Windows Forms 2.0 Data Binding. Informatik IT-Uddannelse og IT-Udvikling

Transcription

1 Windows Forms 2.0 Data Binding

2 Morten Mertner Senior Consultant, Teknologisk Institut / Architect and Software Developer Instructor Speaker (conferences and gatherings) MCSD.NET, MCT Open Source - Gentle.NET (object persistence framework / object-relational mapper) - MbUnit (unit test framework)

3 Agenda Data Binding - Concepts - Interfaces Demonstration - Gentle Data Binding with Windows Forms 2.0 (Brian Noyes) Conclusion

4 Concepts Data Binding What is data binding? - semi-automatic transfer of object state - synchronized state between multiple objects - easy wiring between UI controls and data/business objects Why do we need it? - productivity (less code to write, maintain and understand) - reduced complexity - intuitive programming model - consistent results

5 Concepts Types of Data Binding Simple data binding - single value Complex data binding - multiple values - collections Data binding information - direction (one-way or two-way) - timing (when is data transferred)

6 Concepts Data Binding roles Entity - single object Collection - container class for storing entities Control - UI control

7 Interfaces How it works - we enable support for data binding by implementing interfaces - most are optional - functionality/behavior depends on which interfaces we implement Implementation - interfaces for entities - interfaces for collections - interfaces for controls

8 Interfaces Entities IEditableObject INotifyPropertyChanged IDataErrorInfo ICustomTypeDescriptor

9 Interfaces IEditableObject - support for transactional editing of objects (deferring commit until editing is completed) - entities should maintain internal object state (new or dirty) - allows validation to use final state rather than individual values - use when object has co-dependent properties - code can be placed in base class - low effort

10 Interfaces INotifyPropertyChanged - notify a container class when a property changes (this allows the list to raise a ListChanged event) - performance optimization (less use of reflection by collection class) - flexibility (other code may benefit from events as well) - semi-optional (collection can implement IRaiseItemChangedEvents instead, providing slightly less functionality) - an event must be raised whenever a property is modified - code is difficult to put in base class (affects all properties) - high effort

11 Interfaces IDataErrorInfo - support for storing and exposing error information - exposes a top-level error (for the entire object) - exposes individual errors (for each property) using an indexer - can be used by controls (e.g. DataGridView) to highlight errors - code can be placed in base blass - validation is obviously custom code (but not specific to data binding) - low effort (excl. validation code)

12 Interfaces ICustomTypeDescriptor - allows an object to provide custom property information - increase performance (by avoiding reflection) - increase flexibility (by customizing which properties are exposed) - optional (unless you want to hide properties, etc.) - code can be placed in base class - code may require additional helper classes (e.g. attributes) - medium effort

13 Interfaces Collections IEnumerable<T> IEnumerator<T> ICollection<T> IList<T> IListSource ITypedList IBindingList<T> IBindingListView ICancelAddNew IRaiseItemChangedEvents

14 Interfaces IEnumerable<T> (and IEnumerator<T>) - enable iteration of items in collection - helper class allows for more than one iteration strategy - support for one-way data binding when used with BindingSource - code can be placed in base collection class - easy to implement - low effort

15 Interfaces ICollection<T> - enable direct access to items in a collection - modify the collection (add/remove items) - count items, copy to array, synchronization/locking - extends IEnumerable<T> - code can be placed in base collection class - easy to implement - low effort

16 Interfaces IList<T> - enable positional access to items in a collection (indexing) - support for complex data binding - extends ICollection<T> - code can be placed in base collection class - easy to implement - low effort

17 Interfaces IListSource - find out whether a collection contain entities or other collections - select the default collection for data binding - obtain a collection for data binding from objects that are not collections - code can be placed in base class (when using reflection) - easy to implement - low effort

18 Interfaces ITypedList - expose information on properties of the data binding source (entities) - allows for great flexibility - information is exposed using the PropertyDescriptor class - can be placed in base collection class - fairly easy to implement - low to medium effort

19 Interfaces IBindingList<T> - support for full-featured data binding - sorting - searching - control changes to the collection (allow new/edit/remove) - change notifications (events) - can be implemented in base collection class - medium effort - using base class BindingList<T> can make it slightly easier

20 Interfaces IBindingListView - support for advanced (multi-property) sorting - support for filtering - allows a custom collection to do the same as DataView - can be implemented in base collection class - medium effort

21 Interfaces ICancelAddNew - support for transactional adding or editing of items - allows collection class to handle cancellation of operation (removes the coupling otherwise needed between entity and collection) - can be implemented in base collection class - low effort

22 Interfaces IRaiseItemChangedEvents - collection will notify when property changes on contained items - only works for changes made through PropertyDescriptor class (UI) - use when contained items do not implement INotifyPropertyChanged - can be implemented in base collection class - low effort

23 Interfaces Controls ISupportInitialize ISupportInitializeNotification ICurrencyManagerProvider

24 Interfaces ISupportInitialize - allows a control to wait until all changes (to a data-bound object) have been committed - allows a control to remain ignorant of co-dependent properties - code can be placed in base control - low effort

25 Interfaces ISupportInitializeNotification - notification of interdependent objects when initialization is complete - allows for complex initialization scenarios - low effort

26 Interfaces ICurrencyManagerProvider - lets a control provide its own currency manager - implemented by BindingSource - you should not implement this interface (but might use it to access the CurrencyManager for a data-bound collection within a control) - not required

27 Demonstration Gentle Entity base class - ListBase<TEntity> collection class - Sample project

28 Demonstration Entity base class for (persistent) business objects Data binding interfaces - INotifyPropertyChanged (raise events when properties are modified) - IEditableObject (event handlers for data binding events) - IDataErrorInfo (error tracking) Custom interfaces - IEntity (object identity and persistency state) - IBindingState (expose the data binding new/dirty state information)

29 Demonstration ListBase<TEntity> collection class - inherits from BindingList<T> Data binding interfaces - BindingList<T> - IBindingListView - IRaiseItemChangedEvents - ITypedList

30 Conclusion IList is the minimum requirement - BindingSource transforms an IEnumerable to an IList IBindingList should be the minimum for collections - IBindingListView adds advanced functionality known from DataView INotifyPropertyChanged is important for rich data-binding (also detects programmatic changes to properties) PropertyDescriptor class is the mediator between properties and controls, and is used when a value is modified through the UI)

31 Questions?