DevForce Community Forum : Passing an EntityList?

Passing an EntityList? : In order to use IEnumerable without...

Tue, 09 Sep 2008 21:17:52 -700

Author: jeffdoolittle
Subject: 932
Posted: 09-Sep-2008 at 9:17pm

In order to use IEnumerable without a type parameter, you need a using statement that references System.Collections:

using System.Collections;

To get a reference to the extension method .Cast(), you need a using statement like this:

using System.Linq;

Passing an EntityList? : Thanks for your reply, Jeff....

Tue, 09 Sep 2008 20:43:29 -700

Author: HFloyd
Subject: 932
Posted: 09-Sep-2008 at 8:43pm

Thanks for your reply, Jeff.

Well, I tried leaving the T out:


    private IEnumerable mListMainEntity;

        protected IEnumerable MainEntityList
        {
            get { return mListMainEntity; }
            set { mListMainEntity = value; }
        }

but get a Build error:
Using the generic type 'System.Collections.Generic.IEnumerable' requires '1' type arguments

I was intrigued by your second suggestion, since all I need is the Count, which is a property of Entity, but also cannot get it formatted correctly.
This is what I tried:


base.MainEntityList = mListMainEntity.Cast();

(The mListMainEntity already exists, I just want to pass it to the base)


private EntityList mListMainEntity= new EntityList();

The build error is:
'IdeaBlade.Persistence.EntityList' does not contain a definition for 'Cast' and the best extension method overload 'System.Data.EnumerableRowCollectionExtensions.Cast(System.Data.EnumerableRowCollection)' has some invalid arguments

I tried other combinations, but none were acceptable to the compiler:


base.MainEntityList = mListMainEntity().Cast(); <--Doesn't compile

I was able to compile with this:


base.MainEntityList = (IEnumerable)mListMainEntity;

but then got a runtime exception:
System.InvalidCastException was unhandled by user code
Message="Unable to cast object of type 'IdeaBlade.Persistence.EntityList`1[HS.Admin.Model.HouseholdBusiness]' to type 'System.Collections.Generic.IEnumerable`1[IdeaBlade.Persistence.Entity]'."

I'm not sure how to proceed.

Heather

Edited by HFloyd - 09-Sep-2008 at 8:44pm

Passing an EntityList? : You can't use IEnumerable<Entity>,...

Tue, 09 Sep 2008 08:51:06 -700

Author: jeffdoolittle
Subject: 932
Posted: 09-Sep-2008 at 8:51am

You can't use IEnumerable, you have to just use IEnumerable. Generics collections don't know how to auto-cast their members to a base type, so you can't do this:

IEnumerable collection = new EntityList();

because "T" is not the same for both collections.

You can either just just IEnumerable without a generic type constraint, or you could try this:

IEnumerable collection = new EntityList().Cast();

which uses a Linq extension method to do the list cast for you.

Passing an EntityList? : Hi Jeff, Thanks for your idea,...

Tue, 09 Sep 2008 08:36:50 -700

Author: HFloyd
Subject: 932
Posted: 09-Sep-2008 at 8:36am

Hi Jeff,

Thanks for your idea, but I'm afraid I'm not sure how to implement it.

I put this into BASE:


private IEnumerable mListMainEntity;

        protected IEnumerable MainEntityList
        {
            get { return mListMainEntity; }
            set { mListMainEntity = value; }
        }

But am having trouble assigning it from the Derived form:


private EntityList mListMainEntity = new EntityList();

base.MainEntityList = mListMainEntity;

The message is:
Cannot implicitly convert type 'IdeaBlade.Persistence.EntityList' to 'System.Collections.Generic.IEnumerable'. An explicit conversion exists (are you missing a cast?)

Do you happen to know the cast syntax?

Thanks,

Heather

Passing an EntityList? : How about using IEnumerable instead...

Sun, 07 Sep 2008 22:00:20 -700

Author: jeffdoolittle
Subject: 932
Posted: 07-Sep-2008 at 10:00pm

How about using IEnumerable instead of object? Then make sure you have a reference to System.Linq and you can use the .Count() extension method.

--Jeff

Passing an EntityList? : Hi, I am interested in using a...

Sun, 07 Sep 2008 13:08:27 -700

Author: HFloyd
Subject: 932
Posted: 07-Sep-2008 at 1:08pm

Hi,
I am interested in using a "base" user control for building my various usercontrols for editing each entity. I would like to have some basic functionality code in the "base" to manage operations related to Data Navigation and Adding/Saving, etc. Because I need to be able to fully access the visual controls since each derived uc will look unique, I am not including those visual (form) items in my base uc, but need to reference them (for instance, to enable/disable buttons or respond to "onclicks", etc. I figured that to get around this, I would just pass my form controls from the derived uc to the base through exposed properties. This works fine for form controls, but I am also interested in dealing directly with the EntityList of the main business object being edited on the derived uc, and can't seem to figure out how to format the property in base to accept an EntityList<>, which could be of whatever type.

What I have thought of is to make the base property just an "object", since the dervied uc will define what the actual entity list is, but I am having a hard time accessing properties for the EntityList/object in the base uc code. When I write "mListMainEntity.Count", the compiler won't allow it, since .Count is not defined for generic objects. This is also not allowed: "mListMainEntity["Count"]".

Here is some example code:

derived uc :


private void HouseholdsBusinesses_Load(object sender, EventArgs e)
        {
            base.InitalizePM();
            base.OtherIntitalizing();
            ConfigureBindingSources(); 
            LoadData();

            //Initialize Base Property Values
            base.mCBM = this.dataCBM;
            base.mListMainEntity= mListMainEntity;
            base.mMainBindingSource = this.bsMainEntity;
            base.MainEntityType  = typeof(HouseholdBusiness);
        }

base uc:


protected object mListMainEntity;

protected object MainEntityList
        {
            get { return mListMainEntity; }
            set { mListMainEntity = value; }
        }

private void MainEntityListChanged(object sender, System.ComponentModel.ListChangedEventArgs e)
        {
            if (mListMainEntity == null || mListMainEntity.Count == 0) <---This is the problem area
            {
                SetDNRemoveFalse();
            }
            else
            {
                SetDNRemoveTrue();

                if (!mPersMgr.HasChanges())
                { //Disable Save/Reset Buttons
                    SetDNEndEditFalse();
                    SetDNCancelEditFalse();
                }
                else
                { //Enable Save/Reset Buttons
                    SetDNEndEditTrue();
                    SetDNCancelEditTrue();
                }
            }
        }

Is there some syntax I am missing? Am I going about this the wrong way?

Thanks,

Heather