WPF框架，修改ComboBox控件背景色 ，为何如此困难？

直接修改Background属性不可行

修改控件背景颜色，很多人第一反应便是修改Background属性，但是修改过后便会发现，控件的颜色没有发生任何变化。
于是在网上搜索答案，便会发现一个异常尴尬的情况，要么就行代码简单但是并不管用，要么就是虽然管用，但是要添加一大堆的样式代码，而且修改的样式不仅是背景色，边框，字体，几乎所有的样式都被修改了。

我只想修改背景色这一个样式而已，就这么一个简简单单的要求，为什么要加这么多代码？
最气人的是，网上还没有单独修改背景颜色的方法。要改样式，就逼你全部一起修改。

这是wpf的模板的特性导致的，相比于修改全套的样式，保留原有样式仅仅修改背景色的话，反而要添加最多的代码，这也是为何网上目前没有仅修改背景色的方法。

控件的模板

在刚接触wpf的时候，你可能会认为这个和winform框架差不多，每个控件都是相互独立的。但是如果你了解了控件的模板，也就是ControlTemplate属性，你就会发现，wpf框架的页面布局方式，其实和html更像，绝大数控件，都是可以嵌套的。

这也是为何修改Background属性后，ComboBox的背景色没有变化。因为ComboBox.ControlTemplate属性默认值不为null，它里面自带的嵌套控件覆盖了你修改的背景颜色，所以最后展示出来，背景颜色没有任何变化。

但是，微软仅提供了设置新模板的方法，并没有提供修改原有默认模板的方法。
也就是说，要修改背景颜色，你就必须设计一套全新的模板，来替换掉原有的模板。这也是为什么网上提供的，修改背景颜色的方法，都连带着修改了所有的样式，因为从头设计模板，就意味着从头放置所有需要的嵌套控件，从头设计所有的样式。

唯一仅修改背景颜色的方式，便是将原有模板拷贝一份，在此基础上进行修改。

背景颜色修改

由于模板太大，这里建议放到单独的文件中。

<ComboBox Grid.Row="0" Template="{DynamicResource ComboBoxDiyTemplate}">
    <ComboBox.Resources>
        <ResourceDictionary Source="/Style/ComboboxDiy.xaml"/>
    ComboBox.Resources>
ComboBox>

然后在ComboboxDiy.xaml文件中修改背景颜色

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:theme="clr-namespace:Microsoft.Windows.Themes;assembly=PresentationFramework.Aero2">
    
    <LinearGradientBrush x:Key="ComboBox.Static.Background" EndPoint="0,1" StartPoint="0,0">
        <GradientStop Color="#FFF0F0F0" Offset="0.0"/>
        <GradientStop Color="#FFE5E5E5" Offset="1.0"/>
    LinearGradientBrush>
    <SolidColorBrush x:Key="ComboBox.Static.Border" Color="#FFACACAC"/>
    <SolidColorBrush x:Key="ComboBox.Static.Glyph" Color="#FF606060"/>
    <SolidColorBrush x:Key="ComboBox.Static.Editable.Background" Color="#FFFFFFFF"/>
    <SolidColorBrush x:Key="ComboBox.Static.Editable.Border" Color="#FFABADB3"/>
    <SolidColorBrush x:Key="ComboBox.Static.Editable.Button.Background" Color="Transparent"/>
    <SolidColorBrush x:Key="ComboBox.Static.Editable.Button.Border" Color="Transparent"/>
    <LinearGradientBrush x:Key="ComboBox.MouseOver.Background" EndPoint="0,1" StartPoint="0,0">
        <GradientStop Color="#FFECF4FC" Offset="0.0"/>
        <GradientStop Color="#FFDCECFC" Offset="1.0"/>
    LinearGradientBrush>
    <SolidColorBrush x:Key="ComboBox.MouseOver.Border" Color="#FF7EB4EA"/>
    <SolidColorBrush x:Key="ComboBox.MouseOver.Glyph" Color="#FF000000"/>
    <SolidColorBrush x:Key="ComboBox.MouseOver.Editable.Background" Color="#FFFFFFFF"/>
    <SolidColorBrush x:Key="ComboBox.MouseOver.Editable.Border" Color="#FF7EB4EA"/>
    <LinearGradientBrush x:Key="ComboBox.MouseOver.Editable.Button.Background" EndPoint="0,1" StartPoint="0,0">
        <GradientStop Color="#FFEBF4FC" Offset="0.0"/>
        <GradientStop Color="#FFDCECFC" Offset="1.0"/>
    LinearGradientBrush>
    <SolidColorBrush x:Key="ComboBox.MouseOver.Editable.Button.Border" Color="#FF7EB4EA"/>
    <LinearGradientBrush x:Key="ComboBox.Pressed.Background" EndPoint="0,1" StartPoint="0,0">
        <GradientStop Color="#FFDAECFC" Offset="0.0"/>
        <GradientStop Color="#FFC4E0FC" Offset="1.0"/>
    LinearGradientBrush>
    <SolidColorBrush x:Key="ComboBox.Pressed.Border" Color="#FF569DE5"/>
    <SolidColorBrush x:Key="ComboBox.Pressed.Glyph" Color="#FF000000"/>
    <SolidColorBrush x:Key="ComboBox.Pressed.Editable.Background" Color="#FFFFFFFF"/>
    <SolidColorBrush x:Key="ComboBox.Pressed.Editable.Border" Color="#FF569DE5"/>
    <LinearGradientBrush x:Key="ComboBox.Pressed.Editable.Button.Background" EndPoint="0,1" StartPoint="0,0">
        <GradientStop Color="#FFDAEBFC" Offset="0.0"/>
        <GradientStop Color="#FFC4E0FC" Offset="1.0"/>
    LinearGradientBrush>
    <SolidColorBrush x:Key="ComboBox.Pressed.Editable.Button.Border" Color="#FF569DE5"/>
    <SolidColorBrush x:Key="ComboBox.Disabled.Background" Color="#FFF0F0F0"/>
    <SolidColorBrush x:Key="ComboBox.Disabled.Border" Color="#FFD9D9D9"/>
    <SolidColorBrush x:Key="ComboBox.Disabled.Glyph" Color="#FFBFBFBF"/>
    <SolidColorBrush x:Key="ComboBox.Disabled.Editable.Background" Color="#FFFFFFFF"/>
    <SolidColorBrush x:Key="ComboBox.Disabled.Editable.Border" Color="#FFBFBFBF"/>
    <SolidColorBrush x:Key="ComboBox.Disabled.Editable.Button.Background" Color="Transparent"/>
    <SolidColorBrush x:Key="ComboBox.Disabled.Editable.Button.Border" Color="Transparent"/>
    <Style x:Key="ComboBoxToggleButton" TargetType="{x:Type ToggleButton}">
        "OverridesDefaultStyle" Value="true"/>
        "IsTabStop" Value="false"/>
        "Focusable" Value="false"/>
        "ClickMode" Value="Press"/>
        "Template">
            
                "{x:Type ToggleButton}">
                    
                    x:Name="templateRoot" Background="White" BorderBrush="{StaticResource ComboBox.Static.Border}" BorderThickness="{TemplateBinding BorderThickness}" SnapsToDevicePixels="true">
                        x:Name="splitBorder" BorderBrush="Transparent" BorderThickness="1" HorizontalAlignment="Right" Margin="0" SnapsToDevicePixels="true" Width="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}">
                            x:Name="arrow" Data="F1 M 0,0 L 2.667,2.66665 L 5.3334,0 L 5.3334,-1.78168 L 2.6667,0.88501 L0,-1.78168 L0,0 Z" Fill="{StaticResource ComboBox.Static.Glyph}" HorizontalAlignment="Center" Margin="0" VerticalAlignment="Center"/>
                        
                    
                    
                        
                            
                                "{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="true"/>
                                "{Binding IsMouseOver, RelativeSource={RelativeSource Mode=Self}}" Value="false"/>
                                "{Binding IsPressed, RelativeSource={RelativeSource Mode=Self}}" Value="false"/>
                                "{Binding IsEnabled, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                            
                            "Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Static.Editable.Background}"/>
                            "BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Static.Editable.Border}"/>
                            "Background" TargetName="splitBorder" Value="{StaticResource ComboBox.Static.Editable.Button.Background}"/>
                            "BorderBrush" TargetName="splitBorder" Value="{StaticResource ComboBox.Static.Editable.Button.Border}"/>
                        
                        "IsMouseOver" Value="true">
                            "Fill" TargetName="arrow" Value="{StaticResource ComboBox.MouseOver.Glyph}"/>
                        
                        
                            
                                "{Binding IsMouseOver, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                                "{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="false"/>
                            
                            "Background" TargetName="templateRoot" Value="{StaticResource ComboBox.MouseOver.Background}"/>
                            "BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.MouseOver.Border}"/>
                        
                        
                            
                                "{Binding IsMouseOver, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                                "{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="true"/>
                            
                            "Background" TargetName="templateRoot" Value="{StaticResource ComboBox.MouseOver.Editable.Background}"/>
                            "BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.MouseOver.Editable.Border}"/>
                            "Background" TargetName="splitBorder" Value="{StaticResource ComboBox.MouseOver.Editable.Button.Background}"/>
                            "BorderBrush" TargetName="splitBorder" Value="{StaticResource ComboBox.MouseOver.Editable.Button.Border}"/>
                        
                        "IsPressed" Value="true">
                            "Fill" TargetName="arrow" Value="{StaticResource ComboBox.Pressed.Glyph}"/>
                        
                        
                            
                                "{Binding IsPressed, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                                "{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="false"/>
                            
                            "Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Pressed.Background}"/>
                            "BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Pressed.Border}"/>
                        
                        
                            
                                "{Binding IsPressed, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                                "{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="true"/>
                            
                            "Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Pressed.Editable.Background}"/>
                            "BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Pressed.Editable.Border}"/>
                            "Background" TargetName="splitBorder" Value="{StaticResource ComboBox.Pressed.Editable.Button.Background}"/>
                            "BorderBrush" TargetName="splitBorder" Value="{StaticResource ComboBox.Pressed.Editable.Button.Border}"/>
                        
                        "IsEnabled" Value="false">
                            "Fill" TargetName="arrow" Value="{StaticResource ComboBox.Disabled.Glyph}"/>
                        
                        
                            
                                "{Binding IsEnabled, RelativeSource={RelativeSource Mode=Self}}" Value="false"/>
                                "{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="false"/>
                            
                            "Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Disabled.Background}"/>
                            "BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Disabled.Border}"/>
                        
                        
                            
                                "{Binding IsEnabled, RelativeSource={RelativeSource Mode=Self}}" Value="false"/>
                                "{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="true"/>
                            
                            "Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Disabled.Editable.Background}"/>
                            "BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Disabled.Editable.Border}"/>
                            "Background" TargetName="splitBorder" Value="{StaticResource ComboBox.Disabled.Editable.Button.Background}"/>
                            "BorderBrush" TargetName="splitBorder" Value="{StaticResource ComboBox.Disabled.Editable.Button.Border}"/>
                        
                    
                
            
        
    Style>
    <ControlTemplate x:Key="ComboBoxDiyTemplate" TargetType="{x:Type ComboBox}">
        <Grid x:Name="templateRoot" SnapsToDevicePixels="true">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"/>
                <ColumnDefinition MinWidth="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}" Width="0"/>
            Grid.ColumnDefinitions>
            <Popup x:Name="PART_Popup" AllowsTransparency="true" Grid.ColumnSpan="2" IsOpen="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource Mode=TemplatedParent}}" Margin="1" Placement="Bottom" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}">
                <theme:SystemDropShadowChrome x:Name="shadow" Color="Transparent" MinWidth="{Binding ActualWidth, ElementName=templateRoot}" MaxHeight="{TemplateBinding MaxDropDownHeight}">
                    <Border x:Name="dropDownBorder" Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}" BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}" BorderThickness="1">
                        <ScrollViewer x:Name="DropDownScrollViewer">
                            <Grid x:Name="grid" RenderOptions.ClearTypeHint="Enabled">
                                <Canvas x:Name="canvas" HorizontalAlignment="Left" Height="0" VerticalAlignment="Top" Width="0">
                                    <Rectangle x:Name="opaqueRect" Fill="{Binding Background, ElementName=dropDownBorder}" Height="{Binding ActualHeight, ElementName=dropDownBorder}" Width="{Binding ActualWidth, ElementName=dropDownBorder}"/>
                                Canvas>
                                <ItemsPresenter x:Name="ItemsPresenter" KeyboardNavigation.DirectionalNavigation="Contained" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            Grid>
                        ScrollViewer>
                    Border>
                theme:SystemDropShadowChrome>
            Popup>
            <ToggleButton x:Name="toggleButton" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Grid.ColumnSpan="2" IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource Mode=TemplatedParent}}" Style="{StaticResource ComboBoxToggleButton}"/>
            <ContentPresenter x:Name="contentPresenter" ContentStringFormat="{TemplateBinding SelectionBoxItemStringFormat}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" Content="{TemplateBinding SelectionBoxItem}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" IsHitTestVisible="false" Margin="{TemplateBinding Padding}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
        Grid>
        <ControlTemplate.Triggers>
            <Trigger Property="HasDropShadow" SourceName="PART_Popup" Value="true">
                <Setter Property="Margin" TargetName="shadow" Value="0,0,5,5"/>
                <Setter Property="Color" TargetName="shadow" Value="#71000000"/>
            Trigger>
            <Trigger Property="HasItems" Value="false">
                <Setter Property="Height" TargetName="dropDownBorder" Value="95"/>
            Trigger>
            <MultiTrigger>
                <MultiTrigger.Conditions>
                    <Condition Property="IsGrouping" Value="true"/>
                    <Condition Property="VirtualizingPanel.IsVirtualizingWhenGrouping" Value="false"/>
                MultiTrigger.Conditions>
                <Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
            MultiTrigger>
            <Trigger Property="ScrollViewer.CanContentScroll" SourceName="DropDownScrollViewer" Value="false">
                <Setter Property="Canvas.Top" TargetName="opaqueRect" Value="{Binding VerticalOffset, ElementName=DropDownScrollViewer}"/>
                <Setter Property="Canvas.Left" TargetName="opaqueRect" Value="{Binding HorizontalOffset, ElementName=DropDownScrollViewer}"/>
            Trigger>
        ControlTemplate.Triggers>
    ControlTemplate>
ResourceDictionary>