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POHow do I programmatically position a canvas in Silverlight?
 

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  1. POHow do I programmatically position a canvas in Silverlight?
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    <p>I'm using Silverlight 3/C#, and I'm trying to create some XAML objects programatically in response to a user clicking on a button.</p> <p>However, I can't seem to position a <code>Canvas</code> object that I have created - when I call <code>SetValue()</code> on the new <code>Canvas</code> with the <code>Canvas.LeftProperty</code> value, the browser window clears to an empty screen.</p> <p>I have a simple function that exhibits the problem (I started out with something more complex):</p> <pre><code> private Canvas MakeNewCanvas() { Canvas newCanvas = new Canvas(); newCanvas.Width = newCanvas.Height = 50; newCanvas.SetValue(Canvas.LeftProperty, 10); return newCanvas; } </code></pre> <p>and a simple button click handler that calls this:</p> <pre><code> private void MyButton_Click(object sender, System.Windows.RoutedEventArgs e) { myPage.Children.Add(MakeNewCanvas()); } </code></pre> <p><strong>NB</strong>: myPage is a Canvas object defined in my app's MainPage XAML file.</p> <p>I've traced this through in the VS debugger with the SL app executing in Firefox, and whenever it executes the <code>SetValue()</code> line, the browser goes white and starts trying to download data (according to the status bar). I tried calling <code>SetValue()</code> after I've put the <code>Canvas</code> in the XAML tree with something like:</p> <pre><code> myPage.Children.Add(newCanvas); newCanvas.SetValue(Canvas.LeftProperty, 10); </code></pre> <p>but it makes no difference - as soon as the <code>SetValue()</code> call is hit, the browser goes white.</p> <p>The <code>Canvas</code> class seems to have no direct method of setting Left/Top on itself, apart from the <code>SetValue()</code> function with dependency property enum values. There's also <code>Canvas.SetLeft()</code> and <code>Canvas.SetTop()</code> but I guess they're just shims onto <code>SetValue()</code>. Using them didn't help anyway.</p> <p>If I don't call <code>SetValue()</code>, then my canvas appears (and child objects I've added to it) in the SL app as you might expect, in the very top left.</p> <p>If I create and position a <code>Canvas</code> object in Expression Blend, then the XAML generated includes <code>Canvas.Left</code> and <code>Canvas.Top</code> property values on the <code>Canvas</code> itself, as I would expect, so it seems to me that what I'm trying in C# should work.</p> <p>But I don't seem to be able to set the left/top values myself from C# without the SL in the browser going all weird.</p> <p>Any ideas?</p> <p><em>Edit: my approach is correct, but canvas coords need to be floating point, not integer - see accepted answer for details.</em></p>
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