Question

我们正在跟踪分页指南-https://docs.microsoft.com/en-us/aspnet/core/data/ef-rp/sort-filter-page?view=aspnetcore-2.1，并且在分页的“下一个”和“上一个”按钮方面存在问题：

严重性代码描述项目文件行抑制状态错误CS1061“ IList”没有包含“ HasPreviousPage”的定义，没有可访问的扩展名方法'HasPreviousPage'接受类型的第一个参数可以找到“ IList”（您缺少using指令或程序集引用吗？）

import 'package:flutter/material.dart';
import 'package:connectivity/connectivity.dart';

void main() => runApp(MaterialApp(title: "Wifi Check", home: MyPage()));

class MyPage extends StatefulWidget {
    @override
    _MyPageState createState() => _MyPageState();
}

class _MyPageState extends State<MyPage> {
    bool _tryAgain = false;

    @override
    void initState() {
      super.initState();
      _checkWifi();
    }

    _checkWifi() async {
      // the method below returns a Future
      var connectivityResult = await (new Connectivity().checkConnectivity());
      bool connectedToWifi = (connectivityResult == ConnectivityResult.wifi);
      if (!connectedToWifi) {
        _showAlert(context);
      }
      if (_tryAgain != !connectedToWifi) {
        setState(() => _tryAgain = !connectedToWifi);
      }
    }

    @override
    Widget build(BuildContext context) {
      var body = Container(
        alignment: Alignment.center,
        child: _tryAgain
          ? RaisedButton(
              child: Text("Try again"),
              onPressed: () {
                _checkWifi();
            })
          : Text("This device is connected to Wifi"),
      );

      return Scaffold(
        appBar: AppBar(title: Text("Wifi check")),
        body: body
      );
    }

    void _showAlert(BuildContext context) {
      showDialog(
          context: context,
          builder: (context) => AlertDialog(
            title: Text("Wifi"),
            content: Text("Wifi not detected. Please activate it."),
          )
      );
    }
}

有什么想法吗？

我确实有PaginatedList.cs类：

/*
Write a program in C language that in sequence:
1) create 2 pipes and a child (the 2 pipes will be used for two-way communication between the parent
and son);
2) the father, after the creation of the child, takes in input from the user a file name;
3) send the child the name of the file using the first pipe;
4) make the child look for the number of spaces in the file and communicate this number to the father through the use of the second pipe;
5) let the father print the number received from son;
*/

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/wait.h>

int main (int argc, char *argv[])
{
    int f2s[2]; 
    int s2f[2];
    int fd, n;
    pid_t p;
    char buf[20];
    char c;
    int countspace=0, valueofspace;
    if (argc<2)
    {
        printf("ERROR!\n");
        exit (-1);
    }
    if (pipe (f2s) == -1 && pipe (s2f) == -1)
        exit(-1);
    p=fork();
    if (p>0)
    {
        printf("I'm inside the father process.\n");
        close(f2s[0]);
        close(s2f[1]);
        write(f2s[1],argv[1],sizeof(argv[1]));

        read(s2f[0],&valueofspace, sizeof(int));
        printf("The spaces are %d", valueofspace);      
        printf("Father exit\n");
        exit(0);
    }
    if (p==0)
    {
        printf("I'm inside the child process.\n");
        close(f2s[1]);
        close(s2f[0]);
        read (f2s[0],buf,20);

        if (fd = open(buf, O_RDONLY) == -1)
            printf("Error when opening the file\n");

        while (read(fd,&c,1) > 0)
        {
            if (c==' ')
                countspace++;
        }
        close(fd);
        printf("Count: %d\n",countspace);
        n = write(s2f[1],&countspace, sizeof(countspace));
        printf("WRITE of %d BYTES\n", n);
        printf("Son exit \n");
        exit(0);
    }
}

这是该index.cshtml的后端代码：

@{
    var prevDisabled = !Model.TournamentAtheletes.HasPreviousPage ? "disabled" : "";
    var nextDisabled = !Model.TournamentAtheletes.HasNextPage ? "disabled" : "";
}

<a asp-page="./Index"
   asp-route-sortOrder="@Model.CurrentSort"
   asp-route-pageIndex="@(Model.TournamentAtheletes.PageIndex - 1)"
   asp-route-currentFilter="@Model.CurrentFilter"
   class="btn btn-default @prevDisabled">
    Previous
</a>
<a asp-page="./Index"
   asp-route-sortOrder="@Model.CurrentSort"
   asp-route-pageIndex="@(Model.TournamentAtheletes.PageIndex + 1)"
   asp-route-currentFilter="@Model.CurrentFilter"
   class="btn btn-default @nextDisabled">
    Next
</a>

Answer 1

通过这样声明您的列表：

IList<TournamentAtheleteViewModel> TournamentAtheletes { get; set; }

您明确指出，保证存在的唯一方法是由接口IList<T>声明的方法，而该接口未声明HasPreviousPage或HasNextPage

发生这种情况的原因是我声明：

IList<TournamentAtheleteViewModel> TournamentAtheletes = new List<TournamentAtheleteViewModel>();

List<T>当然不会声明您的方法，因此如果我调用.HasPreviousPage，这将导致运行时异常。

因此，您需要将此声明更改为：

PaginatedList<TournamentAtheleteViewModel> TournamentAtheletes { get; set; }

.Net Core 2.1的Razor页面中的分页问题

1 个答案: