从通用对象列表中读取通用值

Question

我正在尝试遍历通用对象列表调用 Condition<T> 以读取通用字段 Value。我遵循了 this 的问题，以便能够存储 List<Condition<T>>。我现在运行遇到的问题是我无法在循环中使用 Value 字段。我需要更改什么才能使用 Value 字段？

主要

string url = "";
List<ConditionBase> Conditions = new List<ConditionBase>();
Conditions.Add(new Condition<int>(Field.Field1, 1, ConditionOperator.Equal))
Conditions.Add(new Condition<string>(Field.Field2, "test", ConditionOperator.NotEqual))

foreach (ConditionBase c in Conditions)
{
    if (c.GetType() == typeof(string))
    {
        // c.Value throws an error
        url += c.Field + " " + c.ConditionOperator + " '" + c.Value + "' and ";
    }
    else if (c.GetType() == typeof(DateTime))
    {
        // c.Value throws an error
        url += c.Field + " " + c.ConditionOperator + " " + Helpers.FormatDate(c.Value) + " and ";
    }
}

条件基础

public interface ConditionBase
{
    Field Field { get; set; }
    ConditionOperator ConditionOperator { get; set; }
}

条件

public class Condition<T> : ConditionBase
{
    private Field _Field;
    private T _Value;
    private ConditionOperator _ConditionOperator;

    public Condition(Field field, T value, ConditionOperator condition)
    {
        this._Field = field;
        this._Value = value;
        this._ConditionOperator = condition;
    }

    public Field Field
    {
        get
        {
            return this._Field;
        }
        set
        {
            if (this._Field != value)
            {
                this._Field = value;
            }
        }
    }

    public T Value
    {
        get
        {
            return this._Value;
        }
        set
        {
            if (!EqualityComparer<T>.Default.Equals(this._Value, value))
            {
                this._Value = value;
            }
        }
    }

    public ConditionOperator ConditionOperator
    {
        get
        {
            return this._ConditionOperator;
        }
        set
        {
            if (this._ConditionOperator != value)
            {
                this._ConditionOperator = value;
            }
        }
    }
}

枚举

public enum Field{
    Field1,
    Field2
}

public enum ConditionOperator{
    Equal,
    NotEqual,
    GreaterThan,
    LessThan
}

解决方案

此解决方案基于@orhtej2 的评论和@Igor 的回答。

主要 - 测试

static void Main(string[] args)
{
    var x1 = new Condition<int>(new Field(), 123, ConditionOperator.Equal);
    var x2 = new Condition<string>(new Field(), "test", ConditionOperator.Equal);
    var x3 = new Condition<DateTime>(new Field(), new DateTime(2018,5,5), ConditionOperator.Equal);

    var qqq = new List<ConditionBase>();

    qqq.Add(x1);
    qqq.Add(x2);
    qqq.Add(x3);

    foreach (ConditionBase c in qqq)
    {
        Console.WriteLine(c.GetValue());
    }
    Console.ReadLine();
}

条件基础

public interface ConditionBase
{
    Field Field { get; set; }
    ConditionOperator ConditionOperator { get; set; }
    string GetValue();
}

条件

public class Condition<T> : ConditionBase
{
    private Field _Field;
    private T _Value;
    private ConditionOperator _ConditionOperator;

    public Condition(Field field, T value, ConditionOperator condition)
    {
        this._Field = field;
        this._Value = value;
        this._ConditionOperator = condition;
    }

    public Field Field
    {
        get
        {
            return this._Field;
        }
        set
        {
            if (this._Field != value)
            {
                this._Field = value;
            }
        }
    }

    public T Value
    {
        get
        {
            return this._Value;
        }
        set
        {
            if (!EqualityComparer<T>.Default.Equals(this._Value, value))
            {
                this._Value = value;
            }
        }
    }

    public ConditionOperator ConditionOperator
    {
        get
        {
            return this._ConditionOperator;
        }
        set
        {
            if (this._ConditionOperator != value)
            {
                this._ConditionOperator = value;
            }
        }
    }

    public string GetValue()
    {
        if (Value is string)
        {
            return "'" + Value.ToString() + "'";
        }
        else if (Value is DateTime)
        {
            return Helpers.FormatDate(Convert.ToDateTime(Value));
        }
        else
        {
            return Value.ToString();
        }            
    }
}

枚举

public enum Field{
    Field1,
    Field2
}

public enum ConditionOperator{
    Equal,
    NotEqual,
    GreaterThan,
    LessThan
}

Answer 1

您的代码中存在语法错误，例如您的枚举缺少 public 范围和 ConditionOperator.Equal（不是 ConditionOperator.Equals），但这里的旁白是修复方法。

Conditions 应该是类型 List<ConditionBase>
在列表上使用 OfType 检索结果类型并将其转换为 Condition<string>。我认为这是你添加支票的意图 c.GetType() == typeof(string)

string url = "";
List<ConditionBase> Conditions = new List<ConditionBase>();
Conditions.Add(new Condition<int>(Field.Field1, 1, ConditionOperator.Equal));
Conditions.Add(new Condition<string>(Field.Field2, "test", ConditionOperator.NotEqual));

foreach (var c in Conditions.OfType<Condition<string>>())
{
    url += c.Field + " " + c.ConditionOperator + " '" + c.Value + "' and ";
}

如果您想要一个可以在所有实例上访问的通用属性而无需考虑通用类型约束，那么您需要相应地扩展基本接口。

public interface ConditionBase
{
    Field Field { get; set; }
    ConditionOperator ConditionOperator { get; set; }
    object FieldValue { get; }
}

public class Condition<T> : ConditionBase
{
  /* I only included the added code in this type */
  public object FieldValue
  {
      get { return (object) this.Value; }
  }
}

string url = "";
List<ConditionBase> Conditions = new List<ConditionBase>();
Conditions.Add(new Condition<int>(Field.Field1, 1, ConditionOperator.Equal));
Conditions.Add(new Condition<string>(Field.Field2, "test", ConditionOperator.NotEqual));

foreach (var c in Conditions)
{
    url += c.Field + " " + c.ConditionOperator + " '" + c.FieldValue + "' and ";
}

根据您问题的变化，您似乎想将您的值输出到一个字符串中。为您的类型添加一个字符串格式化程序。

/* I only included the added code in this type */
public class Condition<T> : ConditionBase
{
  private Func<T, string> _formatValue;
  public Condition(Field field, T value, ConditionOperator condition, Func<T, string> formatValue)
  {
    this._Field = field;
    this._Value = value;
    this._ConditionOperator = condition;
    this._formatValue = formatValue;
  }

  public override string ToString()
  {
      return this._formatValue(this.Value);
  }
}

string url = "";
List<ConditionBase> Conditions = new List<ConditionBase>();
Conditions.Add(new Condition<int>(Field.Field1, 1, ConditionOperator.Equal, (val)=> val.ToString()));
Conditions.Add(new Condition<string>(Field.Field2, "test", ConditionOperator.NotEqual, (val)=> val));

foreach (var c in Conditions)
{
    url += c.Field + " " + c.ConditionOperator + " '" + c.ToString() + "' and ";
}

从通用对象列表中读取通用值

Reading Generic Value from List of Generic Objects

c#

generics

generic-list

主要

条件基础

条件

枚举

解决方案

主要 - 测试

条件基础

条件

枚举