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I've been trying to interpret the XAML code in a project I've inherited and I want to figure out where some of the values are coming from in certain elements. When I look at an object's properties in the Properties panel, I can see squares next to each property. A white square indicates that the property value is the default, a black square indicates that the property value is "local" meaning it has been changed from the default and that change can be seen in the XAML tag, and a green square means "ambient."

There are styles applied to the objects so I can sort of intuit that the values in ambient properties must come from resource dictionaries. I'm still unsure where to look for the source of the values, which I want to do in order to change them. The documentation for ambient properties is hard for me to follow and doesn't answer all my questions, and I haven't found any documentation discussing the differences between default, local, and ambient.

If this is an appropriate place to ask, can someone explain and discuss the differences between default, local, and ambient?

Is there a word used to distinguish between these types of property values, i.e. is "default" a property value "type" or what?

And are there any property value types beyond those three?

Kyle Delaney
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1 Answers1

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My, what a charming profile you have. ;)

I just want to mention that you can get some information about the source of a dependency property's value using the static helper method DependencyPropertyHelper.GetValueSource(DependencyObject, DependencyProperty) in the System.Windows namespace.

"Default" essentially means that no source has been specified and so the value is taken from some built-in source. Note that some default values are dynamically generated and not constant. "Local" is when the value is explicitly set in that specific dependency object, overriding any values that it would otherwise inherit. "Ambient" is when the value is derived from some other source such as a style. I would refer to the distinction between these as different base value sources.

And yes, there are more than just those three. If you put the attribute TextBlock.FontFamily="Arial" in your Window tag for example, text blocks in that window will inherit that value from it. When you observe the property in the properties panel and roll over the box, it will say "Inherited." Note that the box is still green just like it is with "Ambient."

There is actually an enum that can help illuminate the various possible base value sources. It's called BaseValueSource.

Kyle Delaney
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