How can I determine if an event was fired by a user action or by code?

Question

I have a bunch of controls on a form and all of their "change" events point to the same event handler. Some of these are txtInput1's TextChanged, chkOption1's CheckedChanged, and cmbStuff1's SelectedIndexChanged. Here is the event handler:

private void UpdatePreview(object sender, EventArgs e)
{
    // TODO: Only proceed if event was fired due to a user's clicking/typing, not a programmatical set
    if (sender.IsSomethingThatTheUserDid) // .IsSomethingThatTheUserDid doesn't work
    {
        txtPreview.Text = "The user has changed one of the options!";
    }
}

I would like the if statement to only run when a user changes the TextBox text or clicks a checkbox or whatever. I don't want it to happen if the text or checkbox was changed by some other part of the program.

Answer 1

There isn't a built-in mechanism to do this. You can, however, use a flag.

bool updatingUI = false;

private void UpdatePreview(object sender, EventArgs e)
{
    if (updatingUI) return;

    txtPreview.Text = "The user has changed one of the options!";
}

Then, when you're updating the UI from your code:

updatingUI = true;

checkBox1.Checked = true;

updatingUI = false;

If you want to over-engineer the solution, you could use something like this:

private void UpdateUI(Action action)
{
    updatingUI = true;

    action();

    updatingUI = false;
}

And use it like this:

UpdateUI(()=>
{
    checkBox1.Checked = true;
});

Answer 2

Can't you just check the sender? If it's called from a wired event to a UI control, it will come back with the control. If you're firing the event from code, it will either be the component making the call, or you could make it anything you want:

private void SomewhereElse()
{
   UpdatePreview(null, new EventArgs());
}

private void UpdatePreview(object sender, EventArgs e)
{
    if (sender == null) 
    {
        txtPreview.Text = "The user has changed one of the options!";
    }
}

or you may be able to do this:

private void UpdatePreview(object sender, EventArgs e)
{
    if (!(sender is Control)) 
    {
        txtPreview.Text = "The user has changed one of the options!";
    }
}

Answer 3

Try to go up the call stack and analyze it in some way (system.diagnostics). But keep in mind it's somewhat tricky and hacky.

"From code":

User-triggered: