Usage of Icommand in MVVM WPF

Rama Sagar
Posted by in WPF category on for Beginner level | Points: 250 | Views : 2186 red flag

ICommand Interface in WPF is commonly used for binding. ICommand Interface is implemented in the ViewModel and are exposed to the view controls.

Introduction


This article explains about Icommand usage in MVVM pattern with WPF 

Please have a look at my previous article before proceeding 

The ICommand interface is defined inside the System.Windows.Input namespace. It has two methods and an event.

Methods


 CanExecute:- Defines the method that determines whether the command can execute in its current state.
 Execute  :- Defines the method to be called when the command is invoked.

Events


 CanExecuteChanged:-Occurs when changes occur that affect whether or not the command should execute.


let us try to understand ICommand Interface and RelayCommand Class with following example

Create a view and viewModel  

 View: Lets create the view first.  Three things to note in this view

1. In this view,  WpfApplication1  namespace is included

xmlns:local="clr-namespace:WpfApplication1"

2.  Datacontext of the window is set to the MainWindowViewModel class present in WpfApplication1 namespace


<Window.DataContext>
    <local:MainWindowViewModel/>
</Window.DataContext>  

3. Binding of the command of  button is done with the updateCommand property of MainWindowViewModel class.
 
<Button Content="Update" Grid.Row="1" Height="23" HorizontalAlignment="Left" Margin="310,40,0,0" Name="btnUpdate" 
                VerticalAlignment="Top" Width="141"
                Command="{Binding Path=UpdateCommad}"  />


ViewModel: ViewModel has namespace WpfApplication1 , and property as updateCommand. 

 private ICommand mUpdater;
        public ICommand UpdateCommand
        {
            get
            {
                if (mUpdater == null)
                    mUpdater = new Updater();
                return mUpdater;
            }
            set
            {
                mUpdater = value;
            }
        }
        private class Updater : ICommand
        {
            #region ICommand Members
            public bool CanExecute(object parameter)
            {
                return true;
            }
            public event EventHandler CanExecuteChanged;
            public void Execute(object parameter)
            {
            }
            #endregion
        }
    }
}

When the user clicks on update Button, the application reacts and satisfies the user's requests. This works because of bindings that were established on the Command property of Button displayed in the UI. The command object acts as an adapter that makes it easy to consume a ViewModel's functionality from a view declared in XAML


Conclusion

In this article we have learned about ICommand in MVVM WPF

Reference

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

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About the Author

Rama Sagar
Full Name: RamaSagar Pulidindi
Member Level: Silver
Member Status: Member,MVP
Member Since: 12/30/2012 1:51:40 AM
Country: India
ramasagar
http://www.ramasagar.com
A Software Profesional working in Microsoft .NET technologies since year 2008, and I work for Dake ACE. I am passionate about .NET technology and love to contribute to the .NET community at Dot Net Funda

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