wpf - How to Uncheck Menuitem isCheked property in MenuItemClick event -

i able check menuitem not able uncheck , more on showing previous check in menuitem. once click on menuitem doesn't uncheck previous menuitem. i'm adding menuitem code.

  private void onmenuitemclick(object sender, routedeventargs e)             {                 routedeventargs args = e routedeventargs;                 menuitem item = args.originalsource menuitem;                 string header = item.header.tostring();                 if (header == "b1")                 {                     btnmenu.content = header;                     item.ischecked=true;                 }                 else if (header == "a1")                 {                     btnmenu.content = header;                     item.ischecked=true;                 }              } 

i applying same menuitems , event handler 4 buttons.so if select 1 menuitem first button show check on menuitem,the checked menu item show appear when click on second button.how can achieve this?..any suggestion.

edit:xaml

      <stackpanel grid.row="11" orientation="horizontal" flowdirection="lefttoright">                                     <button  name="btnphone" content="mobile" horizontalalignment="left" verticalalignment="top"  margin="0 0 12 0" width="85" click="onbtnphoneclick"></button>                                                                           <button   horizontalalignment="left"  name="ddbtnphone" verticalalignment="top" width="25"  click="onddbtnphoneclick"  >                                         <button.content>                                             <path x:name="btnarrow1" margin="4" verticalalignment="center" width="10" fill="#ff527db5" stretch="uniform" horizontalalignment="right" data="f1 m 301.14,-189.041l 311.57,-189.041l 306.355,-182.942l 301.14,-189.041 z "/>                                         </button.content>                                         <button.contextmenu>                                             <contextmenu x:name="cmphone">                                              </contextmenu>                                         </button.contextmenu>                                     </button>                                   </stackpanel>                                 <stackpanel grid.row="12" orientation="horizontal" flowdirection="lefttoright">                                     <button  name="btnhome" content="business" horizontalalignment="left"  margin="0,0,12,5" width="85" click="onbtnhomeclick" />                                     <!--<exttoolkit:dropdownbutton x:name="ddbtnhome" verticalalignment="top" width="30" horizontalalignment="right" margin="0 0 30 0" height="20"/>-->                                     <button   horizontalalignment="left"  name="ddbtnhome" verticalalignment="bottom" width="25"  click="onddbtnhomeclick" margin="0,0,0,5"  >                                         <button.content>                                             <path x:name="btnarrow2" margin="4" verticalalignment="center" width="10" fill="#ff527db5" stretch="uniform" horizontalalignment="right" data="f1 m 301.14,-189.041l 311.57,-189.041l 306.355,-182.942l 301.14,-189.041 z "/>                                         </button.content>                                         <button.contextmenu>                                             <contextmenu name="cmhome">                                              </contextmenu>                                         </button.contextmenu>                                     </button>                                 </stackpanel>                                 <stackpanel grid.row="13" orientation="horizontal" flowdirection="lefttoright">                                     <button  name="btnmobile" content="home" horizontalalignment="left" verticalalignment="top"  margin="0 0 12 0" width="85" click="onbtnmobileclick"></button>                                     <!--<exttoolkit:dropdownbutton x:name="ddbtnmobile" verticalalignment="top" width="30" horizontalalignment="right" margin="0 0 30 0" height="20"/>-->                                     <button   horizontalalignment="left" name="ddbtnmobile" width="25" click="onddbtnmobileclick"  margin="0,0,0,5"  >                                         <button.content>                                             <path x:name="btnarrow3" margin="4" verticalalignment="center" width="10" fill="#ff527db5" stretch="uniform" horizontalalignment="right" data="f1 m 301.14,-189.041l 311.57,-189.041l 306.355,-182.942l 301.14,-189.041 z "/>                                         </button.content>                                         <button.contextmenu>                                             <contextmenu name="cmmobile">                                              </contextmenu>                                         </button.contextmenu>                                     </button>                                 </stackpanel>                                 <stackpanel grid.row="14" orientation="horizontal" flowdirection="lefttoright">                                     <button  name="btnfax" content="business fax" horizontalalignment="left" verticalalignment="top"  margin="0 0 12 0" width="85" click="onbtnfaxclick"></button>                                     <!--<exttoolkit:dropdownbutton x:name="ddbtnfax" verticalalignment="top" width="30" horizontalalignment="right" margin="0 0 30 0" height="20"/>-->                                     <button   horizontalalignment="left" name="ddbtnfax" verticalalignment="bottom" width="25" click="onddbtnfaxclick"  margin="0,0,0,5"  >                                         <button.content>                                             <path x:name="btnarrow4" margin="4" verticalalignment="center" width="10" fill="#ff527db5" stretch="uniform" horizontalalignment="right" data="f1 m 301.14,-189.041l 311.57,-189.041l 306.355,-182.942l 301.14,-189.041 z "/>                                         </button.content>                                         <button.contextmenu>                                             <contextmenu name="cmfax">                                              </contextmenu>                                         </button.contextmenu>                                     </button>                                  </stackpanel> 

this how adding menuitems each contextmenu.

  private void addmenuitems(contextmenu cmenu, button btnname)     {         if (cmenu.items.count == 0)         {             mnitem = new menuitem();             mnitem.header = "b1";             cmenu.items.add(mnitem);             mnitem = new menuitem();             mnitem.header = "a1";             cmenu.items.add(mnitem);             mnitem = new menuitem();             mnitem.header = "b2";             cmenu.items.add(mnitem);             mnitem = new menuitem();             mnitem.header = "a2";             cmenu.items.add(mnitem);              cmenu.addhandler(menuitem.clickevent, new routedeventhandler(onmenuitemclick));             cmenu.addhandler(menuitem.mouseleftbuttonupevent, new mousebuttoneventhandler(onmousebuttonupeventclick));             btncommon = btnname;         } 

not sure understand want. if want menuitems checked mutually exclusive should check post: mutually exclusive checkable menu items?