xaml - the attachable property 'triggers' was not found in type 'style' wpf -

i can use <style.triggers>, got message "the attachable property 'triggers' not found in type 'style'"? need use it, change background image picture. can me?

<button content ="a" name="btmeunu" width="77" horizontalalignment="left"     borderbrush="{x:null}" height="75" margin="-8,-16,0,-6"> </button> 

//convertor public class backgroundimageconverter : ivalueconverter {     public object convert(object value, type targettype, object parameter, cultureinfo culture)     {         bool isclicked = (bool)value;     if(isclicked)     {         return new imagebrush([[image1.png bitmap]]//change accordingly)     }     return new imagebrush([[image2.png bitmap]]//change accordingly)     }      public object convertback(object value, type targettype, object parameter, cultureinfo culture)     {         return value;     } }  //xaml  background="{binding relativesource={relativesource self}, path=ispressed,converter={staticresource backgroundimageconverter}}"