Customizing Commands

This article provides a description and examples of how to customize RadCollectionNavigator’s commands in a MVVM-friendly way.

Please note that Telerik introduced this functionality in Q1 2016.

The CollectionNavigatorBaseCommandProvider is a public class that exposes the “execute” and “can-execute” logic of all commands used by RadCollectionNavigator. RadCollectionNavigator processes these commands according to its current provider.

Execute logic methods

The methods listed below in Example 1 identify the logic that is executed when a certain command’s invocation takes place.

Example 1: RadCollectionNavigator's executable commands

void MoveCurrentToFirst(); 
void MoveCurrentToLast(); 
void MoveCurrentToNext(); 
void MoveCurrentToPrevious(); 
void BeginEdit(); 
void Delete(); 
void AddNew(); 
Sub MoveCurrentToFirst() 
Sub MoveCurrentToLast() 
Sub MoveCurrentToNext() 
Sub MoveCurrentToPrevious() 
Sub BeginEdit() 
Sub Delete() 
Sub AddNew() 

Can-execute logic methods

With the help of the methods listed in Example 2 you can identify whether a certain command can be executed or not.

Example 2:RadCollectionNavigator "can-execute" methods

bool CanMoveCurrentToFirstExecute(); 
bool CanMoveCurrentToLastExecute(); 
bool CanMoveCurrentToNextExecute(); 
bool CanMoveCurrentToPreviousExecute(); 
bool CanBeginEditExecute(); 
bool CanDeleteExecute(); 
bool CanAddNewExecute(); 
Function CanMoveCurrentToFirstExecute() As Boolean 
Function CanMoveCurrentToLastExecute() As Boolean 
Function CanMoveCurrentToNextExecute() As Boolean 
Function CanMoveCurrentToPreviousExecute() As Boolean 
Function CanBeginEditExecute() As Boolean 
Function CanDeleteExecute() As Boolean 
Function CanAddNewExecute() As Boolean 

Designing a custom CommandProvider

The first step is to create your own class that inherits from CollectionNavigatorBaseCommandProvider.

Example 3: Creating a class that provides the custom commands

public class CustomCommandProvider : CollectionNavigatorBaseCommandProvider 
{ 
    public CustomCommandProvider() : base(null) 
    { 
    } 
    public CustomCommandProvider(RadCollectionNavigator collectionNavigator) 
        : base(collectionNavigator) 
    { 
    } 
    //. . . 
} 
Public Class CustomCommandProvider 
    Inherits CollectionNavigatorBaseCommandProvider 
    Public Sub New() 
        MyBase.New(Nothing) 
    End Sub 
    Public Sub New(ByVal collectionNavigator As RadCollectionNavigator) 
        MyBase.New(collectionNavigator) 
    End Sub 
    '. . . 
End Class 

You need to override the methods of the commands that will be customized. In the following example we will customize: MoveCurrentToNext, MoveCurrentToPrevious.

MoveCurrentToNext and MoveCurrentToPrevious

If we have a requirement to prompt for the user's approval when moving through the items, the following change in the methods can be done:

Example 4: Overriding the default commands

public override void MoveCurrentToNext() 
{ 
    MessageBoxResult result = MessageBox.Show("MoveCurrentToNext ?", "MoveCurrentToNext", MessageBoxButton.OKCancel); 
    if (result == MessageBoxResult.OK) 
    { 
        this.CollectionNavigator.MoveCurrentToNext(); 
    } 
} 
public override void MoveCurrentToPrevious() 
{ 
    MessageBoxResult result = MessageBox.Show("MoveCurrentToPrevious ?", "MoveCurrentToPrevious", MessageBoxButton.OKCancel); 
    if (result == MessageBoxResult.OK) 
    { 
        this.CollectionNavigator.MoveCurrentToPrevious(); 
    } 
} 
Public Overrides Sub MoveCurrentToNext() 
    Dim result As MessageBoxResult = MessageBox.Show("MoveCurrentToNext ?", "MoveCurrentToNext", MessageBoxButton.OKCancel) 
    If result = MessageBoxResult.OK Then 
        Me.CollectionNavigator.MoveCurrentToNext() 
    End If 
End Sub 
Public Overrides Sub MoveCurrentToPrevious() 
    Dim result As MessageBoxResult = MessageBox.Show("MoveCurrentToPrevious ?", "MoveCurrentToPrevious", MessageBoxButton.OKCancel) 
    If result = MessageBoxResult.OK Then 
        Me.CollectionNavigator.MoveCurrentToPrevious() 
    End If 
End Sub 

The last thing to be done is to set the CommandProvider property of the RadCollectionNavigator to be the newly-created CustomCommandProvider class.

Example 5: Assigning the CommandProvider

<telerik:RadCollectionNavigator x:Name="CollectionNavigator" 
                        Source="{Binding Employees}"/> 

Example 5: Assigning the CommandProvider

this.CollectionNavigator.CommandProvider = new CustomCommandProvider(this.CollectionNavigator); 
Me.CollectionNavigator.CommandProvider = New CustomCommandProvider(Me.CollectionNavigator) 

Modifying the methods will result in the action shown in the image below when trying to move to the next item:

Figure 1: RadCollectionNavigator with customized MoveCurrentToNext command

RadCollectionNavigator with customized MoveCurrentToNext command

See Also

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