Question

使用C＃时，我注意到在使用动态生成类型的实例与简单结构填充列表时，性能存在显着差异。下面的代码包含4种不同的方法，用于填充包含100,000个对象的列表。

每种方法的表现都不同：

Button1：15毫秒

按钮2：31毫秒

Button3＆amp; 4：300毫秒

注意，按钮3和按钮的代码4来自this topic

有人能解释为什么动态创建的对象会变慢吗？

    public struct DataRow
    {
        public double t;
        public double vf;
        public double im;

        public double T { get { return t; } set { t = value; } }
        public double Vf { get { return vf; } set { vf = value; } }
        public double Im { get { return im; } set { im = value; } }
    }

    //Use struct defined above
    private void button1_Click(object sender, EventArgs e)
    {
        int n = 0;

        //adding rows
        List<DataRow> myTable = new List<DataRow>();
        DataRow myRow = new DataRow();

        start = DateTime.Now;

        while (n < 100000)
        {
            myRow.T = n * 1.0;
            myRow.Vf = 2.0;
            myRow.Im = 4.0;

            myTable.Add(myRow);

            n++;
        }
        end = DateTime.Now;
        System.TimeSpan diff = end.Subtract(start);
        label2.Text = diff.Seconds.ToString();
        label4.Text = diff.Milliseconds.ToString();

        dataGridView1.DataSource = myTable;
    }

    //define the list as it is done on buttons 3 & 4 but use the static struct
    private void button2_Click(object sender, EventArgs e)
    {
        Type myType = typeof(DataRow);

        Type listType = typeof(List<>);

        Type myListType = listType.MakeGenericType(myType);

        IList myTable = (IList)Activator.CreateInstance(myListType);

        DataRow bRow = new DataRow();

        int n = 0;
        start = DateTime.Now;
        while (n < 100000)
        {
            bRow.t = n * 1.0;
            bRow.vf = 2.0;
            bRow.im = 4.0;
            myTable.Add(bRow);

            n++;
        }
        end = DateTime.Now;
        System.TimeSpan diff = end.Subtract(start);
        label2.Text = diff.Seconds.ToString();
        label4.Text = diff.Milliseconds.ToString();
        dataGridView1.DataSource = myTable;

    }

    //Create assy at runtime and load dll
    private void button3_Click(object sender, EventArgs e)
    {
        Type myType = CreateDynRow();
        Assembly myAssy = Assembly.LoadFrom("DynaRowAssy.dll");
        Type myRow = myAssy.GetType("DynaRow");

        Type listType = typeof(List<>);

        Type myListType = listType.MakeGenericType(myRow);

        IList myTable = (IList)Activator.CreateInstance(myListType);

        FieldInfo piT = myRow.GetField("t");
        FieldInfo piVf = myRow.GetField("vf");
        FieldInfo piIm = myRow.GetField("im");

        ValueType aRow = (ValueType)Activator.CreateInstance(myRow);

        int n = 0;
        start = DateTime.Now;
        while (n < 100000)
        {
            piT.SetValue(aRow, 1 * n);
            piVf.SetValue(aRow, 2.0);
            piIm.SetValue(aRow, 4.0);
            myTable.Add(aRow);

            n++;
        }
        end = DateTime.Now;
        System.TimeSpan diff = end.Subtract(start);
        label2.Text = diff.Seconds.ToString();
        label4.Text = diff.Milliseconds.ToString();
        dataGridView1.DataSource = myTable;
    }

    //create assy at runtime in memory
    private void button4_Click(object sender, EventArgs e)
    {
        //build the assembly
        Type myType = CreateDynRow();

        Type listType = typeof(List<>);

        Type myListType = listType.MakeGenericType(myType);

        IList myTable = (IList)Activator.CreateInstance(myListType);

        FieldInfo piT = myType.GetField("t");
        FieldInfo piVf = myType.GetField("vf");
        FieldInfo piIm = myType.GetField("im");

        ValueType aRow = (ValueType)Activator.CreateInstance(myType);

        int n = 0;
        start = DateTime.Now;
        while (n < 100000)
        {
            piT.SetValue(aRow, 1 * n);
            piVf.SetValue(aRow, 2.0);
            piIm.SetValue(aRow, 4.0);
            myTable.Add(aRow);

            n++;
        }
        end = DateTime.Now;
        System.TimeSpan diff = end.Subtract(start);
        label2.Text = diff.Seconds.ToString();
        label4.Text = diff.Milliseconds.ToString();
        dataGridView1.DataSource = myTable;
    }

Answer 1

它（主要）不是动态创建：它使用了反射（FieldInfo.SetValue），使得button3和button4版本比编译调用时更慢。

一种可能的方法是声明代码可以编译的接口，并使动态类型实现此接口。您仍然会通过反射实例化并查询该接口的动态类型，但之后它应该与“静态”引用一样快。

Answer 2

简单回答：正在执行更多代码以动态创建对象。

反射总是比预先定义类型然后直接使用该对象慢。您要求运行时为您做更多的工作，而不是预先指定所有内容。根据您使用的反射功能......您的代码会变慢。

如果需要详细信息，请检查代码生成的IL。这应该给你整个故事。

Answer 3

这是我们想出的。它几乎和静态定义的情况一样快：

// Dynamically create DataRow derived from ValueType, 
// List of DataRows, 
// Delegates to properties
//  

private void button4_Click(object sender, EventArgs e)
{
    Type myType = CreateDynRow();  // dynamic version of DataRow, see above
    Type myListType = typeof(List<>).MakeGenericType(myType);
    IList myTable = (IList)Activator.CreateInstance(myListType);
    ValueType myRowBuffer = (ValueType)Activator.CreateInstance(myType);

    var mySet_TDelegate = myRowBuffer.GetInstanceInvoker<Action<Double>>("set_T");
    var mySet_ImDelegate = myRowBuffer.GetInstanceInvoker<Action<Double>>("set_Im");
    var mySet_VfDelegate = myRowBuffer.GetInstanceInvoker<Action<Double>>("set_Vf");

    stopWatch.Reset();
    stopWatch.Start();
    for (int n = 0; n < rowCount; n++)
    {
        mySet_TDelegate(1.0 * n);
        mySet_ImDelegate(4.0);
        mySet_VfDelegate(2.0);

        myTable.Add(myRowBuffer);
    }
    stopWatch.Stop();
    label1.Text = String.Format("{0}", stopWatch.ElapsedMilliseconds);

    dataGridView1.DataSource = myTable;
}

感谢您的帮助。顺便说一句，我们使用贾斯汀的＆amp;马克的答案。 GetInstanceInvoker来自Kenneth Xu的Common.Reflection类。

动态创建类型的性能

3 个答案: