uiknob

Create knob component

Syntax

kb = uiknob

kb = uiknob(style)

kb = uiknob(parent)

kb = uiknob(parent,style)

kb = uiknob(___,Name,Value)

Description

kb = uiknob creates a knob in a new figure window and returns the Knob object. MATLAB^® calls the uifigure function to create the figure.

kb = uiknob(style) specifies the knob style.

kb = uiknob(parent) creates the knob in the specified parent container. The parent can be a Figure object or one of its child containers.

kb = uiknob(parent,style) creates a knob of the specified style in the specified parent container.

kb = uiknob(___,Name,Value) specifies object properties using one or more Name,Value pair arguments. Use this option with any of the input argument combinations in the previous syntaxes.

Examples

Create Continuous Knob

fig = uifigure;
kb = uiknob(fig);

Create Discrete Knob

Specify a Figure object as the parent container.

fig = uifigure('Position',[100 100 300 250]);
kb = uiknob(fig,'discrete');

Set and Access Continuous Knob Property Values

Create a continuous knob in a figure.

fig = uifigure;
kb = uiknob(fig);

Determine the knob limits.

limits = kb.Limits

limits =

     0   100

Change the limits and the knob value.

kb.Limits = [-10 10];
kb.Value = 5;

Set and Access Property Values

Create a discrete knob.

fig = uifigure;
kb = uiknob(fig,'discrete');

Change the knob states. Associate specific data with the knob states by configuring ItemsData. In this case, ItemsData reflects temperatures in degrees Fahrenheit.

kb.Items = {'Cold', 'Warm', 'Hot'};
kb.ItemsData = {32, 80, 212};

Get the temperature associated with the current knob value.

degrees = kb.Value

degrees =

    32

Code Response to Changed Discrete Knob Setting

Create a discrete knob that performs an action after the app user turns it. Turning the knob updates the value of an edit field to reflect the app user's choice.

Copy and paste the following code into a file named displayknobvalue.m on your MATLAB path. This code creates a window containing a discrete knob and an edit field. It specifies a ValueChangedFcn callback to update the edit field when the knob is turned.

function displayKnobValue
% Create figure window

fig = uifigure('Position',[100 100 283 275]);

% Create the text field
txt = uieditfield(fig,'text',...
    'Position', [69 82 100 22]);

% Create the knob
kb = uiknob(fig,'discrete',...
    'Position',[89 142 60 60],...
    'ValueChangedFcn',@(kb,event) knobTurned(kb,txt));
end

% Code the knob callback function
function knobTurned(knob,txt)
txt.Value = knob.Value;
end

Run displayKnobValue, and then turn the knob. When you release the mouse button, the edit field is updated to reflect the new knob value.

Code Response to Changed Continuous Knob Setting

Create a continuous knob that performs an action after the user turns it. Turning the knob updates the value of a label to reflect the user's choice.

Copy and paste the following code into a file named showknobvalue.m on your MATLAB path. This code creates a window containing a continuous knob and a label field. It specifies a ValueChangedFcn callback to update the label when the knob is turned.

function showKnobValue
% Create figure window and components
fig = uifigure('Position',[100 100 283 275]);

% Create label
lbl = uilabel(fig,...
    'Position',[218 177 50 15],...
    'Text','0');

% Create knob
kb = uiknob(fig,...
    'Position',[89 142 60 60],...
    'ValueChangedFcn', @(kb,event) knobTurned(kb,lbl));
end

% Create ValueChangedFcn callback
function knobTurned(kb,lbl)
num = kb.Value;
lbl.Text = num2str(num);
end

Run showKnobValue and turn the knob. When you release the mouse button, the label is updated to reflect the new knob value.

Code Response to Changing Continuous Knob Setting

Create a continuous knob that repeatedly performs an action as the user is turning it. Instead of updating an edit field once when the user releases the mouse button, this knob updates the edit field as the knob is being turned.

Copy and paste the following code into a file named showchangingvalue.m on your MATLAB path. This code creates a window containing a continuous knob and an edit field. It specifies a ValueChangingFcn callback to keep updating the edit field as the knob is being turned.

function showChangingValue
% Create figure window
fig = uifigure('Position',[100 100 283 275]);

% Create numeric edit field
num = uieditfield(fig,'numeric',...
    'Position',[69 82 100 20]);

% Create knob
kb = uiknob(fig,...
    'Position',[89 142 60 60],...
    'ValueChangingFcn',@(kb,event) knobTurned(kb,event,num));
end

% Create ValueChangingFcn callback
function knobTurned(kb,event,num)
num.Value = event.Value;
end

Run showChangingValue, and turn the knob. As you do so, the edit field is updated to show the changing knob values.

Code Response to Invalid Knob Setting

Create a continuous knob that performs an action after the user turns it. Each turn of the knob causes MATLAB to perform a calculation using the current and previous knob values.

Copy and paste the following code into a file named increaseOnly.m on your MATLAB path. This code creates a window containing a continuous knob. It specifies a ValueChangedFcn callback for the knob to display an Invalid Value dialog box when the app user attempts to decrease the knob value.

function increaseOnly
% Create figure window
fig = uifigure('Position',[100 100 400 275]);

% Create knob
kb = uiknob(fig,...
    'Position',[150 125 60 60],...
    'ValueChangedFcn',@(kb,event) nValChanged(kb,event,fig));
end

% Create ValueChangedFcn callback
function nValChanged(kb,event,fig)
newvalue = event.Value;
previousvalue = event.PreviousValue;
if previousvalue >  newvalue
   uialert(fig, 'Increase value only. Value reverted to previous value.', ...
        'Invalid Value');
   kb.Value = previousvalue;
end
end

Run increaseOnly, increase the knob value, and then try to decrease it. When you try to decrease the value, an error dialog box displays and the value is reverted to the previous valid value. You can only increase the knob value.

Input Arguments

style — Style of knob

'continuous' (default) | 'discrete'

Style of knob, specified as one of the following values:

Style	Appearance
'continuous'
'discrete'

parent — Parent container

Figure object (default) | Tab object | Panel object | ButtonGroup object | GridLayout object

Parent container, specified as a Figure object or one of its child containers: Tab, Panel, ButtonGroup, or GridLayout. If you do not specify a parent container, MATLAB calls the uifigure function to create a new Figure object that serves as the parent container.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Each type of knob object supports a different set of properties. For a full list of properties and descriptions for each type, see the associated property page.

• Knob

• DiscreteKnob

Version History

Introduced in R2016a

R2023b: Access index of discrete knob value in list of items

Access the index of the value of a discrete knob in the list of its items by using the ValueIndex property.