c# - WPF ComboBox Set using Grid DataContext -

i new c# wpf, tring set datacontext combobox xml below

<grid name="groupeditarea"  horizontalalignment="stretch" verticalalignment="stretch" background="#ffd8d8d8" margin="-14,0,192,0">                     <label content="group name" fontsize="18" horizontalalignment="left" margin="116,50,0,0" verticalalignment="top" width="136"/>                     <label content="group type" fontsize="18" horizontalalignment="left" margin="116,123,0,0" verticalalignment="top" width="136"/>                     <textbox x:name="groupgroupnametxt" horizontalalignment="left" fontsize="16" height="31" margin="368,50,0,0" textwrapping="wrap" text="{binding path = groupname, mode=twoway, stringformat=\{0:n3\}, updatesourcetrigger=propertychanged}" verticalalignment="top" width="226"  textchanged="groupgroupnametxt_textchanged"  /> <!-- gotfocus="groupgroupnametxt_ongotfocus" textinput="groupgroupnametxt_ontextinput"  -->                     <combobox x:name="groupgroupnamecombo" horizontalalignment="left" margin="368,123,0,0" verticalalignment="top" width="226" height="31" selectionchanged="groupgroupnamecombo_selectionchanged"  displaymemberpath="groupname" selectedvaluepath="categoriesval" selectedvalue="{binding categories}"/>                 </grid> 

my poco below :-

        public class test: inotifypropertychanged         {             public test()             {             }      public virtual string testid { get; set; }             public virtual categories categoriesval { get; set; }      public virtual string name{ get; set; }      public virtual string groupname             {                 { return name; }                 set                 {                     name = value;                     onpropertychanged("groupname");                 }             }     }  public class categories : inotifypropertychanged         {             public categories ()             {             }  public virtual string categorieid { get; set; }      public virtual string name{ get; set; }      public virtual string groupname             {                 { return name; }                 set                 {                     name = value;                     onpropertychanged("groupname");                 }             }     } } 

and in backend code setting datacontext below :-

categories cate = new categories (); cate.categorieid = "cate1id"; cate.groupname = "categroupname1" test test = new test(); test.testid = "testid"; test.categoriesval  = cate; test.name = "testname1"; 

and groupgroupnamecombo set using itemssource , contain entire list on categories when set using below working fine

groupgroupnamecombo.selecteditem = cate; 

but when set using below grid wont work :-

groupeditarea.datacontext = test; 

can guide me how can set combobox setting grid datacontext instead of setting manually combobox.

instead

selectedvaluepath="categoriesval" selectedvalue="{binding categories}" 

write

selecteditem="{binding categoriesval}" 

selectedvaluepath means: name of property (from comboboxitem datacontex - categories class in our case) value of selectedvalue provided.
useful in case want representation of instance-item (each form combobox.items) not done item itself, 1 characteristic. in case not see point in it.

see more: difference between selecteditem, selectedvalue , selectedvaluepath