RadDropDown

[Mark]

Is there an event that is triggered when the READONLY flag is set on this control (or any other control in fact)?

 

Thanks in advanced.

[Dess | Tech Support Engineer, Principal]

Hi, Mark,

Setting the RadDropDownList.ReadOnly property internally sets the DropDownListElement.ListElement.ReadOnly property. Indeed, there is no event being triggered when the property is modified.

However, I have prepared a sample code snippet demonstrating how to create a custom ReadOnlyChanged event and use it to track the changes in the event:  

        public class CustomDropDown : RadDropDownList
        {
            public event EventHandler<ReadOnlyEventArgs> ReadOnlyChanged;
            public override string ThemeClassName
            {
                get
                {
                    return typeof(RadDropDownList).FullName;
                }
            }
            protected virtual void OnReadOnlyChanged(bool _readOnly)
            {
                if (ReadOnlyChanged != null)
                    ReadOnlyChanged(this, new ReadOnlyEventArgs(_readOnly));
            }
            public void SetReadOnly(bool isReadOnly)
            {
                this.ReadOnly = isReadOnly;
                ReadOnlyChanged(this, new ReadOnlyEventArgs(isReadOnly));
            }

        }

        public class ReadOnlyEventArgs : EventArgs
        {
            public ReadOnlyEventArgs(bool isReadOnly)
            {
                ReadOnly = isReadOnly;
            }

            public bool ReadOnly { get; private set; }
        }

  ((CustomDropDown)this.radDropDownList1).ReadOnlyChanged += DropDown_ReadOnlyChanged;

        private void RadDropDownList1_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            Console.WriteLine(  e.PropertyName);
        }

I hope this information helps. If you need any further assistance please don't hesitate to contact me. 

Regards,
Dess | Tech Support Engineer, Principal
Progress Telerik

[Mark]

Thank you, This is exactly what I was looking for.  I will try this out.

 

Thank You.

[Mark]

okay, so looking at the code above, both the SetReadOnly and OnReadONlyChanged are never called.  I am going to have to use these methods instead of just setting the ReadOnly property in our code?  This is not a problem, just wanted to understand the approach.

[Mark]

I am workign through the code above, and see that I have to call the "SetReadOnly" method, instead of just setting the "ReadOnly" property in order for the ReadOnlyChanged event to get executed.   What is the purpose of the OnReadOnlyChanged() method?

[Mark]

Thanks for your input,  but I think I found a simpler solution, which allows me to just set the property of ReadOnly, instead of calling the SetReadOnly method

public class CustomDropDown : RadDropDownList
   {
      public event EventHandler<ReadOnlyEventArgs> ReadOnlyChanged;

      protected virtual void OnReadOnlyChanged(bool _readOnly)
      {
         ReadOnlyChanged?.Invoke(this, new ReadOnlyEventArgs(_readOnly));
      }
      
      public override string ThemeClassName
      {
         get
         {
            return typeof(RadDropDownList).FullName;
         }
      }

      public override bool ReadOnly
      {
         get => base.ReadOnly;
         set
         {
            base.ReadOnly = value;
            OnReadOnlyChanged(value);
         }
      }
   }

   public class ReadOnlyEventArgs : EventArgs
   {
      public ReadOnlyEventArgs(bool isReadOnly)
      {
         ReadOnly = isReadOnly;
      }

      public bool ReadOnly { get; private set; }
   }

 

[Dess | Tech Support Engineer, Principal]

Hi, Mark,

The purpose of the OnReadOnlyChanged method is to raise the event handler if there is any subscriptions to the event. Additional information about the demonstrated approach with creating a custom event is demonstarted here: https://learn.microsoft.com/en-us/dotnet/desktop/winforms/controls/defining-an-event-in-windows-forms-controls?view=netframeworkdesktop-4.8 

As to the alternative solution in your last post, I can confirm that it is OK and you can use it in your scenario. Should you have further questions please let me know.