Check out example codes for "c# control lost focus event". It will help you in understanding the concepts better.

Code Example 1

// This method handles the LostFocus event for textBox1 by setting the 
// dialog's InitialDirectory property to the text in textBox1.
private void textBox1_LostFocus(object sender, System.EventArgs e)
{
    openFileDialog1.InitialDirectory = textBox1.Text;
}

Learn ReactJs, React Native from akashmittal.com