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POIs this WPF ProgressBar Odd render behaviour a Bug?
 

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  1. POIs this WPF ProgressBar Odd render behaviour a Bug?
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    <p>Hope someone can help. I have a simple scenario where clicking checkboxes is driving a progress bar in <a href="http://en.wikipedia.org/wiki/Windows_Presentation_Foundation" rel="nofollow noreferrer">WPF</a>. The checkboxes are contained in a UserControl and the Progress bar is in a simple WPF client window. On the user control I am using two dependency properties: 1) the existing Tag property has the value I wish to bind to the progress bar value and 2) a DP called CbCount which represents the total number of checkboxes.</p> <p><strong>The problem:</strong> When the application runs the progress bar's progress shows as being 100% complete even though via Snoop I can see the value is in fact 0. Clicking on the checkboxes everything works fine as expected.</p> <p>Code: UserControl - within namespace ProgBarChkBxs:</p> <pre><code>public partial class ucChkBoxes : UserControl { #region CbCount public static readonly DependencyProperty CbCountProperty = DependencyProperty.Register("CbCount", typeof(double), typeof(ucChkBoxes), new FrameworkPropertyMetadata((double)0)); /// &lt;summary&gt; /// Gets or sets the CbCount property. This dependency property /// indicates the number of checkBoxes /// &lt;/summary&gt; public double CbCount { get { return (double)GetValue(CbCountProperty); } private set { SetValue(CbCountProperty, value); } } #endregion double _totalCount = 0; double _numberChecked = 0; double DEFAULT = 0; public ucChkBoxes() { InitializeComponent(); this.Tag = DEFAULT; this.Loaded += new RoutedEventHandler(ucChkBoxes_Loaded); } void ucChkBoxes_Loaded(object sender, RoutedEventArgs e) { if (this.ourContainer.Children.Count != 0) { _totalCount = this.ourContainer.Children.Count; } this.CbCount = (double)_totalCount; } private void CheckBox_Checked(object sender, RoutedEventArgs e) { if (e.OriginalSource.GetType() == typeof(CheckBox)) { CheckBox cb = (CheckBox)e.OriginalSource; if (cb.IsChecked == true) { _numberChecked++; } if (cb.IsChecked != true) { _numberChecked--; } //simple POC progress metric this.Tag = (double)(_numberChecked / _totalCount * _totalCount); } } } </code></pre> <p>XAML:</p> <pre><code>&lt;UserControl x:Class="ProgBarChkBxs.ucChkBoxes" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Height="Auto" Width="Auto"&gt; &lt;StackPanel&gt; &lt;TextBlock Text="Please select options" &gt;&lt;/TextBlock&gt; &lt;StackPanel Name="ourContainer" CheckBox.Checked="CheckBox_Checked" CheckBox.Unchecked="CheckBox_Checked"&gt; &lt;CheckBox&gt;Fruit Juice&lt;/CheckBox&gt; &lt;CheckBox&gt;Coffee&lt;/CheckBox&gt; &lt;CheckBox&gt;Toast&lt;/CheckBox&gt; &lt;CheckBox&gt;Cereal&lt;/CheckBox&gt; &lt;CheckBox&gt;Grapefruit&lt;/CheckBox&gt; &lt;/StackPanel&gt; &lt;/StackPanel&gt; &lt;/UserControl&gt; </code></pre> <p>The Client which just has the databindings is a simple window - the local namespace below refers to the project namespace xmlns:local="clr-namespace:ProgBarChkBxs", the meat of the code is:</p> <pre><code>&lt;StackPanel&gt; &lt;local:ucChkBoxes x:Name="chkBoxes"/&gt; &lt;ProgressBar Name="pb" Background="Azure" Minimum="0" Height="30" Value="{Binding ElementName=chkBoxes,Path=Tag }" Maximum="{Binding ElementName=chkBoxes,Path=CbCount }" /&gt; &lt;/StackPanel&gt; </code></pre> <p>The really weird thing is if within the DP definition of the CbCount if I change the FrameworkPropertyMetadata to a really small value to say (double)0.001 the problem goes away.</p> <p>I am running this on XP.</p> <p>All help gratefully received - thanks.</p> <p><strong>Update:</strong> I have been digging into this again as it gnaws at my sole (who said get a life!)</p> <p>Things I did:</p> <p>1) Adding a slider which also like progressBar inherits from RangeBase gives me the expected behaviour.</p> <p>2) Spinning up reflector I can see the static ctor for ProgressBar sets the default value first to 100, RangeBase.MaximumProperty.OverrideMetadata(typeof(ProgressBar), new FrameworkPropertyMetadata(100.0)); Should AffectMeasure? whereas in the slider: RangeBase.MaximumProperty.OverrideMetadata(typeof(Slider), new FrameworkPropertyMetadata(10.0, FrameworkPropertyMetadataOptions.AffectsMeasure));</p> <p>3) So we need another layout pass after a I set the ProgressBar.Value Going back to my simple POC application if within a the progressBar loaded handler in the client window I jig the layout on the first run through:</p> <pre><code>this.Width += 1; //trigger another layout pass </code></pre> <p>Then, hey, presto it works.</p> <p><strong>So is this a bug?</strong></p> <p>I still do not fully understand though how the progressBar value which is calculated from Minimum and Maximum values is affected in this way and not the Slider - the default value of Maximum appears to be having an effect and it looks as if the ProgressBar default should affect the measure pass. (missing <code>FrameworkPropertyMetadataOptions.AffectsMeasure</code>.)</p> <p><strong>Can anyone help, either confirm my thinking or explain what is really happening here?</strong></p>
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    1. CO@Andrew - my edit fixed the code for you. Roll the post back to version 2 and you should see all the code.
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      1. POIs this WPF ProgressBar Odd render behaviour a Bug?
      1. USChrisF
    2. COChris - thanks - sorry excuse my ignorance first day contributing to StackOverFlow how do I roll the post back to version 2?
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      1. POIs this WPF ProgressBar Odd render behaviour a Bug?
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    3. CO@Andrew - select the "edit" link. There's a drop down at the top of the page "Rev". Select the revision you want from that list and then "Save Your Edits".
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