c# - 如何通过 XAML、WPF 中的数据绑定(bind)设置 VisualState INITIALIZATION

Question

我想知道我可以用 XAML 做什么，以使用正确的 VisualState 初始化我的 UI 元素。 没有背后的代码。因为我知道如何使用 C# 代码来完成。

我的 UI 元素的 XAML 是这样的:

<Border x:Name="PART_Border" >

    <VisualStateManager.VisualStateGroups>
        <VisualStateGroup x:Name="CriticalnessStates">
            <VisualState x:Name="NonCritical"/>
            <VisualState x:Name="Critical"/>
        </VisualStateGroup>
    </VisualStateManager.VisualStateGroups>

    <i:Interaction.Triggers>

        <ei:DataTrigger Binding="{Binding IsCritical}" Value="False">
            <ei:GoToStateAction StateName="NonCritical"/>
        </ei:DataTrigger>

        <ei:DataTrigger Binding="{Binding IsCritical}" Value="True">
            <ei:GoToStateAction StateName="Critical"/>
        </ei:DataTrigger>

    </i:Interaction.Triggers>

</Border>

当 IsCritical 属性设置加载 UI 元素时，它工作得很好，但问题是，我需要该元素, 以加载正确的 VisualState；我的意思是，

IsCritical = true => 处于临界状态的元素加载
IsCritical = false => 元素在非临界状态下加载

通过 C# 代码隐藏文件是可行的，您可以为您的元素编写一个加载的事件处理程序，通过检查相应的 DataContext 属性来设置视觉状态。我想知道如何使用纯 XAML 完成此操作。

顺便说一下，ei 和 i 指向这些 XML 命名空间:

xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"

谢谢。

Answer 1

我实现了这个行为类:

using System;
using System.Windows;
using System.Collections.Generic;
using System.Windows.Interactivity;
using System.Windows.Markup;

[ContentProperty("Conditions")]
public class VisualStateInitializer : Behavior<FrameworkElement>
{
    private bool _useTransitions = true;
    public bool UseTransitions
    {
        get { return _useTransitions; }
        set { _useTransitions = value; }
    }

    public List<VisualStateCondition> Conditions { get; set; }

    public VisualStateInitializer()
    {
        Conditions = new List<VisualStateCondition>();
    }

    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.Loaded += AssociatedObject_Loaded;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
    }

    private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
    {
        if (AssociatedObject.DataContext == null)
            return;

        foreach (var item in Conditions)
        {
            var dataContextType = AssociatedObject.DataContext.GetType();
            System.Reflection.PropertyInfo propertyInfo;
            object value = null;

            var properties = item.PropertyName.Split('.');

            if (properties.Length > 1)
            {
                for (int i = 0; i < properties.Length; i++)
                {
                    if(value != null)
                    {
                        dataContextType = value.GetType();
                        propertyInfo = dataContextType.GetProperty(properties[i]);
                        value = propertyInfo.GetValue(value);
                    }
                    else
                    {
                        propertyInfo = dataContextType.GetProperty(properties[i]);
                        value = propertyInfo.GetValue(AssociatedObject.DataContext);
                    }
                }
            }
            else
            {
                value = AssociatedObject.DataContext.GetType().GetProperty(item.PropertyName).GetValue(AssociatedObject.DataContext);
            }

            if (value != null && value.Equals(item.Value))
                VisualStateManager.GoToElementState(AssociatedObject, item.DesiredState, UseTransitions);
        }
    }
}

VisualStateCondition 类是这样的:

public class VisualStateCondition
{
    /// <summary>
    /// The PropertyName to look for in the associated object's <see cref="FrameworkElement.DataContext"/>.
    /// </summary>
    public string PropertyName { get; set; }
    /// <summary>
    /// The Value to check for equality.
    /// </summary>
    public object Value { get; set; }
    /// <summary>
    /// The <see cref="VisualState.Name"/> that is desired for the condition.
    /// </summary>
    public string DesiredState { get; set; }
}

在正确的初始状态下初始化我的 View 类所需要做的就是定义 VisualStateConditions，如下所示:

注意=> xaml中的“i”命名空间是指BlendSdk的“System.Windows.Interactivity”xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"

<Border>

    <VisualStateManager.VisualStateGroups>
        <VisualStateGroup x:Name="CriticalnessStates">
            <VisualState x:Name="NonCritical"/>
            <VisualState x:Name="Critical"/>
        </VisualStateGroup>
    </VisualStateManager.VisualStateGroups>

    <i:Interaction.Behaviors>
        <viewHelpers:VisualStateInitializer>

            <viewHelpers:VisualStateCondition PropertyName="IsCritical" DesiredState="Critical">
                <viewHelpers:VisualStateCondition.Value>
                    <system:Boolean>
                        True
                    </system:Boolean>
                </viewHelpers:VisualStateCondition.Value>
            </viewHelpers:VisualStateCondition>

            <viewHelpers:VisualStateCondition PropertyName="IsCritical" DesiredState="NonCritical">
                <viewHelpers:VisualStateCondition.Value>
                    <system:Boolean>
                        False
                    </system:Boolean>
                </viewHelpers:VisualStateCondition.Value>
            </viewHelpers:VisualStateCondition>

        </viewHelpers:VisualStateInitializer>
    </i:Interaction.Behaviors>

</border>

其中 ViewHelpers 是我的 VisualStateInitializer 和 VisualStateCondition 类的命名空间。谁能提出更好的方法？

更新 1 => 编辑属性值检索，以便我们可以传递嵌套属性，例如:

<viewHelpers:VisualStateCondition PropertyName="X.Y.NestedProperty"
    Value="False"
    DesiredState="StateForNestedProperty"/>