Question

快速提问即使SomeObject.SomeDelegateProperty为null并且不会发生invokation，是否会对someOtherDelegate进行求值？我假设没有，因为（？。）是停止执行如果为null但我需要确认。

SomeObject.SomeDelegateProperty?.Invoke(someOtherDelegate());

谢谢

Answer 1

她的测试示例：

internal class Program
{
    private static void Main( string[] args )
    {
        var SomeObject = new FakeClass();
        SomeObject.SomeDelegateProperty?.Invoke( someOtherDelegate() );
    }

    public static string someOtherDelegate()
    {
        return String.Empty;
    }

    public class FakeClass
    {
        public Action<string> SomeDelegateProperty;
    }
}

和IL代码：

.method private hidebysig static void  Main(string[] args) cil managed
{
    .entrypoint
    // Размер кода:       31 (0x1f)
    .maxstack  2
    .locals init ([0] class StackOverflow.Examples.Program/FakeClass SomeObject)
    IL_0000:  nop
    IL_0001:  newobj     instance void 
    StackOverflow.Examples.Program/FakeClass::.ctor()
    IL_0006:  stloc.0
    IL_0007:  ldloc.0
    IL_0008:  ldfld      class [mscorlib]System.Action`1<string> 
    StackOverflow.Examples.Program/FakeClass::SomeDelegateProperty
    IL_000d:  dup
    IL_000e:  brtrue.s   IL_0013
    IL_0010:  pop
    IL_0011:  br.s       IL_001e
    IL_0013:  call       string      StackOverflow.Examples.Program::someOtherDelegate()
    IL_0018:  callvirt   instance void class 
    [mscorlib]System.Action`1<string>::Invoke(!0)
    IL_001d:  nop
    IL_001e:  ret
} // end of method Program::Main

如何查看说明IL_000e: brtrue.s IL_0013检查SomeDelegateProperty，如果不是空，请拨打地址someOtherDelegate上的IL_0013，否则转到结束地址IL_001e。< / p>

Answer 2

当SomeObject.SomeDelegateProperty == null时，它将停止执行。正如Jeroen van Langen评论的那样

C＃Elvis操作员 - 将评估参数吗？

2 个答案: