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Design Patterns
Design patterns are recurring solutions to software design problems you find again and again in real-world application development. Patterns are about design and interaction of objects, as well as providing a communication platform concerning elegant, reusable solutions to commonly encountered programming challenges.
The Gang of Four (GoF) patterns are generally considered the foundation for all other patterns. They are categorized in three groups: Creational, Structural, and Behavioral. Here you will find information on these important patterns.
To give you a head start, the C# source code is provided in 2 forms: ‘structural’ and ‘real-world’. Structural code uses type names as defined in the pattern definition and UML diagrams. Real-world code provides real-world programming situations where you may use these patterns.
A third form, ‘.NET optimized’ demonstrates design patterns that exploit built-in .NET 4.0 features, such as, generics, attributes, delegates, object and collection initializers, automatic properties, and reflection.
| Creational Patterns | |
| Abstract Factory | Creates an instance of several families of classes |
| Builder | Separates object construction from its representation |
| Factory Method | Creates an instance of several derived classes |
| Prototype | A fully initialized instance to be copied or cloned |
| Singleton | A class of which only a single instance can exist |
| Structural Patterns | |
| Adapter | Match interfaces of different classes |
| Bridge | Separates an object’s interface from its implementation |
| Composite | A tree structure of simple and composite objects |
| Decorator | Add responsibilities to objects dynamically |
| Facade | A single class that represents an entire subsystem |
| Flyweight | A fine-grained instance used for efficient sharing |
| Proxy | An object representing another object |
| Behavioral Patterns | |
| Chain of Resp. | A way of passing a request between a chain of objects |
| Command | Encapsulate a command request as an object |
| Interpreter | A way to include language elements in a program |
| Iterator | Sequentially access the elements of a collection |
| Mediator | Defines simplified communication between classes |
| Memento | Capture and restore an object’s internal state |
| Observer | A way of notifying change to a number of classes |
| State | Alter an object’s behavior when its state changes |
| Strategy | Encapsulates an algorithm inside a class |
| Template Method | Defer the exact steps of an algorithm to a subclass |
| Visitor | Defines a new operation to a class without change |
A good explanation can be found at : http://www.dotnetuncle.com/Design-Patterns/dot-net-design-pattern-interview-questions.aspx
WPF Triggers
There are three types of triggers:
· Property triggers— Invoked when the value of a dependency property changes
· Data triggers— Invoked when the value of a plain .NET property changes
· Event triggers— Invoked when a routed event is raised
Property Triggers
A property trigger (represented by the Trigger class) executes a collection of Setters when a specified property has a specified value. And when the property no longer has this value, the property trigger “undoes” the Setters.
For example, the following update to buttonStyle makes the rotation only happen when the mouse pointer is hovering over the Button (and sets the Foreground to Black rather than White):
<Style x:Key=”buttonStyle” TargetType=”{x:Type Button}”>
<Style.Triggers>
<Trigger Property=”IsMouseOver” Value=”True”>
<Setter Property=”RenderTransform”>
<Setter.Value>
<RotateTransform Angle=”10″/>
</Setter.Value>
</Setter>
<Setter Property=”Foreground” Value=”Black”/>
</Trigger>
</Style.Triggers>
<Setter Property=”FontSize” Value=”22″/>
<Setter Property=”Background” Value=”Purple”/>
<Setter Property=”Foreground” Value=”White”/>
<Setter Property=”Height” Value=”50″/>
<Setter Property=”Width” Value=”50″/>
<Setter Property=”RenderTransformOrigin” Value=”.5,.5″/>
</Style>
Data Triggers
Data triggers are just like property triggers, except that they can be triggered by any .NET property rather than just dependency properties. (The Setters inside a data trigger are still restricted to setting dependency properties, however.) To use a data trigger, add a DataTrigger object to the Triggers collection and specify the property/value pair. To support plain .NET properties, you specify the relevant property with a Binding rather than a simple property name. The following TextBox has a Style that triggers the setting of IsEnabled based on the value of its Text property, which is not a dependency property. When Text is the string “disabled,” IsEnabled is set to false (which is admittedly an unusual application of a data trigger):
<StackPanel Width=”200″>
<StackPanel.Resources>
<Style TargetType=”{x:Type TextBox}”>
<Style.Triggers>
<DataTrigger Binding=”{Binding RelativeSource={RelativeSource Self}, Path=Text}” Value=”disabled”>
<Setter Property=”IsEnabled” Value=”False”/>
</DataTrigger>
</Style.Triggers>
<Setter Property=”Background” Value=”{Binding RelativeSource={RelativeSource Self}, Path=Text}”/>
</Style>
</StackPanel.Resources> <TextBox Margin=”3″/>
</StackPanel>
Expressing More Complex Logic with Triggers The logic expressed with the previous triggers has been of the form “when property=value, set the following properties.” But more powerful options exist: · Multiple triggers can be applied to the same element (to get a logical OR). · Multiple properties can be evaluated for the same trigger (to get a logical AND).
Logical OR
Because Style.Triggers can contain multiple triggers, you can create more than one with the exact same Setters to express a logical OR relationship:
<Style.Triggers>
<Trigger Property=”IsMouseOver” Value=”True”>
<Setter Property=”RenderTransform”>
<Setter.Value>
<RotateTransform Angle=”10″/>
</Setter.Value>
</Setter>
<Setter Property=”Foreground” Value=”Black”/>
</Trigger>
<Trigger Property=”IsFocused” Value=”True”>
<Setter Property=”RenderTransform”>
<Setter.Value>
<RotateTransform Angle=”10″/>
</Setter.Value>
</Setter>
<Setter Property=”Foreground” Value=”Black”/>
</Trigger>
</Style.Triggers>
This means, “if IsMouseOver is true or if IsFocused is true, apply the rotation and black foreground.”
Logical AND
To express a logical AND relationship, you can use a variation of Trigger called MultiTrigger, or a variation of DataTrigger called MultiDataTrigger. MultiTrigger and MultiDataTrigger have a collection of Conditions that contain the information you would normally put directly inside a Trigger or DataTrigger. Therefore, you can use MultiTrigger as follows:
<Style.Triggers>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property=”IsMouseOver” Value=”True”/>
<Condition Property=”IsFocused” Value=”True”/>
</MultiTrigger.Conditions>
<Setter Property=”RenderTransform”>
<Setter.Value>
<RotateTransform Angle=”10″/>
</Setter.Value>
</Setter>
<Setter Property=”Foreground” Value=”Black”/>
</MultiTrigger>
</Style.Triggers>
This means, “if IsMouseOver is true and if IsFocused is true, apply the rotation and black foreground.” MultiDataTrigger works the same way as MultiTrigger, but with support for plain .NET properties.
EventTriggers
An event trigger (represented by the EventTrigger class) is activated when a routed event is raised. The event is specified by the trigger’s RoutedEvent property, and it can contain one or more actions (objects deriving from the abstract TriggerAction class) in its Actions collection. Animation classes such as DoubleAnimation are not actions themselves, so you can’t add them directly to an EventTrigger’s Actions collection. Instead, animations are placed inside an object known as a Storyboard, which is wrapped in an action called BeginStoryboard. Therefore, placing the preceding DoubleAnimation inside an event trigger that is activated when a Button is clicked can look as follows:
<Button> OK
<Button.Triggers>
<EventTrigger RoutedEvent=”Button.Click”>
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard TargetProperty=”Width”>
<DoubleAnimation From=”50″ To=”100″ Duration=”0:0:5″ AutoReverse=”True”/>
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
</Button.Triggers>
</Button>
Call User Interface (UI) thread from a Asynchronous method
using System.Window.Threading;
public static class UIThread
{
public static Dispatcher {get; set;}
public static void Run(Action a)
{
Dispatcher.BeginEnvoke(a);
}
}
and call it inside a Asynchronous method like,
public void AsynchronousMethod()
{
….
….
UIThread.Run(delegate()
{
CustomUIMethod();
});
}
Open a ‘File Save Dialog’ window in Silverlight – During Asynchronous Call
Generally its not possible to open a SaveFileDialog window in Synchronous complete method like,
Wrong Method :
private void Method(Object param)
{
Client consoleClient = new Client(“”);
consoleClient.XXXCompleted+=new EventHandler<XXXCompletedEventArgs>(Method_Completed);
XXXRequest request = new XXXRequest();
request.p_Parameters = param;
consoleClient.XXXAsync(request);
}
void Method_Completed(object sender, XXXCompletedEventArgs e)
{
var result = (YYY)e.Result.XXXResult;
UIThread.Run(delegate() {
SaveFileDialog dlg = new SaveFileDialog(); // This will throw a Exception
dlg.DefaultExt = “.zip”; // Default file extension
dlg.Filter = “Zip Archive (.zip)|*.zip”; // Filter files by extension
if (dlg.ShowDialog() == true)
{
…
}
}
}
Right Method:
private void Method(Object param)
{
Client consoleClient = new Client(“”);
consoleClient.XXXCompleted+=new EventHandler<XXXCompletedEventArgs>(Method_Completed);
XXXRequest request = new XXXRequest();
request.p_Parameters = param;
consoleClient.XXXAsync(request);
}
void Method_Completed(object sender, XXXCompletedEventArgs e)
{
var result = (YYY)e.Result.XXXResult;
ChildWindowDlg _confirmationWnd = new ChildWindowDlg ();
_confirmationWnd.Show();
}
and inside that ChildWindowDlg class create a method and call SaveDialog window, like
void Save_ButtonClick(object sender, routedEventArg e)
{
SaveFileDialog dlg = new SaveFileDialog();
dlg.DefaultExt = “.zip”;
dlg.Filter = “Zip Archive (.zip)|*.zip”;
if (dlg.ShowDialog() == true)
{
using(Stream s = (Stream)dlg.OpenFile())
{
s.Write(data, index, length);
s.Close();
}
}
}
