Question

我正在研究MVC2应用程序，并希望设置文本输入的maxlength属性。

我已经使用数据注释在Model对象上定义了stringlength属性，并且正确地验证了输入字符串的长度。

我不希望在模型已经拥有信息时手动设置max length属性，在我的视图中重复相同的设置。有没有办法做到这一点？

以下代码段：

从模型：

[Required, StringLength(50)]
public string Address1 { get; set; }

从视图：

<%= Html.LabelFor(model => model.Address1) %>
<%= Html.TextBoxFor(model => model.Address1, new { @class = "text long" })%>
<%= Html.ValidationMessageFor(model => model.Address1) %>

我想避免做的是：

<%= Html.TextBoxFor(model => model.Address1, new { @class = "text long", maxlength="50" })%>

我想得到这个输出：

<input type="text" name="Address1" maxlength="50" class="text long"/>

有没有办法做到这一点？

Answer 1

如果您正在使用不显眼的验证，您也可以处理此客户端：

$(document).ready(function ()
{
    $("input[data-val-length-max]").each(function ()
    {
        var $this = $(this);
        var data = $this.data();
        $this.attr("maxlength", data.valLengthMax);
    });
});

Answer 2

我不知道如何在不诉诸反思的情况下实现这一目标。你可以编写一个辅助方法：

public static MvcHtmlString CustomTextBoxFor<TModel, TProperty>(
    this HtmlHelper<TModel> htmlHelper, 
    Expression<Func<TModel, TProperty>> expression, 
    object htmlAttributes
)
{
    var member = expression.Body as MemberExpression;
    var stringLength = member.Member
        .GetCustomAttributes(typeof(StringLengthAttribute), false)
        .FirstOrDefault() as StringLengthAttribute;

    var attributes = (IDictionary<string, object>)new RouteValueDictionary(htmlAttributes);
    if (stringLength != null)
    {
        attributes.Add("maxlength", stringLength.MaximumLength);
    }
    return htmlHelper.TextBoxFor(expression, attributes);
}

你可以这样使用：

<%= Html.CustomTextBoxFor(model => model.Address1, new { @class = "text long" })%>

Answer 3

我使用CustomModelMetaDataProvider来实现这个

步骤1.添加新的CustomModelMetadataProvider类

public class CustomModelMetadataProvider : DataAnnotationsModelMetadataProvider
{   
    protected override ModelMetadata CreateMetadata(
        IEnumerable<Attribute> attributes,
        Type containerType,
        Func<object> modelAccessor,
        Type modelType,
        string propertyName)
    {
        ModelMetadata metadata = base.CreateMetadata(attributes,
            containerType,
            modelAccessor,
            modelType,
            propertyName);

        //Add MaximumLength to metadata.AdditionalValues collection
        var stringLengthAttribute = attributes.OfType<StringLengthAttribute>().FirstOrDefault();
        if (stringLengthAttribute != null)
            metadata.AdditionalValues.Add("MaxLength", stringLengthAttribute.MaximumLength);

        return metadata;
    }
}

步骤2.在Global.asax中注册CustomModelMetadataProvider

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();
    RegisterRoutes(RouteTable.Routes);
    ModelMetadataProviders.Current = new CustomModelMetadataProvider();
}

步骤3.在Views / Shared / EditorTemplates中添加名为String.ascx的部分视图

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %>
<%if (!ViewData.ModelMetadata.AdditionalValues.ContainsKey("MaxLength")) { %>
    <%: Html.TextBox("", ViewData.TemplateInfo.FormattedModelValue,  new { @class = "text-box single-line" }) %>
<% } else {
    int maxLength = (int)ViewData.ModelMetadata.AdditionalValues["MaxLength"];
    %>
    <%: Html.TextBox("", ViewData.TemplateInfo.FormattedModelValue, new { @class = "text-box single-line", MaxLength = maxLength  })%>
<% } %>

完成......

修改。如果你想在文本框中添加更多内容，第3步可能会变得丑陋。如果是这种情况，您可以执行以下操作：

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %>
<%
    IDictionary<string, object> Attributes = new Dictionary<string, object>();
    if (ViewData.ModelMetadata.AdditionalValues.ContainsKey("MaxLength")) {
        Attributes.Add("MaxLength", (int)ViewData.ModelMetadata.AdditionalValues["MaxLength"]);
    }
    if (ViewData.ContainsKey("style")) {
        Attributes.Add("style", (string)ViewData["style"]);
    }
    if (ViewData.ContainsKey("title")) {
        Attributes.Add("title", (string)ViewData["title"]);
    }
%>
<%: Html.TextBox("", ViewData.TemplateInfo.FormattedModelValue, Attributes)%>

Answer 4

如果您希望使用元数据类，则需要使用以下代码。我知道它不漂亮，但它完成了工作并阻止你在Entity类和View中编写你的maxlength属性：

public static MvcHtmlString TextBoxFor2<TModel, TProperty>
(
  this HtmlHelper<TModel> htmlHelper,
  Expression<Func<TModel, TProperty>> expression,
  object htmlAttributes = null
)
{
  var member = expression.Body as MemberExpression;

  MetadataTypeAttribute metadataTypeAttr = member.Member.ReflectedType
    .GetCustomAttributes(typeof(MetadataTypeAttribute), false)
    .FirstOrDefault() as MetadataTypeAttribute;

  IDictionary<string, object> htmlAttr = null;

  if(metadataTypeAttr != null)
  {
    var stringLength = metadataTypeAttr.MetadataClassType
      .GetProperty(member.Member.Name)
      .GetCustomAttributes(typeof(StringLengthAttribute), false)
      .FirstOrDefault() as StringLengthAttribute;

    if (stringLength != null)
    {
      htmlAttr = new RouteValueDictionary(htmlAttributes);
      htmlAttr.Add("maxlength", stringLength.MaximumLength);
    }                                    
  }

  return htmlHelper.TextBoxFor(expression, htmlAttr);
}

示例类：

[MetadataType(typeof(Person.Metadata))]
public partial class Person
{
  public sealed class Metadata
  {

    [DisplayName("First Name")]
    [StringLength(30, ErrorMessage = "Field [First Name] cannot exceed 30 characters")]
    [Required(ErrorMessage = "Field [First Name] is required")]
    public object FirstName { get; set; }

    /* ... */
  }
}

Answer 5

虽然我个人非常喜欢jrummel的jquery修复，但这是另一种在你的模型中保持单一事实来源的方法......

不漂亮，但是..已经工作了o.k.对我来说......

我只是在我的模型库/ dll中定义一些命名良好的公共常量，而不是使用属性装饰，然后通过HtmlAttributes在我的视图中引用它们，例如

Public Class MyModel

    Public Const MAX_ZIPCODE_LENGTH As Integer = 5

    Public Property Address1 As String

    Public Property Address2 As String

    <MaxLength(MAX_ZIPCODE_LENGTH)>
    Public Property ZipCode As String

    Public Property FavoriteColor As System.Drawing.Color

End Class

然后，在剃须刀视图文件中，在EditorFor ...中使用过载中的HtmlAttirubte对象，提供所需的max-length属性并引用常量..你必须通过完全合格的方式提供常量命名空间路径... MyCompany.MyModel.MAX_ZIPCODE_LENGTH ..因为它不会挂在模型上，但是，它可以工作。

Answer 6

我发现达林基于反思的方法特别有用。我发现使用元数据ContainerType作为获取属性信息的基础更加可靠，因为可以在mvc编辑器/显示模板中调用此方法（其中TModel最终成为简单类型，例如string）。

public static MvcHtmlString CustomTextBoxFor<TModel, TProperty>(
    this HtmlHelper<TModel> htmlHelper, 
    Expression<Func<TModel, TProperty>> expression, 
    object htmlAttributes
)
{
    var metadata = ModelMetadata.FromLambdaExpression( expression, new ViewDataDictionary<TModel>( htmlHelper.ViewDataContainer.ViewData ) );
    var stringLength = metadata.ContainerType.GetProperty(metadata.PropertyName)
        .GetCustomAttributes(typeof(StringLengthAttribute), false)
        .FirstOrDefault() as StringLengthAttribute;

    var attributes = (IDictionary<string, object>)new RouteValueDictionary(htmlAttributes);
    if (stringLength != null)
    {
        attributes.Add("maxlength", stringLength.MaximumLength);
    }
    return htmlHelper.TextBoxFor(expression, attributes);
}

Answer 7

以下是一些可用于获取StringLength或任何其他属性的静态方法。

using System;
using System.Linq;
using System.Reflection;
using System.ComponentModel.DataAnnotations;
using System.Linq.Expressions;

public static class AttributeHelpers {

public static Int32 GetStringLength<T>(Expression<Func<T,string>> propertyExpression) {
    return GetPropertyAttributeValue<T,string,StringLengthAttribute,Int32>(propertyExpression,attr => attr.Length);
}

//Optional Extension method
public static Int32 GetStringLength<T>(this T instance,Expression<Func<T,string>> propertyExpression) {
    return GetStringLength<T>(propertyExpression);
}


//Required generic method to get any property attribute from any class
public static TValue GetPropertyAttributeValue<T, TOut, TAttribute, TValue>(Expression<Func<T,TOut>> propertyExpression,Func<TAttribute,TValue> valueSelector) where TAttribute : Attribute {
    var expression = (MemberExpression)propertyExpression.Body;
    var propertyInfo = (PropertyInfo)expression.Member;
    var attr = propertyInfo.GetCustomAttributes(typeof(TAttribute),true).FirstOrDefault() as TAttribute;

    if (attr==null) {
        throw new MissingMemberException(typeof(T).Name+"."+propertyInfo.Name,typeof(TAttribute).Name);
    }

    return valueSelector(attr);
}

}

使用静态方法......

var length = AttributeHelpers.GetStringLength<User>(x => x.Address1);

或者在实例上使用可选的扩展方法......

var player = new User();
var length = player.GetStringLength(x => x.Address1);

或者对任何其他属性使用完整的静态方法......

var length = AttributeHelpers.GetPropertyAttributeValue<User,string,StringLengthAttribute,Int32>(prop => prop.Address1,attr => attr.MaximumLength);

灵感来自这里的答案...... https://stackoverflow.com/a/32501356/324479

来自Asp.Net MVC中的DataAnnotations StringLength的文本框的maxlength属性

7 个答案: