我想創建一個方法(在運行時)爲所有類型的委託創建包裝。這爲創建注入附加日誌記錄的靈活方式(在這種情況下)。在這第一步中,我試圖圍繞給定的input
-參數創建一個try-catch環繞。「變量」的類型'System.Boolean'從範圍''引用,但它沒有被定義「在表達式
try
{
Console.WriteLine(....);
// Here the original call
Console.WriteLine(....);
}
catch(Exception ex)
{
Console.WriteLine(.....);
}
我使用的是通用的方法調用CreateWrapper2
(見下文)
private static readonly MethodInfo ConsoleWriteLine = typeof(Console).GetMethod("WriteLine", new[] { typeof(string), typeof(object[]) });
private static MethodCallExpression WriteLinExpression(string format, params object[] args)
{
Expression[] expressionArguments = new Expression[2];
expressionArguments[0] = Expression.Constant(format, typeof(string));
expressionArguments[1] = Expression.Constant(args, typeof(object[]));
return Expression.Call(ConsoleWriteLine, expressionArguments);
}
public T CreateWrapper2<T>(T input)
{
Type type = typeof(T);
if (!typeof(Delegate).IsAssignableFrom(type))
{
return input;
}
PropertyInfo methodProperty = type.GetProperty("Method");
MethodInfo inputMethod = methodProperty != null ? (MethodInfo)methodProperty.GetValue(input) : null;
if (inputMethod == null)
{
return input;
}
string methodName = inputMethod.Name;
ParameterInfo[] parameters = inputMethod.GetParameters();
ParameterExpression[] parameterExpressions = new ParameterExpression[parameters.Length];
// TODO: Validate/test parameters, by-ref /out with attributes etc.
for (int idx = 0; idx < parameters.Length; idx++)
{
ParameterInfo parameter = parameters[idx];
parameterExpressions[idx] = Expression.Parameter(parameter.ParameterType, parameter.Name);
}
bool handleReturnValue = inputMethod.ReturnType != typeof(void);
ParameterExpression variableExpression = handleReturnValue ? Expression.Variable(inputMethod.ReturnType) : null;
MethodCallExpression start = WriteLinExpression("Starting '{0}'.", methodName);
MethodCallExpression completed = WriteLinExpression("Completed '{0}'.", methodName);
MethodCallExpression failed = WriteLinExpression("Failed '{0}'.", methodName);
Expression innerCall = Expression.Call(inputMethod, parameterExpressions);
LabelTarget returnTarget = Expression.Label(inputMethod.ReturnType);
LabelExpression returnLabel = Expression.Label(returnTarget, Expression.Default(returnTarget.Type)); ;
GotoExpression returnExpression = null;
if (inputMethod.ReturnType != typeof(void))
{
// Handle return value.
innerCall = Expression.Assign(variableExpression, innerCall);
returnExpression = Expression.Return(returnTarget, variableExpression, returnTarget.Type);
}
else
{
returnExpression = Expression.Return(returnTarget);
}
List<Expression> tryBodyElements = new List<Expression>();
tryBodyElements.Add(start);
tryBodyElements.Add(innerCall);
tryBodyElements.Add(completed);
if (returnExpression != null)
{
tryBodyElements.Add(returnExpression);
}
BlockExpression tryBody = Expression.Block(tryBodyElements);
BlockExpression catchBody = Expression.Block(tryBody.Type, new Expression[] { failed, Expression.Rethrow(tryBody.Type) });
CatchBlock catchBlock = Expression.Catch(typeof(Exception), catchBody);
TryExpression tryBlock = Expression.TryCatch(tryBody, catchBlock);
List<Expression> methodBodyElements = new List<Expression>();
if(variableExpression != null) methodBodyElements.Add(variableExpression);
methodBodyElements.Add(tryBlock);
methodBodyElements.Add(returnLabel);
Expression<T> wrapperLambda = Expression<T>.Lambda<T>(Expression.Block(methodBodyElements), parameterExpressions);
Console.WriteLine("lambda:");
Console.WriteLine(wrapperLambda.GetDebugView());
return wrapperLambda.Compile();
}
對於無效的方法(如Action<>
)這個代碼做什麼,我需要的。但是,當有一個返回值,我得到的例外「‘式的'變量’System.Boolean‘從範圍引用’,但它沒有定義」
許多其他職位談論Expression.Parameter
調用一次以上爲參數;對我來說它看起來像這裏是其他地方是錯誤的,但我找不到它。一切順利,直到.Compile
行,它崩潰。
對於Func<int, bool> target = i => i % 2 ==0;
,下面是生成的表達式的DebugView。
.Lambda #Lambda1<System.Func`2[System.Int32,System.Boolean]>(System.Int32 $i) {
.Block() {
$var1;
.Try {
.Block() {
.Call System.Console.WriteLine(
"Starting '{0}'.",
.Constant<System.Object[]>(System.Object[]));
$var1 = .Call LDAP.LdapProgram.<Main>b__0($i);
.Call System.Console.WriteLine(
"Completed '{0}'.",
.Constant<System.Object[]>(System.Object[]));
.Return #Label1 { $var1 }
}
} .Catch (System.Exception) {
.Block() {
.Call System.Console.WriteLine(
"Failed '{0}'.",
.Constant<System.Object[]>(System.Object[]));
.Rethrow
}
};
.Label
.Default(System.Boolean)
.LabelTarget #Label1:
}
}
我在想什麼? (在調試小時我嘗試:
- 從試體內部移動
Expression.Variable
到頂層 - 經由typed-得到追趕塊相同Body.Type作爲在try塊。
Expression.Return
。
)