I met a strange problem while I was evaluating the Xaml Services that introduced in .net 4.
I created 2 types for Xaml Serialization Test:
So I can create a test instance of Foo by calling Foo(int a), e.g:
Xaml doesn’t support serialize fields, I cannot apply AmbientAttribute to field, so the compilation fails. So I changed the field Complex of Class Foo to a property:
Then the code compiles correct. But when I executed the code, I found the Temp property of Complex is empty guid. But I found I do called the Init method in the constructor of Foo. What’s the problem?
I believe that the problem must be special behavior related to ValueType. So I omitted to call Init(), I try to assign the Complex in Foo’s Constructor as following code
Compiles fails! Visual Studio tells me “Cannot modify the return value of ‘structTest.Foo.Complex’ because it is not a variable”
Still now, everything is explainable:
- It is because this.Complex is pointed to the variable itself that Code Complex.Init() works when Complex is field.
- It is because this.Complex is a return value, a copy of the original variable, instead of the original variable that the Code Complex.Init() doesn’t work when Complex is a property. this.Complex.Init() do changed the value of the Temp, but it modified the new copy instead of the original one.
So we need to be careful while change a value type field into a property, which may modify the program behavior a lot, and really difficult to debug while the code is complicated.