Grid add modify and delete

I used smartGWT 4.0. My browser is firefox.
I want to edit multi rows in the client using right-click menuitem "add" for add a new record,"modify" for modify a record,"delete" for delete a record,then use button "save" to save all my edit to server.my code like this:
listGrid setting:
listGrid.setAutoSaveEdits(false);
listGrid.setCanEdit(true);
listGrid.setEditEvent(ListGridEditEvent.NONE);
listGrid.setListEndEditAction(RowEndEditAction.DON E);

three function for add,modify and delete

private void gridDelete(){
Object operateGrid=appElement.get("mms0000113");
if(operateGrid instanceof ListGridExtend){
Integer rowNum=((ListGridExtend) operateGrid).getFocusRow();
if(rowNum !=null){
SC.say(Integer.toString(rowNum));
((ListGridExtend) operateGrid).markRecordRemoved(rowNum);
}else{
SC.say("no current row");
}
}
}

private void gridModify(){
Object operateGrid=appElement.get("mms0000113");
if(operateGrid instanceof ListGridExtend){
Integer rowNum=((ListGridExtend) operateGrid).getFocusRow();
if(rowNum !=null){
SC.say(Integer.toString(rowNum));
((ListGridExtend) operateGrid).startEditing(rowNum);
}else{
SC.say("no current row");
}
}
}

private void gridAdd(){
Object operateGrid=appElement.get("mms0000113");
if(operateGrid instanceof ListGridExtend){
((ListGridExtend) operateGrid).startEditingNew();
}
}

my question is :
when I add some rows in the grid,I cannot select a row to modify or delete.
but if the record of listgrid is fetch from server,then I can modify and delete them.

can you give me some suggestion to result this problem?

thank you!