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   How to: Access Data in SQL Query Results
   How to: Bind an XPCollection to a LookUp
   How to: Bind an XPCollection to Standard Controls
   How to: Bind an XPCollection to the DataGrid
   How to: Bind an XPCollection to the Grid
   How to: Build Complex Criteria
   How to: Build Simple Criteria
   How to: Change Inheritance Mapping
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   How to: Connect XPO to a Database Other than MS SQL or MS Access
   How to: Control Automatic Saving of Objects when Editing in a Grid
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   How to: Handle Persistent Object Initialization
   How to: Implement a Custom Criteria Language Function Operator
   How to: Implement a Full-Text Search
   How to: Implement Custom Functions and Criteria in LINQ to XPO
   How to: Implement Many-to-Many Relationships
   How to: Implement One-to-One Relationships
   How to: Link Classes Located in Different Assemblies
   How to: Make a Class or Property Non-Persistent
   How to: Make XPCollection Create Objects of Specific Type when They are Created via Bound Controls
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How to: Make XPCollection Create Objects of Specific Type when They are Created via Bound Controls

In certain scenarios, a collection may be designed to hold objects of derived types, but must be base-typed. To simplify working in such scenarios, the XPCollection provides a way to create derived-type objects via bound controls when the collection itself is base-typed.

To make a collection create objects of a specific type, derive from the XPCollection class, and override the protected virtual XPBaseCollection.CreateAddNewInstance method, to return an object of the required type. This method is automatically called, for example, when the Append button of the Grid control's embedded data navigator is clicked.

The following code snippets illustrate this. The sample Windows Forms application has two business classes defined - the BaseClass and DerivedClass:

The application contains a single Form1 form. On the form there is the gridControl1 XtraGrid control with the enabled data navigator. The XtraGrid control is bound to a MyXPCollection<BaseClass>-type collection, which derives from the XPCollection<BaseClass>. The derived collection has the CreateAddNewInstance method overridden, to return a new DerivedClass-type object:

So, the collection is BaseClass-typed, but objects created via the XtraGrid control's embedded data navigator will be DerivedClass-typed.

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