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The list base classes inherit from ExtendedBindingList(Of T), which is a specialized subclass of BindingList(Of T) that adds a couple important features missing from the standard .NET base class. Most notably, it adds the RemovingItem event, which notifies a business object author that a child object is being removed, including providing a reference to the child object. The standard ListChanged event is useful, but it is raised after the child has been removed, so there s no way to get a reference to the removed child. This class also implements a ChildChanged event. Unlike the PropertyChanged or ListChanged events, the ChildChanged event bubbles up through all parent objects to the root object. This means the UI developer can handle the ChildChanged event on any editable root object to be notified when any child object has been changed. The ExtendedBindingList class also adds an AddRange() method, which makes it easier for a business developer to add multiple items to a collection. This feature is particularly useful when using LINQ to SQL or LINQ to Entities to initialize a collection with data from the data store. Finally, the class implements the IsSelfBusy and IsBusy properties and related functionality required to support the asynchronous object persistence behaviors discussed in 15. The IsBusy property returns true while any asynchronous operation is in progress for this object or objects contained in the collection. The IsSelfBusy property returns true while any asynchronous operation is in progress for this object (but not the child objects it contains).

private ref class XYZHandle : SafeHandle { public: XYZHandle() : SafeHandle(IntPtr::Zero, true) {} property virtual bool IsInvalid { bool get() override { return SafeHandle::handle == IntPtr::Zero; } } // this function is an override that is called within a CER [ReliabilityContract(Consistency::WillNotCorruptState, Cer::Success)] virtual bool ReleaseHandle() override { ::XYZDisconnect(SafeHandle::handle.ToPointer()); return true; } }; ... definition of class XYZConnection is discussed soon ... Like the DllImportAttribute, the SafeHandle class is defined in the namespace System::Runtime::InteropServices. It is not by accident that both types are defined in this namespace the features of SafeHandle are enabled by custom P/Invoke marshaling. This means that you have to write P/Invoke functions yourself instead of relying on the C++/CLI compiler and the linker to actually create these functions for you. This is an extra piece of work, but since C++/CLI is able to use native types in managed code, it is much less work in C++/CLI than in other .NET languages. You can write this P/Invoke function simply by modifying normal C and C++ function declarations. P/Invoke functions for XYZConnect and XYZGetData are necessary for writing the XYZConnection class: extern "C" __declspec(dllimport) HXYZ XYZConnect();

While BindingList(Of T) does nearly everything required to support data binding, ExtendedBindingList(Of T) adds some important features that improve the usability of all CSLA .NET collection base classes.

Recall that one of the framework s goals is to simplify and standardize the creation of business and validation rules. It also automates the tracking of broken validation rules. An important side benefit of this is that the UI developer will have read-only access to the list of broken rules, which means that the descriptions of the broken rules can be displayed to the user in order to explain what s making the object invalid. The support for tracking broken business rules is available to all editable business objects, so it s implemented at the BusinessBase level in the framework. To provide this functionality, each business object has an associated collection of broken business rules. Additionally, a rule is defined as a method that returns a Boolean value indicating whether the business requirement is met. In the case that the result is False (the rule is broken), a rule also returns a text description of the problem for display to the user. To automate this process, each business object has an associated list of rule methods for each property in the object. Figure 2-13 illustrates all the framework classes required to implement both the management of rule methods and the maintenance of the list of broken rule descriptions.

extern "C" __declspec(dllimport) double XYZGetData(HXYZ hxyz); The extern "C" linkage modifier is neither allowed nor necessary in P/Invoke functions In C++, it is used to ensure that global functions can be called from C code When generating a managed-to-unmanaged thunk from a P/Invoke function, the JIT compiler automatically looks for functions without mangled names in the target DLL You can replace the __declspec(dllimport) specification by applying the DllImportAttribute with the name of the target DLL to the P/Invoke function [DllImport("XYZLibdll")] .. function declaration goes here .. Key to enabling the features of SafeHandle is the replacement of the native handle type with XYZHandle^ a tracking handle to the SafeHandle-derived handle class To avoid naming conflicts with the global functions from the native API, the P/Invoke functions are defined as private static member functions of the native class: public ref class XYZConnection { [DllImport("XYZLibdll")] static XYZHandle^ XYZConnect(); [DllImport("XYZLib.

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