使用反射，从作为对象数组的属性中获取单个项 [英] Using reflection, get an individual item from a property that is an object array

问题描述

我有一个特殊设置的数据集 - 一个列类的数组，其属性为Name，DataType和Values



后一个属性是一个值数组，例如

I have a data set that is in a peculiar setup - an array of "column" classes with properties "Name", "DataType" and "Values"

The latter property is an array of values e.g.

public partial class UsageColumn  {

    private string nameField;

    private string dataTypeField;

    private object[] valuesField;


    public string Name {
        get {
            return this.nameField;
        }
        set {
            this.nameField = value;
        }
    }

    public string DataType {
        get {
            return this.dataTypeField;
        }
        set {
            this.dataTypeField = value;
        }
    }

    public object[] Values {
        get {
            return this.valuesField;
        }
        set {
            this.valuesField = value;
        }
    }

    }
}

我目前正在将其转换为.NET集合： -

I am currently turning this into a .NET collection thus:-

public static List<TRecord> ConvertResultToList<TRecord>(object[] columns, int rowCount) where TRecord : DTO.IDataScopeDTOClass
{
    List<TRecord> ret = new List<TRecord>();

    // The object that we got in columns should have a property called Name and a property called DataType and Values[]
    if (rowCount > 0)
    {
        if (columns.Count() > 0)
        {
            System.Reflection.PropertyInfo piName = columns[0].GetType().GetProperty(@"Name" );
            System.Reflection.PropertyInfo piDataType = columns[0].GetType().GetProperty(@"DataType");
            System.Reflection.PropertyInfo piValues = columns[0].GetType().GetProperty(@"Values");

            System.Reflection.ConstructorInfo ciTarget = typeof(TRecord).GetConstructor(Type.EmptyTypes );


            for (int i = 0; i < rowCount ; i++)
            {
                TRecord newValue = (TRecord)ciTarget.Invoke(null);
                foreach (var thisColumn in columns)
                {
                    string name = piName.GetValue(thisColumn).ToString();
                    string dataType = piDataType.GetValue(thisColumn).ToString();
                    object[] value = (object[])piValues.GetValue(thisColumn);
                    newValue.SetProperty(name, dataType, value[i]);
                }
                ret.Add(newValue);
            }

        }


    }

    return ret;
}

然而行 object [] value =（object [] ）piValues.GetValue（thisColumn）; 每次都复制整个数组。我如何获得index [i]的值？

However the line object[] value = (object[])piValues.GetValue(thisColumn); is copying the whole array every time. How do I just get the value at index [i] ?

推荐答案

它不是复制数组;它只是获得对现有数组的引用。



您可以使用反射检索单个值，但这几乎肯定比将值转换为数组并直接访问它更慢：

It's not copying the array; it's just getting a reference to the existing array.

You could retrieve a single value using reflection, but that would almost certainly be slower than casting the value to an array and accessing it directly:

System.Reflection.MethodInfo miGet = piValues.PropertyType.GetMethod("Get");
...
object values = piValues.GetValue(thisColumn);
object value = miGet.Invoke(values, new object[] { i });
newValue.SetProperty(name, dataType, value);

其他评论：



拨打 GetType（）很慢;你应该缓存并重新使用 columns [0]的结果.GetType（）：

Other comments:

A call to GetType() is slow; you should cache and re-use the result of columns[0].GetType():

Type columnType = columns[0].GetType();
System.Reflection.PropertyInfo piName = columnType.GetProperty(@"Name" );
System.Reflection.PropertyInfo piDataType = columnType.GetProperty(@"DataType");
System.Reflection.PropertyInfo piValues = columnType.GetProperty(@"Values");

您可以通过添加<反射来避免通过反射调用 TRecord 的构造函数code> new（）对类型参数的约束：

You can avoid calling the TRecord's constructor via reflection by adding a new() constraint to the type parameter:

where TRecord : DTO.IDataScopeDTOClass, new()
...
TRecord newValue = new TRecord();

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