DiscreteKnob
Discrete knob UI component
Description
A discrete knob UI component represents an instrument control knob and allows an
app user to select an option from a discrete set in an app. Use the
DiscreteKnob
object to modify the appearance and behavior of a discrete
knob after you create it.
Creation
Create a discrete knob in an app using the uiknob
function, specifying the knob style as
"discrete"
.
Properties
Knob
Value
— Value
element of Items
| element of ItemsData
Value, specified as an element of the Items
or
ItemsData
arrays. By default, Value
is the
first element in Items
.
Specifying Value
as an element of Items
sets the knob selector to the corresponding label on the knob. If
ItemsData
is not empty, then Value
must be
set to an element of ItemsData
, and the knob selector will point
to the associated label.
Items
— Knob options
{'Off','Low','Medium','High'}
(default) | cell array of character vectors | string array | ...
Knob options, specified as a cell array of character vectors, string array, or 1-D
categorical array. The array must contain at least two elements. The knob displays as
many options as there are elements in the Items
array. The
options display in clockwise order. If you specify this property as a categorical
array, MATLAB® uses the values in the array, not the full set of categories.
Example: {'Off','Slow','Fast'}
Example: {'1','2','3','4'}
ItemsData
— Data associated with each element of Items
empty array []
(default) | 1-by-n numeric array | 1-by-n cell array
Data associated with each element of the Items
property value,
specified as a 1-by-n numeric array or a 1-by-n cell array. It is valid to specify
duplicate array elements in the ItemsData
value.
When the number of array elements in the ItemsData
and
Items
do not match:
If the
ItemsData
value is empty, then allItems
elements are presented to the app user.If the
ItemsData
value has more elements than theItems
value, then all theItems
elements are presented to the app user and MATLAB ignores the extraItemsData
elements.If the
ItemsData
value has fewer elements than theItems
value (but greater than none), then the onlyItems
elements presented to the app user are those that have a correspondingItemsData
value.
Example: {'One' 'Two' 'Three'}
Example: {10 20 30 40}
ValueIndex
— Index of value in items
1
(default) | positive integer
Index of the component value in the list of items or item data, specified as a positive integer.
In most cases, you can use the Value
property to query and
update the component value. However, the ValueIndex
property can
be useful when both the Items
and ItemsData
properties are nonempty. In this case, you can use the ValueIndex
property to query the element of Items
that corresponds to the
current
value.
fig = uifigure; k = uiknob(fig,"discrete", ... "Items",["Off","Slow","Fast"], ... "ItemsData",[0 20 50]); idx = k.ValueIndex; disp(k.Items(idx) + ": " + k.Value)
Off: 0
Font
FontName
— Font name
system supported font name
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'
FontSize
— Font size
positive number
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
FontWeight
— Font weight
'normal'
(default) | 'bold'
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.
FontAngle
— Font angle
'normal'
(default) | 'italic'
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.
FontColor
— Font color
[0 0 0]
(default) | RGB triplet | hexadecimal color code | 'r'
| 'g'
| 'b'
| ...
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 from0
toF
. 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 Name | Short Name | RGB Triplet | Hexadecimal Color Code | Appearance |
---|---|---|---|---|
"red" | "r" | [1 0 0] | "#FF0000" | |
"green" | "g" | [0 1 0] | "#00FF00" | |
"blue" | "b" | [0 0 1] | "#0000FF" | |
"cyan"
| "c" | [0 1 1] | "#00FFFF" | |
"magenta" | "m" | [1 0 1] | "#FF00FF" | |
"yellow" | "y" | [1 1 0] | "#FFFF00" | |
"black" | "k" | [0 0 0] | "#000000" | |
"white" | "w" | [1 1 1] | "#FFFFFF" |
Here are the RGB triplets and hexadecimal color codes for the default colors MATLAB uses in many types of plots.
RGB Triplet | Hexadecimal Color Code | Appearance |
---|---|---|
[0 0.4470 0.7410] | "#0072BD" | |
[0.8500 0.3250 0.0980] | "#D95319" | |
[0.9290 0.6940 0.1250] | "#EDB120" | |
[0.4940 0.1840 0.5560] | "#7E2F8E" | |
[0.4660 0.6740 0.1880] | "#77AC30" | |
[0.3010 0.7450 0.9330] | "#4DBEEE" | |
[0.6350 0.0780 0.1840] | "#A2142F" |
Interactivity
Visible
— State of visibility
'on'
(default) | on/off logical value
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.
Enable
— Operational state
'on'
(default) | on/off logical value
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
— Tooltip
''
(default) | character vector | cell array of character vectors | string array | 1-D categorical array
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.
ContextMenu
— Context menu
empty GraphicsPlaceholder
array (default) | ContextMenu
object
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
Position
— Location and size of knob
[100 100 60 60]
(default) | [left bottom width height]
Location and size of the knob, excluding the state marks and labels, specified as
the vector, [left bottom width height]
. This table describes each
element in the vector.
Element | Description |
---|---|
left | Distance from the inner left edge of the parent container to the outer left edge of the knob |
bottom | Distance from the inner bottom edge of the parent container to the outer bottom edge of the knob |
width | Distance between the right and left outer edges of the knob, excluding tick marks and labels |
height | Distance 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 each other. 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]
InnerPosition
— Inner location and size of knob
[100 100 60 60]
(default) | [left bottom width height]
Inner location and size of the knob, excluding state marks and state 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 Position
for knob
components.
OuterPosition
— Outer location and size of knob
[73 100 127 76]
(default) | [left bottom width height]
This property is read-only.
Outer location and size of the knob, including state marks and labels, returned as
the vector, [left bottom width height]
. Position values are
relative to the parent container. All measurements are in pixel units.
Layout
— Layout options
empty LayoutOptions
array (default) | GridLayoutOptions
object
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 discrete knob in the third row and second column of its parent grid.
g = uigridlayout([4 3]);
k = uiknob(g,'discrete');
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
ValueChangedFcn
— Value changed callback
''
(default) | function handle | cell array | character vector
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 turns the knob selector in the app. The
callback does not execute if the Value
property changes
programmatically.
This callback 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.
Property | Value |
---|---|
Value | Value of knob after the app user’s most recent interaction |
PreviousValue | Value of knob before the app user’s most recent interaction |
ValueIndex | Index of knob value in items after the app user’s most recent interaction |
PreviousValueIndex | Index of knob value in items before the app user’s most recent interaction with it |
Source | Component that executes the callback. |
EventName | 'ValueChanged' |
For more information about writing callbacks, see Callbacks in App Designer.
CreateFcn
— Creation function
''
(default) | function handle | cell array | character vector
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.
DeleteFcn
— Deletion function
''
(default) | function handle | cell array | character vector
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
Interruptible
— Callback interruption
'on'
(default) | on/off logical value
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, theBusyAction
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
, orSizeChangedFcn
callback, then the interruption occurs regardless of theInterruptible
property value.If the running callback is currently executing the
waitfor
function, then the interruption occurs regardless of theInterruptible
property value.If the interrupting callback is owned by a
Timer
object, then the callback executes according to schedule regardless of theInterruptible
property value.
BusyAction
— Callback queuing
'queue'
(default) | 'cancel'
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:
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.
BeingDeleted
— Deletion status
on/off logical value
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
— Parent container
Figure
object (default) | Panel
object | Tab
object | ButtonGroup
object | GridLayout
object
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.
HandleVisibility
— Visibility of object handle
'on'
(default) | 'callback'
| 'off'
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 Value | Description |
---|---|
'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
Type
— Type of graphics object
'uidiscreteknob'
This property is read-only.
Type of graphics object, returned as 'uidiscreteknob'
.
Tag
— Object identifier
''
(default) | character vector | string scalar
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.
UserData
— User data
[]
(default) | array
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
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.
Version History
Introduced in R2016aR2023b: Access index of component value in list of items
Access the index of the component value in the list of items by using the
ValueIndex
property.
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