使用 DynamicResource 如何“神奇地”将画笔转换为颜色？

Question

I have defined some brush resources in terms of system colors like the following:

<SolidColorBrush 
   x:Key="brushKey1" 
   Color="{x:Static SystemColors.ControlColor}" 
   />

(This is done because some third-party code expects to find brushKey1 defined).

But I noticed that the following also compiles and appears to work:

<SolidColorBrush 
   x:Key="brushKey1" 
   Color="{DynamicResource {x:Static SystemColors.ControlBrush}}" 
   />

The first one uses a COLOR object, but the second uses a BRUSH.

Why does this work? Is DynamicResource automatically figuring out how to do some sort of cast or conversion?

Note that this does not work:

<SolidColorBrush 
   x:Key="brushKey1" 
   Color="{x:Static SystemColors.ControlBrush}" 
   />

This line will compile but throws a runtime exception.

Answer 1

There is no magic or conversion. Take a look to the Resources , there must be an entry with a SystemColors.ControlBrush object as key.

So in case

<SolidColorBrush x:Key="brushKey1"  Color="{DynamicResource {x:Static SystemColors.ControlBrush}}"/>

you get "value" of an entry from ResourceDictionary .

in another case

<SolidColorBrush x:Key="brushKey1"  Color="{x:Static SystemColors.ControlBrush}"/>

you try to assign the object, which being used as "key" in ResourceDictionary .

Answer 2

Compiles? Yes. Your brushKey1 references a resource with an x:Key of {x:Static SystemColors.ControlBrush} using the DynamicResource markup extension. You could set the key to anything. It would still compile.

Works? No, not unless you have defined a Color resource with an x:Key of {x:Static SystemColors.ControlBrush} :

<Color x:Key="{x:Static SystemColors.ControlBrush}">Red</Color>