Action as a optional parameter in a function

Question

Is it possible to have an Action as an optional parameter in a function? The button2Action should be optional.

public void DrawWindow(Rect p_PositionAndSize, string p_Button2Text = "NotInUse", Action p_Button2Action)
{
 // Stuff happens here
}

I tried it with e.g p_Button2Action = delegate{ Debug.Log("NotInUse"); } but it does not compile due to Default parameter value for p_Button2Action must be a compile-time constant. How do you make an optional Action that is a compile time constant?

score 22 · Accepted Answer · answered Jun 27 '13 at 07:40

22

You must specify a constant value for a default parameter, so the only default value you can specify for an Action is null.

However, it's easy to check for null and substitute the correct value:

public void DrawWindow(Rect p_PositionAndSize, string p_Button2Text = "NotInUse", Action p_Button2Action = null)
{
    if (p_Button2Action == null)
        p_Button2Action = delegate{ Debug.Log("NotInUse"); }

    ...
}

answered Jun 27 '13 at 07:40

Matthew Watson

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2

if you want null as default action you can use: p_Button2Action?.Invoke(); – RustemMazitov Mar 13 '17 at 09:50
@RMazitov Note that the null coalescing operator is only available in C# 6 or later - so it's correct to use that now (but obviously it didn't exist in 2013) – Matthew Watson Mar 13 '17 at 11:06
yes, good point. thanks for bringing that up) – RustemMazitov Mar 13 '17 at 13:27

score 4 · Answer 2 · answered Jun 27 '13 at 07:37

One workaround for this may be to just use classical overloading:

public void DrawWindow(Rect p_PositionAndSize, string p_Button2Text = "NotInUse")
{
    DrawWindow(p_PositionAndSize, delegate{ Thread.Sleep(1); }, p_Button2Text);
}

public void DrawWindow(Rect p_PositionAndSize, Action p_Button2Action, string p_Button2Text = "NotInUse")
{
 // Stuff happens here
}

This way you can specify the default action in the overload with two parameters.

Action as a optional parameter in a function

2 Answers2