Advanced WPF Part 3 of 5: Styles in Windows Presentation Foundation

 

Styles

Styles give our applications and elements consistent look and feel. In this section we will see how style hooks up to the resource system and property system in WPF. We will also see how to specify triggers in styles and how to specify default and custom styles.

A style is a named group of settings that will define the elements will appear. As you can see in the image below the basic structure of style contains a list of setter elements which specify a target property and a value. A style provides a way to set properties of a type of element and in WPF these properties are Dependency properties.

 

WPF Styles

WPF Styles

Applying Style

All the elements in WPF have style property. Generally we use a resource reference in the elements style property however we can also set it inline. The main motive behind defining a style is that the same style will apply to multiple elements and will give consistent look and feel to the application. We can define style at the

  • Element scope
  • Window Scope
  • Application scope

We provide the x:key attribute to the style so that the elements can refer that resource.

 

WPF Applying Styles

WPF Applying Styles

We can also define the style as shown below by specifying the TargetType of the style and this style will automatically apply to all the elements that are of that type unless specified otherwise.

 

WPF Applying Styles

WPF Applying Styles

We can use this property of the styles to skin our applications by the use of resource dictionaries. We can put the styles defining target types in both the resource dictionaries and switch between then to change the theme of the application.

Extending Styles

In WPF we can define new styles that are using other styles as the starting point. This can be done by using the BasedOn property of a style. We can change or add the needed properties. You should remember that we cannot apply multiple custom styles to an element so this BasedOn property helps us.

 

WPF Extending Styles

WPF Extending Styles

Styles vs. Local Properties

When we set a property using a style it works the same way as setting the property any other way.

But there is something that only style can do and not properties. In a style we can add properties that do not match the target type as shown below. In this case the WPF elements will apply the property that makes sense and will ignore the rest of the properties.

 

WPF Styles vs. Local Properties

WPF Styles vs. Local Properties

 

Triggers

The styles support same range of triggers as control templates. However the targets of the trigger in style are the target elements whereas in the ControlTemplate the targets are the named elements.

 

WPF Triggers

WPF Triggers

Animation Property Trigger

As we have seen in the graphics section that the only trigger we set on an element is the Event trigger. We cannot set a Property trigger on an element directly so we can use style for this. That style can be inline or resource style.

 

Animation Property Trigger

Animation Property Trigger

Animation Event Triggers

As we can see in the image below we can also put event triggers in the style.

 

Animation Event Triggers

Animation Event Triggers

Items Container Style

When we are working with ItemsControls like the ListBox or a TreeView we generally define the DataTemplates for the ListBoxItem or a TreeViewItem to make use of DataBinding. When are not proving these specified conatiners to the items then WPF is doing that for us. This means WPF wraps the contents of DataTemplate in a ListBoxItem for a ListBox and in a TreeViewItem for a TreeView. Now, if we apply properties to these will not work well while working with Data Binding. So what we need to do is define the style of type ItemContainerStyle.

 

Items Container Style

Items Container Style

 

Items Container Style

Items Container Style

Styles, Templates and Controls

Styles enable controls to be visible by default. As we have seen in the previous sections that the controls depend on templates for their appearance. Also the controls get their templates form the themes\generic.xaml or theme specific resource dictionary. These default styles set much more than a template. We should hard code as less as possible about a control in the template. The default styles sets properties like default background, font, etc. As you can see in the image below we have applied a local style to a button but we have just set the font size where does the button get the other properties form?

 

WPF Styles, Templates and Controls

WPF Styles, Templates and Controls

So what’s happening is that the local style for the button is setting the font size for the button and default style sets all the other properties for this button. So both the styles are merged and used in the button.

Any questions comments or feedback is most welcome.

The Code for this post can be found here.

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