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POString bound to TextBox is not updating
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  1. POString bound to TextBox is not updating
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    copied!<p>I've got a <code>TextBox</code> and a search <code>Button</code> which has to be enabled only if the <code>TextBox</code> is not empty.</p> <p>Since I'm using <code>MVVM Light</code>, I've bound the button to a <code>RelayCommand</code> which has a <code>CanExecute</code> function which just returns a boolean value.</p> <p>Here's the <code>Button</code>'s code:</p> <pre><code>&lt;Button Grid.Row="0" Grid.Column="1" HorizontalAlignment="Center" Margin="10" VerticalAlignment="Center" BorderThickness="1" Style="{StaticResource ButtonNoPadding}" Command="{Binding SearchCommand}"&gt; &lt;Rectangle Fill="{StaticResource PhoneForegroundBrush}" Width="40" Height="40" &gt; &lt;Rectangle.OpacityMask&gt; &lt;ImageBrush ImageSource="../Assets/AppBar/feature.search.png" /&gt; &lt;/Rectangle.OpacityMask&gt; &lt;/Rectangle&gt; &lt;/Button&gt; </code></pre> <p>and here's the <code>Command</code> and the property returned by the <code>CanExecute</code> function:</p> <pre><code>/// &lt;summary&gt; /// Boolean that enables/disables the search button /// &lt;/summary&gt; public bool CanSearch { get { return !string.IsNullOrEmpty(SearchQuery) &amp;&amp; NetworkUtils.IsNetworkAvailable; } } /// &lt;summary&gt; /// Command used to search for data /// &lt;/summary&gt; private RelayCommand _searchCommand; public RelayCommand SearchCommand { get { return _searchCommand ?? new RelayCommand(ExecuteSearch, () =&gt; CanSearch); } } </code></pre> <p>Now, as you may have noticed, the <code>CanSearch</code> property depends on the lenght of the <code>SearchQuery</code> string.</p> <p>The problem here is that this string is always null until I go back and load the page again. This means that my text, and my property, is updated only if I reload the page.</p> <p>I've followed <a href="https://stackoverflow.com/a/12099094/1094430">this answer</a> to fix this problem and having my <code>SearchQuery</code> update everytime that the text changes (and not only when it loses focus!) but it still won't work.</p> <p>Here's my <code>TextBox</code> code:</p> <pre><code>&lt;TextBox Grid.Row="0" Grid.Column="0" Text="{Binding SearchQuery, Mode=TwoWay}" VerticalAlignment="Center"&gt; &lt;i:Interaction.Behaviors&gt; &lt;utils:UpdateSourceOnTextChangedBehavior/&gt; &lt;/i:Interaction.Behaviors&gt; &lt;/TextBox&gt; </code></pre> <p>and here's the attached behavior:</p> <pre><code>public class UpdateSourceOnTextChangedBehavior : Behavior&lt;TextBox&gt; { protected override void OnAttached() { base.OnAttached(); AssociatedObject.TextChanged += OnTextChanged; } protected override void OnDetaching() { base.OnDetaching(); AssociatedObject.TextChanged -= OnTextChanged; } private void OnTextChanged(object sender, RoutedEventArgs e) { AssociatedObject.GetBindingExpression(TextBox.TextProperty).UpdateSource(); } } </code></pre> <p>The funny thing is that it actually does what it has to do, because the <code>AssociatedObject.GetBindingExpression(TextBox.TextProperty).UpdateSource();</code> gets called everytime I change a character in my <code>TextBox</code>.</p> <p>Of course the <code>SearchQuery</code> property raises all the needed events:</p> <pre><code>/// &lt;summary&gt; /// Query used to search in the API /// &lt;/summary&gt; private string _searchQuery; public string SearchQuery { get { return _searchQuery; } set { if (_searchQuery == value) return; _searchQuery = value; RaisePropertyChanged(() =&gt; SearchQuery); RaisePropertyChanged(() =&gt; CanSearch); SearchCommand.RaiseCanExecuteChanged(); } } </code></pre> <p>Any idea?</p>
 

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