如何在C＃Winforms中覆盖Control.Enabled属性？

Question

I have a custom control I am working on. I want to change its color when it is enabled or disabled. So I wrote a code inside OnEnabledChanged .

        protected override void OnEnabledChanged(EventArgs e)
        {
            if (!Enabled)
            {
                temp1 = colorOn;
                temp2 = colorOff;
                colorOff = colorOn = Color.LightGray;
            }
            else
            {
                colorOn = temp1;
                colorOff = temp2;
            }
            Invalidate();
            base.OnEnabledChanged(e);
        }

This code works fine in runtime but not design time. It wasn't raised when I changed the Enabled property in design time. So I want to override the Enabled property of the control. But it doesn't show up when typing it.

So how can I override it? If there is another way I want to use it.

Answer 1

That is entirely normal. One job of a control designer is to intercept the behavior of certain properties and methods that interfere with the use of the control in the design view. The Enabled property is one of them, if that would work at design-time as well then you could never select the control again. The designer can't let that happen of course, it always forces Enabled = true at design time and intercepts assignments to the property. As you found out. Overriding it can work either, it is not a virtual property, but wouldn't give you what you want anyway. The Visible property is another one that's intercepted like that, you can imagine how that goes wrong :)

You would have to create your own designer to do something about it. This in general tends to be a bazooka to kill a mosquito, especially in this case since you still can't do anything with Enabled. And worse, this behavior is implemented by the ControlDesigner class, the kind of class you need as a base class to get a designer going. I seriously doubt it is practical.

Doing nothing at all to fix this is entirely reasonable, given that none of the other controls in the toolbox change their appearance either when you change their Enabled property in the designer.