The difference and application of e.Cancel and e.Handled in C#

In C#, e.Cancel and e.Handled are two properties in event parameters used to control event execution and propagation.

1. The e.Cancel property:
2. The e.Cancel attribute is used to halt the execution of the event. When the e.Cancel attribute is set to true, the event will no longer continue to execute.
3. Usually in event handlers, the decision of whether or not to cancel the execution of an event is based on specific conditions, and the feature of cancellation is achieved by setting the e.Cancel property.
4. Example code:
   private void Button_Click(object sender, EventArgs e)
   {
   if (someCondition)
   {
   e.Cancel = true; // Cancel the execution of the event
   }
   }
5. Handled property:
6. The e.Handled property is used to stop the propagation of an event. When the e.Handled property is set to true, the event will no longer be passed to other event handlers.
7. Typically in event handlers, a specific condition is used to determine whether to stop the propagation of the event, and the e.Handled property is set to achieve this.
8. Example code:
   private void Button_Click(object sender, EventArgs e)
   {
   if (someCondition)
   {
   e.Handled = true; // Stop the event from propagating
   }
   }

   private void Button_Click2(object sender, EventArgs e)
   {
   // This event handler will not be called because the previous event handler stopped the event propagation.
   }

Summary:

1. The e.Cancel property is used to halt the execution of the event, while the e.Handled property is used to stop the propagation of the event.
2. The application of the e.Cancel property is commonly used to prevent an action, such as canceling the closing of a window or canceling the pressing of a key.
3. The use of the e.Handled property is typically to prevent event bubbling, which stops the event from propagating to other controls or event handlers.