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.