创建一个包含 UnixTimestamp 帮助器方法的 DynamicAssembly

此示例通过生成使用已存在和新创建的成员以及基本异常处理的代码来显示 ILGenerator 的用法。以下代码发出 DynamicAssembly，其中包含与此 C#代码等效的内容：

public static class UnixTimeHelper
{
    private readonly static DateTime EpochTime = new DateTime(1970, 1, 1);

    public static int UnixTimestamp(DateTime input)
    {
        int totalSeconds;
        try
        {
            totalSeconds = checked((int)input.Subtract(UnixTimeHelper.EpochTime).TotalSeconds);
        }
        catch (OverflowException overflowException)
        {
            throw new InvalidOperationException("It's to late for an Int32 timestamp.", overflowException);
        }
        return totalSeconds;
    }
}

//Get the required methods
var dateTimeCtor = typeof (DateTime)
    .GetConstructor(new[] {typeof (int), typeof (int), typeof (int)});
var dateTimeSubstract = typeof (DateTime)
    .GetMethod(nameof(DateTime.Subtract), new[] {typeof (DateTime)});
var timeSpanSecondsGetter = typeof (TimeSpan)
    .GetProperty(nameof(TimeSpan.TotalSeconds)).GetGetMethod();
var invalidOperationCtor = typeof (InvalidOperationException)
    .GetConstructor(new[] {typeof (string), typeof (Exception)});

if (dateTimeCtor == null || dateTimeSubstract == null ||
    timeSpanSecondsGetter == null || invalidOperationCtor == null)
{
    throw new Exception("Could not find a required Method, can not create Assembly.");
}

//Setup the required members
var an = new AssemblyName("UnixTimeAsm");
var dynAsm = AppDomain.CurrentDomain.DefineDynamicAssembly(an, AssemblyBuilderAccess.RunAndSave);
var dynMod = dynAsm.DefineDynamicModule(an.Name, an.Name + ".dll");

var dynType = dynMod.DefineType("UnixTimeHelper",
    TypeAttributes.Abstract | TypeAttributes.Sealed | TypeAttributes.Public);

var epochTimeField = dynType.DefineField("EpochStartTime", typeof (DateTime),
    FieldAttributes.Private | FieldAttributes.Static | FieldAttributes.InitOnly);

var cctor =
    dynType.DefineConstructor(
        MethodAttributes.Private | MethodAttributes.HideBySig | MethodAttributes.SpecialName |
        MethodAttributes.RTSpecialName | MethodAttributes.Static, CallingConventions.Standard,
        Type.EmptyTypes);

var cctorGen = cctor.GetILGenerator();
cctorGen.Emit(OpCodes.Ldc_I4, 1970); //Load the DateTime constructor arguments onto the stack
cctorGen.Emit(OpCodes.Ldc_I4_1);
cctorGen.Emit(OpCodes.Ldc_I4_1);
cctorGen.Emit(OpCodes.Newobj, dateTimeCtor); //Call the constructor
cctorGen.Emit(OpCodes.Stsfld, epochTimeField); //Store the object in the static field   
cctorGen.Emit(OpCodes.Ret);

var unixTimestampMethod = dynType.DefineMethod("UnixTimestamp",
    MethodAttributes.Public | MethodAttributes.HideBySig | MethodAttributes.Static,
    CallingConventions.Standard, typeof (int), new[] {typeof (DateTime)});

unixTimestampMethod.DefineParameter(1, ParameterAttributes.None, "input");

var methodGen = unixTimestampMethod.GetILGenerator();
methodGen.DeclareLocal(typeof (TimeSpan));
methodGen.DeclareLocal(typeof (int));
methodGen.DeclareLocal(typeof (OverflowException));

methodGen.BeginExceptionBlock(); //Begin the try block
methodGen.Emit(OpCodes.Ldarga_S, (byte) 0); //To call a method on a struct we need to load the address of it
methodGen.Emit(OpCodes.Ldsfld, epochTimeField);
    //Load the object of the static field we created as argument for the following call
methodGen.Emit(OpCodes.Call, dateTimeSubstract); //Call the substract method on the input DateTime
methodGen.Emit(OpCodes.Stloc_0); //Store the resulting TimeSpan in a local
methodGen.Emit(OpCodes.Ldloca_S, (byte) 0); //Load the locals address to call a method on it
methodGen.Emit(OpCodes.Call, timeSpanSecondsGetter); //Call the TotalSeconds Get method on the TimeSpan
methodGen.Emit(OpCodes.Conv_Ovf_I4); //Convert the result to Int32; throws an exception on overflow
methodGen.Emit(OpCodes.Stloc_1); //store the result for returning later
//The leave instruction to jump behind the catch block will be automatically emitted
methodGen.BeginCatchBlock(typeof (OverflowException)); //Begin the catch block
//When we are here, an OverflowException was thrown, that is now on the stack
methodGen.Emit(OpCodes.Stloc_2); //Store the exception in a local.
methodGen.Emit(OpCodes.Ldstr, "It's to late for an Int32 timestamp.");
    //Load our error message onto the stack
methodGen.Emit(OpCodes.Ldloc_2); //Load the exception again
methodGen.Emit(OpCodes.Newobj, invalidOperationCtor);
    //Create an InvalidOperationException with our message and inner Exception
methodGen.Emit(OpCodes.Throw); //Throw the created exception
methodGen.EndExceptionBlock(); //End the catch block
//When we are here, everything is fine
methodGen.Emit(OpCodes.Ldloc_1); //Load the result value
methodGen.Emit(OpCodes.Ret); //Return it

dynType.CreateType();

dynAsm.Save(an.Name + ".dll");