Emit学习(3) - OpCodes - 循环和异常

本来准备直接进入Dapper的, 但是昨天初步看了一下, 内容不少, Dapper不愧是一款成熟的框架, 里面对各种情况的考虑, 很实用, 不过这也使得我短时间内看不完, 所以得等几天了.

那就先来看看循环和异常吧, 看IL跳转的时候, 有一个标签, 跳来跳去的, 在OpCodes里面, 也是有对应的实现的.

一、示例

public static void Xunhuan(int num)
        {
            try
            {
                int sum = ;
                if (num < )
                {
                    throw new Exception("num is less than 1");
                }
                for (int i = ; i <= num; i++)
                {
                    sum += i;
                }
                Console.WriteLine("executed successfully : Sum = " + sum);
            }
            catch (Exception e)
            {
                Console.WriteLine("error happened : " + e.Message);
            }
        }

在调用Xunhuan()的时候, 传入小于1的值时, 会抛出异常, 进入异常处理部分,  否则进入循环(此处为了演示, 使用循环, 否则应该使用算法计算结果), 求和. 结果我就不贴了.

二、OpCodes实现

static Action<int> action;
        static void Main(string[] args)
        {
            //定义一个动态方法
            var method = new DynamicMethod("Xunhuan", null, new Type[] { typeof(int) });
            ILGenerator IL = method.GetILGenerator();

            //定义标签
            var label1 = IL.DefineLabel();
            var xunLabel = IL.DefineLabel();
            var endLabel = IL.DefineLabel();

            //定义本地变量
            var sum = IL.DeclareLocal(typeof(int));
            var i = IL.DeclareLocal(typeof(int));

            IL.Emit(OpCodes.Ldc_I4_0);
            IL.Emit(OpCodes.Stloc_0); //sum = 0

            IL.Emit(OpCodes.Ldc_I4_1);
            IL.Emit(OpCodes.Stloc_1); // i = 1
            IL.Emit(OpCodes.Ldstr, "enter number : num = ");
            IL.Emit(OpCodes.Ldarg_0);
            //实现方式一 装箱
            IL.Emit(OpCodes.Box, typeof(int));   //装箱
            IL.Emit(OpCodes.Call, typeof(string).GetMethod("Concat", new Type[] { typeof(string), typeof(object) }));
            IL.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }));

            Label tryLabel = IL.BeginExceptionBlock(); //try
            IL.Emit(OpCodes.Ldarg_0);  //num
            IL.Emit(OpCodes.Ldc_I4_1); //
            IL.Emit(OpCodes.Bge, label1); //num >= 1 -> label1, 注: try里面的跳转, 不能跳出try语句, 只能在内部

            IL.Emit(OpCodes.Ldstr, "num is less than 1");
            IL.Emit(OpCodes.Newobj, typeof(Exception).GetConstructor(new Type[] { typeof(string) })); //new Exception();
            IL.Emit(OpCodes.Throw); //throw

            IL.MarkLabel(label1);
            IL.Emit(OpCodes.Ldloc_1); //i
            IL.Emit(OpCodes.Ldarg_0); //num
            IL.Emit(OpCodes.Bgt, xunLabel); // i > num -> endLabel

            IL.Emit(OpCodes.Ldloc_0);
            IL.Emit(OpCodes.Ldloc_1);
            IL.Emit(OpCodes.Add);
            IL.Emit(OpCodes.Stloc_0); // sum += i;

            IL.Emit(OpCodes.Ldloc_1);
            IL.Emit(OpCodes.Ldc_I4_1);
            IL.Emit(OpCodes.Add);
            IL.Emit(OpCodes.Stloc_1); //i+=1;
            IL.Emit(OpCodes.Br_S, label1);

            IL.MarkLabel(xunLabel);
            IL.Emit(OpCodes.Ldstr, "executed successfully : Sum = ");
            IL.Emit(OpCodes.Ldloc_0);
            //实现方式二 调用Convert.ToString(int num)方法
            IL.Emit(OpCodes.Call, typeof(Convert).GetMethod("ToString", new Type[] { typeof(int) }));
            IL.Emit(OpCodes.Call, typeof(string).GetMethod("Concat", new Type[] { typeof(string), typeof(string) }));
            IL.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(object) }));

            IL.MarkLabel(endLabel);
            IL.Emit(OpCodes.Nop);

            IL.BeginCatchBlock(typeof(Exception)); //catch
            IL.Emit(OpCodes.Callvirt, typeof(Exception).GetMethod("get_Message"));
            IL.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }));
            IL.EndExceptionBlock(); //end

            IL.Emit(OpCodes.Ret);

            action = (Action<int>)method.CreateDelegate(typeof(Action<int>)); //此处通过委托的方式来调动方法, 而不再是保存成dll文件了

            Console.WriteLine("-------------正常执行---------------");
            action.Invoke();
            Console.WriteLine("-------------异常执行---------------");
            action.Invoke(-);
            Console.ReadKey();
        }

实现的方式并不是唯一的, 我写的这个方法, 并不是最简的. 下面贴出reflector反编译的IL代码, 与我写的这个还是有不少不同的.

   .method public hidebysig static void Xunhuan(int32 num) cil managed
    {
        .maxstack
        .locals init (
            [] int32 num2,
            [] int32 num3,
            [] class [mscorlib]System.Exception exception,
            [] bool flag)
        L_0000: nop
        L_0001: nop
        L_0002: ldc.i4.
        L_0003: stloc.
        L_0004: ldarg.
        L_0005: ldc.i4.
        L_0006: clt
        L_0008: ldc.i4.
        L_0009: ceq
        L_000b: stloc.
        L_000c: ldloc.
        L_000d: brtrue.s L_001b
        L_000f: nop
        L_0010: ldstr "num is less than 1"
        L_0015: newobj instance void [mscorlib]System.Exception::.ctor(string)
        L_001a: throw
        L_001b: ldc.i4.
        L_001c: stloc.
        L_001d: br.s L_0029
        L_001f: nop
        L_0020: ldloc.
        L_0021: ldloc.
        L_0022: add
        L_0023: stloc.
        L_0024: nop
        L_0025: ldloc.
        L_0026: ldc.i4.
        L_0027: add
        L_0028: stloc.
        L_0029: ldloc.
        L_002a: ldarg.
        L_002b: cgt
        L_002d: ldc.i4.
        L_002e: ceq
        L_0030: stloc.
        L_0031: ldloc.
        L_0032: brtrue.s L_001f
        L_0034: ldstr "executed successfully : Sum = "
        L_0039: ldloc.
        L_003a: box int32
        L_003f: call string [mscorlib]System.String::Concat(object, object)
        L_0044: call void [mscorlib]System.Console::WriteLine(string)
        L_0049: nop
        L_004a: nop
        L_004b: leave.s L_0068
        L_004d: stloc.
        L_004e: nop
        L_004f: ldstr "error happened : "
        L_0054: ldloc.
        L_0055: callvirt instance string [mscorlib]System.Exception::get_Message()
        L_005a: call string [mscorlib]System.String::Concat(string, string)
        L_005f: call void [mscorlib]System.Console::WriteLine(string)
        L_0064: nop
        L_0065: nop
        L_0066: leave.s L_0068
        L_0068: nop
        L_0069: ret
        .try L_0001 to L_004d catch [mscorlib]System.Exception handler L_004d to L_0068
    }

以前总是懒, 对于新的知识, 都是看看, 看懂就成, 但是在实际写的过程中, 会碰到很多看不会遇到的问题, 编码还真不是看看就能写好的, 好记性不如烂笔头, 还是得自己一行一行敲一下, 才能发现里面的问题.