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'MediaElement.SetSource()' isn't updating consistently

My program should play a video when the user presses the 'Play' button. While it normally does this, the very first time they press the 'Play' button nothing will happen.
I have traced this bug back to the following code, which sets my MediaElement 'VideoPlayer':
public void playVideo_Tapped(object sender, TappedRoutedEventArgs e)
{
setUpVideo();
VideoPlayer.Play();
}
public async void setUpVideo()
{
if(vm == null) return;
StorageFile videoFile = vm.videoFile;
if (videoFile == null || !videoFile.ContentType.Equals("video/mp4")) return;
using (IRandomAccessStream fileStream = await videoFile.OpenAsync(FileAccessMode.Read))
{
VideoPlayer.SetSource(fileStream, videoFile.ContentType);
}
}
The culprit seems to be the 'SetSource()' method at the end. The only variable that changes from the first click of 'Play' to the next is the variable 'VideoPlayer.PlayToSource', which is changed from null to a real value.
(As a side note, the variable 'VideoPlayer.CurrentState' also changes from 'Closed' to 'Opening' but resets itself to 'Closed' before the second click. Only 'PlayToSource' changes the functionality.)
I figured that I could do a quick-fix by doing this in my first method:
setUpVideo();
setUpVideo();
VideoPlayer.Play();
Not great code but it ought to set things straight, right? Nope! This causes a NullReferenceException. On the second call to 'setUpVideo()' I find that 'PlayToSource' still has a value and 'VideoPlayer.CurrentState' is still set to 'Opening'... which somehow triggers the NullReferenceException.
I'm expecting the solution to be one of the following things:
1.) Set 'VideoPlayer.PlayToSource' on the first click before calling 'SetSource'.
2.) In the quick-fix, set 'VideoPlayer.CurrentState' back to 'Closed' in between calls.
3.) Some other thing that mimics what the first click is doing.
Of course, both of my ideas involve changing a read-only variable. Which is where I'm getting stuck. I'll include the .xaml code for good measure, but I'm confident that it's the method 'SetSource' that's the root of my troubles:
<Grid x:Name="VideoViewerParentGrid" Background="DarkGreen" Height="{Binding VideoViewerParentGridHeight }" Width="{Binding VideoViewerParentGridWidth}">
<MediaElement x:Name="VideoPlayer" HorizontalAlignment="Center" VerticalAlignment="Bottom" Stretch="Uniform"
Visibility="{Binding VideoVisibility, Converter={StaticResource visibilityConverter}}"/>
<Button Style="{StaticResource BackButtonStyle}" Tapped="VideoViewerClose_Tapped" HorizontalAlignment="Left" VerticalAlignment="Top"/>
<Button Name="Play_Button" Content="Play Video" FontSize="26" Tapped="playVideo_Tapped"
VerticalAlignment="Top" HorizontalAlignment="Left" Height="60" Width="180" Margin="0,80,0,0"/>
</Grid>
---- UPDATE ----
Some more poking has revealed that on the first click 'VideoPlayer.CurrentState' never reaches the 'Playing' state, instead going from 'Opening' right back to 'Closed'. It does not do this on any subsequent clicks for as long as the program is running. Still investigating the cause of this.

You are missing the "await" keyword. Do this:-
await setUpVideo();

Short version, this issue is fixed by changing this:
using (IRandomAccessStream fileStream = await videoFile.OpenAsync(FileAccessMode.Read))
{
VideoPlayer.SetSource(fileStream, videoFile.ContentType);
}
...to be this:
IRandomAccessStream fileStream = await videoFile.OpenAsync(FileAccessMode.Read);
VideoPlayer.SetSource(fileStream, videoFile.ContentType);
Longer version, my code was failing because of the error "mf_media_engine_err_src_not_supported hresult - 0xc00d36c4", which was closing my MediaElement instead of playing it. This was happening because when I left the 'using' block of code the 'IRandomAccessStream' would close in the middle of my reading of the file. I'm not 100% clear why it gets through the whole thing after the first run of the code, but at least it now works reliably.
I've also got to give credit where credit is due, and I found this answer here: Windows 8 app - MediaElement not playing ".wmv" files

Metro application directly focuses on my first field

I'm creating this test Metro application using Windows 8, VS2012, C# and XAML. There are different TextBox in the application page arranged in a StackPanel. When the application is launched the focus is on the first TextBox.
I was wondering how to "deactivate" this.
Here's a pic, as you can see the first field is focused (color changed and ToolTip displayed).

When your UI is loaded you can remove focus from the TextBox by applying a Programmatic focus state to any other control.
Imagine that you have a Button named myButton. You can:
myButton.Focus(FocusState.Programmatic);
You cannot however use FocusState.Unfocused state to remove focus from the TextBlock because it is not allowed and will throw an exception.

One simple fix for this is place something to catch it first with IsTabStop="True" with a 0 Opacity which is a bit hacky but the only way I know. So something like;
<TextBox IsTabStop="True" Opacity="0" Height="1" Width="1"/>
<!-- Then the rest of your content like your other TextBox stuff -->

Windows 8 Data Binding

I'm developing an application using C# and XAML and I've encountered a problem that is confusing me. I have a property in my data called GroupImage and have used binding to set the Source property of an Image with it. That worked fine but when I wanted to do the same thing a second time it doesn't show the image in the second Image control.
<Image Source="{Binding Group.GroupImage}" Width="250" Height="500" Stretch="UniformToFill" />
<Image VerticalAlignment="Bottom" Stretch="UniformToFill" Source="{Binding Group.GroupImage}" Grid.RowSpan="2"/>
The top one works fine the bottom one doesn't. I have been reading about Data Binding and have gotten the impression that you need to specify something in the DataContext to use a property more than once. Is this right? It seems a very strange way of doing this.
I am relatively new to C# so sorry if I'm missing something obvious. I'd appreciate a more knowledgeable cluing me in.
Thanks
Update Following the assistance I received I figured out that the context was being set to
DataContext="{Binding Group}"
And as a result my second line needed to change to the following since the Data Context was already set to Group.
<Image VerticalAlignment="Bottom" Stretch="UniformToFill" Source="{Binding GroupImage}" Grid.RowSpan="2"/>

You don't need to specify something in the DataContext to use a property more than once. But your two Image have to have the right DataContext (you can easily test it with the debugger), depending on their location on the visual tree (You didn't provide any code for the DataContext part ?) .
You can also check that your Image's Width/Height are not 0.

Nullpointer error on event listeners when using StaticResource and MouseDown handler

I have a very odd error case that sprung up the moment I used a StaticResource converter on a Rectangle for coloring its background and at the same time using a MouseDown handler on another component next to it within a DataTemplate. If I narrow the code down a bit, this is what is required to reproduce the error :
In the top I have these resources, one pointing to a converter that takes the boolean from the binding and converts it to a fill background color):
<Window.Resources>
<vm:DesktopViewModel x:Key="DesktopVM" />
<vm:BooleanToColorConverter x:Key="converter" />
</Window.Resources>
And later in the same xaml file I iterate over a list of Alarm objects using this (I have replaced a Grid layout with a StackPanel and removed some other components for shorter code sample, this code snippet below still fails):
<ItemsControl ItemsSource="{Binding Alarms}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel>
<Rectangle Height="20" Stroke="Black" Width="20" RadiusX="4" RadiusY="4" Fill="{Binding Alarm, Converter={StaticResource converter}}"/>
<Image Source="/MyNamespace;component/images/chart.png" Stretch="None" MouseDown="Image_MouseDown" Cursor="Hand"/>
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
If I remove the MouseDown handler on the image it runs just fine without the nullpointer error in the start. If I remove the Fill tag in the Rectangle the code works just fine WITH the MouseDown handler!!! (and the handler works just fine too). It seems like the StaticResource reference in Fill is messing up something that makes locating the mouse handler function fail?!?
Note that it fails when the window is created, not while running or clicking anything.
Edit: I had the same nullpointer issue if I replaced the converter with a style using a StaticResource with triggers to do the same as the converter. Its pretty clear that the StaticResource reference in an attribute is the culprit but I have no idea why it should affect the event listener.
Also the order of the compoents dont matter either. If I place the Image before the Rectangle the error is exactly the same.

My guess is that the problem is in your converter code, that it does not take into account that it can get a null value.
Why the effect of the mouseDown? Probably it causes the rendering of the image element at an earlier moment and to request the value of the Fill property at a moment that your ViewModel has not been created yet.
There is too little information to state it with certainty, but converters that do not handle null values properly can be a major pain in WPF development in my experience. A lot of design time instability has had root in converters that did not handle the null values properly.

Can't Update WPF ProgressBar (not the standard tight-loop issue)

I am trying to use the ProgressBar as a representation of a percent value (I have not found an alternative control that looks right).
I am trying to set the value. It is my understanding that just setting the Value property should work, and update the control when my current event handler ends and control passes back to the UI.But no matter what I set the value to, the bar stays empty.
Here is my XAML:
<ProgressBar Name="LevelProgress" Maximum="100" Minimum="0" />
and my C#:
LevelProgress.Value = 43.0;
I have also tried:
LevelProgress.SetValue(ProgressBar.ValueProperty,43.0);
Even setting the Value property in the XAML definition does not work.
I really don't want to have to setup some big background thread thing just to set this value. Can anyone recommend a solution, or an alternative control?

Works for me
Do you
InitializeComponent();
Before?
LevelProgress.Value = 43.0;
I put it in the Loaded event and it worked there.
And I tried
<ProgressBar Name="LevelProgress" Maximum="100" Minimum="0" Value="43" />
And it works there. Something is wrong with the progress bar.