Main Content

Knob

Knob UI component

expand all in page
  • Knob UI component

Description

A knob UI component represents an instrument control knob and allows an app user to adjust a value in an app. Use the Knob object to modify the appearance and behavior of a knob after you create it.

Creation

Create a knob in an app using the uiknob function.

Properties

expand all

Knob

Value of the knob, specified as a numeric value. The value must be within the range specified by Limits.

Example: 10

Data Types: double

Minimum and maximum knob values, specified as a two-element numeric array. The first value in the array must be less than the second value.

If you change Limits such that the Value property is less than the new lower limit, then the Value property updates to the new lower limit. Similarly, if you change Limits such that the Value is greater than the new upper limit, then Value property updates to the new upper limit.

For example, suppose Limits is [0 100] and the Value property is 20. If the Limits property changes to [50 100], then the Value updates to 50.

Data Types: double

Ticks

Major tick mark locations, specified as a vector of numeric values or an empty vector. If you do not want to show major tick marks, specify this property as an empty vector.

Tick locations that are outside the range of the Limits property do not display.

MATLAB® removes duplicate tick values. However, if a major tick falls on the same value as a minor tick, only the major tick displays.

Setting the MajorTicks property sets the MajorTicksMode property to 'manual'.

Major tick creation mode, specified as one of the following:

  • 'auto' — MATLAB determines the placement of major ticks.

  • 'manual' — You specify the MajorTicks value array.

Major tick labels, specified as a cell array of character vectors, string array, or 1-D categorical array. If you do not want to show tick labels, specify this property as an empty cell array. If you want to remove a label from a specific tick mark, specify an empty character vector or empty string scalar for the corresponding element in the MajorTickLabels property. If you specify this property as a categorical array, MATLAB uses the values in the array, not the full set of categories.

If the length of the MajorTickLabels array is different from the length of the MajorTicks vector, MATLAB ignores the extra entries of the longer array. If there are extra labels, they are ignored. If there are extra tick marks, they display without labels.

Setting MajorTickLabels changes the MajorTickLabelsMode value to 'manual'.

Major tick labels mode, specified as one of the following:

  • 'auto' — MATLAB specifies the major tick labels.

  • 'manual' — You specify the major tick labels using the MajorTickLabels property.

Minor tick mark locations, specified as a vector of numeric values or an empty vector. If you do not want to show minor tick marks, specify this property as an empty vector.

Tick locations that are outside the range of the Limits property do not display.

MATLAB removes duplicate tick values. However, if a minor tick falls on the same value as a major tick, only the major tick displays.

Setting the MinorTicks property value sets the MinorTicksMode property value to 'manual'.

Minor tick creation mode, specified as one of the following:

  • 'auto' — MATLAB determines the placement of minor ticks. MATLAB does not generate minor ticks for major ticks that are beyond scale limits. If the Limits property value changes, then MATLAB updates minor ticks to populate the full scale range (the MinorTicks property is updated accordingly).

  • 'manual' — You specify the MinorTicks property numeric array. The MinorTicks property value does not change size or content on its own.

Font

Font name, specified as a system supported font name. The default font depends on the specific operating system and locale.

If the specified font is not available, then MATLAB uses the best match among the fonts available on the system where the app is running.

Example: 'Arial'

Font size, specified as a positive number. The units of measurement are pixels. The default font size depends on the specific operating system and locale.

Example: 14

Font weight, specified as one of these values:

  • 'normal' — Default weight as defined by the particular font

  • 'bold' — Thicker character outlines than 'normal'

Not all fonts have a bold font weight. For fonts that do not, specifying 'bold' results in the normal font weight.

Font angle, specified as 'normal' or 'italic'. Not all fonts have an italic font angle. For fonts that do not, specifying 'italic' results in the normal font angle.

Font color, specified as an RGB triplet, a hexadecimal color code, or one of the options listed in the table.

RGB triplets and hexadecimal color codes are useful for specifying custom colors.

  • An RGB triplet is a three-element row vector whose elements specify the intensities of the red, green, and blue components of the color. The intensities must be in the range [0,1]; for example, [0.4 0.6 0.7].

  • A hexadecimal color code is a character vector or a string scalar that starts with a hash symbol (#) followed by three or six hexadecimal digits, which can range from 0 to F. The values are not case sensitive. Thus, the color codes "#FF8800", "#ff8800", "#F80", and "#f80" are equivalent.

Alternatively, you can specify some common colors by name. This table lists the named color options, the equivalent RGB triplets, and hexadecimal color codes.

Color NameShort NameRGB TripletHexadecimal Color CodeAppearance
"red""r"[1 0 0]"#FF0000"

Sample of the color red

"green""g"[0 1 0]"#00FF00"

Sample of the color green

"blue""b"[0 0 1]"#0000FF"

Sample of the color blue

"cyan" "c"[0 1 1]"#00FFFF"

Sample of the color cyan

"magenta""m"[1 0 1]"#FF00FF"

Sample of the color magenta

"yellow""y"[1 1 0]"#FFFF00"

Sample of the color yellow

"black""k"[0 0 0]"#000000"

Sample of the color black

"white""w"[1 1 1]"#FFFFFF"

Sample of the color white

Here are the RGB triplets and hexadecimal color codes for the default colors MATLAB uses in many types of plots.

RGB TripletHexadecimal Color CodeAppearance
[0 0.4470 0.7410]"#0072BD"

Sample of RGB triplet [0 0.4470 0.7410], which appears as dark blue

[0.8500 0.3250 0.0980]"#D95319"

Sample of RGB triplet [0.8500 0.3250 0.0980], which appears as dark orange

[0.9290 0.6940 0.1250]"#EDB120"

Sample of RGB triplet [0.9290 0.6940 0.1250], which appears as dark yellow

[0.4940 0.1840 0.5560]"#7E2F8E"

Sample of RGB triplet [0.4940 0.1840 0.5560], which appears as dark purple

[0.4660 0.6740 0.1880]"#77AC30"

Sample of RGB triplet [0.4660 0.6740 0.1880], which appears as medium green

[0.3010 0.7450 0.9330]"#4DBEEE"

Sample of RGB triplet [0.3010 0.7450 0.9330], which appears as light blue

[0.6350 0.0780 0.1840]"#A2142F"

Sample of RGB triplet [0.6350 0.0780 0.1840], which appears as dark red

Interactivity

State of visibility, specified as 'on' or 'off', or as numeric or logical 1 (true) or 0 (false). A value of 'on' is equivalent to true, and 'off' is equivalent to false. Thus, you can use the value of this property as a logical value. The value is stored as an on/off logical value of type matlab.lang.OnOffSwitchState.

  • 'on' — Display the object.

  • 'off' — Hide the object without deleting it. You still can access the properties of an invisible UI component.

To make your app start faster, set the Visible property to 'off' for all UI components that do not need to appear at startup.

Operational state, specified as 'on' or 'off', or as numeric or logical 1 (true) or 0 (false). A value of 'on' is equivalent to true, and 'off' is equivalent to false. Thus, you can use the value of this property as a logical value. The value is stored as an on/off logical value of type matlab.lang.OnOffSwitchState.

  • If you set this property to 'on', the app user can interact with the component.

  • If you set this property to 'off', the component appears dimmed, indicating that the app user cannot interact with it, and that it will not trigger a callback.

Tooltip, specified as a character vector, cell array of character vectors, string array, or 1-D categorical array. Use this property to display a message when the user hovers the pointer over the component at run time. The tooltip displays even when the component is disabled. To display multiple lines of text, specify a cell array of character vectors or a string array. Each element in the array becomes a separate line of text. If you specify this property as a categorical array, MATLAB uses the values in the array, not the full set of categories.

Context menu, specified as a ContextMenu object created using the uicontextmenu function. Use this property to display a context menu when you right-click on a component.

Position

Location and size of the knob, excluding tick marks and labels, specified as the vector, [left bottom width height]. This table describes each element in the vector.

ElementDescription
leftDistance from the inner left edge of the parent container to the outer left edge of the knob
bottomDistance from the inner bottom edge of the parent container to the outer bottom edge of the knob
widthDistance between the right and left outer edges of the knob, excluding tick marks and labels
heightDistance between the top and bottom outer edges of the knob, excluding tick marks and labels

All measurements are in pixel units. Due to aspect ratio constraints, you cannot change the knob height and width independently of one another. To increase the knob size, set width and height using Position(3:4) = [width height].

The Position values are relative to the drawable area of the parent container. The drawable area is the area inside the borders of the container and does not include the area occupied by decorations such as a menu bar or title.

Example: [100 200 60 60

Inner location and size of the knob, excluding tick marks and tick labels, specified as the vector, [left bottom width height]. Position values are relative to the parent container. All measurements are in pixel units. This property value is identical to the Position property.

This property is read-only.

Outer location and size of knob, including tick marks and tick labels, specified as the vector, [left bottom width height]. Position values are relative to the parent container. All measurements are in pixel units.

Layout options, specified as a GridLayoutOptions object. This property specifies options for components that are children of grid layout containers. If the component is not a child of a grid layout container (for example, it is a child of a figure or panel), then this property is empty and has no effect. However, if the component is a child of a grid layout container, you can place the component in the desired row and column of the grid by setting the Row and Column properties on the GridLayoutOptions object.

For example, this code places a knob in the third row and second column of its parent grid.

g = uigridlayout([4 3]);
k = uiknob(g);
k.Layout.Row = 3;
k.Layout.Column = 2;

To make the knob span multiple rows or columns, specify the Row or Column property as a two-element vector. For example, this knob spans columns 2 through 3:

k.Layout.Column = [2 3];

Callbacks

Value changed callback, specified as one of these values:

  • A function handle.

  • A cell array in which the first element is a function handle. Subsequent elements in the cell array are the arguments to pass to the callback function.

  • A character vector containing a valid MATLAB expression (not recommended). MATLAB evaluates this expression in the base workspace.

This callback executes when the user changes the knob selector to point to a different value.

This callback function can access specific information about the user’s interaction with the knob. MATLAB passes this information in a ValueChangedData object as the second argument to your callback function. In App Designer, the argument is called event. You can query the object properties using dot notation. For example, event.PreviousValue returns the previous value of the knob. The ValueChangedData object is not available to callback functions specified as character vectors.

The following table lists the properties of the ValueChangedData object.

PropertyValue
ValueValue of knob after app user’s most recent interaction with it.
PreviousValueValue of knob before app user’s most recent interaction with it.
SourceComponent that executes the callback.
EventName'ValueChanged'

For more information about writing callbacks, see Callbacks in App Designer.

Value changing callback, specified as one of these values:

  • A function handle.

  • A cell array in which the first element is a function handle. Subsequent elements in the cell array are the arguments to pass to the callback function.

  • A character vector containing a valid MATLAB expression (not recommended). MATLAB evaluates this expression in the base workspace.

This callback executes as the user turns the knob in the app. It does not execute if the Value property changes programmatically.

This callback function can access specific information about the user’s interaction with the knob. MATLAB passes this information in a ValueChangingData object as the second argument to your callback function. In App Designer, the argument is called event. You can query the object properties using dot notation. For example, event.Value returns the current value of the knob. The ValueChangingData object is not available to callback functions specified as character vectors.

The following table lists the properties of the ValueChangingData object.

PropertyValue
ValueCurrent value of the knob as the app user is interacting with it.
SourceComponent that executes the callback.
EventName'ValueChanging'

The Value property of the Knob object is not updated until the app user releases the knob. Therefore, to get the knob values as the knob is being turned, your code must get the Value property of the ValueChangingData object.

Note

Avoid updating the Value property of the Knob object from within its own ValueChangingFcn callback, as this might result in unexpected behavior. To update the knob value in response to user input, use a ValueChangedFcn callback instead.

The callback executes as follows:

  • If the app user clicks the knob value, the callback executes once. For example, if the knob is on 1.0, and the app user single-clicks 1.1, the callback executes.

  • If the app user clicks and drags the knob to a new position, the callback executes repeatedly. For example, if the knob value is 1.0, and the app user clicks, holds, and drags to value 10.0, the callback executes multiple times until the app user releases the knob.

For more information about writing callbacks, see Callbacks in App Designer.

Object creation function, specified as one of these values:

  • Function handle.

  • Cell array in which the first element is a function handle. Subsequent elements in the cell array are the arguments to pass to the callback function.

  • Character vector containing a valid MATLAB expression (not recommended). MATLAB evaluates this expression in the base workspace.

For more information about specifying a callback as a function handle, cell array, or character vector, see Callbacks in App Designer.

This property specifies a callback function to execute when MATLAB creates the object. MATLAB initializes all property values before executing the CreateFcn callback. If you do not specify the CreateFcn property, then MATLAB executes a default creation function.

Setting the CreateFcn property on an existing component has no effect.

If you specify this property as a function handle or cell array, you can access the object that is being created using the first argument of the callback function. Otherwise, use the gcbo function to access the object.

Object deletion function, specified as one of these values:

  • Function handle.

  • Cell array in which the first element is a function handle. Subsequent elements in the cell array are the arguments to pass to the callback function.

  • Character vector containing a valid MATLAB expression (not recommended). MATLAB evaluates this expression in the base workspace.

For more information about specifying a callback as a function handle, cell array, or character vector, see Callbacks in App Designer.

This property specifies a callback function to execute when MATLAB deletes the object. MATLAB executes the DeleteFcn callback before destroying the properties of the object. If you do not specify the DeleteFcn property, then MATLAB executes a default deletion function.

If you specify this property as a function handle or cell array, you can access the object that is being deleted using the first argument of the callback function. Otherwise, use the gcbo function to access the object.

Callback Execution Control

Callback interruption, specified as 'on' or 'off', or as numeric or logical 1 (true) or 0 (false). A value of 'on' is equivalent to true, and 'off' is equivalent to false. Thus, you can use the value of this property as a logical value. The value is stored as an on/off logical value of type matlab.lang.OnOffSwitchState.

This property determines if a running callback can be interrupted. There are two callback states to consider:

  • The running callback is the currently executing callback.

  • The interrupting callback is a callback that tries to interrupt the running callback.

MATLAB determines callback interruption behavior whenever it executes a command that processes the callback queue. These commands include drawnow, figure, uifigure, getframe, waitfor, and pause.

If the running callback does not contain one of these commands, then no interruption occurs. MATLAB first finishes executing the running callback, and later executes the interrupting callback.

If the running callback does contain one of these commands, then the Interruptible property of the object that owns the running callback determines if the interruption occurs:

  • If the value of Interruptible is 'off', then no interruption occurs. Instead, the BusyAction property of the object that owns the interrupting callback determines if the interrupting callback is discarded or added to the callback queue.

  • If the value of Interruptible is 'on', then the interruption occurs. The next time MATLAB processes the callback queue, it stops the execution of the running callback and executes the interrupting callback. After the interrupting callback completes, MATLAB then resumes executing the running callback.

Note

Callback interruption and execution behave differently in these situations:

  • If the interrupting callback is a DeleteFcn, CloseRequestFcn, or SizeChangedFcn callback, then the interruption occurs regardless of the Interruptible property value.

  • If the running callback is currently executing the waitfor function, then the interruption occurs regardless of the Interruptible property value.

  • If the interrupting callback is owned by a Timer object, then the callback executes according to schedule regardless of the Interruptible property value.

Note

When an interruption occurs, MATLAB does not save the state of properties or the display. For example, the object returned by the gca or gcf command might change when another callback executes.

Callback queuing, specified as 'queue' or 'cancel'. The BusyAction property determines how MATLAB handles the execution of interrupting callbacks. There are two callback states to consider:

  • The running callback is the currently executing callback.

  • The interrupting callback is a callback that tries to interrupt the running callback.

The BusyAction property determines callback queuing behavior only when both of these conditions are met:

  • The running callback contains a command that processes the callback queue, such as drawnow, figure, uifigure, getframe, waitfor, or pause.

  • The value of the Interruptible property of the object that owns the running callback is 'off'.

Under these conditions, the BusyAction property of the object that owns the interrupting callback determines how MATLAB handles the interrupting callback. These are possible values of the BusyAction property:

  • 'queue' — Puts the interrupting callback in a queue to be processed after the running callback finishes execution.

  • 'cancel' — Does not execute the interrupting callback.

This property is read-only.

Deletion status, returned as an on/off logical value of type matlab.lang.OnOffSwitchState.

MATLAB sets the BeingDeleted property to 'on' when the DeleteFcn callback begins execution. The BeingDeleted property remains set to 'on' until the component object no longer exists.

Check the value of the BeingDeleted property to verify that the object is not about to be deleted before querying or modifying it.

Parent/Child

Parent container, specified as a Figure object created using the uifigure function, or one of its child containers: Tab, Panel, ButtonGroup, or GridLayout. If no container is specified, MATLAB calls the uifigure function to create a new Figure object that serves as the parent container.

Visibility of the object handle, specified as 'on', 'callback', or 'off'.

This property controls the visibility of the object in its parent's list of children. When an object is not visible in its parent's list of children, it is not returned by functions that obtain objects by searching the object hierarchy or querying properties. These functions include get, findobj, clf, and close. Objects are valid even if they are not visible. If you can access an object, you can set and get its properties, and pass it to any function that operates on objects.

HandleVisibility ValueDescription
'on'The object is always visible.
'callback'The object is visible from within callbacks or functions invoked by callbacks, but not from within functions invoked from the command line. This option blocks access to the object at the command-line, but allows callback functions to access it.
'off'The object is invisible at all times. This option is useful for preventing unintended changes to the UI by another function. Set the HandleVisibility to 'off' to temporarily hide the object during the execution of that function.

Identifiers

This property is read-only.

Type of graphics object, returned as 'uiknob'.

Object identifier, specified as a character vector or string scalar. You can specify a unique Tag value to serve as an identifier for an object. When you need access to the object elsewhere in your code, you can use the findobj function to search for the object based on the Tag value.

User data, specified as any MATLAB array. For example, you can specify a scalar, vector, matrix, cell array, character array, table, or structure. Use this property to store arbitrary data on an object.

If you are working in App Designer, create public or private properties in the app to share data instead of using the UserData property. For more information, see Share Data Within App Designer Apps.

Examples

collapse all

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;

Continuous knob with values from -10 to 10. The knob is pointing to the value 5.

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.

UI figure window with a discrete knob and an edit field. The knob is pointing to the value Medium, and the edit field contains the text "Medium".

Version History

Introduced in R2016a

See Also

Functions

Tools