Check if collection is empty or not

问题:

public ActionResult Create(FormCollection collection, FormCollection formValue)
{
    try
    {
        Project project = new Project();

        TryUpdateModel(project, _updateableFields);

        var devices = collection["devices"];
        string[] arr1 = ((string)devices).Split(',');
        int[] arr2 = Array.ConvertAll(arr1, s => int.Parse(s));

        project.User = SessionVariables.AuthenticatedUser;
        var time = formValue["Date"];
        project.Date = time;
        project.SaveAndFlush();

        foreach (int i in arr2)
        {
            Device d = Device.Find(i);
            d.Projects.Add(project);
            d.SaveAndFlush();
        }

        return RedirectToAction("Index");
    }
    catch (Exception e)
    {
        return View(e);
    }
}

I want to wrap the foreach in a if statement which checks if

var devices = collection["devices"];

is empty or not. If its empty the for each should not be executed. For the record, collection["devices"] is a collection of checkbox values from a form.

回答1:

You do not need to check if the collection is empty, if it is empty the code inside the ForEach will not be executed, see my example below.

using System;
using System.Collections.Generic;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            List<string> emptyList = new List<string>();

            foreach (string item in emptyList)
            {
                Console.WriteLine("This will not be printed");
            }

            List<string> list = new List<string>();

            list.Add("item 1");
            list.Add("item 2");

            foreach (string item in list)
            {
                Console.WriteLine(item);
            }

            Console.ReadLine();
        }
    }
}

回答2:

You can use the Count field to check if the collection is empty or not

so you will end up with something like this :

if(devices.Count > 0)
{
   //foreach loop
}

回答3:

You can use the method Any to know if a collection as any element.

if (devices.Any())
{
   //devices is not empty
}

回答4:

Your code, as it stands, won't work, as you say that collection["devices"] is a collection of checkbox values, and yet you're casting it to a string. Do you mean collection is the checkbox values? What is the exact type of collection?

Any object that implements ICollection or ICollection<T> can be checked whether it's empty or not by checking if the Count property is greater than zero.

回答5:

How about checking the array length

if (arr2.length > 0)
{
    foreach (int i in arr2)
    {
        Device d = Device.Find(i);
        d.Projects.Add(project);
        d.SaveAndFlush();
    }
}

回答6:

This worked for me in Dot Net Core but only for IEnumerable of Models not Entities (I got a bit of help from AutoMapper)

Cast it as a List then check the Capacity

IEnumerable<vwPOD_Master> podMasters = _podRepository.GetNewPods(PartNumber);

IEnumerable<NewPODsDTO> podList = Mapper.Map<IEnumerable<NewPODsDTO>>(podMasters);

if (((List<NewPODsDTO>)podList).Capacity == 0) {
    return NotFound(); 
}