本來准備直接進入Dapper的, 但是昨天初步看了一下, 內容不少, Dapper不愧是一款成熟的框架, 裡面對各種情況的考慮, 很實用, 不過這也使得我短時間內看不完, 所以得等幾天了.
那就先來看看循環和異常吧, 看IL跳轉的時候, 有一個標簽, 跳來跳去的, 在OpCodes裡面, 也是有對應的實現的.
一、示例
public static void Xunhuan(int num)
{
try
{
int sum = 0;
if (num < 1)
{
throw new Exception("num is less than 1");
}
for (int i = 1; i <= num; i++)
{
sum += i;
}
Console.WriteLine("executed successfully : Sum = " + sum);
}
catch (Exception e)
{
Console.WriteLine("error happened : " + e.Message);
}
}
在調用Xunhuan()的時候, 傳入小於1的值時, 會拋出異常, 進入異常處理部分, 否則進入循環(此處為了演示, 使用循環, 否則應該使用算法計算結果), 求和. 結果我就不貼了.
二、OpCodes實現
static Action<int> action;
static void Main(string[] args)
{
//定義一個動態方法
var method = new DynamicMethod("Xunhuan", null, new Type[] { typeof(int) });
ILGenerator IL = method.GetILGenerator();
//定義標簽
var label1 = IL.DefineLabel();
var xunLabel = IL.DefineLabel();
var endLabel = IL.DefineLabel();
//定義本地變量
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);
//實現方式一 裝箱
IL.Emit(OpCodes.Box, typeof(int)); //裝箱
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); // 1
IL.Emit(OpCodes.Bge, label1); //num >= 1 -> label1, 注: try裡面的跳轉, 不能跳出try語句, 只能在內部
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);
//實現方式二 調用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>)); //此處通過委托的方式來調動方法, 而不再是保存成dll文件了
Console.WriteLine("-------------正常執行---------------");
action.Invoke(10);
Console.WriteLine("-------------異常執行---------------");
action.Invoke(-10);
Console.ReadKey();
}
實現的方式並不是唯一的, 我寫的這個方法, 並不是最簡的. 下面貼出reflector反編譯的IL代碼, 與我寫的這個還是有不少不同的.
.method public hidebysig static void Xunhuan(int32 num) cil managed
{
.maxstack 2
.locals init (
[0] int32 num2,
[1] int32 num3,
[2] class [mscorlib]System.Exception exception,
[3] bool flag)
L_0000: nop
L_0001: nop
L_0002: ldc.i4.0
L_0003: stloc.0
L_0004: ldarg.0
L_0005: ldc.i4.1
L_0006: clt
L_0008: ldc.i4.0
L_0009: ceq
L_000b: stloc.3
L_000c: ldloc.3
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.i4.1
L_001c: stloc.1
L_001d: br.s L_0029
L_001f: nop
L_0020: ldloc.0
L_0021: ldloc.1
L_0022: add
L_0023: stloc.0
L_0024: nop
L_0025: ldloc.1
L_0026: ldc.i4.1
L_0027: add
L_0028: stloc.1
L_0029: ldloc.1
L_002a: ldarg.0
L_002b: cgt
L_002d: ldc.i4.0
L_002e: ceq
L_0030: stloc.3
L_0031: ldloc.3
L_0032: brtrue.s L_001f
L_0034: ldstr "executed successfully : Sum = "
L_0039: ldloc.0
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.2
L_004e: nop
L_004f: ldstr "error happened : "
L_0054: ldloc.2
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
}
以前總是懶, 對於新的知識, 都是看看, 看懂就成, 但是在實際寫的過程中, 會碰到很多看不會遇到的問題, 編碼還真不是看看就能寫好的, 好記性不如爛筆頭, 還是得自己一行一行敲一下, 才能發現裡面的問題.
