How to set default value of a slider in GUI?

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D B
D B 2016-9-13
编辑： Stephen23 2016-9-13
Hello,
so long story short, I have a slider and static text box. I want to be able to move the slider in order to change the value inside text box.
This is just a part of a program, so it's also essential for me to:
  • set the min and max values
  • set the default position of the slider. I don't want it to be in 0-position once I run the program. Say, I want it to set itself in the half of range.
That's what I have:
set(handles.slider1, 'Min', f(1));
set(handles.slider1, 'Max', f(501));
set(handles.slider1, 'SliderStep', [1/501, 10/501]);
set(handles.slider1, 'Value', f(250);
a=get(handles.slider1,'Value');
set(handles.text1,'string',num2str(a));
guidata(hObject, handles);
And it doesn't get the current position of the slider, when I run it it is constantly showing value of f(250)
Please help. Thanks in advance.
  2 个评论
Stephen23
Stephen23 2016-9-13
Because you keep setting the value:
set(handles.slider1, 'Value', f(250);
a=get(handles.slider1,'Value');
the value is going to be exactly what you set it to: f(250).
Adam
Adam 2016-9-13
编辑：Adam 2016-9-13
If you have an array, f (or is it a function?), that you are using to supply values for your slider you might as well just use the array indices in the slider itself and only map these onto f when reporting the value for your text box.
You'll have to do some rounding anyway for when you move the slider unless you want to report values with lots of decimal places in your text box.

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回答（2 个）

Mischa Kim
Mischa Kim 2016-9-13
D B, please attach the entire code (see paper clip). A couple of comments:
  • There is at least one round, closing bracket missing: in the fourth command and before the semi-colon.
  • Where is function f defined? Is it executed? Setting breakpoints will help you pin point the problem.
Stephen23
Stephen23 2016-9-13
编辑：Stephen23 2016-9-13
Try using this minimum working example, which includes a text box and a slider that updates its value:
function main
%
bnd = [5,45]; % slider bounds
stp = [1,5]; % slider steps
htx = uicontrol('Style','text', 'Position',[300,20,100,20]);
hsl = uicontrol('Style','slider','Position',[10,20,200,20],...
'Min',bnd(1),'Max',bnd(2),'SliderStep',stp/diff(bnd),'Value',mean(bnd));
addlistener(hsl, 'Value', 'PostSet',@subfun);
%
% Callback function:
function subfun(~,~)
val = get(hsl,'Value');
set(htx,'String',num2str(val))
end
%
% Set default textbox value:
subfun()
%
end
  2 个评论
D B
D B 2016-9-13
Thanks! That one works. uicontrol seems to be necessary for some reason. When I try to use set(...) I am able to move the slider, but once I loose the button, slider jumps back to the default position.
I cannot however apply your solution to my code...
Error using uicontrol
Value must be a 2 element vector
Error in GUT_1>GUT_1_OpeningFcn (line 73)
handles.slider1 = uicontrol('Style','slider','Min',f(1),'Max',f(501),'SliderStep',(1/501),'Value',f_min);
Error in gui_mainfcn (line 221)
feval(gui_State.gui_OpeningFcn, gui_hFigure, [], guidata(gui_hFigure), varargin{:});
Error in GUT_1 (line 42)
gui_mainfcn(gui_State, varargin{:});
Do you have any idea why may I get this error?
Stephen23
Stephen23 2016-9-13
编辑：Stephen23 2016-9-13
When you read the uicontrol properties documentation you would learn that the SliderStep property must be a two-element vector, whereas you are defining it like this:
'SliderStep',(1/501)

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