I have simple solution.
-(BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{
    if(range.length == 1 && [text length] == 0){
        NSLog(@"backspace");
    }
}
However, If the user to delete the dragged text?
Above code will not be obtain event.
But, article detail view of facebook does not have this problem.
How do I solve this problem?
 
     
    