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POHow to correct this sample illustrating WPF DependencyProperty usage?
 

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  1. POHow to correct this sample illustrating WPF DependencyProperty usage?
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    <p>I am trying to run the code from the article "<a href="http://miteshsureja.blogspot.ru/2011/07/dependency-properties-in-wpf.html" rel="nofollow noreferrer">Dependency Properties in WPF</a>" I've attached below. </p> <p>But app breaks on line <code>SetValue(MyDependencyProperty, value);</code> with exception: </p> <pre><code>System.Windows.Markup.XamlParseException "'' is not a valid value for property 'MyProperty'." </code></pre> <p>Inner exception: </p> <blockquote> <p>{"'The invocation of the constructor on type '_3DP_CallBack_DefaultValue.MainWindow' that matches the specified binding constraints threw an exception.' Line number '3' and line position '9'."}</p> </blockquote> <p><img src="https://i.stack.imgur.com/Qye4h.jpg" alt="enter image description here"></p> <p>What should I change in order to run this app? </p> <p>The code of WPF app: </p> <pre><code>namespace _3DP_CallBack_DefaultValue { public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); DependencyPropertySample dpSample = new DependencyPropertySample(); dpSample.MyProperty = "Dependency Property Test";//??? Binding mybinding = new Binding("MyProperty"); mybinding.Mode = BindingMode.OneWay; mybinding.Source = dpSample; BindingOperations.SetBinding(MyTextblock, TextBox.TextProperty, mybinding); } } public class DependencyPropertySample : DependencyObject { //Register Dependency Property public static readonly DependencyProperty MyDependencyProperty = DependencyProperty.Register ( "MyProperty", typeof(string), typeof(DependencyPropertySample), new PropertyMetadata ( "Test", new PropertyChangedCallback(OnMyPropertyChanged), new CoerceValueCallback(OnCoerceValue) ), new ValidateValueCallback(OnValidateMyProperty) ); public string MyProperty { get { return (string)GetValue(MyDependencyProperty); } set { //*************************** //breaking on the following line trying to set any string value // in this case "Dependency Property Test" SetValue(MyDependencyProperty, value); } } public static void OnMyPropertyChanged(DependencyObject dObject, DependencyPropertyChangedEventArgs e) { MessageBox.Show(e.NewValue.ToString()); } public static string OnCoerceValue(DependencyObject dObject, object val) { if (val.ToString().CompareTo("Test") == 1) { return val.ToString(); } return string.Empty; } public static bool OnValidateMyProperty(object myObj) { if (myObj.ToString() == string.Empty) return false; return true; } } } </code></pre> <p>XAML: </p> <pre><code>&lt;Window x:Class="_3DP_CallBack_DefaultValue.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="350" Width="525"&gt; &lt;Grid&gt; &lt;Grid.RowDefinitions&gt; &lt;RowDefinition /&gt; &lt;/Grid.RowDefinitions&gt; &lt;Label Content="Enter String:" Grid.Row="0" VerticalAlignment="Center" /&gt; &lt;TextBox Text="" Name="MyTextblock" Height="25" Width="150" HorizontalAlignment="Right" /&gt; &lt;/Grid&gt; &lt;/Window&gt; </code></pre> <h1>Update:</h1> <p>Above was a 3d (incremental) version of WPF app with 2 previous WPF app, I've run without any errors </p> <p>The second version had : </p> <ul> <li>exactly the same XAML code</li> <li>exactly the same C# <code>MainWindow()</code>'s body of constructor/method; </li> <li>the absent methods in <code>class DependencyPropertySample : DependencyObject{}</code> <ul> <li><code>OnMyPropertyChanged( DependencyObject dObject, DependencyPropertyChangedEventArgs e)</code> </li> <li><code>OnValidateMyProperty(object myObj)</code> </li> <li><code>OnCoerceValue(DependencyObject dObject, object val)</code> </li> </ul></li> </ul> <p>and the <code>public static readonly DependencyProperty MyDependencyProperty = DependencyProperty.Register()</code> was different: </p> <p>Here is the code of <code>DependencyPropertySample</code> class <strong>from working 2nd version:</strong> </p> <pre><code>public class DependencyPropertySample : DependencyObject { //Register Dependency Property public static readonly DependencyProperty MyDependencyProperty = DependencyProperty.Register ("MyProperty", typeof(string), typeof(DependencyPropertySample)); public string MyProperty { get { return (string)GetValue(MyDependencyProperty); } set { SetValue(MyDependencyProperty, value); } } </code></pre> <p>Here is the code of <code>DependencyPropertySample</code> class <strong>from failing 3d version of app</strong>: </p> <pre><code> public class DependencyPropertySample : DependencyObject { //Register Dependency Property public static readonly DependencyProperty MyDependencyProperty = DependencyProperty.Register ( "MyProperty", typeof(string), typeof(DependencyPropertySample), new PropertyMetadata ( "Test", new PropertyChangedCallback(OnMyPropertyChanged), new CoerceValueCallback(OnCoerceValue) ), new ValidateValueCallback(OnValidateMyProperty) ); public string MyProperty { get { return (string)GetValue(MyDependencyProperty); } set { SetValue(MyDependencyProperty, value); } } public static void OnMyPropertyChanged(DependencyObject dObject, DependencyPropertyChangedEventArgs e) { MessageBox.Show(e.NewValue.ToString()); } public static string OnCoerceValue(DependencyObject dObject, object val) { if (val.ToString().CompareTo("Test") == 1) { return val.ToString(); } return string.Empty; } public static bool OnValidateMyProperty(object myObj) { if (myObj.ToString() == string.Empty) return false; return true; } } </code></pre>
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    1. COI don't see you specifying anywhere the property you want to bind against. Use mybinding.Path = "MyProperty"
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      1. POHow to correct this sample illustrating WPF DependencyProperty usage?
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    2. CO@Erti-ChrisEelmaa, `mybinding.Path = "MyPropertyPath";` gives compilation error `"Cannot convert source type 'string' to target type 'System.Windows.PropertyPath'`. Anyway, it is not clear why the previous version of the same app did not have any problems without any path setting. Please, see update in my question
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