Skip to main content

How to call Commands from UI Control in MVVM pattern

Image
By
We will use RelayCommands to register Execute and CanExcute command handlers in MVVM pattern.
To achieve this we will create a class RelayCommand.

    /// <summary>
    /// To register commands in MMVM pattern
    /// </summary>
    public class RelayCommand : ICommand
    {
        readonly Action<object> _execute;
        readonly Predicate<object> _canExecute;

        /// <summary>
        /// Constructer takes Execute events to register in CommandManager.
        /// </summary>
        /// <param name="execute">Execute method as action.</param>
        public RelayCommand(Action<object> execute)
            : this(execute, null)
        {
            try
            {
                if (null == execute)
                {
                    throw new NotImplementedException("Not implemented");
                }

                _execute = execute;
            }
            catch (Exception)
            {

                throw;
            }
        }

        /// <summary>
        /// Constructer takes Execute and CanExcecute events to register in CommandManager.
        /// </summary>
        /// <param name="execute">Execute method as action.</param>
        /// <param name="canExecute">CanExecute method as return bool type.</param>
        public RelayCommand(Action<object> execute, Predicate<object> canExecute)
        {
            try
            {
                if (null == execute)
                {
                    _execute = null;
                    throw new NotImplementedException("Not implemented");
                }

                _execute = execute;
                _canExecute = canExecute;
            }
            catch (Exception)
            {

            }
        }

        /// <summary>
        /// Can Executed Changed Event
        /// </summary>
        public event EventHandler CanExecuteChanged
        {
            add
            {
                CommandManager.RequerySuggested += value;
            }
            remove
            {
                CommandManager.RequerySuggested -= value;
            }
        }

        /// <summary>
        /// Execute method.
        /// </summary>
        /// <param name="parameter">Method paramenter.</param>
        public void Execute(object parameter)
        {
            _execute(parameter);
        }

        /// <summary>
        /// CanExecute method.
        /// </summary>
        /// <param name="parameter">Method paramenter.</param>
        /// <returns>Return true if can execute.</returns>
        public bool CanExecute(object parameter)
        {
            return _canExecute == null ? true : _canExecute(parameter);
        }
    }


Now in MVVM pattern we need to declare a command in View Model that will be bind with the Command property of the WPF Control.

We will create a ICommand property and in get section will register the Execute and CanExecute handlers for the command. The arguments “Param” would be used for Command Parameter.

        ICommand _saveSettingsCommand;

        public ICommand SaveSettingsCommand
        {
            get
            {
                if (_saveSettingsCommand == null)
                    _saveSettingsCommand = new RelayCommand(param => this.SaveSettingsCommand_Execute(param), param => this.SaveSettingsCommand_CanExecute(param));
                return _saveSettingsCommand;
            }
        }

        bool SaveSettingsCommand_CanExecute(object param)
        {
            return true;
        }

        void SaveSettingsCommand_Execute(object param)
        {
            if (_applicationVM == null || _configurationLabwareVM == null || !_isEditable)
                return;
            Configure(!IsSelected);
        }


This is done!
Now just call this command from the control in the view which is bounded with the view model where this command defined.
The Command Binding will look like this.

<telerik:RadButton Grid.Column="1"
                   Name="radButton1"
                   MinWidth="70"
                   HorizontalAlignment="Stretch"
                   VerticalAlignment="Center"
                   Background="{Binding StatusBrush}"
                   Height="20"
                   Command="{Binding SaveSettingsCommand}"
                   CommandParameter="{Binding LabwareID}"
                   >


Go through the steps I defined above. It is very easy to work with commands in WPF.
Enjoy!!!

Labels:

Comments

Post a Comment

Popular posts from this blog

WPF-MVVM: RelayCommand Implementation

By
In WPF if we are implementing MVVM pattern then we need to play with Command rather than Events. You can use ICommand interface to create each command class. Implementation of ICommand in a class gives you CanExecute(), Execute() methods which take part in the action performed by Command.   Rather than making Command Class for each Command we can implement a generic Relay Command to get Command. Below is a RelayCommand class that we will implement.   ///   <summary>      ///  To register commands in MMVM pattern      ///   </summary>      class   RelayCommands  :  ICommand     {          readonly   Action < object > _execute;          readonly   Predicate < object > _canExecute;  ...
Post a Comment
Read more

.Net List with Changed event

By
Sometimes we need a List which can notify user when an item is added. Here is the way that you can implement a generic ArrayList which notifies user at the time of an element is added.   using  System; using  System.Collections; namespace  ArchiveData.Logging {    // A delegate type for hooking up change notifications.    public   delegate   void   ChangedEventHandler ( object  sender,  EventArgs  e);    public   class   ListWithChangedEvent  :  ArrayList   {      // An event that clients can use to be notified whenever the      // elements of the list change.      public   event   ChangedEventHandler  Changed;      public   object  NewlyAddedItem {...
Post a Comment
Read more

What is DispatcherTimer in wpf?

By
DispatcherTimer When you want to set a timer working with GUI, you always come across threading problem. The problem is that if you want to send some changes to UI that is constantly/continuously changing then that will make your UI unresponsive or in other words it will hang your UI.   To overcome from this situation, WPF gives us DispatcherTimer threading functionality that will take care of such continuously changing processing on UI thread and that will not hang your UI. We can accomplish same scenario in Win Form , through System.Windows.Forms.Timer and in WPF it is System.Windows.Threading.DispatcherTimer .   Difference between DispatcherTimer and Regular timer (System.Timers.Timer) DispatcherTimer is the regular timer. It fires its Tick event on the UI thread, you can do anything you want with the UI. System.Timers.Timer is an asynchronous timer, its Elapsed event runs on a thread pool thread. You have to be very careful in your event handler...
Post a Comment
Read more