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The field manager is responsible for storing the values of all managed fields for each object instance. Each BusinessBase and ReadOnlyBase object contains an instance of FieldDataManager, which is the object responsible for storing the managed field values. These two base classes expose the FieldDataManager object as a Protected property named FieldManager.
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The BusinessBase and ReadOnlyBase classes expose a Protected property named FieldManager to make the FieldDataManager available to the business object s code. For example, this code is in BusinessBase: Protected ReadOnly Property FieldManager() As FieldManager.FieldDataManager Get If _fieldManager Is Nothing Then _fieldManager = New FieldManager.FieldDataManager(Me.GetType) UndoableBase.ResetChildEditLevel(_fieldManager, Me.EditLevel, Me.BindingEdit) End If Return _fieldManager End Get End Property
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This property is designed to create an instance of the FieldDataManager only on demand. The idea is that if your business class never uses any managed backing fields, no FieldDataManager object will be created. I chose to do this to minimize the overhead involved in creating a business object when managed fields aren t used. This does complicate the use of the FieldManager property throughout the rest of BusinessBase and ReadOnlyBase. For example, BusinessBase includes this code: Public Overridable ReadOnly Property IsDirty() As Boolean Get Return IsSelfDirty OrElse _ (_fieldManager IsNot Nothing AndAlso FieldManager.IsDirty()) End Get End Property A parent object is considered dirty, or changed, if it or any of its child objects have been changed. To know whether the object has been changed, the IsDirty property checks the FieldManager to find out whether any managed fields or child objects have been changed. But before accessing the FieldManager property, it checks to see whether the _fieldManager field is Nothing. This prevents the accidental creation of a FieldDataManager instance when there are no managed fields in the business object. Getting back to the FieldManager property, you should see that a method called UndoableBase. ResetChildEditLevel() is called after the FieldDataManager instance is created. Technically, the FieldDataManager is a child object contained within the business object. Because it is a child object, its edit level for n-level undo must be kept in sync with the business object itself. I ll discuss the concept of edit levels in 11. For now, it is enough to know that the ResetChildEditLevel() call ensures that the new child object is in sync with its parent.
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The FieldDataManager class itself is relatively complex. Each instance of this class is a child of a business object. Also, because the field manager is responsible for storing the values of the business object s properties, it must participate in the n-level undo process discussed in 11. Here s the declaration of the class: <Serializable()> _ Public Class FieldDataManager Implements IUndoableObject Implements IMobileObject End Class The class is Serializable, because the data it contains may be serialized when the business object is cloned or moved across the network between a client and application server. It implements the IUndoableObject interface because it must participate in the n-level undo behaviors covered in 11.
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The IMobileObject interface exists to support serialization through the MobileFormatter, which is part of CSLA .NET for Silverlight. CSLA .NET for Silverlight is outside the scope of this book, and IMobileObject has no impact on how CSLA .NET works within the .NET runtime.
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The field manager s primary job is to maintain the values of all properties that use managed backing fields. Simplistically, it might seem that you could store these values in a Dictionary, keyed off the property name. That would work technically, but accessing elements in a Dictionary turns out to be a relatively slow operation.
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My first implementation of the field manager did use a Dictionary, but the performance was too poor, so I shifted to the implementation I m discussing here to address the issue.
Instead, the field values are maintained in an array of IFieldData objects. Private _fieldData As IFieldData() I ll discuss the IFieldData interface later. For now, I ll discuss how the property values are indexed into this array.
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