function varargout = Prev_Next_Callback(h, eventdata, handles, str)
%獲取索引指針和地址
index = handles.Index;
Addresses = handles.Addresses;
%根據被單擊的按鈕修改顯示結果
switch str
case 'Prev'
    %索引值減1
    i = index - 1;	
    %如果索引值小于1，設置其為Addresses數組最后一個元素的索引 
    if i < 1
        i = length(Addresses);
    end
case 'Next'
    %索引值增加1
    i = index + 1;
    
    %如果索引值超出范圍，設置其為Addresses數組第一個元素的索引
    if i > length(Addresses)
        i = 1;
    end	
end
%為被選索引獲取相應數據
Current_Name = Addresses(i).Name;
Current_Phone = Addresses(i).Phone;
set(handles.Contact_Name,'string',Current_Name)
set(handles.Contact_Phone,'string',Current_Phone)
%刷新索引指針以反映新的索引
handles.Index = i;
guidata(h,handles)