some events that expose a CancelEventArgs (or similar), allowing to to cancel some external behaviour via the args – form-closing being the most obvious example (set e.Cancel = true;).

Note that in this scenario I would not have an automatic dialog-result on the button; apply that manually when (if) the handler completes successfully.