Question

I have a form with a multiline textInput. I need to update the content of the textInput from an object outside the form.

How can I achieve this? Should I use events, or perhaps pass the textInput to the outside object’s constructor?

Answer 1

Have a look at the MVP pattern – you could have your form implement an IView interface. Your other object would be the Presenter that would call, for example, IView.UpdateText() when something changes (or have your view subscribe to the presenters events – i prefer the method approach).

This separates your concerns and makes your solution more testable as you can mock up implementations of IView, IPresenter and IModel.

The form should check if this.InvokeRequired == true to determine if the incoming request is on the UI thread. If it is not you will need to use a delegate.

public delegate void UpdateTextDelegate(string text);

public void UpdateText(string text)
{
  // Check we are on the right thread.
  if (!this.InvokeRequired)
  {
      // Update textbox here
  }
  else
  {
      UpdateTextDelegate updateText = new UpdateTextDelegate(this.UpdateText);

      // Executes a delegate on the thread that owns the control's underlying window handle.
      this.Invoke(updateText, new object[] { text });
  }

}