Develop Reference

Change Font Size of all UI Elements in using Static Resource from App.xaml in WPF

I'm need to change the font size of all text across the application.
I have tried doing as follows, but that doesn't work:-
<Style x:Key="fontsize" TargetType="{x:Type FrameworkElement}">
<Setter Property="Control.FontSize" Value="20"/>
</Style>
<Style TargetType="{x:Type FrameworkElement}" BasedOn="{StaticResource fontsize}"/>
When I try setting as follows then that works fine but doesn't get applied to all elements & needs to apply that for all different types of elements aperately.
<Style TargetType="TextBlock" BasedOn="{StaticResource fontsize}"/>
<Style TargetType="TextBox" BasedOn="{StaticResource fontsize}"/>
<Style TargetType="DataGridCell" BasedOn="{StaticResource fontsize}"/>
<Style TargetType="MenuItem" BasedOn="{StaticResource fontsize}"/>
<Style TargetType="DatePicker" BasedOn="{StaticResource fontsize}"/>
Also I would like to ask that, is there a way that I can override the Global Style for a particular element, like Heading text should be of different size on a user control?

in App.xaml
<Style TargetType="TextBlock">
<Setter Property="FontSize" Value="20"/>
<Setter Property="FontWeight" Value="Bold"/>
</Style>

Create a global style for the window in App.xaml.
<Application.Resources>
<Style x:Key="WindowStyle" TargetType="{x:Type Window}">
<Setter Property="FontStyle" Value="Italic" />
<Setter Property="FontSize" Value="24" />
<Setter Property="Foreground" Value="Green"/>
</Style>
</Application.Resources>
and set that style for the required windows.
<Window x:Class="YourNamespace.MainWindow" Style="{StaticResource WindowStyle}".....>
for overriding the style for a usercontrol
<local:UserControl1>
<local:UserControl1.Style>
<Style TargetType="UserControl">
<Setter Property="FontSize" Value="10"/>
</Style>
</local:UserControl1.Style>
</local:UserControl1>

There are two controls this involves.
You're maybe thinking "hey what about this cell or that calendar".
Their templates show text in a textblock.
When you set Header on a menuitem or content on a label, you get a textblock generated.
You therefore "only" need to set style on both textblock and textbox:
<Application.Resources>
<ResourceDictionary>
<Style TargetType="TextBlock">
<Setter Property="FontSize" Value="20"/>
</Style>
<Style TargetType="TextBox">
<Setter Property="FontSize" Value="20"/>
</Style>
</ResourceDictionary>
</Application.Resources>
</Application>
Having said that.
As Clemens pointed out.
The Font size and styling dependency properties are marked as inherits, so if you just have mainwindow then you could just set on that.
It's not just "obvious" that a label ends up with a textblock in it when you set content though. Similarly a menuitem and header. Hence I thought it worth posting this answer.

How to repeat programming lines in XAML?

... by the term "programming lines" I mean parts of code .
I am currently creating an UI using c# and XAML. But the XAML code is getting longer and longer, so I realised that if I could somehow set inside the code or store separately, repeatable parts of code and use them every time I needed, the whole XAML code would be shorter and clearer.
For example, let's say that I have a specific label which I want to repeat in several points of the code:
<Label Name="myLabel" Content="something">
</Label>
How could I possibly apply and repeat that label inside my XAML code?

There is a quick example of how the XAML code can be shared between different views/windows. Create a ResourceDictionary, define the shared properties/styles/control templates, like this
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Style TargetType="{x:Type Label}">
<Setter Property="Foreground" Value="Black" />
<Setter Property="FontFamily" Value="Segoe UI" />
</Style>
<Style TargetType="{x:Type Button}">
<Setter Property="Foreground" Value="Black" />
<Setter Property="FontFamily" Value="Segoe UI" />
</Style>
<Style TargetType="{x:Type TextBox}">
<Setter Property="Foreground" Value="Black" />
<Setter Property="FontFamily" Value="Segoe UI" />
</Style>
<Style TargetType="{x:Type ScrollBar}">
<Setter Property="Foreground" Value="Black" />
<Setter Property="FontFamily" Value="Segoe UI" />
</Style>
<Style TargetType="Label" x:Key="TitleStyle" BasedOn="{StaticResource {x:Type Label}}">
<Setter Property="HorizontalContentAlignment" Value="Center"/>
<Setter Property="VerticalContentAlignment" Value="Center" />
<Setter Property="HorizontalAlignment" Value="Stretch" />
<Setter Property="VerticalAlignment" Value="Stretch"/>
<Setter Property="FontSize" Value="16" />
</Style>
</ResourceDictionary>
Than you can add this dictionary to App/Window MergedDictionaries to use them, like
<Window.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Styles.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Window.Resources>
Please, note that this is just a quick example to briefly explain the idea. You can also have look at Style.TargetType docs to see explanation between TargetType and x:Key in styles

Can I apply style to a view based on type of interface it inherits?

I have a style declared in my resource dictionary.
<Style TargetType="Window">
<Setter Property="Width" Value="500"/>
<Setter Property="Height" Value="300"/>
</Style>
<Style TargetType="Window">
<Setter Property="Width" Value="800"/>
<Setter Property="Height" Value="600"/>
</Style>
I want the first style to apply to views who inherit from IDialogWindow, and second style to apply to views that inherit from IMainWindow.
Edit: The idea is to enforce style based on type of window throughout entire application.

How to set attributes without overriding the Mahapps theme?

I'm using Mahapps for a GUI, however I want to set some attributes different than visual ones such as margins and verticalAlignment, so I added this to the UserControl.resources section
<Style x:Key="{x:Type TextBox}" TargetType="TextBox" BasedOn="{StaticResource ResourceKey={x:Type TextBox}}">
<Setter Property="Margin" Value="2"/>
<Setter Property="VerticalAlignment" Value="Center"/>
</Style>
However it overrides all the visual styles attributes of the TextBoxes, how can I just add those attributes without overriding all the visual styles settings?

give the style a key
<Style x:Key="myCustomTextBoxStyle"
TargetType="TextBox"
BasedOn="{StaticResource ResourceKey={x:Type TextBox}}">
<Setter Property="Margin" Value="2"/>
<Setter Property="VerticalAlignment" Value="Center"/>
</Style>
and use it where you need it
<TextBox Style={StaticResource myCustomTextBoxStyle} />
EDIT
or put it to the main resource dictionary of user control or window resource without a key
<Window.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
</ResourceDictionary.MergedDictionaries>
<Style TargetType="TextBox"
BasedOn="{StaticResource ResourceKey={x:Type TextBox}}">
<Setter Property="Margin" Value="2"/>
<Setter Property="VerticalAlignment" Value="Center"/>
</Style>
</ResourceDictionary>
</Window.Resources>
hope that helps

Setting foreground for whole Windows Phone's application

How to change foreground color for all controls in the application? I need to change color for: textboxes, textblocks, borders of buttons.
It will take too long to do it one by one (over 100 controls).

This is what styles are for. You can add styles in your app.xaml file. Something like:
<Application.Resources>
<Style TargetType="TextBlock">
<Setter Property="Foreground" Value="White" />
</Style>
<Style TargetType="TextBox">
<Setter Property="Foreground" Value="White" />
</Style>
</Application.Resources>

Assuming you are programming for Windows Phone 7.1 (Mango) or later, you can use a Style in your App.xaml file, add the following code inside your Application.Resources tag and customize as needed. The styles will be applied to all Pages in your application (you can still override individual properties directly in the corresponding element tags).
<Application.Resources>
<Style TargetType="Button">
<Setter Property="Foreground" Value="Red"/>
<Setter Property="FontSize" Value="20"/>
</Style>
<Style TargetType="TextBlock">
<Setter Property="Foreground" Value="Blue" />
</Style>
</Application.Resources>