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POUnderstanding MVVM: simple non-working code
 

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  1. POUnderstanding MVVM: simple non-working code
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    <p>I'm trying to understand this pattern and all the logic that's behind it.</p> <p>I don't think it's that hard, but still I'm failing in some easy tasks.</p> <p>Let's make it clear with a non-working example that I wrote:</p> <p>Model:</p> <pre><code>public class Model { public string Name { get; set; } public string Description { get; set; } public Categories Category { get; set; } public Grid PresenterContent { get; set; } } </code></pre> <p>ViewModel:</p> <pre><code>public class ViewModel : ViewModelBase { private Model _model; public Model Model { get { return _model; } set { if (_model != value) { _model = value; RaisePropertyChanged(() =&gt; Model); } } } public Grid PresenterContent { get { return Model.PresenterContent; } private set { } } public ViewModel() { Model = new Model(); } } </code></pre> <p>View:</p> <pre><code>&lt;UserControl.DataContext&gt; &lt;Binding Source="ViewModel"/&gt; &lt;/UserControl.DataContext&gt; &lt;Grid x:Name="LayoutRoot" Background="{StaticResource PhoneChromeBrush}"&gt; &lt;ContentPresenter Content="{Binding PresenterContent}"/&gt; &lt;/Grid&gt; </code></pre> <p>Now, I expect this to work when I run it, as I'm setting the <code>DataContext</code> to <code>ViewModel</code> which has a <code>PresenterContent</code> property.</p> <p>(This property is both in the <code>Model</code> and the <code>ViewModel</code> because I don't know to work with child's property, in this case <code>Model.PresenterContent</code>.)</p> <p>What actually happens is that an exception is thrown:</p> <blockquote> <p>System.Windows.Data Error: BindingExpression path error: 'PresenterContent' property not found on 'ViewModel' 'System.String' (HashCode=-903444198). BindingExpression: Path='PresenterContent' DataItem='ViewModel' (HashCode=-903444198); target element is 'System.Windows.Controls.ContentPresenter' (Name=''); target property is 'Content' (type 'System.Object')..</p> </blockquote> <p>and this says that there's no <code>PresenterContent</code> in the <code>ViewModel</code>, which is clearly wrong. The exception is the same if I try to bind to <code>Model</code> property.</p> <p>What am I doing wrong?</p>
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      1. USSeyyed Puya Soofbaf
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    1. CODude, you're getting it all wrong. You're not supposed to put a property of type `Grid` in your Model. The idea is to `separate` UI and data, not to tie them together even more.
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      1. POUnderstanding MVVM: simple non-working code
      1. USFederico Berasategui
    2. COForget the types, this is just an example. As I wrote, the error comes even with the `Model` property (and even with a string that I removed from the code).
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    3. COi think you have not added the ViewModel in your usercontrol resource...before using it in binding you need to add it as a usercontrol resource
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      1. USDinesh
 

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