In code-behind how can I override tabitem colors set by an application-wide theme?

问题

I change the background color of my TabItem conditionally in code behind. This works fine as long as no theme is set in the App.xaml. How can I change colors of a TabItem (in code) while keeping an application-wide theme?

Background:

I'm using a free WPF theme from Nukeation Reuxables. The theme is set in the Application.Resources section of my App.xaml:

<ResourceDictionary Source="/ReuxablesLegacy;component/Edge.xaml" />.

I'm trying to conditionally set the background color of a TabItem in code behind:

MyTabItem.Background = new SolidColorBrush(Colors.Gray);

The background color changes if I remove or comment out the App.xaml line that sets the theme. Why does the theme break my code? I'm changing the tab color (as data is loaded) to show which tabs contain data.

I'm aware that XAML and binding are typically used to change colors, but the solutions I've attempted seem overly complex. Here is my related StackOverflow question seeking an all XAML and binding solution. The answers given just raised more questions which I haven't found answers to.

Thanks in advance.

Edit:

The problem does not happen when changing the background of a button:

button1.Background = new SolidColorBrush(Colors.Red);

The button changes color as expected (while using an application-wide theme).

回答1:

It REALLY depends on how the theme itself is implemented. If the theme was using TemplateBinding to bind to the background color of the tab to the theme's controls, then your code behind solution would work. That is probably why your button properly changes background colors in your example.

You'll probably have to dig deep into the tab's style xaml, and modify it there first for the codebehind solution to work.

回答2:

If you look at the ControlTemplate of TabItem its Background property is bound to a internal resource it doesn't do TemplateBinding, I presume the theme has just given colors to it. For your code to work you have to restyle it.

 <Style TargetType="{x:Type TabItem}">
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate TargetType="{x:Type TabItem}">
                            <Grid>
                                <Border 
                Name="Border"
                Margin="0,0,-4,0" 
                Background="{TemplateBinding Background}"
                BorderBrush="{StaticResource SolidBorderBrush}" 
                BorderThickness="1,1,1,1" 
                CornerRadius="2,12,0,0" >
                                    <ContentPresenter x:Name="ContentSite"
                  VerticalAlignment="Center"
                  HorizontalAlignment="Center"
                  ContentSource="Header"
                  Margin="12,2,12,2"
                  RecognizesAccessKey="True"/>
                                </Border>
                            </Grid>
                            <ControlTemplate.Triggers>
                                <Trigger Property="IsSelected" Value="True">
                                    <Setter Property="Panel.ZIndex" Value="100" /> 
                                    <Setter TargetName="Border" Property="BorderThickness" Value="1,1,1,0" />
                                </Trigger>
                                <Trigger Property="IsEnabled" Value="False">
                                    <Setter TargetName="Border" Property="Background" Value="{StaticResource DisabledBackgroundBrush}" />
                                    <Setter TargetName="Border" Property="BorderBrush" Value="{StaticResource DisabledBorderBrush}" />
                                    <Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}" />
                                </Trigger>
                            </ControlTemplate.Triggers>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Style>

I have made two changes to the normal ControlTemplate, you can do the same to your theme.xaml.

Changed Background="{StaticResource LightBrush}" to Background="{TemplateBinding Background}"
Removed Background setter in IsSelected = True trigger.

回答3:

Unfortunately, this is a simple problem with no simple answer (that I have found so far). Taking a different path to satisfy users was my final solution.

Instead of attempting to change the TabItem Background color I simply change the TabItem Foreground color to Gray if NO data exists. I also add the word "Blank" like this: "Tab 1 Blank", "Tab 2 Blank", etc. This an effective solution to the original problem. I describe it in detail here.

来源：https://stackoverflow.com/questions/6861532/in-code-behind-how-can-i-override-tabitem-colors-set-by-an-application-wide-them

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