Question

I have a simple WPF window that has 12 buttons on it. I want the same style to be applied to all of them. This code produces the same error:

<Window x:Class="TestApp.TestWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="TestWindow" Height="400" Width="500"
        WindowStyle="None" WindowState="Maximized">
    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="Resources/AllResources.xaml"/>
                <ResourceDictionary>
                    <Style TargetType="{x:Type Button}">
                        <Setter Property="FontSize" Value="100"/>
                    </Style>
                </ResourceDictionary>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Window.Resources>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <Button Grid.Column="0" Content="1" Name="Button1"/>
        <Button Grid.Column="1" Content="2" Name="Button2"/>
    </Grid>
</Window>

The first button does not get the style applied to it, but the second one does. I could set a key and use that on every button, but I would prefer to let WPF handle that for me. I just found out while writing this that when I do not include the outside ResourceDictionary, it works as expected. This will be a problem in the future as my application expands as I have multiple windows that need to share the same resources. The modified code is as follows:

<Window x:Class="TestApp.TestWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="TestWindow" Height="400" Width="500"
        WindowStyle="None" WindowState="Maximized">
    <Window.Resources>
        <Style TargetType="{x:Type Button}">
            <Setter Property="FontSize" Value="100"/>
        </Style>
    </Window.Resources>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <Button Grid.Column="0" Content="1" Name="Button1"/>
        <Button Grid.Column="1" Content="2" Name="Button2"/>
    </Grid>
</Window>

It also works if I (instead of removing the merged dictionaries) add an x:Key=”key” attribute and then explicitly assign that style to each button.

What is the issue here? Why does the first one skip “Button1” and the second not?

Answer 1

I’ve seen this problem a couple of times before and it’s a pretty weird “bug”. It happends when you put a Style directly in a ResourceDictionary inside <ResourceDictionary.MergedDictionaries>. The Style is skipped for the first item. This code produces the same result, the Style is skipped for the first ListBoxItem

<Window.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary>
                <Style TargetType="{x:Type ListBoxItem}">
                    <Setter Property="Foreground" Value="Green"/>
                </Style>
            </ResourceDictionary>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Window.Resources>
<ListBox>
    <ListBoxItem Content="Item 1"/>
    <ListBoxItem Content="Item 2"/>
    <ListBoxItem Content="Item 3"/>
</ListBox>

To get both the styles and MergedDictionaries to work, do it like this instead

<Window.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="Resources/AllResources.xaml"/>
        </ResourceDictionary.MergedDictionaries>
        <Style TargetType="{x:Type Button}">
            <Setter Property="FontSize" Value="100"/>
        </Style>
    </ResourceDictionary>
</Window.Resources>
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition/>
        <ColumnDefinition/>
    </Grid.ColumnDefinitions>
    <Button Grid.Column="0" Content="1" Name="Button1"/>
    <Button Grid.Column="1" Content="2" Name="Button2"/>
</Grid>