在GUI中如何修改Simulink的仿真结束时间

bazziking

通过在GUI界面里的edit text输入数据，来改变simulink里的参数。
load_system('gen');
x=str2double(get(hObject,'String'));
set_param('gen/Constant','Constant','x');
改不了，怎么回事啊？

load_system('gen');
st=str2num(get(hObject,'String'));
set_param('gen','StopTime','st');
会把仿真时间改成变量st，然后sim（'gen'）就会报错，
??? Error using ==> sim
Error evaluating expression 'st' for 'Stop time' specified in the Configuration Parameters dialog for
block diagram 'gen': Error using ==> sim
Undefined function or variable 'st'.
Error in ==> gen_zong>pushbutton1_Callback at 258
sim('gen.mdl');
Error in ==> gui_mainfcn at 96
        feval(varargin{:});
Error in ==> gen_zong at 42
    gui_mainfcn(gui_State, varargin{:});
??? Error while evaluating uicontrol Callback
谁能回答下？？？

另外，edit text怎么enable啊？不能输入，显示灰色的那种。