Restore dynamic resource value

Question

I have a textblock tb with style.

<TextBlock x:Name="tb"  Style="{DynamicResource H1Style}" Text="Test"/>

<Style TargetType="{x:Type TextBlock}" x:Key= "H1Style">
    <Setter Property="FontSize" Value="18" />
    <Setter Property="FontWeight" Value="Light"/>
</Style>

Then i change size

tb.FontSize = 5;

How do i restore style H1Style of tb?

I tried set SetResourceReference, but FontSize still 5 instead of 18.

tb.SetResourceReference(Control.StyleProperty, "H1Style");

Answer 1

this line - tb.FontSize = 5; - assigns local value to FontSize property of TextBlock. There is a way to undo assignment - ClearValue() method:

 tb.ClearValue(TextBlock.FontSizeProperty);

FontSize is a dependency property and its value is computed according to DP value precedence

There are 3 sources from DP value precedence list:

• local value 5

• Style Setter value 18

• default value of FontSize DP

ClearValue() removes local value, causes recompute, and next value is provided by Style Setter which has highest priority from present sources