TachTongDiep doesn't know what the handle is for PhatHienLSB. So when you call handles.PhatHienLSB.Edit1 in TachTongDiep, it doesn't know you want to use the handles structure for PhatHienLSB. You need to pass the handles structure for PhatHienLSB to TachTongDiep. See getappdata and setappdata in the Matlab documentation, or use global variables, either way:
function PushMo_Callback(hObject, eventdata, handles)
[filename, pathname] = uigetfile( ...
{'*.bmp','BMP (*.bmp)'; ...
'*.png','PNG(*.png)'; ...
'*.jpg', 'JPG (*.jpg)'; ...
'*.*', 'All Files (*.*)'}, ...
'Moi ban chon tep anh');
set(handles.Edit1,'String',[filename,pathname]);
setappdata(0,'handles_PhatHienLSB',handles)
function TachThongDiep_OpeningFcn(hObject, eventdata, handles, varargin)
handles.output = hObject;
guidata(hObject, handles);
handles_PhatHienLSB = getappdata(0,'handles_PhatHienLSB');
filename = get(handles_PhatHienLSB.Edit1,'String');
set(handles.Edit2,'String',filename);
At least I think that's the answer, I'm still kind of a novice though, some of the other guys here should be able to help out more.
