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MarkDirty Method
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There s a corresponding MarkDirty() method as well. This method is called from various points in an object s lifetime, including any time a property value is changed or when the MarkNew() method is called. When a property value is changed, a specific PropertyChanged event is raised for that property. If MarkDirty() is called at other times, when a specific property value isn t changed, the PropertyChanged event for all object properties should be raised. That way, data binding is notified of the change if any object property is bound to a UI control. To be clear, the goal is to ensure that at least one PropertyChanged event is raised any time the object s state changes. If a specific property is changed, the PropertyChanged event should be raised for that property. But if there s no way to tell which properties are changed (like when the object is persisted to the database), there s no real option but to raise PropertyChanged for every property. Implementing this requires a couple of overloads of the MarkDirty() method: Protected Sub MarkDirty() MarkDirty(False) End Sub <EditorBrowsable(EditorBrowsableState.Advanced)> _ Protected Sub MarkDirty(ByVal suppressEvent As Boolean) _isDirty = True If Not suppressEvent Then OnUnknownPropertyChanged() End If End Sub
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CHAPTER 8 OB JECT STATUS MAN AGEM ENT
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The first overload can be called by a business developer if she wants to manually mark the object as changed. This is intended for use when unknown properties may have changed.
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PropertyHasChanged Method
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The second overload is called by the PropertyHasChanged() method: Protected Overridable Sub PropertyHasChanged(ByVal propertyName As String) MarkDirty(True) Dim propertyNames = ValidationRules.CheckRules(propertyName) If ApplicationContext.PropertyChangedMode = _ ApplicationContext.PropertyChangedModes.Windows Then OnPropertyChanged(propertyName) Else For Each name In propertyNames OnPropertyChanged(name) Next End If End Sub The PropertyHasChanged() method is called by the SetProperty() methods discussed in 7 to indicate that a specific property has changed. Notice that in this case, any validation rules for the property are checked (the details on this are discussed in 11).
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This method is Overridable, allowing you to add extra steps to the process if needed. Additionally, this means you can override the behavior to implement field-level dirty tracking if desired.
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Then the object is marked as being dirty by raising the PropertyChanged event for the specific property that is changed. This isn t as simple as I would like because the code needs to behave differently when used by WPF as opposed to any other UI technology such as Windows Forms or Web Forms. Since there s no way to automatically detect whether this object is being used by WPF, there s a configuration switch the business developer can set to indicate how this method should behave.
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Configuring the PropertyChangedMode
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The Csla.ApplicationContext.PropertyChangedMode setting can be configured through the application s config file or in code. In code, the UI developer will typically set the value by running the following line of code exactly once as the application starts up: Csla.ApplicationContext.PropertyChangedMode = Csla.ApplicationContext.PropertyChangedModes.Xaml This needs to be done only in a WPF application, because the default is Windows, which is the correct setting for any non-WPF application. The value can also be set in the application s app.config file by adding the following element to the <appSettings> element: <add key="CslaPropertyChangedMode" value="Xaml" /> Either way, the result is that the PropertyChanged events are raised as required by WPF rather than as needed for Windows Forms or Web Forms.
CHAPTER 8 OBJECT S TA TUS MA NAGE MENT
Raising Events for WPF
In WPF, when a PropertyChanged event is handled by data binding, only the control(s) bound to that specific property are refreshed in the UI. This makes a lot of sense but causes a bit of complexity. When a property is changed, it triggers the execution of the business and validation rules associated with that property (see 11 for details). It also triggers the execution of rules associated with dependent properties. This means that changing one property can execute rules for multiple properties. When a validation rule fails, the UI will display something to the user indicating that the value is invalid. WPF data binding knows to change the display for a control because it handles the PropertyChanged event for the property to which the control is data bound. If the only PropertyChanged event raised is for the property that is changed, any broken validation rules for dependent properties will be ignored by data binding and won t be visible to the user. Notice that the CheckRules() method call returns an array containing the names of all the properties for which business or validation rules are executed. This allows the PropertyHasChanged() method to raise PropertyChanged events for all those property names, not just for the property that is actually changed. The result is that broken validation rules are reflected in the UI, even for properties other than the one that is actually changed.
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