通用渲染局部视图 - 将 PropertyInfo 转换为具体对象

Question

我目前正在 MVC (c#) 中制作向导。但是我的向导视图中有一个 if 语句，如下所示：

if (Model.Wizard.ClientDetails.GetStep() == Model.Wizard.CurrentStep)
{
    @Html.PartialFor(x => x.Wizard.ClientDetails, "_Step");
}
else if (Model.Wizard.Preferences.GetStep() == Model.Wizard.CurrentStep)
{
    @Html.PartialFor(x => x.Wizard.ClientPreferences, "_Step")
}
else if (Model.Wizard.ClientQuestions.GetStep() == Model.Wizard.CurrentStep)
{
    @Html.PartialFor(x => x.Wizard.ClientQuestions, "_Step")
}

除了我选择显示哪个部分的视图的这一部分之外，向导的设置非常通用。从上面的代码可以看出，每个if 都遵循相同的结构。唯一改变的部分是Model.Wizard.**Property** 部分。

我想尝试删除此 if 语句，这样我就不必担心为添加到新向导的每个步骤编写 if 语句。

我想把代码改成这样：

@Html.PartialFor(x => x.ExampleWizardTransaction.GetStepObject(), "_Step");

我目前对GetStepObject方法的尝试如下：

public static T GetStepObject<T>(this IWizardTransaction wizardTransaction) 
     where T : class, new()
{
    var properties = wizardTransaction.GetType().GetProperties()
            .Where(x => x.PropertyType.GetCustomAttributes(typeof(StepAttribute), true).Any());

    PropertyInfo @object = properties.FirstOrDefault(x => ((StepAttribute)Attribute
            .GetCustomAttribute(x.PropertyType, typeof(StepAttribute))).Step == wizardTransaction.CurrentStep);

}

PropertyInfo @object 部件正在正确选择向导中当前步骤的属性信息。我需要能够将 PropertyInfo @object PropertyInfo 作为正确类型及其当前值返回并以某种方式返回。

这可能吗？

编辑#1：

现有的PartialFor 在正常情况下工作。

public static MvcHtmlString PartialFor<TModel, TProperty>(
    this HtmlHelper<TModel> helper, Expression<Func<TModel, TProperty>> expression, string partialViewName)
{
    var name = ExpressionHelper.GetExpressionText(expression);
    var model = ModelMetadata.FromLambdaExpression(expression, helper.ViewData).Model;
    var viewData = new ViewDataDictionary(helper.ViewData)
    {
        TemplateInfo = new TemplateInfo { HtmlFieldPrefix = name }
    };
    return helper.Partial(partialViewName, model, viewData);
}

编辑#2：

值未绑定的原因是var name = ExpressionHelper.GetExpressionText(expression); 部分返回一个空白字符串。如果我将name 变量硬编码为实际属性，则绑定有效。例如：

public static MvcHtmlString PartialFor<TModel, TProperty>(this HtmlHelper<TModel> helper,
    Expression<Func<TModel, TProperty>> expression, string partialViewName)
{
    var compiled = expression.Compile();
    var result = compiled.Invoke(helper.ViewData.Model);

    var name = ExpressionHelper.GetExpressionText(expression); 
    //Should be ExampleWizardTransaction.ClientDetails for this step but is blank

    var viewData = new ViewDataDictionary(helper.ViewData)
    {
        TemplateInfo = new TemplateInfo 
        { 
             //HtmlFieldPrefix = name
             HtmlFieldPrefix = "ExampleWizardTransaction.ClientDetails" 
        }
        //Hard coded this to ExampleWizardTransaction.ClientDetails and the bindings now work
    };

    return helper.Partial(partialViewName, result, viewData);
 }

看来我需要能够将向导对象的名称和当前步骤对象作为字符串值传递给TemplateInfo。

Answer 1

我要对你的班级结构进行疯狂的猜测。假设您的课程是这样的：

[AttributeUsage(AttributeTargets.Property, AllowMultiple =false)]
public class StepAttribute: Attribute
{
    public StepEnum Step { get; set; }
}

public interface IWizardStep
{

}

public interface IWizardTransaction
{

}

public enum StepEnum
{
    Previous,
    CurrentStep
}

public class WizardStep: IWizardStep
{
    public string StepName { get; set; }

    public override string ToString()
    {
        return StepName;
    }
}

public class Wizard : IWizardTransaction
{
    [Step(Step = StepEnum.Previous)]
    public WizardStep ClientDetails => new WizardStep() { StepName = "ClientDetails" };
    [Step(Step = StepEnum.CurrentStep)]
    public WizardStep ClientQuestions => new WizardStep() { StepName = "ClientQuestions" };
}

假设也实现了 PartialFor 方法

    public static MvcHtmlString PartialFor<TModel, TProperty>(this HtmlHelper<TModel> html, 
            Expression<Func<TModel, TProperty>> expression, string partialViewName)
    {
        var compiled = expression.Compile();
        var result = compiled.Invoke(html.ViewData.Model);
        return html.Partial(partialViewName, result);
    }

那么GetStepObject的这个实现就可以工作了

    public static TProperty GetStepObject<TProperty>(this IWizardTransaction wizardTransaction)
        where TProperty : class
    {
        var properties = wizardTransaction.GetType().GetProperties()
                .Where(x => x.GetCustomAttributes(typeof(StepAttribute), true).Any());
        PropertyInfo @object = properties.FirstOrDefault(x => 
                    (x.GetCustomAttributes(typeof(StepAttribute), true).SingleOrDefault()
                                as StepAttribute).Step == StepEnum.CurrentStep);
        return @object.GetValue(wizardTransaction) as TProperty;
    }

有了这个名为 _Step.cshtml 的局部视图的实现，像这样

@model PartialView.Models.WizardStep

@Model

你的视图可以这样称呼它

@model PartialView.Models.Wizard
@using PartialView.Models;
@{
    ViewBag.Title = "Partial view calling";
}

@Html.PartialFor(m=>m.GetStepObject<WizardStep>(), "_Step")

视觉结果将是一个带有 html 文本 ClientQuestions

的空白页面