Question

我有一个包含许多不同字符串值的类

我有一个集合类，包含一些排序函数。目前我有很多重现的代码，用于＆＃34; GetListOfDifferentProducts＆＃34; ＆＃34; GetListOfDifferentManufacturers＆＃34;等

这可能吗？或者我是以错误的方式解决这个问题。

这些都是简单的foreach循环

        public List<string> GetListOfDifferentProducts()
    {
        List<string> listOfResults = new List<string>();
        foreach (Product prod in listOfProducts)
        {
            if (listOfResults.Contains(prod.Name.ToLower()) == false)
                listOfResults.Add(prod.Name.ToLower());
        }
        return listOfResults;
    }

我想传递一个类变量（比如LINQ？）

    public List<string> GetListOfDifferentVariables(variableType)
    {
        List<string> listOfResults = new List<string>();
        foreach (Product prod in listOfProducts)
        {
            if (listOfResults.Contains(prod.variableType.ToLower()) == false)
                listOfResults.Add(prod.variableType.ToLower());
        }
        return listOfResults;
    }

示例用法：

ProductList.GetListOfDifferentVariables(o => o.Name);

示例输入（变量字符串名称）

苹果
苹果
苹果
梨
香蕉
香蕉

输出

苹果
梨
香蕉

MVC

    class Product
{
    public string Name;
    public string Manufacturer;
    public string Description;
    public string Location;
}
class ProductCollection
{
    List<Product> listOfProducts;

    public List<string> GetListOfDifferentProducts()
    {
        List<string> listOfResults = new List<string>();
        foreach (Product prod in listOfProducts)
        {
            if (listOfResults.Contains(prod.Name.ToLower()) == false)
                listOfResults.Add(prod.Name.ToLower());
        }
        return listOfResults;
    }
}

Answer 1

如果您正在寻找不同的名称集，请考虑：

listOfProducts.Select(z => z.Name.ToLower()).Distinct();

类似于variableType：

listOfProducts.Select(z => z.variableType.ToLower()).Distinct();

这将避免您需要编写明确的GetListOfDifferentVariables等方法。

如果您真的想要这些方法，请尝试以下方法：

public List<string> GetDistinctNames()
{
    return GetDistinctProperties(product => product.Name.ToLower());
}


public List<string> GetDistinctProperties(Func<Product, string> evaluator)
{
    return listOfProducts.Select(evaluator).Distinct().ToList();
}

GetDistinctNames通过特定字段（即Name）和感兴趣的操作（即ToLower）。

Answer 2

string[] tmp =
{
    "Apple",
    "Apple",
    "Apple",
    "Pear",
    "Banana",
    "Banana"
};

string[] tmp2 =
{
    "Pear",
    "Banana"
};

IEnumerable<string> uniqueList = tmp.Distinct(); // Removes doubles
IEnumerable<string> notInTmp2 = tmp.Distinct().Except(tmp2); // could be also interesting ;)

Console.WriteLine(string.Join(", ", uniqueList));
Console.WriteLine(string.Join(", ", notInTmp2));

Answer 3

创建通用方法：

    public IEnumerable<T2> GetListOfDifferent<T1, T2>(Func<T1,T2> selector, IEnumerable<T1> inputs)
    {
        var result = inputs.Select(selector).Distinct();
        return result;
    }

    public IEnumerable<T2> GetListOfDifferent<T1, T2>(string propertyName, IEnumerable<T1> inputs)
    {
        var paramExp = Expression.Parameter(typeof(T1), "p1");
        var member = Expression.PropertyOrField(paramExp, propertyName);
        var lamdaExp = Expression.Lambda<Func<T1, T2>>(member, new[] { paramExp });
        var selector = lamdaExp.Compile();

        var result = GetListOfDifferent(selector, inputs);
        return result;
    }

用法：

var result =GetListOfDifferent<Product,string>(product => product.Name, items)

或

 var result = GetListOfDifferent<Product,string>(nameof(Product.Name), items);

Answer 4

如果要将Property属性作为参数传递，则可以使用Reflection。您需要稍微调整Product类以获得公共属性。

public class Product
{
    private string _name, _manufacturer;


    public string Name
    {
        get
        {
            return _name;
        }
        set
        {
            _name = value;
        }
    }
    public string Manufacturer
    {
        get
        {
            return _manufacturer;
        }
        set
        {
            _manufacturer = value;
        }
    }

}

然后您可以将GetListOfDifferentVariables函数编写为

public List<string> GetListOfDifferentVariables(string propertyName)
    {
        List<string> listOfResults = new List<string>();
        foreach (Product prod in listOfProducts)
        {
            string propertyValue = (string)prod.GetType().GetProperty(propertyName).GetValue(prod);
            if (listOfResults.Contains(propertyValue.ToLower()) == false)
                listOfResults.Add(propertyValue.ToLower());
        }
        return listOfResults.Distinct().ToList();
    }

您可以使用属性名称

调用该函数

var names = GetListOfDifferentVariables("Name");
var manufacturers = GetListOfDifferentVariables("Manufacturer");

c＃在类LINQ方法中将类变量作为参数传递给？

4 个答案: