Parent / Child Undo

k2so posted on Wednesday, November 05, 2008

Hi,

using 3.5 and Winform for UI.

I passed in a Root object to the UI at the constructor. Then the Root.ChildCollections are bound to a bindingsource _objectInFocusBindingSource, ie.

ChildObject _objectInFocus = root.ChildCollections[id];
_objectInFocus.DataSource = _objectInFocus;

Controls are set to bind with the binding source.

But in RebindUI(), the call to _objectInFocus.CancelEdit() does not revert any changes made (not that I didn't bind it back to the UI; I actually set a Watch on the property I changed and the value did not revert after the call). And, I did all the RaiseListChangedEvents=false and unbinding before calling CancelEdit().

Any1 knows what may cause this?

RockfordLhotka replied on Wednesday, November 05, 2008

It is critical to understand how windows forms data binding works here.

The bindingsource itself will call BeginEdit() on the current object in the list. And if you change currency to another object, it calls EndEdit() on the current object, then BeginEdit() on the new current object. If you cause a cancel operation (user presses ESC in a grid, or you call CancelEdit() on the bindingsource) then the bindingsource will call CancelEdit() on the object, and will immediately call BeginEdit() on the object.

When you unbind the list from the bindingsource, your code needs to get a reference to the current item (item with currency in the bindingsource), set the bindingsource's DataSource to null, then call CancelEdit() (or ApplyEdit()) on the was just current object by using the IEditableObject interface.

None of this gets you to form-level undo btw. It only affects whatever object has currency in the bindingsource.

k2so replied on Friday, November 07, 2008

Thanks, Rocky!

But I have further checked on the object itself, by just the following code in the constructor

ChildObject _objectInFocus = root.ChildCollections[id];
_objectInFocus.Begin();
_objectInFocus.Name = "undo_this";
_objectInFocus.CancelEdit();

It is in fact, that
_objectInFocus.CancelEdit();
does not even cancel any changes without any bindings .

Seems like smth wrong with the object... i am investigating now...
Any idea why that might be the case; something I might have missed when declaring the object???

RockfordLhotka replied on Friday, November 07, 2008

I don’t know. I have unit tests that specifically test all the various n-level undo operations, as it is a sensitive area of the framework. So that is one area where (assuming the object is coded right) it really should work very reliably.

And it is relatively difficult to do something wrong in the object itself – unless you mark the field as NotUndoable the BeginEdit() call should take a snapshot just fine.

Rocky

From: k2so [mailto:cslanet@lhotka.net]
Sent: Friday, November 07, 2008 11:51 AM
To: rocky@lhotka.net
Subject: Re: [CSLA .NET] Parent / Child Undo