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POTo pass a delegate/command as a parameter to another command in MVVM
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copied!<p>I have a user control 'A' that has another user control 'B' as its child. The usecase scenario being, when the user clicks a button on 'A', it should <em>request</em> 'B' to process some information (typically relating to the state of 'B') and get the result, which will then be used in some calculation in 'A'.</p> <p>Now, I am using MVVM pattern. The viewmodel of 'A' does not have any reference to either the UI of A or B. I am exactly looking for this: When a user cliks a button on the UI of 'A', I need to call a command in 'B', by passing a delegate in the viewmodel of 'A' as a parameter to that command. This way, when the command in 'B' processes information, it can <em>then</em> call the callback function passed from 'A'.</p> <p>Now, the delegate is parameter-less. Once the command in usercontrol 'B' processes some information, it updates <em>its state</em>. This state is a dependency property which will be binded to a property in the viewmodel of 'A'.</p> <p>Is there a way to achieve something like this?</p> <p>I have a working solution currently. But I want to improvise the code and make it better. This is my current temporary workaround to this problem:</p> <p>When the user clicks a button in 'A', I am having an Event Handler in 'A' (xaml.cs). In the event handler, as I have the reference of 'B', I am checking if the command in 'B' can be executed, and then call it. Then, I check if command (in viewmodel of 'A') can be executed, and then call it.</p> <p>If my question was not descriptive enough, here is a code sample to support it:</p> <p><strong>XAML of 'A':</strong></p> <pre><code><bNameSpace:B x:Name="BObject" DepenPropertyInB="{Binding PropInA, Mode=OneWayToSource}"/> .... <telerik:RadButton Content="Process" HorizontalAlignment="Right" Height="30" Width="80" Grid.Column="2" Click="ProcessButton_Click" /> </code></pre> <p><strong>XAML.cs of A:</strong></p> <pre><code>private void ProcessButton_Click(object sender, RoutedEventArgs e) { if (BObject.StateDataRequestedCommand.CanExecute("")) BObject.StateDataRequestedCommand.Execute(""); if(ViewModel.ProcessInfoRequestedCommand.CanExecute("")) ViewModel.ProcessInfoRequestedCommand.Execute(""); } </code></pre> <p><strong>ViewModel of A:</strong></p> <pre><code>private void OnProcessInfoRequestedCommand(string anyValue) { // read the value of PropInA and do some processing } </code></pre> <p><strong>ViewModel of B:</strong></p> <pre><code>private void OnStateDataRequestedCommand(string anyValue) { // Bases on B's state do some calc and update DepenPropertyInB } </code></pre>

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