XAML Combine styles going beyond BasedOn? - wpf

Question

Is there any way to combine mutliple styles in XAML to make a new style that has all of the desired settings?
For example (pseudo code);
<Style x:key="A">
...
</Style>
<Style x:key="B">
...
</Style>
<Style x:key="Combined">
<IncludeStyle Name="A"/>
<IncludeStyle Name="B"/>
... other properties.
</Style>
I know that there is a BasedOn property for styles, but that feature will only take you so far. I am really just looking for an easy way (in XAML) to create these 'combined' styles. But like I said before, I doubt it exists, unless anyone has heard of such a thing??

Answer 1

You can make a custom markup extensions that will merge styles properties and triggers into a single style. All you need to do is add a MarkupExtension-derived class to your namespace with the MarkupExtensionReturnType attribute defined and you're off and running.
Here is an extension that will allow you to merge styles using a "css-like" syntax.
MultiStyleExtension.cs
[MarkupExtensionReturnType(typeof(Style))]
public class MultiStyleExtension : MarkupExtension
{
private string[] resourceKeys;
/// <summary>
/// Public constructor.
/// </summary>
/// <param name="inputResourceKeys">The constructor input should be a string consisting of one or more style names separated by spaces.</param>
public MultiStyleExtension(string inputResourceKeys)
{
if (inputResourceKeys == null)
throw new ArgumentNullException("inputResourceKeys");
this.resourceKeys = inputResourceKeys.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
if (this.resourceKeys.Length == 0)
throw new ArgumentException("No input resource keys specified.");
}
/// <summary>
/// Returns a style that merges all styles with the keys specified in the constructor.
/// </summary>
/// <param name="serviceProvider">The service provider for this markup extension.</param>
/// <returns>A style that merges all styles with the keys specified in the constructor.</returns>
public override object ProvideValue(IServiceProvider serviceProvider)
{
Style resultStyle = new Style();
foreach (string currentResourceKey in resourceKeys)
{
object key = currentResourceKey;
if (currentResourceKey == ".")
{
IProvideValueTarget service = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));
key = service.TargetObject.GetType();
}
Style currentStyle = new StaticResourceExtension(key).ProvideValue(serviceProvider) as Style;
if (currentStyle == null)
throw new InvalidOperationException("Could not find style with resource key " + currentResourceKey + ".");
resultStyle.Merge(currentStyle);
}
return resultStyle;
}
}
public static class MultiStyleMethods
{
/// <summary>
/// Merges the two styles passed as parameters. The first style will be modified to include any
/// information present in the second. If there are collisions, the second style takes priority.
/// </summary>
/// <param name="style1">First style to merge, which will be modified to include information from the second one.</param>
/// <param name="style2">Second style to merge.</param>
public static void Merge(this Style style1, Style style2)
{
if(style1 == null)
throw new ArgumentNullException("style1");
if(style2 == null)
throw new ArgumentNullException("style2");
if(style1.TargetType.IsAssignableFrom(style2.TargetType))
style1.TargetType = style2.TargetType;
if(style2.BasedOn != null)
Merge(style1, style2.BasedOn);
foreach(SetterBase currentSetter in style2.Setters)
style1.Setters.Add(currentSetter);
foreach(TriggerBase currentTrigger in style2.Triggers)
style1.Triggers.Add(currentTrigger);
// This code is only needed when using DynamicResources.
foreach(object key in style2.Resources.Keys)
style1.Resources[key] = style2.Resources[key];
}
}
Your example would then be solved by going:
<Style x:key="Combined" BasedOn="{local:MultiStyle A B}">
... other properties.
</Style>
We have defined a new style named "Combined" by merging two other styles "A" and "B" within the built-in BasedOn attribute (used for style inheritance). We can optionally add other properties to the new "Combined" style as per usual.
Other Examples:
Here, we define 4 button styles, and can use them in various combinations with little repetition:
<Window.Resources>
<Style TargetType="Button" x:Key="ButtonStyle">
<Setter Property="Width" Value="120" />
<Setter Property="Height" Value="25" />
<Setter Property="FontSize" Value="12" />
</Style>
<Style TargetType="Button" x:Key="GreenButtonStyle">
<Setter Property="Foreground" Value="Green" />
</Style>
<Style TargetType="Button" x:Key="RedButtonStyle">
<Setter Property="Foreground" Value="Red" />
</Style>
<Style TargetType="Button" x:Key="BoldButtonStyle">
<Setter Property="FontWeight" Value="Bold" />
</Style>
</Window.Resources>
<Button Style="{local:MultiStyle ButtonStyle GreenButtonStyle}" Content="Green Button" />
<Button Style="{local:MultiStyle ButtonStyle RedButtonStyle}" Content="Red Button" />
<Button Style="{local:MultiStyle ButtonStyle GreenButtonStyle BoldButtonStyle}" Content="green, bold button" />
<Button Style="{local:MultiStyle ButtonStyle RedButtonStyle BoldButtonStyle}" Content="red, bold button" />
You can even use the "." syntax to merge the "current" default style for a type (context-dependent) with some additional styles:
<Button Style="{local:MultiStyle . GreenButtonStyle BoldButtonStyle}"/>
The above will merge the default style for TargetType="{x:Type Button}" with the two supplemental styles.
Credit
I found the original idea for the MultiStyleExtension at bea.stollnitz.com and modified it to support the "." notation to reference the current style.

Answer 2

You can use BasedOn property in style, for example:
<Style x:Key="BaseButtons" TargetType="{x:Type Button}">
<Setter Property="BorderThickness" Value="0"></Setter>
<Setter Property="Background" Value="Transparent"></Setter>
<Setter Property="Cursor" Value="Hand"></Setter>
<Setter Property="VerticalAlignment" Value="Center"></Setter>
</Style>
<Style x:Key="ManageButtons" TargetType="{x:Type Button}" BasedOn="{StaticResource BaseButtons}">
<Setter Property="Height" Value="50"></Setter>
<Setter Property="Width" Value="50"></Setter>
</Style>
<Style x:Key="ManageStartButton" TargetType="{x:Type Button}" BasedOn="{StaticResource BaseButtons}">
<Setter Property="FontSize" Value="16"></Setter>
</Style>
and use:
<Button Style="{StaticResource ManageButtons}"></Button>
<Button Style="{StaticResource ManageStartButton}"></Button>