Tool Development 10 - MVVM, Tool Chains

Tool Development
Chapter 10: MVVM, Tool Chains
Nick Prühs

Assignment Solution #9
DEMO
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Objectives
• To understand the implications of the MVVM
pattern
• To get an overview of approaches for tool chains
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Model-View-Controller
• Architectural pattern that separates data from its
visual representation
• Model: Data, such as names, phone numbers, or health
points.
• View: Visual representation of that data, such as console
output, UI textfields or health bars.
• Controller: Layer that separates model from view,
serving as interface for any interaction with the data.
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Model-View-Controller
• Allows exchanging views or modifying the model
without breaking existing functionality.
• For instance, write console client first and GUI client
after.
• Greatly improves your application architecture
through separation of concerns.
• Anybody always knows where to look in your code.
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Model-View-View Model
• Architectural pattern that separates data from its
visual representation
• Model: Data, such as names, phone numbers, or health
points.
• View: Visual representation of that data, such as console
output, UI textfields or health bars.
• View Model: Responsible for exposing data from the
model in such a way that those objects are easily
managed and consumed
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Model-View-View Model
• Attempts to gain both the advantages of separation
of functional development provided by MVC as well
as leveraging the advantages of data bindings
• binds data as close to the pure application model as
possible
• uses inherent data checking features to validate any
incoming data
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Where Is The Controller?
• Substituted by bindings
• Synchronize the view model and view
• Key enablers of the pattern
• Controller sometimes included anyway
• Ongoing area of discussion regarding the standardization
of the MVVM pattern
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Drawbacks of MVVM
• Overkill for simple UI operations
• Can result in considerable memory consumption in
very large applications
• Where to put event handlers for e.g. button clicks?
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Data Conversion
• Sometimes, you might be willing to bind a property
to a value of a different type (e.g. Color to Brush)
• WPF allows to you implement the IValueConverter
interface for
• changing data from one type to another
• translating data based on cultural information
• modifying other aspects of the presentation
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Data Conversion
XAML
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<Window x:Class="DataConversionExample.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:DataConversionExample"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<local:NotConverter x:Key="NotConverter"/>
</Window.Resources>
<CheckBox
Content="Prohibited"
IsChecked="{Binding Allowed, Converter={StaticResource NotConverter}}">
</CheckBox>
</Window>

Data Conversion
C#
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class NotConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
bool boolValue;
if (value == null || !bool.TryParse(value.ToString(), out boolValue)) return null;
return !boolValue;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return new NotImplementedException();
}
}

Data Validation
• Most of the time, you need to validate that the
user has entered the expected information in the
correct format.
• Validation checks can be based on type, range,
format, or other application-specific requirements.
• WPF data binding allows you to associate
ValidationRules with your bindings.
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Data Validation
XAML
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<Application x:Class="DataValidationExample.App"
xmlns:local="clr-namespace:DataValidationExample"
StartupUri="MainWindow.xaml">
<Application.Resources>
<ControlTemplate x:Key="ErrorLabel">
<StackPanel>
<Border BorderBrush="Red" BorderThickness="1">
<AdornedElementPlaceholder Name="MyAdorner" />
</Border>
<TextBlock
Foreground="Red"
FontSize="8pt"
Text="{Binding ElementName=MyAdorner,
Path=AdornedElement.(Validation.Errors)[0].ErrorContent}" />
</StackPanel>
</ControlTemplate>
</Application.Resources>
</Application>

Data Validation
XAML
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<Window x:Class="DataValidationExample.MainWindow"
xmlns:local="clr-namespace:DataValidationExample"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<TextBox Validation.ErrorTemplate="{StaticResource ErrorLabel}">
<TextBox.Text>
<Binding Path="Name">
<Binding.ValidationRules>
<local:StringNotEmptyValidationRule />
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
</Window>

Data Validation
C#
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public class StringNotEmptyValidationRule : ValidationRule
{
public override ValidationResult Validate(object value, CultureInfo cultureInfo)
{
var s = value as string;
if (s == null || string.IsNullOrEmpty(s))
{
return new ValidationResult(false, "Must not be empty.");
}
return ValidationResult.ValidResult;
}
}

Data Bind for Unity
DEMO
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Cancelling Events
• Many of the events in WPF can be cancelled by
your code to implement special event handling.
• These events usually are provided twice by WPF,
one for the actual event, and one for signaling that
the event is about to occur
• OnClosing
• OnClosed
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Cancelling Events
WPF
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<Window x:Class="CancelEventExample.MainWindow"
xmlns:local="clr-namespace:CancelEventExample"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525" Closing="MainWindow_OnClosing">

Cancelling Events
C#
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private void MainWindow_OnClosing(object sender, CancelEventArgs e)
{
var result = MessageBox.Show(
"Do you want to save your progress before exiting?",
"Unsaved Data",
MessageBoxButton.YesNo,
MessageBoxImage.Question,
MessageBoxResult.Yes);
if (result == MessageBoxResult.Yes)
{
e.Cancel = true;
// Show save file dialog.
}
}

Tool Chains
• Output of one tool is used as input for another
• Photoshop -> Sprite Packer, Texture Compression
• Build Server -> Git, MSbuild, Unity, NUnit
• Visual Studio -> Post-build events
• Excel -> VBA
• Localization
• Unity Editor Scripts
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Tool Chains
• Technical Requirements
• Command-line parameters
• Non-blocking operation (i.e. must not require user input
for proceeding)
• Robust error (code) handling
• User Requirements
• Good understanding of file systems and working
directories
• Sometimes: Access to system environment variables
• Sometimes: Understanding of different OS
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What You Have Learned
 Basic development process of good Desktop apps
 Importance of good UI and UX design
 Developing basic Desktop applications with WPF
 How to approach common I/O tasks in .NET
 Best practices of file and stream I/O in general
 Advanced XML concepts such as XPath and XSLT
 Overview of other common text-based file formats
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What You Have Learned
 How to use reflections to your advantage
 How to create reactive UIs with worker threads
 How to implement an undo/redo stack
 How to interact with the Windows shell
 How to globalize and localize WPF applications
 How to properly set up automatic tests
How to work in teams using GitFlow
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And now…
Go out and make
some tools!
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References
• Wikipedia. Model View ViewModel.
http://en.wikipedia.org/wiki/Model_View_ViewMo
del, June 23, 2014.
• MSDN. Data Binding Overview.
https://msdn.microsoft.com/en-
us/library/ms752347(v=vs.110).aspx, May 2016.
• MSDN. IValueConverter interface.
https://msdn.microsoft.com/en-
us/library/system.windows.data.ivalueconverter(v=
vs.110).aspx, May 2016.
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Thank you!
http://www.npruehs.de
https://github.com/npruehs
@npruehs
dev@npruehs.de

Thank you for your attention!
Contact
Mail
dev@npruehs.de
Blog
http://www.npruehs.de
Twitter
@npruehs
Github
https://github.com/npruehs
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Tool Development 10 - MVVM, Tool Chains

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