在 UnitOfWork.SaveChanges 之后 DataGrid 的 SelectedItem 丢失了绑定

Question

I currently developing an application in which the EntityFramework is used. In this application, there is a DataGrid, the SelectedItem is bound to a property on the ViewModel:

<DataGrid AutoGenerateColumns="False"
          CanUserDeleteRows="True"
          IsReadOnly="True"
          IsSynchronizedWithCurrentItem="False"
          ItemsSource="{Binding ZuvTextCollection}"
          SelectedItem="{Binding SelectedEntity,
                                 UpdateSourceTrigger=PropertyChanged,
                                 Mode=TwoWay}">

Now I have the problem that once data is stored, the binding to the SelectedItem seems almost lost.

edit: I forgot a very important point! I'm sorry! And this error occurs ONLY on after creating a new record.

protected override void OnSave()
{
    if (!this.OnCanSave())
    {
        return;
    }

    this.UnitOfWork.SaveChanges();
    this.IsDirty = this.UnitOfWork.ChangeTracker.HasChanges;
}

After calling this.UnitOfWork.SaveChanges, the binding is to Property in ViewModel no longer exists. The rows in the DataGrid can indeed select, but the changes of the Selection not arrive in the ViewModel.

What could it possibly be?

PS: I have read the following post http://www.devexpress.com/Support/Center/Question/Details/Q509665 but I must confess that gave me no idea how I could solve my problem. Thanks for any help!

Answer 1

@lll: I forgot a very important point! I'm sorry! And this error occurs ONLY on after creating a new record.

public ZuvText SelectedEntity
{
    get
    {
        return this.selectedEntity;
    }

    set
    {
        var entity = value;

        if (this.selectedEntity != null)
        {
            this.selectedEntity.PropertyChanged -= this.OnEntityPropertyChanged;
            this.selectedEntity.DisableContinuousValidation();
        }

        if (entity != null)
        {
            entity.PropertyChanged += this.OnEntityPropertyChanged;
            entity.EnableContinuousValidation();
        }

        this.SetProperty(ref this.selectedEntity, entity);
    }
}

The entity is set before saving, namely, when a new item is created. (As the cursor is moved to the new entity, thus it is SelectedEntity)

Now, a team-mate has found the cause. In the base class of our entities Equals and GetHashCode is overwritten:

public bool Equals(TEntity other)
{
    if (object.ReferenceEquals(null, other))
    {
        return false;
    }

    if (object.ReferenceEquals(this, other))
    {
        return true;
    }

    return this.id == other.Id;
}

public override bool Equals(object obj)
{
    if (object.ReferenceEquals(null, obj))
    {
        return false;
    }

    if (object.ReferenceEquals(this, obj))
    {
        return true;
    }

    if (obj.GetType() != this.GetType())
    {
        return false;
    }

    return this.Equals(obj as TEntity);
}

public override int GetHashCode()
{
    // ReSharper disable once NonReadonlyFieldInGetHashCode
    return this.id.GetHashCode();
}

The override of GetHashCode causes the id's before and after storing each provide a different hashCode and the object is no longer detected. For now we have commented out the override of GetHashCode. However, a real solution to this problem is not known to me. My team mate is already looking for a solution, but maybe you have an idea?

Answer 2

We have a solution! The DataGrid Selector can not find the selected object, after the update the ID. That is why we have now put the actual EntityCollection in an adapter or wrapper class.

public class ZuvTextAdapter
{
    public ZuvText ZuvText
    {
        get;
        set;
    }
}

The DataSorce looks just like this:

public ObservableCollection<ZuvTextAdapter> ZuvTextAdapterCollection...

And just the selected entity as:

public ZuvTextAdapter SelectedAdapter

Thus, the problem is resolved with our GetHeshCode and the binding is working properly after saving. (Solved by my teammates!)