.NetCore 分页控件实现原理处理以及条件分页处理

说明

自定义一个类继承TagHelper，注意自定义类的 必须以TagHelper结尾，这个有点类是属性 Attribute的写法

protected TagHelper();

        //
        // 摘要:
        //     When a set of Microsoft.AspNetCore.Razor.TagHelpers.ITagHelpers are executed,
        //     their Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.Init(Microsoft.AspNetCore.Razor.TagHelpers.TagHelperContext)'s
        //     are first invoked in the specified Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.Order;
        //     then their Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.ProcessAsync(Microsoft.AspNetCore.Razor.TagHelpers.TagHelperContext,Microsoft.AspNetCore.Razor.TagHelpers.TagHelperOutput)'s
        //     are invoked in the specified Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.Order.
        //     Lower values are executed first.
        //
        // 备注:
        //     Default order is 0.
        public virtual int Order { get; }

        //
        // 摘要:
        //     Initializes the Microsoft.AspNetCore.Razor.TagHelpers.ITagHelper with the given
        //     context. Additions to Microsoft.AspNetCore.Razor.TagHelpers.TagHelperContext.Items
        //     should be done within this method to ensure they're added prior to executing
        //     the children.
        //
        // 参数:
        //   context:
        //     Contains information associated with the current HTML tag.
        //
        // 备注:
        //     When more than one Microsoft.AspNetCore.Razor.TagHelpers.ITagHelper runs on the
        //     same element, TagHelperOutput.GetChildContentAsync may be invoked prior to Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.ProcessAsync(Microsoft.AspNetCore.Razor.TagHelpers.TagHelperContext,Microsoft.AspNetCore.Razor.TagHelpers.TagHelperOutput).
        public virtual void Init(TagHelperContext context);
        //
        // 摘要:
        //     Synchronously executes the Microsoft.AspNetCore.Razor.TagHelpers.TagHelper with
        //     the given context and output.
        //
        // 参数:
        //   context:
        //     Contains information associated with the current HTML tag.
        //
        //   output:
        //     A stateful HTML element used to generate an HTML tag.
        public virtual void Process(TagHelperContext context, TagHelperOutput output);
        //
        // 摘要:
        //     Asynchronously executes the Microsoft.AspNetCore.Razor.TagHelpers.TagHelper with
        //     the given context and output.
        //
        // 参数:
        //   context:
        //     Contains information associated with the current HTML tag.
        //
        //   output:
        //     A stateful HTML element used to generate an HTML tag.
        //
        // 返回结果:
        //     A System.Threading.Tasks.Task that on completion updates the output.
        //
        // 备注:
        //     By default this calls into Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.Process(Microsoft.AspNetCore.Razor.TagHelpers.TagHelperContext,Microsoft.AspNetCore.Razor.TagHelpers.TagHelperOutput).
        public virtual Task ProcessAsync(TagHelperContext context, TagHelperOutput output);

重写一个 ProcessAsync 这里我以异步为例子

首先说明下分页需要的重要参数 定义一个分页参数类

 public class PagerOptions
    {

        /// <summary>
        /// 每页数据条数
        /// </summary>
        public int PageSize { get; set; }
        /// <summary>
        /// 当前页码
        /// </summary>
        public int CurrentPageIndex { get; set; }
        /// <summary>
        /// 数据总条数
        /// </summary>
        public int ItemTotal { get; set; }
        /// <summary>
        /// 总页数
        /// </summary>
        public int PageTotal
        {
            get
            {
                return ItemTotal % PageSize >  ? ItemTotal / PageSize +  : ItemTotal / PageSize;
            }
        }
        /// <summary>
        /// 显示的页面个数（只显示5个页码）
        /// </summary>
        public int EveryCount { get; set; }
        /// <summary>
        /// 允许选择页码
        /// </summary>
        public bool IsSelectPageSize { get; set; }
        /// <summary>
        /// 每页数据条数范围
        /// </summary>
        public int[] SelectPageSize { get; set; }
        /// <summary>
        /// 是否显示转到页码
        /// </summary>
        public bool IsGoPage { get; set; }
        /// <summary>
        /// 分页访问地址
        /// </summary>
        public string PageUri { get; set; }
    }

PagerOptions

 public class PagerTagHelper : TagHelper
    {

        public PagerOptions PagerOption { get; set; }

        public override Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
        {

            output.TagName = "div";
            if (PagerOption.PageSize <= )
            {
                PagerOption.PageSize = ;
            }
            if (PagerOption.CurrentPageIndex <= )
            {
                PagerOption.CurrentPageIndex = ;
            }
            if (PagerOption.CurrentPageIndex > PagerOption.PageTotal)
            {
                PagerOption.CurrentPageIndex = PagerOption.PageTotal;
            }
            if (PagerOption.PageTotal <= )
            {
                return Task.CompletedTask;
            }

            string ax = PagerOption.PageUri;
            //接下来就是拼写html样式而已
            return base.ProcessAsync(context, output);
        }

    }

PagerTagHelper

样式具体没有实现值说下原理，添加以上类注意对命名空间的引用，不然是无法编写服务器标签的

找到_ViewImports.cshtml文件 中添加

@addTagHelper "ExpressUser.PagerTagHelper,ExpressUser"
@addTagHelper "ExpressUser.PagerOptions,ExpressUser"

然后在页面上编写pager服务器标签 这是是pager 对应的是类  PagerTagHelper  参数类型 PagerOptions 在 PagerTagHelper 中的变量是  PagerOption 所以这里对应 pager-option

其实就这样简单，当然在代码中可以这样使用 ，如果点击分页按钮要保持查询条件分页，这里就需要获取条件了，这就你是什么方式的请求的了

这里分页我以Get为例子

处理下这个对象

public abstract IQueryCollection Query { get; set; }

或者

public abstract IFormCollection Form { get; set; }

 var list = Request.Query.ToList();
            string querystring = string.Empty;
            foreach (var item in list)
            {
                querystring += "&" + item.Key + "=" + item.Value;
            }
            ViewBag.PagerOption = new PagerOptions()
            {
                ItemTotal = ,
                PageUri = Request.Path + (string.IsNullOrEmpty(querystring) ? "" : "?" + querystring.Substring())
            };

赋值PagerUri 就行了

下面在回到PagerTagHelper中访问看下