Question

在ASP.NET Core 1.1中使用以下DataAnnotations。最好将我的MVC视图中的输入的最大长度设置为限制用户输入。

型号

[Display(Name = "Post Code")]
[MaxLength(8, ErrorMessage = "Maximum number of characters that can be entered is 8!")]
public string PostCode
{ get; set; }

查看

<label asp-for="PostCode"></label>
<input style="font-weight: normal;" class="form-control" placeholder="Post Code" asp-for="PostCode" data-val="true" autofocus />

呈现为

<input style="font-weight: normal;" class="form-control valid" placeholder="Post Code" data-val="true" autofocus="" type="text" data-val-maxlength="Maximum number of characters that can be entered is 8!" data-val-maxlength-max="8" id="PostCode" name="PostCode" value="" wtx-context="FA5749C8-68AC-44FE-88B9-4BBDF9D48DAE" aria-invalid="false" aria-describedby="PostCode-error">

我希望生成来自我的类数据注释的maxlength属性，如下所示。（滚动到结尾）;

<input style="font-weight: normal;" class="form-control valid" placeholder="Post Code" data-val="true" autofocus="" type="text" data-val-maxlength="Maximum number of characters that can be entered is 8!" data-val-maxlength-max="8" id="PostCode" name="PostCode" value="" wtx-context="FA5749C8-68AC-44FE-88B9-4BBDF9D48DAE" aria-invalid="false" aria-describedby="PostCode-error" maxlength="8">

感谢任何建议。

Answer 1

您可能需要通过TagHelper实现此功能，TagHelper可以读取此属性并在呈现时将其添加到元素，因为默认asp-for将无法处理此属性。

扩展输入TagHelper

尝试在项目中按如下方式声明TagHelper，这将占用现有的asp-for帮助程序并处理读取任何现有属性/元数据并将必要的属性附加到元素：

namespace YourProject.TagHelpers
{
    [HtmlTargetElement("input", Attributes = "asp-for")]
    public class MaxLengthTagHelper : TagHelper
    {
        public override int Order { get; } = 999;

        [HtmlAttributeName("asp-for")]
        public ModelExpression For { get; set; }

        public override void Process(TagHelperContext context, TagHelperOutput output)
        {
            base.Process(context, output);

            // Process only if 'maxlength' attr is not present
            if (context.AllAttributes["maxlength"] == null) 
            {
                // Attempt to check for a MaxLength annotation
                var maxLength = GetMaxLength(For.ModelExplorer.Metadata.ValidatorMetadata);
                if (maxLength > 0)
                {
                    output.Attributes.Add("maxlength", maxLength);
                }
            }
        }

        private static int GetMaxLength(IReadOnlyList<object> validatorMetadata)
        {
            for (var i = 0; i < validatorMetadata.Count; i++)
            {
                var stringLengthAttribute = validatorMetadata[i] as StringLengthAttribute;
                if (stringLengthAttribute != null && stringLengthAttribute.MaximumLength > 0)
                {
                    return stringLengthAttribute.MaximumLength;
                }

                var maxLengthAttribute = validatorMetadata[i] as MaxLengthAttribute;
                if (maxLengthAttribute != null && maxLengthAttribute.Length > 0)
                {
                    return maxLengthAttribute.Length;
                }
            }
            return 0;
        }
    }
}

使用TagHelper

然后直接在特定视图中添加对它的引用，或者在_ViewImports.cshtml文件中全局添加引用，如下所示：

@using YourProject
@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
@addTagHelper *, YourProject

添加后，此扩展TagHelper应使用相应的maxlength属性自动装饰您的元素（如果您的属性中存在）：

<!-- Input -->
<label asp-for="PostCode"></label>
<input style="font-weight: normal;" class="form-control" placeholder="Post Code" asp-for="PostCode" data-val="true" autofocus />

<!-- Rendered -->
<label for="PostCode">Post Code</label>
<input style="font-weight: normal;" class="form-control" placeholder="Post Code" data-val="true" autofocus="" type="text" data-val-maxlength="Maximum number of characters that can be entered is 8!" data-val-maxlength-max="8" id="PostCode" name="PostCode" value="" maxlength="8">

MaxLength注释到maxlength输入属性

1 个答案: