在视图模型中有条件地更改显示名称

Question

我是剃刀和视图模型的新手，我只想问是否可以在[Display(Name = "")]中显示不同的字符串

我尝试在显示和变量之间添加条件，但它显示错误

也试过这个

public string Color {get;set;}
public String ColorDisplay
{
get
{
String name = "";
if (ColorId == 25 || ColorId == 26)
{
name = "Purple";
}
else
{
name = "Green";
}
return name;
}
}

那么在我看来@Html.LabelFor(m => m.ColorDisplay)

但似乎不起作用，因为它只是支付ColorDisplay

Answer 1

在本期中，您可能需要自定义属性来根据属性属性中提供的值更改文本。假设您需要像这样使用自定义属性：

[DisplayWhen("ColorId", 25, 26, "Purple", "Green")]
public String Color { get; set; }

并使用像这样的 HTML 帮助程序：

@Html.LabelFor(m => m.Color)

然后，您应该执行以下步骤：

1( 创建从类继承Attribute自定义属性。

public class DisplayWhenAttribute : Attribute
{
private string _propertyName;
private int _condition1;
private int _condition2;
private string _trueValue;
private string _falseValue;
public string PropertyName 
{
get
{
return _propertyName;
}
}
public int Condition1
{
get
{
return _condition1;
}
}
public int Condition2
{
get
{
return _condition2;
}
}
public string TrueValue
{
get
{
return _trueValue;
}
}
public string FalseValue
{
get
{
return _falseValue;
}
}
public DisplayWhenAttribute(string propertyName, int condition1, int condition2, string trueValue, string falseValue)
{
_propertyName = propertyName;
_condition1 = condition1;
_condition2 = condition2;
_trueValue = trueValue;
_falseValue = falseValue;
}
}

2( 创建自定义元数据提供程序类，用于检查自定义属性是否存在。

public class CustomModelMetadataProvider : DataAnnotationsModelMetadataProvider
{
protected override ModelMetadata CreateMetadata(IEnumerable<Attribute> attributes, Type containerType, Func<object> modelAccessor, Type modelType, string propertyName)
{
var metadata = base.CreateMetadata(attributes, containerType, modelAccessor, modelType, propertyName);
var additionalAttribute = attributes.OfType<DisplayWhenAttribute>().FirstOrDefault();
if (additionalAttribute != null)
{
metadata.AdditionalValues.Add("DisplayWhenAttribute", additionalValues);
}
return metadata;
}
}

3(将CustomModelMetadataProvider注册到Global.asax中的Application_Start()方法中，如下所示：

protected void Application_Start()
{
ModelMetadataProviders.Current = new CustomModelMetadataProvider();
}

4( 创建您自己的(或覆盖现有的(LabelFor助手，以便它检查DisplayWhenAttribute，如下例所示：

public static MvcHtmlString LabelFor<TModel, TProperty>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TProperty>> expression, IDictionary<string, object> htmlAttributes)
{
string result = string.Empty;
var modelMetaData = expression.Compile().Invoke(helper.ViewData.Model);
string fieldName = ExpressionHelper.GetExpressionText(expression);
var containerType = typeof(TModel);
var containerProperties = containerType.GetProperties();
var propertyInfo = containerProperties.SingleOrDefault(x => x.Name == modelMetaData.PropertyName);
var attribute = propertyInfo.GetCustomAttributes(false).SingleOrDefault(x => x is DisplayWhenAttribute) as DisplayWhenAttribute;
var target = attribute.PropertyName; // target property name, e.g. ColorId
var condition1 = attribute.Condition1; // first value to check
var condition2 = attribute.Condition2; // second value to check
var targetValue = (int)containerType.GetProperty(target).GetValue(helper.ViewData.Model);  
// checking provided values from attribute
if (targetValue == condition1 || targetValue == condition2)
{
result = attribute.TrueValue;
}      
else
{
result = attribute.FalseValue;
}
// create <label> tag with specified true/false value
TagBuilder tag = new TagBuilder("label");
tag.MergeAttributes(htmlAttributes);
tag.Attributes.Add("for", helper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldId(fieldName));
tag.SetInnerText(result);
return MvcHtmlString.Create(tag.ToString(TagRenderMode.Normal));
}

需要考虑的一些参考资料：

是否可以创建条件属性作为 DisplayIf？

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