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

Morten Mertner

ƒ Senior Consultant, Teknologisk Institut

[email protected] / [email protected]

ƒ Architect and Software Developer

ƒ Instructor

ƒ Speaker (conferences and gatherings)

ƒ MCSD.NET, MCT

ƒ Open Source

- Gentle.NET (object persistence framework / object-relational mapper) - MbUnit (unit test framework)

Agenda

- Data Binding with Windows Forms 2.0 (Brian Noyes)

Concepts – Data Binding

ƒ What is data binding?

- semi-automatic transfer of object state

- synchronized state between multiple objects

- easy wiring between UI controls and data/business objects

ƒ Why do we need it?

- productivity (less code to write, maintain and understand) - reduced complexity

- intuitive programming model - consistent results

Concepts – Types of Data Binding

ƒ Simple data binding - single value

ƒ Complex data binding - multiple values - collections

ƒ Data binding information

- direction (one-way or two-way) - timing (when is data transferred)

Concepts – Data Binding ”roles”

ƒ Entity

- single object

ƒ Collection

- container class for storing entities

ƒ Control

Interfaces

ƒ How it works

- we enable support for data binding by implementing interfaces - most are optional

- functionality/behavior depends on which interfaces we implement

ƒ Implementation

- interfaces for entities - interfaces for collections - interfaces for controls

Interfaces – Entities

ƒ IEditableObject

ƒ INotifyPropertyChanged

ƒ IDataErrorInfo

Interfaces – IEditableObject

ƒ Purpose

- 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

ƒ Implementation Effort

- code can be placed in base class - low effort

Interfaces – INotifyPropertyChanged

ƒ Purpose

- 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)

ƒ Implementation Effort

- an event must be raised whenever a property is modified - code is difficult to put in base class (affects all properties) - high effort

Interfaces – IDataErrorInfo

ƒ Purpose

- 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

ƒ Implementation Effort

- code can be placed in base blass

- validation is obviously custom code (but not specific to data binding) - low effort (excl. validation code)

Interfaces – ICustomTypeDescriptor

ƒ Purpose

- 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.)

ƒ Implementation Effort

- code can be placed in base class

- code may require additional helper classes (e.g. attributes) - medium effort

Interfaces – Collections

Interfaces – IEnumerable<T> (and IEnumerator<T>)

ƒ Purpose

- 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

ƒ Implementation Effort

- code can be placed in base collection class - easy to implement

Interfaces – ICollection<T>

ƒ Purpose

- enable direct access to items in a collection - modify the collection (add/remove items)

- count items, copy to array, synchronization/locking - extends IEnumerable<T>

ƒ Implementation Effort

- code can be placed in base collection class - easy to implement

Interfaces – IList<T>

ƒ Purpose

- enable positional access to items in a collection (indexing) - support for complex data binding

- extends ICollection<T>

ƒ Implementation Effort

- code can be placed in base collection class - easy to implement

Interfaces – IListSource

ƒ Purpose

- 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

ƒ Implementation Effort

- code can be placed in base class (when using reflection) - easy to implement

Interfaces – ITypedList

ƒ Purpose

- expose information on properties of the data binding source (entities) - allows for great flexibility

- information is exposed using the PropertyDescriptor class

ƒ Implementation Effort

- can be placed in base collection class - fairly easy to implement

Interfaces – IBindingList<T>

ƒ Purpose

- support for full-featured data binding - sorting

- searching

- control changes to the collection (allow new/edit/remove) - change notifications (events)

ƒ Implementation Effort

- can be implemented in base collection class - medium effort

Interfaces – IBindingListView

ƒ Purpose

- support for advanced (multi-property) sorting - support for filtering

- allows a custom collection to do the same as DataView

ƒ Implementation Effort

- can be implemented in base collection class - medium effort

Interfaces – ICancelAddNew

ƒ Purpose

- 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)

ƒ Implementation Effort

- can be implemented in base collection class - low effort

Interfaces – IRaiseItemChangedEvents

ƒ Purpose

- 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

ƒ Implementation Effort

- can be implemented in base collection class - low effort

Interfaces – Controls

ƒ ISupportInitialize

ƒ ISupportInitializeNotification

Interfaces – ISupportInitialize

ƒ Purpose

- 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

ƒ Implementation Effort

- code can be placed in base control - low effort

Interfaces – ISupportInitializeNotification

ƒ Purpose

- notification of interdependent objects when initialization is complete - allows for complex initialization scenarios

ƒ Implementation Effort - low effort

Interfaces – ICurrencyManagerProvider

ƒ Purpose

- 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)

ƒ Implementation Effort - not required

Demonstration

ƒ Gentle 2.0

- Entity base class

- ListBase<TEntity> collection class - Sample project

Demonstration

ƒ Entity base class for (persistent) business objects

ƒ Data binding interfaces

- INotifyPropertyChanged (raise events when properties are modified) - IEditableObject (event handlers for data binding events)

- IDataErrorInfo (error tracking)

ƒ Custom interfaces

- IEntity (object identity and persistency state)

Demonstration

ƒ ListBase<TEntity> collection class - inherits from BindingList<T>

ƒ Data binding interfaces - BindingList<T> - IBindingListView

- IRaiseItemChangedEvents - ITypedList

Conclusion

ƒ IList is the minimum requirement

- BindingSource transforms an IEnumerable to an IList

ƒ IBindingList should be the minimum for collections

- IBindingListView adds advanced functionality known from DataView

ƒ INotifyPropertyChanged is important for rich data-binding (also detects programmatic changes to properties)

ƒ PropertyDescriptor class is the mediator between properties and controls, and is used when a value is modified through the UI)