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Listing 8-37 Client to Custom Control Supporting Validation Configuration
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<%@ Page Language='C#' %> <%@ Register TagPrefix='eadn' Diagnostics and error handling Namespace='EssentialAspDotNetCustomControls' Assembly='Validation' %> Validation <html> <body> Data binding <form runat=server> <eadn:ValidatableControl id='ctb' runat='server' /> Custom controls <asp:RequiredFieldValidator runat='server' Caching ControlToValidate='ctb'>* </asp:RequiredFieldValidator>
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<input type='submit' value='submit' />
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852 Data-Bound Controls
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Many controls in the WebControls hierarchy support the concept of data binding You can add data binding support to your custom controls as well by exposing a DataSource property When your control renders itself, it pulls data from the data source and uses it as part of its rendering To begin with, it is important to understand how clients expect data-bound controls to work Typically, a client prepares a connection to a data source in the Load event of a Page class and connects that data source to the DataSource property that all data-bound controls provide The data source could be a simple collection, such as an ArrayList; a forward-only data reader, such as an IDataReader; or a fully cached Table of Contents data source, such as a DataSet,DataView, or DataTable As an author of data-bound controls, you need Essential ASPNETpossibilities Because all the data-bound controls in the base class hierarchy retain to accommodate all these with Examples in C# ByFritz Onion their state across post-backs, clients expect any data-bound control you write to do the same, so that a control need be populated only the first time a page is accessed Once the client has attached a data source to the control, she may need to set the DataTextField and DataValueField properties of the control to Publisher : Addison Wesley indicate Pub Date which field from a tabular data source should be used Note that if your control can render tabular : February 11, 2003 data (rows with multiple columns), there is no need to support these properties Finally, once the data ISBN : 0-201-76040-1 source,DataTextField, and DataValueField properties have been correctly populated, the client calls Pages : 432 DataBind(), at which point your control's OnDataBinding method is called Your control should iterate over the attached data source, saving the data locally within itself so that when your Render() method is called, you have the data to display This interaction between a client page and a data-bound control is shown in Figure 8-5 "This well-conceived and well-written book has extensive knowledge and priceless experience overflowing from its pages It Figure 8-5 Interaction between a Page and the reader to a high level of technical and captures the true essence of ASPNET and walks a Data-Bound Control architectural skill"-J Fred Maples, Director of Software Engineering, NASDAQcom
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Essential ASPNET with Examples in C# is the C# programmer's definitive reference for ASPNET through version 11 It provides experienced programmers with the information needed to fully understand the technology, and is a clear guide to using ASPNET to build robust and well architected Web applications This book begins with a discussion of the rationale behind the design of ASPNET and an introduction to how it builds on top of the NET framework Subsequent chapters explore the host of new features in ASPNET, including the server-side compilation model, code-behind classes, server-side controls, form validation, the data binding model, and custom control development Throughout the book, working examples illustrate best practices for building Web-based applications in C# Among the topics explored in depth are:
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ASPNET architecture Web forms Configuration HTTP pipeline Diagnostics and error handling Validation Data binding Custom controls Caching State management
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853 Implementing a Data-Bound Control
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The first step in creating a data-bound control is to define a DataSource property This involves adding a public property called DataSource to your class of type object Next you need to override the virtual functionOnDataBinding, inherited from the Control base class Your implementation of OnDataBinding should iterate across the data source that was assigned through your control's property, saving the data to a local data structure for future rendering Note that it is not safe to assume that the data source will be around during your Render method, so you must take this step to ensure that you save the data that your control needs to be able to render itself during the OnDataBinding method call
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If your control expects only a list of items, not a tabular set of data, to be bound to it, you should expose another property, called DataTextField This field will contain the index into a rowset that the client expects you to dereference when you perform the data binding If you have the capability of associating values with the data items, you can also expose a property called DataValueField (most of the databound list controls in the base class hierarchy expose both of these fields) You should also be as accommodating as possible in what your control supports for data sources All the data binding controls in the base class Table of Contents binding to any class that supports the IEnumerable or IList interface, hierarchy support plus they support binding directly to DataSets or DataTables by locating the default Data Table within a Essential ASPNET with Examples in C# DataSet and the default DataView within a DataTable ByFritz Onion Clients of data-bound controls expect the controls to retain their state across post-backs This lets page
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Publisherpopulate a control once if IsPostBack is false, and avoid additional round-trips to the database if : Addison Wesley authors Pub page is : February 11, 2003 the author of a data bound control, you are responsible for making sure that Date the posted to again As ISBN control's state is retained across a post-back Typically, you do this by using the ViewState : 0-201-76040-1 your Pages 432 mechanism:described earlier in this chapter Because data-bound controls usually need to persist collections
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of data into view state, it is typically most efficient to override the LoadViewState and SaveViewState methods in your control to explicitly populate and retrieve collections of data from view state Keep in mind that clients can always disable view state on your control, so even if you suspect it will be inefficient for clients to rely on state retention for your control, you should leave that decision to the client overflowing "This well-conceived and well-written book has extensive knowledge and priceless experienceand support it nonetheless for consistency from its pages It captures the true essence of ASPNET and walks the reader to a high level of technical and
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architectural skill"-J Fred Maples, Director of Software Engineering, NASDAQcom Listing 8-38 shows a sample control that supports data binding to all the different data source types with state retention It with Examples in C# is the and caches the contents of the data for ASPNET through Essential ASPNET renders itself as an item listC# programmer's definitive referencesource in an ArrayList This control It provides helper functions that should be useful for any implementer of data-bound the version 11 defines two experienced programmers with the information needed to fully understandcontrols The first is and is a clear guide to using ASPNET to build robust and well architected Web applications technology,GetResolvedDataSource, which takes the data source as an object and returns a reference to an IEnumerable interface This function accounts for the fact that the data source may be a collection class, an begins with a a DataView a rationale behind the design of returns and an introduction to how This bookIDataReader,discussion of ,theDataTable, or a DataSet, andASPNET the enumeration interface on the correct of the NET framework Subsequent chapters function is host of new features takes an item it builds on topelement of the data source The second helperexplore the GetDataItem, which in ASPNET, pointed to by an enumerator and indexes it code-behind classes, server-side if is a rowset, or simply including the server-side compilation model,with the m_DataTextField value controls, form validation, the returns the object as a string if not This is necessary Throughout the items stored in simple collections data binding model, and custom control developmentto accommodate book, working examples illustrate and items stored in tabular data sets best practices for building Web-based applications in C# Among the topics explored in depth are: Listing 8-38 A Data-Bound Control
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ASPNET architecture public class DataBoundControl : Control { Web forms private ArrayList _cachedData = new ArrayList();
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private object _dataSource; privatepipeline _dataTextField; HTTP string private string _dataValueField;
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