C# performance optimization best practices-C#.Net Tutorial-php.cn

1. The explicitly registered EvenHandler must be explicitly unregistered to avoid memory leaks

Registering a member method to an event of an object will cause the latter to hold A reference to the former. The former will not be garbage collected until the event is logged out.

private void Form1_Load()
{
  ……
  //注册事件
  CommandRemotingContext.CmdChanged += new ReciverCmdStateChangedEventHandler(this.CommandRemotingContext_CmdChanged);
  ……
}
private void Form1_FromClosed()
{
  ……
  //关闭窗体时及时释放事件
  CommandRemotingContext.CmdChanged -= new ReciverCmdStateChangedEventHandler(this.CommandRemotingContext_CmdChanged);
  ……
}

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Memory leak problem caused by events:

Object A subscribes to events in object B
The life cycle of object A is much longer than that of object B
Object A does not unsubscribe from object B
Eventually, object B cannot be released

2. Batch operations on the data source bound to the control should avoid automatic refresh

When the client operates data in batches, the refresh operation of the control will cause unnecessary time consumption
When the data source (such as When a DataTable, Array, List, ObservableCollection or other IListSource, etc.) is bound to a control, you should disconnect the binding or suspend the refresh of the control when operating data in batches.
```
this.gcBillList.DataSource = null;
DataRowCollection rows = this.ds.Tables[0].Rows;
foreach (DataRow row in rows)
{
    // DataRow数据操作
}
this.gcBillList.DataSource = this.ds.Tables[0].DefaultView;
```
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3. Reduce the number of communications between the client and the server

The fewer WebService calls, the better. If the amount of data to be transmitted is large, consider splitting it into multiple calls.

For short WebService calls, they should be merged as much as possible to reduce the number of interactions

//多次调用了相同的WS  
txtCompanyName.Text=SCPubFunctionClient.PublicWSCal<string>(“ForTest”, “GetCompanyNameByID”,“0001”);  txtCompanyInnerName.Text=SCPubFunctionClient.PublicWSCal<string>(“ForTest”, “GetCompanyInnerNameByID”,“0001”);
//合并相邻的WS  
string[] result=SCPubFunctionClient.PublicWSCal<string>(“ForTest”, “GetCompanyNameAndInnerNameByID”,“0001”);
txtCompanyName.Text=result[0];
txtCompanyInnerName.Text= result[1];

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4. Reduce the number of communications between the client and the server

If not necessary, try to avoid calling WebService repeatedly in the loop body

//循环调用了相同的WS  
List<Person> persons;
……
foreach(string personID in personIDs)
{
	person=HRPubWsClient.getPerson(personID);
	persons.Add(person);
}
//合并WS  
List<Person> persons;
……
persons =HRPubWsClient.getPersonList(personIDs);

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5. Use generics to avoid boxing and unboxing operations (reduce garbage collection pressure)

Boxing operations will cause GC pressure; if it occurs in a collection , should be avoided by using generic collections.

For collections of value types, use List instead of ArrayList, and use Dictionary instead of Hashtable.

ArrayList h=new ArrayList();  //不建议
h.Add(1);
 
List<object> h = new List<object>();  //不建议
h.Add(1);
 
List<int> h = new List<int>();    //建议
h.Add(1);

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6. String operation:

C# String operation--reduce Garbage collection pressure7. Use constants to avoid creating objects

In the following example, there are a lot of new decimal(0) codes in the program, which will cause small Objects are created and recycled frequently; the correct approach is to use the Decimal.Zero constant.

private string CurrencyCalc()
{
    if (firstValue == new decimal(0))  ……
    if (secondValue == new decimal(0)) ……
    if (thirdValue == new decimal(0)) ……
    if (fourthValue == new decimal(0)) ……
    ……
}

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8. Avoid unnecessary exception throwing

C# Exception handling ( Catch Throw) IL analysis

9. Use RemoveAll instead of RemoveAt to delete multiple elements

When using the RemoveAll method to delete multiple elements in a collection (such as a List) at one time, only one resize operation will be performed on the internal array of the List, which is significantly more efficient than calling RemoveAt in a loop.
```
List<string>  lst = new List<string> {"1", "2", "3", "1", "2", "4"};
//不建议：
for (int i = lst.Count - 1; i >= 0; i--)
{
    if (lst[i] == "1" || lst[i] == "2")
    {
        lst.RemoveAt(i);
     }
}
 
//建议：
lst.RemoveAll(s => s == "1" || s == "2");
```
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10. C# DataSet performance best practices

11. Reflection and dynamic binding--reduce CPU Occupy

# Reflection technology converts static binding during compilation into dynamic binding that is delayed to runtime.
C# mainly supports 5 ways to dynamically create objects (the time consumption comes from the network, which is quite different from my actual measurement. See the specific test below) :

动态创建对象的方式	与Direct Create
1.Type.InvokeMember	慢40倍以上
2.ContructorInfo.Invoke	慢40倍以上
3.Activator.CreateInstance(Type)	慢7倍
4.Activator.CreateInstance(assemblyName, typeName)	慢1000倍以上
5.Assembly.CreateInstance(typeName)	慢40倍以上

应尽量避免使用反射和动态绑定；如必须使用，要遵循以下原则：

1．使用接口调用方式将动态绑定改造为早期绑定（Direct Call）
2．使用 Activator.CreateInstance(Type)方式动态创建对象

3．使用typeof操作符代替GetType调用

小注：

通过循环创建实例记录时间如下：

加载程序集、获取类型在循环外部时间如下（这时不同创建方式消耗时间差距挺大）：

代码如下：

 public void TestCreateInstance()
        {
            Stopwatch watch1 = new Stopwatch();
            var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
            Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
            int num = 100000;
            watch1.Start();

            for (int i = 0; i < num; i++)
            {
                //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                Activator.CreateInstance(type);
            }
            watch1.Stop();
            label1.Text = "Activator.CreateInstance(Type type)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                Activator.CreateInstance("ReflectiveClassLibrary", "ReflectiveClassLibrary.TestClass");
            }
            watch1.Stop();
            label2.Text = "Activator.CreateInstance(string assemblyName,string typeName)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //加载程序集                
                asmb.CreateInstance("TestClass");
            }
            watch1.Stop();
            label3.Text = "assembly.CreateInstance(string typeName)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                object obj = type.InvokeMember(null, BindingFlags.Public |
               BindingFlags.Instance | BindingFlags.CreateInstance, null, null, null);
            }
            watch1.Stop();
            label4.Text = "Type.InvokeMember(string name, BindingFlags invokeAttr, Binder binder, object target, object[] args)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                ConstructorInfo constructorInfo = type.GetConstructors()[0];
                constructorInfo.Invoke(null);
            }
            watch1.Stop();
            label5.Text = "ContructorInfo.Invoke(object[] parameters)时间：" + watch1.ElapsedMilliseconds + "毫秒";

        }

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加载程序集、获取类型在循环内部时间如下（这时不同创建方式消耗时间差距比较小）：

代码如下：

 public void TestCreateInstance()
        {
            Stopwatch watch1 = new Stopwatch();
            //var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
            //Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
            int num = 100000;
            watch1.Start();

            for (int i = 0; i < num; i++)
            {
                var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                Activator.CreateInstance(type);
            }
            watch1.Stop();
            label1.Text = "Activator.CreateInstance(Type type)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                Activator.CreateInstance("ReflectiveClassLibrary", "ReflectiveClassLibrary.TestClass");
            }
            watch1.Stop();
            label2.Text = "Activator.CreateInstance(string assemblyName,string typeName)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                //加载程序集                
                asmb.CreateInstance("TestClass");
            }
            watch1.Stop();
            label3.Text = "assembly.CreateInstance(string typeName)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                object obj = type.InvokeMember(null, BindingFlags.Public |
               BindingFlags.Instance | BindingFlags.CreateInstance, null, null, null);
            }
            watch1.Stop();
            label4.Text = "Type.InvokeMember(string name, BindingFlags invokeAttr, Binder binder, object target, object[] args)时间：" + watch1.ElapsedMilliseconds + "毫秒";

            watch1.Reset();
            watch1.Start();
            for (int i = 0; i < num; i++)
            {
                var asmb = Assembly.LoadFrom("ReflectiveClassLibrary.dll");
                Type type = asmb.GetType("ReflectiveClassLibrary.TestClass");
                ConstructorInfo constructorInfo = type.GetConstructors()[0];
                constructorInfo.Invoke(null);
            }
            watch1.Stop();
            label5.Text = "ContructorInfo.Invoke(object[] parameters)时间：" + watch1.ElapsedMilliseconds + "毫秒";

        }

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测试代码如下：