MSDN Magazine - August 2008 - (Page 26)

one? This would be close to other instant-search technologies, such as that found in Microsoft Outlook®. Incremental Search A great feature of LINQ is that it supports deferred execution. Queries are not executed at the point that they are written in code; they are merely defined at that point. They are not actually executed until the call to MoveNext on the returned enumerator. You can take advantage of this to search the data incrementally and only spend a minimal amount of time possibly blocking the UI. I defined a class called IncrementalSearch that works on any object implementing IEnumerable. All LINQ queries implement this interface. IncrementalSearch supports the concept of stopping a search after a certain time period expires. The algorithm is to get the next value by calling MoveNext until the specified time period has expired. At that point, the data found is returned in a new Result object (see Figure 4). The Search method returns a Result object based on the data it finds, including the values found in the current call to Search, the list of all values found in all previous calls to Search, and the current status of the search. This means that the UI can now return data in chunks. The maximum time you can delay will be for getting the next element instead of the entire set of rows: Figure 4 IncrementalSearch Class Public Enum SearchStatus InProgress Completed End Enum Public Class Result Private m_allValues As IList Private m_incrementalValues As IList Private m_status As SearchStatus Public ReadOnly Property AllValues() As IList Get Return m_allValues End Get End Property Public ReadOnly Property IncrementalValues() As IList Get Return m_incrementalValues End Get End Property Public ReadOnly Property SearchStatus() As SearchStatus Get Return m_status End Get End Property Sub New(ByVal allValues As IList, _ ByVal incrementalValues As IList, _ ByVal status As SearchStatus) m_allValues = allValues m_incrementalValues = incrementalValues m_status = status End Sub End Class Public Class IncrementalSearch Private m_enumerable As IEnumerator Private m_allFound As New List(Of Object) Private m_status As SearchStatus = SearchStatus.InProgress Private m_delay As TimeSpan Dim found As New List(Of Object) Dim start = DateTime.Now Do If Not m_enumerable.MoveNext() Then m_enumerable = Nothing m_status = SearchStatus.Completed Exit Do End If found.Add(m_enumerable.Current) Loop Until DateTime.Now - start > m_delay The goal is for the UI to display the data through data binding and to provide an efficient search. Displaying the data should not cause the UI to hang. Return values are displayed in a custom DataGridView using the incremental search pattern. The example implementation is called DataGridViewIncrementalSearch and derives from DataGridView (see Figure 5). This implementation works great with data binding and is designed to perform well with large sets of data. There is one extra property of the same type called IncrementalSearch. Whenever this value is set, the control will call the Search method and continually update the displayed set of values. To achieve this, the control will have to call the Search method at regular intervals until the data source is exhausted. A Windows® Forms timer is ideal for this scenario. It can be configured to call a method on the UI thread at a particular interval and Public ReadOnly Property SearchStatus() As SearchStatus Get Return m_status End Get End Property Public Property Delay() As TimeSpan Get Return m_delay End Get Set(ByVal value As TimeSpan) m_delay = value End Set End Property Public Sub New(ByVal e As IEnumerable) m_delay = TimeSpan.FromSeconds(0.1) m_enumerable = e.GetEnumerator() End Sub Public Function Search() As Result If m_status = SearchStatus.Completed Then Return New Result(m_allFound, New List(Of Object), m_status) End If Dim found As New List(Of Object) Dim start = DateTime.Now Do If Not m_enumerable.MoveNext() Then m_enumerable = Nothing m_status = SearchStatus.Completed Exit Do End If found.Add(m_enumerable.Current) Loop Until DateTime.Now - start > m_delay m_allFound.AddRange(found) Return New Result(m_allFound, found, m_status) End Function End Class 26 msdn magazine Basic Instincts

Table of Contents Feed for the Digital Edition of MSDN Magazine - August 2008

MSDN Magazine - August 2008 Toolbox CLR Inside Out Basic Instincts Cutting Edge Patterns in Practice Data 2.0 - Expose And Consume Data In A Web Services World Biztalk EDI - Build A Robust EDI Solution With BizTalk Server Silverlight - Create Animations With XAML And Expression Blend Write On! - Create Web Apps You Can Draw On With Silverlight 2 Wicked Code - Craft Custom Controls For Silverlight 2 Team System Foundations Windows With C++ Concurrent Affairs Going Places { End Bracket }

MSDN Magazine - August 2008

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