如何公开内部控件的样式？

Question

The problem seems easy: I have a UserControl , my control contains a Button .

Button elements can be styled. But I don't want to have style definitions in my control. My control doesn't even have XAML. All I want to set style like this in XAML:

<Style TargetType="local:MyControl">
    <Setter Property="ItsButton.Padding" Value="8" />
</Style>

It doesn't work that way. How does it work? I know I can bind any internal control's properties to my UserControl dependency properties and it will work. However it's overkill to bind many properties, does it really require so much coding to do the simple thing, or is it an easier / quicker / simpler way?

BTW, it doesn't look like an overkill to you, imagine I have many internal controls like button, let's say InputBox es and such.

Here's the example control code:

class Installable : UserControl {

    public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
        "Value",
        typeof(object),
        typeof(Installable),
        new FrameworkPropertyMetadata(OnValueChanged));

    public static readonly DependencyProperty InstallButtonProperty = DependencyProperty.Register(
        "InstallButton",
        typeof(Button),
        typeof(Installable),
        new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.None));

    public static readonly DependencyProperty InstallTextProperty = DependencyProperty.Register(
        "InstallText",
        typeof(string),
        typeof(Installable),
        new FrameworkPropertyMetadata(OnInstallTextChanged));

    public static readonly DependencyProperty CommandProperty = DependencyProperty.Register(
        "Command",
        typeof(ICommand),
        typeof(Installable),
        new FrameworkPropertyMetadata(OnCommandChanged));

    public static readonly DependencyProperty CommandParameterProperty = DependencyProperty.Register(
        "CommandParameter",
        typeof(object),
        typeof(Installable),
        new FrameworkPropertyMetadata(OnCommandParameterChanged));

    public object Value {
        get => GetValue(ValueProperty);
        set => SetValue(ValueProperty, value);
    }

    public Button InstallButton {
        get => (Button)GetValue(InstallButtonProperty);
        set => SetValue(InstallButtonProperty, value);
    }

    public string InstallText {
        get => (string)GetValue(InstallTextProperty);
        set => SetValue(InstallTextProperty, value);
    }

    public ICommand Command {
        get => (ICommand)GetValue(CommandProperty);
        set => SetValue(CommandProperty, value);
    }

    public object CommandParameter {
        get => GetValue(CommandParameterProperty);
        set => SetValue(CommandParameterProperty, value);
    }


    public Installable() {
        InstallButton = new Button();
        Content = Value ?? InstallButton;
        InstallText = "Install";
    }

    private static void OnValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
        var control = d as Installable;
        var value = e.NewValue;
        control.Content = value ?? control.InstallButton;
    }

    private static void OnInstallTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
        var control = d as Installable;
        var text = e.NewValue as string;
        control.InstallButton.Content = text;
    }


    private static void OnCommandChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
        var control = d as Installable;
        var command = e.NewValue as ICommand;
        control.InstallButton.Command = command;
    }

    private static void OnCommandParameterChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
        var control = d as Installable;
        var value = e.NewValue;
        control.InstallButton.CommandParameter = value;
    }

}

The control displays its Value when not null, InstallButton otherwise. Like if value unset - it contains button, when value set - contains value. The control works like charm, but when I set the Button style in MainWindow XAML, it doesn't affect the button within my UserControl .

Maybe my Button could somehow inherit style from Button style defined in MainWindow XAML?

Answer 1

The control Style may define a default Button Style in its Resources, which will automatically be applied to all of the control's Button child elements.

<Style TargetType="local:MyControl">
    <Style.Resources>
        <Style TargetType="Button">
            <Setter Property="Margin" Value="8"/>
        </Style>
    </Style.Resources>
</Style>