[英]C# Constructor base keyword
我正在使用反射器插入Microsoft.Practices.Prism程序集,並遇到了DelagateCommand構造函數的以下定義:
public DelegateCommand(Action executeMethod, Func<bool> canExecuteMethod)
: base(action, func)
{
Action<object> action = null;
Func<object, bool> func = null;
if (action == null)
{
action = o => executeMethod();
}
if (func == null)
{
func = o => canExecuteMethod();
}
if ((executeMethod == null) || (canExecuteMethod == null))
{
throw new ArgumentNullException(
"executeMethod",
Resources.DelegateCommandDelegatesCannotBeNull);
}
}
這段代碼無法編譯,因為: base(action, func)
指向ctor中的前兩個變量。
是否可以復制這種行為? 也許通過使用匿名方法?
預先感謝您的輸入。
此方法的反射器IL:
.method public hidebysig specialname rtspecialname instance void .ctor(class [mscorlib]System.Action executeMethod, class [mscorlib]System.Func`1<bool> canExecuteMethod) cil managed
{
.maxstack 5
.locals init (
[0] class [mscorlib]System.Action`1<object> action,
[1] class [mscorlib]System.Func`2<object, bool> func,
[2] class Microsoft.Practices.Prism.Commands.DelegateCommand/<>c__DisplayClass6 class2)
L_0000: ldnull
L_0001: stloc.0
L_0002: ldnull
L_0003: stloc.1
L_0004: newobj instance void Microsoft.Practices.Prism.Commands.DelegateCommand/<>c__DisplayClass6::.ctor()
L_0009: stloc.2
L_000a: ldloc.2
L_000b: ldarg.1
L_000c: stfld class [mscorlib]System.Action Microsoft.Practices.Prism.Commands.DelegateCommand/<>c__DisplayClass6::executeMethod
L_0011: ldloc.2
L_0012: ldarg.2
L_0013: stfld class [mscorlib]System.Func`1<bool> Microsoft.Practices.Prism.Commands.DelegateCommand/<>c__DisplayClass6::canExecuteMethod
L_0018: ldarg.0
L_0019: ldloc.0
L_001a: brtrue.s L_0029
L_001c: ldloc.2
L_001d: ldftn instance void Microsoft.Practices.Prism.Commands.DelegateCommand/<>c__DisplayClass6::<.ctor>b__2(object)
L_0023: newobj instance void [mscorlib]System.Action`1<object>::.ctor(object, native int)
L_0028: stloc.0
L_0029: ldloc.0
L_002a: ldloc.1
L_002b: brtrue.s L_003a
L_002d: ldloc.2
L_002e: ldftn instance bool Microsoft.Practices.Prism.Commands.DelegateCommand/<>c__DisplayClass6::<.ctor>b__3(object)
L_0034: newobj instance void [mscorlib]System.Func`2<object, bool>::.ctor(object, native int)
L_0039: stloc.1
L_003a: ldloc.1
L_003b: call instance void Microsoft.Practices.Prism.Commands.DelegateCommandBase::.ctor(class [mscorlib]System.Action`1<object>, class [mscorlib]System.Func`2<object, bool>)
L_0040: ldloc.2
L_0041: ldfld class [mscorlib]System.Action Microsoft.Practices.Prism.Commands.DelegateCommand/<>c__DisplayClass6::executeMethod
L_0046: brfalse.s L_0050
L_0048: ldloc.2
L_0049: ldfld class [mscorlib]System.Func`1<bool> Microsoft.Practices.Prism.Commands.DelegateCommand/<>c__DisplayClass6::canExecuteMethod
L_004e: brtrue.s L_0060
L_0050: ldstr "executeMethod"
L_0055: call string Microsoft.Practices.Prism.Properties.Resources::get_DelegateCommandDelegatesCannotBeNull()
L_005a: newobj instance void [mscorlib]System.ArgumentNullException::.ctor(string, string)
L_005f: throw
L_0060: ret
}
同樣,在codeplex上查看了實際的源代碼之后,方法定義如下:
public DelegateCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod)
: base((o) => executeMethod((T)o), (o) => canExecuteMethod((T)o))
{
if (executeMethod == null || canExecuteMethod == null)
throw new ArgumentNullException("executeMethod", Resources.DelegateCommandDelegatesCannotBeNull);
#if !WINDOWS_PHONE
Type genericType = typeof(T);
// DelegateCommand allows object or Nullable<>.
// note: Nullable<> is a struct so we cannot use a class constraint.
if (genericType.IsValueType)
{
if ((!genericType.IsGenericType) || (!typeof(Nullable<>).IsAssignableFrom(genericType.GetGenericTypeDefinition())))
{
throw new InvalidCastException(Resources.DelegateCommandInvalidGenericPayloadType);
}
}
#endif
}
我認為這可能只是一個反射器錯誤,試圖表示對lambda的后備委托進行緩存的方式。 真正的代碼很可能是:
: base(o => executeMethod(), o => canExecuteMethod())
你有IL嗎?
編輯:嗯...我不能復制。 但是,還有其他兩種選擇:在C ++和IL中,您幾乎可以做任何事情。 該代碼看起來...很時髦。
恕我直言,這是Reflector的失敗。 您為什么不查看Prism的源代碼?
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