WPF Trigger Properties

Question

I am fairly new to WPF and I am currently working with triggers. I have a question regarding a simple trigger. By simple trigger, I mean one that watches for a change in a dependency property and uses a setter to change the style.

Example:

<Style.Triggers>
    <Trigger Property="Control.IsFocused" Value ="True">
        <Setter Property=" Control.Foreground" Value =" DarkRed" />
    </Trigger>
</Style.Triggers>

All examples I have seen have used the following trigger properties:

• <Trigger Property="Control.IsFocused" Value ="True">
• <Trigger Property="Control.IsMouseOver" Value ="True">
• <Trigger Property="Button.IsPressed" Value ="True">

Question: Are these the only trigger properties available? If not, what others exist?

I have searched online but to no avail. Maybe someone could shed some light on this.

Solution 1

These are not the only properties that you can use in your Triggers, however, they are common examples because they are easily understandable and easy to demonstrate.

In truth, you can have your Trigger watch any DependencyProperty, but because it is "triggered" when the value changes (and matches the Value you tell it to watch for), it only makes sense to use properties that will change at runtime, often from user action (such as focus, mouse over, pressed, etc). Only certain DependencyProperties actual change value under these circumstances, so not all of them make sense to use in Triggers.

Microsoft has added several DependencyProperties to the standard controls so that you can easily create triggers based on changes. However you can also create your own controls with your own DependencyProperties and have triggers that respond when your custom DependencyProperties change.

Keep in mind, PropertyTriggers are only one flavor of Trigger in WPF. There are also EventTriggers and DataTriggers and MultiTriggers. These other triggers fire based on events or changes in data, or in the case of MultiTriggers multiple property (or data) values.

Is there something specific you're trying to do with Triggers? This other answer provides a good explanation of what each type of trigger does.

Solution 2

There are multiple types of triggers in WPF, but the two most commonly used are regular Triggers and DataTriggers

Both types of triggers will watch a value, and when it changes to match the specified Value then they apply your Style Setters.

Regular triggers can be used for any Dependency Property of the object. This includes properties like Text, Visibility, Background, etc in addition to the more commonly triggered properties that you specified: IsFocused, IsMouseOver, and IsPressed.

Note that per the MSDN page about Trigger.Property, you don't need to specify the class name prefix if the Style or Template containing the trigger has it's TargetType property set

An easy way to remember it is if you can bind the property, you can set a Trigger on it.

DataTriggers are triggers that watch a bound value instead of a Dependency Property. They allow you to watch a bound expression, and will react when that binding evaluates equal to your Value.

For example, you could set a DataTrigger on "{Binding Value}" or "{Binding ElementName=MyTextBox, Path=IsChecked}". You can even use Converters with DataTriggers, such as

<DataTrigger
    Binding="{Binding SomeInt, Converter={StaticResource IsGreaterThanZero}}"
    Value="True">

Solution 3

Use this code for better experience with trigger in wpf.

<Window x:Class="DataBinding.Trigger2"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Trigger2" Height="500" Width="500">
<Window.Resources>
    <Style TargetType="Button">
        <Style.Setters>
            <Setter Property="FontFamily" Value="Tahoma"></Setter>
            <Setter Property="FontSize" Value="15"></Setter>
            <Setter Property="FontWeight" Value="Bold"></Setter>
            <Setter Property="Height" Value="25"></Setter>
            <Setter Property="Width" Value="100"></Setter>

        </Style.Setters>
        <Style.Triggers>
            <Trigger Property="IsFocused" Value="True">
                <Setter Property="Background" Value="Purple"></Setter>
                <Setter Property="Foreground" Value="DarkCyan"></Setter>
                <Setter Property="FontFamily" Value="Franklin Gothic"></Setter>
                <Setter Property="FontSize" Value="10"></Setter>
                <Setter Property="FontWeight" Value="Normal"></Setter>
                <Setter Property="Height" Value="50"></Setter>
                <Setter Property="Width" Value="200"></Setter>
            </Trigger>
            <Trigger Property="IsMouseOver" Value="True">
                <Setter Property="Background" Value="Red"></Setter>
                <Setter Property="Foreground" Value="White"></Setter>
                <Setter Property="FontFamily" Value="Calibri"></Setter>
                <Setter Property="FontSize" Value="25"></Setter>
                <Setter Property="FontWeight" Value="Heavy"></Setter>
                <Setter Property="Height" Value="100"></Setter>
                <Setter Property="Width" Value="400"></Setter>
            </Trigger>
            <Trigger Property="IsPressed" Value="True">
                <Setter Property="Background" Value="Green"></Setter>
                <Setter Property="Foreground" Value="Violet"></Setter>
                <Setter Property="FontFamily" Value="Times New Roman"></Setter>
                <Setter Property="FontSize" Value="20"></Setter>
                <Setter Property="FontWeight" Value="Thin"></Setter>
                <Setter Property="Height" Value="250"></Setter>
                <Setter Property="Width" Value="250"></Setter>
            </Trigger>
        </Style.Triggers>
    </Style>
</Window.Resources>
<Button>It's a Magic.</Button>

Comments

[Dom]

So for regular triggers, there is no property like... Control.IsMouseDown?

[Rachel]

@Dom I just added an update to my answer. You don't need to include the class name prefix on the triggered property if you have the TargetType property set on the Style or Template containing the trigger. So if your TargetType has an IsMouseDown property, then you can set a trigger on IsMouseDown instead of using Control.IsMouseDown

[Rachel]

I forgot EventTriggers and MultiTriggers in my answer because I almost never use them. Thanks for reminding me! :)

[Brian S]

Don't forget EventTriggers.

[Brian S]

:). Agreed @Rachel, EventTriggers are far less common. I've probably only used them a handful of times.