Tag Archives: C#

Master-Detail Forms & Object Scope (Context)

November 19, 2010 •

Imagine a master-detail form. The top portion of the window contains a grid listing people’s names. Below is a form where the currently-selected person’s details may be edited. Should data-binding be used to connect the edit form’s fields directly to the grid’s currently selected record (row)? To put it another way, should the grid’s selected item and the edit form both be referencing the same in-memory object instance? Continue reading →

Emulating C/C++’s switch Fall Through with C#’s goto

November 10, 2010 •

Today, while doing some research in the MSDN Library, I came across an interesting use of C#’s goto statement. Instead of causing the application’s execution to jump to a named label—a practice frowned upon in the programming world—this example used goto to emulate C/C++’s switch statement’s fall through behavior. Continue reading →

The Null-Coalescing Operator

October 13, 2010 •

C#’s null-coalescing operator (??) simplifies the syntax required to say “the value of an expression is x unless x is null in which case the value is y.”

Suppose we want to set the variable salary to a value fetched from the database. However, if the database returns null, salary should be set to 0. Continue reading →

How is a WPF XAML file tied into the application’s executable environment?

September 24, 2010 •

By hidden source code file…

A hidden source code file is auto-generated for each WPF XAML file. The names used for this file and for the class it contains are based off the XAML file’s filename. In a C# application, the file MyWindow.xaml will have a hidden code-behind file named MyWindow.g.cs containing a class named MyWindow.

…containing a class…

The contained class inherits from the WPF core class corresponding to the associated XAML file’s root element. If the root element in the XAML file is <Window>, the class in the hidden code-behind file will inherit from Window.

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Keeping the Selected Item Selected When Changing a ListView’s ItemsSource

September 14, 2010 •

A ListView’s data display needs to be updated. The revised dataset, retrieved from the service layer, is contained in a new collection containing new object instances. Setting this IList<T> as the control’s new ItemsSource causes the control to display the revised data and…whoa…clears the currently selected item.

From the technical perspective, this clearing makes sense. A new collection has been displayed making the selected item from the previous collection irrelevant. However, from the user’s perspective, the same collection is displayed both before and after the refresh (albeit with revised data), so the current item selection is still pertinent and should be maintained.

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WPF, Where Is Your “static Main()” Method?

August 26, 2010 •

The typical WPF application—as viewed in Solution Explorer—consists primarily of XAML files (.xaml) paired with code-behind files (.xaml.cs) and ordinary source code files (.cs). None of these files contains a static Main() method—the starting point of execution in a C# program. Where then does execution begin in a C#.Net WPF application?

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Bug: Single <Application.Resources> Entry Ignored

August 19, 2010 •

Crash! The offending XAML sets a control’s style property to a StaticResource (e.g. <Button Style=”{StaticResource myStyle}” />). The named style is defined in <Application.Resources>. Why then the XamlParseException “Cannot find resource…” exception?

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Event Arguments == Static Snapshots?

July 26, 2010 •

Is the event argument that’s passed to an event handler/handler override always a non-changing snapshot taken the moment the event occurred?

No! While convention suggests a “yes” answer, no technical constrain enforces this assumption (as I discovered recently). The properties of an event argument can (and sometimes do) return information about the current (live) state of the system instead of describing the moment the event occurred.

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DataGrid – Per-Row Running Totals

July 14, 2010 •

The program I’m working on lists transactions in a WPF Toolkit DataGrid. Each grid row displays a transaction’s date, amount, etc. Each row in the grid needed to show the sum of all transaction amounts prior to and including that row. You might call this a per-row running total. Example:

Date       | Check #   | Payee       | Amount    | Balance
2/1/10                   Frank         10.00       10.00
3/6/10       101         John          -6.95        3.05
4/9/10       102         Tom           -1.05        2.00

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