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WPF ComboBox PreviewMouseDown

I have a combobox that is editable and a textbox.
<TextBox x:Name="textBox" HorizontalAlignment="Left" Height="23" Margin="86,149,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
<ComboBox x:Name="comboBox" HorizontalAlignment="Left" VerticalAlignment="Top" Width="120" Margin="282,150,0,0" IsEditable="True" PreviewMouseDown="ComboBox_PreviewMouseDown"/>
I don't understand why ComboBox_PreviewMouseDown does not trigger, when the focus is on the textbox and I click on the combobox. It just highlights the text in the combobox and sets the focus. Clicking in the combobox when it already has the focus, PreviewMouseDown fires.
Is that what's happening here? Why is a PreviewMouseDown in an unfocused combobox not working?

When ComboBox.IsEditable is set to True, the ComboBox internally sets the focus (and keyboard focus) to the edit TextBox to make it instantly available for text input. This makes total sense as the intention when clicking the edit TextBox is always to enter or edit some text. Otherwise, the user would have to click the TextBox twice to make it receive focus for text input (keyboard focus).
So, to prevent focus stealing, the author marked the MouseDown event as handled i.e. RoutedEventArgs.Handled is set to true. (This is the reason why most non-preview events are marked handled by most controls).
Also, the author wanted to prevent the moving of the caret when clicked into the edit TextBox for the first time (to give it focus): the PreviewMouseDown event's RoutedEventArgs.Handled will only be set to true, if the edit TextBox has no keyboard focus and the drop-down panel is closed. (That's why the second click into the TextBox will pass through to be handled by an added event handler).
To achieve the behavior you expect, you have to handle the UIElement.PreviewGotKeyboardFocus event or the attached Keyboard.PreviewGotKeyboardFocusevent on the ComboBox.
Alternatively register the event handler using the UIElement.AddHandler method and set the handledEventsToo parameter to true:
this.MyComboBox.AddHandler(
UIElement.PreviewMouseDownEvent,
new RoutedEventHandler(MyComboBox_PreviewMouseDown),
true);

I ran into this same issue myself. A simple and effective workaround is to wrap your ComboBox in a lightweight ContentPresenter, then attach your PreviewMouseDown handler to that, like so:
<ContentPresenter x:Name="MyComboBoxWrapper"
PreviewMouseDown="MyComboBoxWrapper_PreviewMouseDown">
<ContentPresenter.Content>
<ComboBox x:Name="MyComboBox" />
</ContentPresenter.Content>
</ContentPresenter>
Additionally, since this control gets the PreviewMouseDown event before the ComboBox does, you not only can use it to pre-process events before the ComboBox even sees them, but you can cut off the ComboBox entirely by setting the event arg's handled property to 'true.'
Works like a charm! No subclassing or other tricks needed and it only requires a lightweight control in the tree!
Notes
As some may have considered, technically you could attach the PreviewMouseDown event to any ancestor of your ComboBox, but you then may have to include logic in that handler to determine if you're actually clicking on the ComboBox vs something else.
By using an explicit ContentPresenter (an incredibly lightweight element that itself doesn't have any rendering logic. It simply hosts other elements), you now have a dedicated PreviewMouseDown handler just for this control. Plus, it makes it more portable should you need to move it around since the two items can travel together.

How to set focus to a textbox in a View (User control) selected by a tab view

This is a MVVM WPF Question., c#.
Within a Window I have a Tab control that looks like this
<TabControl TabStripPlacement="Top" >
<TabItem Style="{StaticResource Tabitemstyle}">
<TabItem.Header>
<Label Content="Home" Style="{StaticResource Tablablestyle}"/>
</TabItem.Header>
<v:HomePageView/>
</TabItem>
<TabItem ....
<v:OtherPageView/>
The trick is that there exists a textbox within the 2nd tab item that I wish to have input focus when the user selects the 2nd tab.
I've tried a few solutions, but the closest one so far (using data trigger style, or focused element) almost works:
I can see that the cursor is intended to be within the text box, but it doesn't blink. It seems the focus is still on the tab control in the outside window, not the text box element in the view that is defined by OtherPageView.xaml. When I hit tab once, it is all ok, but this is what I am trying to relieve the users of having to do.

I would use the code behind:
Listen to visibility changed event on the TabItem content (i.e., v:HomePageView)
Find the textbox UI element (you can simply give the textbox a name
in the xaml and refer to it from code behind)
Next, set focus on the text box using the UIElement.Focus() method
Finally if the keyboard did not focus , then use the
Keyboard.Focus(...) method to focus the keyboard on the textbox.

Remove WPF IsDefault

I have 3 conrtols placed on my Window in WPF, each control contains one or more TextBox and Button, when a new control is selected I would like to change the IsDefault to that button. What I am currently doing is when the TextBox's GotFocus event is fired, I change my Button to IsDefault. This works the first time but when I change from one control to another, and back to the first selected control the second controls IsDefault is still true and when enter is pressed it fires the Click event on the incorrect control.
Is there a way that i can clear all IsDefault properties on my window or what is a better solution to my current way of doing this? See image below for example, when enter is pressed the Button with "..." is fired instead of quick search.
XAML (Update)
<odc:OdcTextBox Text="{Binding AccountNumber, UpdateSourceTrigger=PropertyChanged}" MinWidth="100" Name="txtAccountNumber" Grid.Row="1" Grid.Column="1" VerticalAlignment="Center" Margin="{Binding TextMargin}">
<odc:OdcTextBox.Buttons>
<Button IsDefault="{Binding ElementName=txtAccountNumber, Path=IsKeyboardFocusWithin}" Width="30" Style="{StaticResource DionysusButton}" x:Name="btnCdv" Content="...">
</Button>
</odc:OdcTextBox.Buttons>
</odc:OdcTextBox>

<Button IsDefault={Binding IsKeyboardFocusWithin, ElementName=ThisGroupBox} />
EDIT:
Your code is slightly different in that you are providing buttons to some custom control. These buttons are declared in a different scope to where they end up (ie I assume they end up inside the OdcTextBox template somewhere). I suspect this is why WPF can't find the named element since that element is named in an outer scope.
You could try using RelativeSource to find the parent OdcTextBox instead:
<Button IsDefault="{Binding IsKeyboardFocusWithin, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type odc:OdcTextBox}}}"
Width="30" Style="{StaticResource DionysusButton}" x:Name="btnCdv" Content="...">

Similarly to how you're using the TextBox GotFocus event, you could do the inverse of this and use the LostFocus event to reset the IsDefault Property

ContentControl With ScrollViewer, Focus

In my Windows 8 Metro project, I'm using a class derived from ContentControl (let's call it MyControl) to present my content. Inside MyControl I have a ScrollViewer. Because I want my control to handle keyboard events, I need to be able to set the focus to my control. However, I also want the option to let the scrollviewer handle keyevents, such as arrow keys and PageUp/Down. More precisely, I want this to be an option that another programmer can turn on or off. This means that sometimes, I want MyControl to be a tab-stop, and sometimes I want ScrollViewer to be a tab-stop, but never both.
The issue is that I don't want to expose the inner workings of MyControl to other programmers. That is, they ideally should be able to use MyControl.IsTabStop and leave the logic of placing the actual tab-stop with my Control (to put in MyControl or ScrollViewer).
Is there any good way to achieve this, or do I somehow have to work around it by providing a separate function to make my control a tab stop?

If you look at my test XAML you'll see I'm doing nothing, yet the up/down keys in the TextBox work to go between lines of text and they scroll the ScrollViewer when there is no line of text to go to. This is likely achieved by the KeyDown handlers setting the e.Handled value to true when they don't want the key event to bubble up (as when the TextBox already handled it) and leaving it false when the event is not handled, which lets the ScrollViewer handle it. The event will always trigger on the TextBox if it has focus, but it bubbles up the visual tree if it is not handled. It does not seem that you have to do anything more than just deciding whether you want to mark the key events as handled or not.
<Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
<ScrollViewer
IsTabStop="True">
<Grid
Width="2000"
Height="2000">
<Button
Margin="149,342,0,311">
<Button>
<TextBox
AcceptsReturn="True"
Height="400"
Width="200"/></Button>
</Button>
</Grid>
</ScrollViewer>
</Grid>

(WP7DEV) Textbox background changes when typing

I have made a textbox in XAML, which goes like this:
<TextBox x:Name="search"
TextWrapping="Wrap"
VerticalAlignment="Top"
Margin="-12,-13,45,0"
Background="#FFB2B2B8"
BorderBrush="Transparent"
Foreground="White"
inputScope="Search"
SelectionForeground="#FF72BCE6" />
and whenever I tap on the textbox to write something, its background changes. How can I set the background so that it is always on the same color?

Make use of the focus event handler.
Edit: Explaining further,
attach an onfocus event handler to the textbox
in the method, set the background colour of the textbox to the colour you desire.
Expanded even further, in case you want to find out more on what i mean, check this out
http://www.limguohong.com/2012/09/windows-phone-7-textbox-on-focus-color/

You may try creating a new template and making the background color stay constant when focused.