MVVM Fundamentals

8/10/2019 MVVM Fundamentals

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mod pattern



MODEL-VIEW-X



with a limited or no code-behin

along with business and validation logic.

The view model then provides data from the model in a form that the view can easily use

The view model also provides impcommands that a user of the application initiates in the view.



So why MVVM for WPF?



So why MVVM for WPF?

DependencyProperty and DependencyObject

resolved dynamically



If no local value is set, the dependenproperty navigates up the logical tree until it finds a value.

a built-in change notification me



• // Dependency Property

// .NET Property wrapper



Attached Properties

<Canvas> <Button Canvas.Top="20" Canvas.Left="20" Content="Cl

me!"/> </Canvas>



Notifications for binding to normalproperties

• ObservableCollection<T> Class:

(implements



public class Person : INotifyPropertyChanged

{private string name;

// Declare the event

public event PropertyChangedEventHandler PropertyChanged;

………………………………………..

public string PersonName

{get { return name; }

set {

name = value;

// Call OnPropertyChanged whenever the property is updated OnPropertyChanged("PersonName");

}

}

// Create the OnPropertyChanged method to raise the event

protected void OnPropertyChanged(string name){

PropertyChangedEventHandler handler = PropertyChanged;

if (handler != null){

handler(this, new PropertyChangedEventArgs(name));}

}

}



the object that invokes a command from the logic that exthe command. This allows for multiple and disparate sourinvoke the same command logic, and it allows the commato be customized for different targets.



indicate whether an available.



ICommand

http://msdn.microsoft.com/en-us/library/system.windows.input.icommand.aspx

http://msdn.microsoft.com/en-us/library/system.windows.input.icommand.aspx



RelayCommand

<Button Content=“BOO" Height="30" Command="{BindinPath=BOOCommand}"></Button>



How do we do it all?

NO CODE-BEHIND, NO USAGREFFERENCES OF THE ViewModel



Threading

DON’T FREEZE THE UI



belongs to a thread



• You can have one thread per Window but in practice, a Wapplication has one single Dispatcher and one thread to hUI (The UI thread/Main Thread).

• Don’t touch the UI from the wrong thread

• The application can only be responsive (the UI working) wUI thread is free and running the message loop

• Don’t block the UI thread

• How?



Async Work

• Dispatcher.BeginInvoke – pass a delegate to the method sends a message to the dispatcher and when that messagpicked up, the delegate will be invoked on the UI thread.



• ThreadPool



automaticaevent on the UI thread

BackgroundWorker BackgroundWorker

DoWorkEventHandler



MVVM in a threading scenario



More advanced topics

• Threading

• Unit Testing

• ToolKits

MVVM Fundamentals

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