C# – Window Sitters – layered windows colorkeying and clickthrough

clayered-windowsvb6winapi

I made a window sitter in Visual Basic 6 a few years back, which used layered windows colorkeying to painlessly make the form nonrectangular.

I tried to rewrite the window sitter in C# earlier this week, judging that the old code was a mess, and noticed that any clicks within the form's client rectangle were caught by the form, while the VB6 version's clicks fell through to whatever was below if you didn't click within any visible parts. This is a very important matter ofcourse.

Is there some difference between calling the Layered Windows API by hand (VB6) and the TransparancyKey property (.Net) that I'm not aware of, or is there more at hand here?

Best Answer

There are a couple of bugs related to TransparencyKey. Neither seems to be the case you're discussing here, but I wouldn't be surprised if there are more issues with the API.

We'll need to see some code to try and diagnose what is going on exactly.

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – the difference between const and readonly in C#

Apart from the apparent difference of

having to declare the value at the time of a definition for a const VS readonly values can be computed dynamically but need to be assigned before the constructor exits.. after that it is frozen.
const's are implicitly static. You use a ClassName.ConstantName notation to access them.

There is a subtle difference. Consider a class defined in AssemblyA.

public class Const_V_Readonly
{
  public const int I_CONST_VALUE = 2;
  public readonly int I_RO_VALUE;
  public Const_V_Readonly()
  {
     I_RO_VALUE = 3;
  }
}

AssemblyB references AssemblyA and uses these values in code. When this is compiled:

in the case of the const value, it is like a find-replace. The value 2 is 'baked into' the AssemblyB's IL. This means that if tomorrow I update I_CONST_VALUE to 20, AssemblyB would still have 2 till I recompile it.
in the case of the readonly value, it is like a ref to a memory location. The value is not baked into AssemblyB's IL. This means that if the memory location is updated, AssemblyB gets the new value without recompilation. So if I_RO_VALUE is updated to 30, you only need to build AssemblyA and all clients do not need to be recompiled.

So if you are confident that the value of the constant won't change, use a const.

public const int CM_IN_A_METER = 100;

But if you have a constant that may change (e.g. w.r.t. precision).. or when in doubt, use a readonly.

public readonly float PI = 3.14;

Update: Aku needs to get a mention because he pointed this out first. Also I need to plug where I learned this: Effective C# - Bill Wagner

Best Answer

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C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – the difference between const and readonly in C#

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