Develop Reference

UWP - Subclassing built-in controls and inheriting styling behaviors

Is it possible to subclass a control (AppBarToggleButton in my case) and "inherit" TargetType of the base class? What I want to achieve is to have a slightly customized AppBarToggleButton (with disabled auto-toggle behavior) put into CommandBar and make it look exactly as if it was regular AppBarToggleButton (i.e. receive style whatever is defined for AppBarToggleButton inside given command bar control template). They say, DefaultStyleKey should help, but it is inherited fine, but, alas, doesn't seem to participate in local style resolution/lookup.

I may need to subclass other controls for various purposes, so the ultimate goal here is to understand how local style resolution works internally and does target instance has any involvement in it or is it a completely external process.
In general, we need make Templated Control for custom AppBarToggleButton. When we make Templated Control with Visual Studio, it will generate Generic.xaml file in the Themes folder that used to declare the custom control's style. And the the custom control cs file like the following.
public sealed class CustomAppBarToggleButton : AppBarToggleButton
{
public CustomAppBarToggleButton()
{
this.DefaultStyleKey = typeof(CustomAppBarToggleButton);
}
}
If you don't want to edit the default style you could remove DefaultStyleKey line that used to binding current control with the style in the Generic.xaml file.
Open Generic.xaml file you will find the following. And it's empty style. If we want to do some small changes, you need copy the complete AppBarToggleButton style to replace it and edit the TargetType to local:CustomAppBarToggleButton. Then you can edit the style base on your requirement.
<Style TargetType="local:CustomAppBarToggleButton" >
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="local:CustomAppBarToggleButton">
<Border
Background="{TemplateBinding Background}"
BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}">
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
And if your want to make a new dependency property, please define it in the cs file then use TemplateBinding to bind the property in the style. For more please check this document.

For anyone still stumbling upon this. I managed to solve a similar issue, inheriting from Button, using the approach described here https://stackoverflow.com/a/71338869/10468107
Specifically, adding
<Style BasedOn="{StaticResource DefaultButtonStyle}" TargetType="local:MyButton" />
solved it for me. So maybe it works for other types as well, using {StaticResource Default<TYPE>Style}

I have a similar need and am wondering if the answer is still the same. I have extended the basic ComboBox control to meet some behavioral requirements.
class ExtendedComboBox : ComboBox
I want the ExtendedComboBox instances to inherit the latest platform styling but they are instead getting styled differently. The first of these is an ExtendedComboBox (square corners, larger glyph), while the second is a generic ComboBox (rounded corners, smaller glyph).
The requirement is to have the two combo boxes styled the same way. I am reluctant to create an explicit Style for ExtendedComboBox because then if the style for the generic ComboBox changes the ExtendedComboBox will no longer match. Is there some way to just inherit the standard style?

How to handle Click event on a custom WPF control composed of controls that don't have Click events

I am creating a custom ToolBar control that I will be able to use in my WPF application.
My CustomToolBar control is based on a StackPanel control and will contain multiple CustomToolBarButton controls.
My CustomToolBarButtons are based on a vertical StackPanel and contain an Image control and a Label control.
I want to programmatically create a Click event for my CustomToolBarButtons that will fire when Image or label gets clicked. Unfortunately, neither Image nor Label controls have Click events in WPF.
It's a surprise for me because I am used to WinForms controls and vast majority of them have Click events by default. Do I have to create custom Image and Label controls and create Click events for them or is there a cleaner and simpler way of doing this?
Thanks for any help!

Well, there's not a great and simple way using standard functionality. I got around this by making my own trigger (derived from System.Windows.Interactivity.TriggerBase from the Blend SDK) so that in my projects I can do the following:
<Label>
<i:Interaction.Triggers>
<mu:MouseTrigger MouseButton="Middle" MouseAction="Click">
<i:InvokeCommandAction Command="{Binding Path=Close}" />
</mu:MouseTrigger>
</i:Interaction.Triggers>
</Label>
Effectively the MouseTrigger class will handle MouseDown and MouseUp events from the UIElement it's attached to and use that to invoke the actions associated with the trigger. The code is a bit more complex than just that, though, since I also do mouse capturing & I utilize an internal helper class so that I could add multiple triggers to the same element with only one instance of a helper class handling events & capturing the mouse for that element.
For the actual actions, I just use existing Blend or Prism actions such as InvokeCommandAction.
Here is the project if you're interested. It was too large to paste into this format. It uses some C# 6.0 features but you could easily modify it to work on an older version of C# by removing some null conditional operators. It requires you install the Blend SDK as it depends on System.Windows.Interactivity (should install with Visual Studio as long as you select that option). MouseTrigger is the publicly visible class that is the point of interaction with the functionality. MouseCatcher is the internal helper class mentioned.
I'd recommend not going down the route of custom controls, but rather of using some mechanism (this one or otherwise) to extend the existing functionality using the attached property framework that WPF and XAML bring to the table.

In WinForms you would create custom controls simply to get a nonstandard look, in WPF this is no longer necessary.
The WPF way: instead of making a Stackpanel's children implement Click behaviour, let's make a Button look like the desired Stackpanel.
Could do this setting the Content:
<Button>
<StackPanel >
<Image Source="C:\myFiles\myPic.png"/>
<Label HorizontalAlignment="Center">SomeTxt</Label>
</StackPanel>
</Button>
But this way it still looks like a Button, to overcome this we can set the Template instead:
<Button>
<Button.Template>
<ControlTemplate TargetType="Button">
<StackPanel >
<Image Source="C:\myFiles\myPic.png"/>
<Label HorizontalAlignment="Center">SomeTxt</Label>
</StackPanel>
</ControlTemplate>
</Button.Template>
</Button>
Both solutions will raise a Click event clicking the image or label.

WPF - Access parent properties from internal control's part ControlTemplate trigger

Short question:
In case you have a control consisting of multiple parts (like DatePicker, which consists of PART_Root, PART_Button, PART_Textbox etc...), how can you bind a trigger of an inner part's control template to validity of the entire control?
Long question:
I am trying to customize the DatePicker control template, and it consists of several major parts, most importantly:
PART_Root
PART_Button
PART_TextBox
I am overriding the template of PART_TextBox by targeting DatePickerTextBox with a style, which in essence replaces only the PART_TextBox content of DatePicker.
Now, I want to implement some special custom validation elements in the control template of PART_Textbox, but I am unable to trigger them to show. I have tried using
<DataTrigger Binding="{Binding Path=Validation.HasError, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DatePicker}}}">
but for some reason it does not work...

Please be sure that the object that you are binding implements the interface INotifyDataErrorInfo. For an example on the implementation see here

customize Style CheckList RadTreeView

Is there a way to change the style of checkboxes when the ItemsOptionListType="CheckList"
inside a RadTreeView?

There are a couple of ways of doing this that I can think of, but sadly neither of them is particularly easy.
One way is to use Blend or a similar tool to obtain the template for the RadTreeViewItem class. The RadTreeViewItem class and its template are in the Telerik.Windows.Controls.Navigation assembly. Take a copy of this template and modify the CheckBox within this template to customise its appearance as you wish.
To use the template, add a ControlTemplate and a Style to the <UserControl.Resources> element of a XAML page, as follows:
<UserControl.Resources>
<ControlTemplate x:Key="myRadTreeViewItemTemplate" TargetType="telerik:RadTreeViewItem">
<!-- modified template goes here... -->
</ControlTemplate>
<Style TargetType="telerik:RadTreeViewItem">
<Setter Property="Template" Value={StaticResource myRadTreeViewItemTemplate}" />
</Style>
</UserControl.Resources>
This should then apply the modified template to any RadTreeViews in the same XAML file.
Note that we have to use an implicit style (i.e. one without an x:Key), since there seems to be no other way to tell a RadTreeView to apply a given style to its child items.
Alternatively, you can modify a built-in theme. This approach could also change the styles of CheckBoxes used within other Telerik controls in your application, for example in a GridViewCheckBoxColumn within a RadGridView.
EDIT: if you want the template for the CheckBox as used in the RadTreeView by default,
you'll find it in Themes\Office\Black\System.Windows.Controls.xaml within the Telerik.Windows.Controls assembly. This assumes you're using the 'Office Black' theme; adjust the path of this file if you're using a different Telerik theme.

Difference between Style and ControlTemplate

Could you tell me what is the main differences between Style and ControlTemplate ?
When or why to use one or the other ?
To my eyes, they are exactly the very same. As I am beginner I think that I am wrong, thus my question.

In a style you set properties of a control.
<Style x:Key="MyButtonStyle" TargetType="Button">
<Setter Property="Background" Value="Red"/>
</Style>
<Button Style="{StaticResource MyButtonStyle}"/>
All buttons that use this style will have their Backgrounds set to Red.
In a template you define the UI (structure) of the control.
<ControlTemplate x:Key="MyButtonTemplate" TargetType="Button">
<Grid>
<Rectangle Fill="Green"/>
<ContentPresenter/>
</Grid>
</ControlTemplate>
<Button Template="{StaticResource MyButtonTemplate}"/>
All buttons that use this template will have a green background that cannot be changed.
Values set in a template can only be replaced by replacing the entire template. Values in a style can be replaced by setting the value explicitly when using the control. That is why is better to use the properties of the control by using TemplateBinding instead of coding values.
<ControlTemplate x:Key="MyButtonTemplate" TargetType="Button">
<Grid>
<Rectangle Fill="{TemplateBinding Background}"/>
<ContentPresenter/>
</Grid>
</ControlTemplate>
Now the template uses the value of the Background property of the button it is applied to, so it can be customized:
<Button Template="{StaticResource MyButtonTemplate}" Background="Yellow"/>
Another useful feature is that controls can pick up a default style without having a specific style being assigned to them. You can't do that with a template.
Just remove the x:Key attribute of the style (again: you can't do this with templates). All buttons in the visual tree below the style will have this style applied.
Combining Templates and Styles is extra powerful: you can set the Template property in the style:
<Style TargetType="Button">
<Setter Property="Background" Value="Red"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="Button">
<Grid>
<Rectangle Fill="{TemplateBinding Background}"/>
<ContentPresenter/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

No indeed you are quite wrong.
Styles set properties on controls. ControlTemplate is a property shared by most controls that specify how they are rendered.
To elaborate, you can use a style to group settings for a bunch of properties so you can re-use that to standardize your controls. Styles can be set explicitly on controls or applied too all of a certain type.
Control Templates can be set by a style or set explicitly on a control to change the way it appears. All controls have default templates (and styles for that matter) that are embedded in the .net wpf assemblies. It is quite enlightening to see these and understand how the wpf developers implemented the normal versions of all controls. If you have Expression blend installed, look in its "SystemThemes" folder.
UPDATE:
To understand how Styles and ControlTemplates can "add controls". In some way or another, the ControlTemplate is the only way to define the controls a control is made up of. But, some default .net controls allow you to use controls in place of text.
For example:
<GroupBox>
<GroupBox.Header>
<CheckBox/>
</GroupBox.Header>
</GroupBox>
This "adds" a checkbox to the groupbox without changing the ControlTemplate, but this is because the default ControlTemplate for GroupBox allows anything as the Header. This is done by using special controls such as ContentPresenter.
However, sometimes the default ControlTemplate for a control doesn't allow you to change something that you want to change via properties. Then you must change the ControlTemplate.
Whether you set the Properties of a control (Content, Header, ControlTemplate, IsEnabled, etc.) directly or via a style does not matter, Styles are only a convenience.
Hopefully this answers your question more clearly.

You can think of a Style as a convenient way to apply a set of property values to more than one element. You can change the default appearance by setting properties, such as FontSize and FontFamily, on each TextBlock element directly. However, if you want your TextBlock elements to share some properties, you can create a Style in the Resources section of your XAML file.
On the other hand, a ControlTemplate specifies the visual structure and visual behavior of a control. You can customize the appearance of a control by giving it a new ControlTemplate. When you create a ControlTemplate, you replace the appearance of an existing control without changing its functionality. For example, you can make the buttons in your application round instead of the default square shape, but the button will still raise the Click event.
Ref: http://msdn.microsoft.com/en-us/library/ms745683.aspx

I found some interesting differences in
The difference between styles and templates (msdn)
Style:
You can set only pre-existing properties in the style. For example, you cannot set a default value for a property that belongs to a new part that you added to the template.
Template:
When you modify a template, you have access to more parts of a control than when you modify a style. For example, you can change the way the pop-up list appears in a combo box, or you change the look of the button that triggers the pop-up list in the combo box by modifying the items template.
Style:
You can use styles to specify the default behavior of a control. For example, in a style for a button, you can specify a trigger so that when users move their mouse pointer over the button, the background color will change. These property changes are instantaneous (they cannot be animated gradually).
Template:
You can specify the behavior of any new and existing parts in a template by using triggers. For example, you can specify a trigger so that when users move their mouse pointer over a button, the color of one of the parts will change. These property changes can be instantaneous or animated gradually to produce a smooth transition.

OK, I had the exact same question and the answers I found in this thread pointed me in the right direction so I'm sharing, if only so I can understand it better myself.
A Style is more flexible than a ControlTemplate.
From Windows Presentation Foundation Unleashed, Adam Nathan and gang (writers) state this:
"Besides the convenience of combining a template [with a style using the Style's ControlTemplate setter] with arbitrary property settings, there are important advantages of doing this [setting the ControlTemplate setter on a style]:
It gives you the effect of default templates. For example, when a typed Style gets applied to elements by default, and that Style contains a custom control template, the control template gets applied without any explicitly markings on those elements.
It enables you to provide default yet overridable property valus that control the look of the template. In other words, it enables you to respect the templated parent's properties but still provide your own default values."
In other words, creating a style allows the user of the Style's Template setter to override the values set, even if they did not use a TemplateBinding ({TemplateBinding Width} for example). If you hardcoded the Width in your style, the user of the Style could still override it, but if you hardcoded that Width property in a Template, the user is stuck with it.
Also, (and this is kind of confusing) when using a ContentTemplate with a TemplateBinding the onus is on the user to set that property otherwise it will use the default property for the TargetType. If you use a style, you can override the default property of the TargetType by using a setter for the property and then applying a TemplateBinding referencing back to that setter. The book explains it better, page 338 (Mixing Templates with Styles)