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POAction, Func and Predicate delegates - C#
 

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    <p>I'm trying to understand the differences between the <code>Action&lt;T&gt;, Func&lt;T&gt; and Predicate&lt;T&gt;</code> delegates as part of my WPF/MVVM learning.</p> <p>I know <code>Action&lt;T&gt; and Func&lt;T&gt;</code> both take zero to one+ parameters, only <code>Func&lt;T&gt;</code> returns a value while <code>Action&lt;T&gt;</code> don't.</p> <p>As for <code>Predicate&lt;T&gt;</code> - I have no idea.</p> <p>Therefore, I came up with this following questions: </p> <ol> <li>What does <code>Predicate&lt;T&gt;</code> do? (Examples welcomed!)</li> <li>If <code>Action&lt;T&gt;</code> returns <strong>nothing</strong>, wouldn't it be simpler to just use <code>void</code> instead? (Or any other type if it's <code>Func&lt;T&gt;</code> we're talking about.)</li> </ol> <p>I'd like you to avoid LINQ/List examples in your questions.<br> I've seen those already but they just make it more confusing as the code that got me 'interested' in these delegates have nothing to do with it (I think!).<br> Therefore, I'd like to use a code I'm familiar with to get my answer. </p> <p>Here it is: </p> <pre><code>public class RelayCommand : ICommand { readonly Action&lt;object&gt; _execute; readonly Predicate&lt;object&gt; _canExecute; public RelayCommand(Action&lt;object&gt; execute) : this(execute, null) { } public RelayCommand(Action&lt;object&gt; execute, Predicate&lt;object&gt; canExecute) { if (execute == null) throw new ArgumentNullException("execute"); _execute = execute; _canExecute = canExecute; } [DebuggerStepThrough] public bool CanExecute(object parameters) { return _canExecute == null ? true : _canExecute(parameters); } public event EventHandler CanExecuteChanged { add { CommandManager.RequerySuggested += value; } remove { CommandManager.RequerySuggested -= value; } } public void Execute(object parameters) { _execute(parameters); } } </code></pre> <p><strong>Note:</strong><br> I took out the comments to avoid super-long block of code.<br> The full code can be found <a href="http://rachel53461.wordpress.com/2011/05/08/simplemvvmexample/" rel="nofollow">HERE</a>.</p> <p>Any help is appreciated! Thanks! :)</p> <p>P.S: Please don't point me to other questions. I did try to search but I couldn't find anything simple enough for me to understand.</p>
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    1. COA `Predicate` must return a boolean. I *will* point you to another question: http://stackoverflow.com/questions/1710301/what-is-a-predicate-in-c
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