UI components in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this MATLAB UI code?

Consider the following MATLAB code that creates a simple UI figure with a button. What will be displayed when the button is clicked?

MATLAB

fig = uifigure('Name','Test UI');
btn = uibutton(fig,'push','Text','Click me');
btn.ButtonPushedFcn = @(btn,event) disp('Button clicked!');

A A message box pops up with 'Button clicked!'

B Nothing happens when the button is clicked

C The text 'Button clicked!' is printed in the MATLAB command window

D An error occurs because ButtonPushedFcn is not a valid property

💡 Hint

Think about where disp outputs text in MATLAB.

The disp function prints text to the MATLAB command window, so clicking the button will print 'Button clicked!' there.

🧠 Conceptual

intermediate

Which UI component is best for selecting one option from many?

In MATLAB UI design, which component allows the user to select exactly one option from a list?

A uilistbox

B uiradiobutton

C uicheckbox

D uiradiobuttongroup

💡 Hint

Think about grouping radio buttons to allow only one selection.

A uiradiobuttongroup contains multiple radio buttons and ensures only one can be selected at a time.

🔧 Debug

advanced

Why does this MATLAB UI code cause an error?

Examine the code below. Why does it cause an error when run?

MATLAB

fig = uifigure;
btn = uibutton(fig,'Text','Press');
btn.ButtonPushedFcn = @buttonCallback;

function buttonCallback(src,event)
    disp('Pressed');
end

A The callback function must be nested inside the main script or saved separately

B The ButtonPushedFcn property does not accept function handles

C The uibutton function requires a position argument

D The disp function cannot be used inside callbacks

💡 Hint

Consider MATLAB's rules about local functions in scripts.

In MATLAB scripts, local functions must be at the end of the file or saved separately. Here, the callback is defined after the script code, causing an error.

📝 Syntax

advanced

Which option correctly creates a dropdown UI component in MATLAB?

Choose the correct syntax to create a dropdown menu with options 'Red', 'Green', 'Blue' in a MATLAB UI figure.

A dd = uidropdown('Parent',fig,'Items',{'Red','Green','Blue'},'Value','Red');

B dd = uidropdown(fig,'Items',{'Red','Green','Blue'});

C dd = uidropdown(fig,'Items',{'Red','Green','Blue'},'Value','Red');

D dd = uidropdown('Items',{'Red','Green','Blue'},'Parent',fig);

💡 Hint

Check the order and names of input arguments for uidropdown.

The correct syntax uses name-value pairs with 'Parent' first, then 'Items', then 'Value'. Passing the figure as first argument without name is invalid.

🚀 Application

expert

How many items are in the dropdown after this code runs?

Given the code below, how many items will the dropdown contain?

MATLAB

fig = uifigure;
dd = uidropdown(fig,'Items',{'One','Two','Three'});
items = dd.Items;
items{end+1} = 'Four';
dd.Items = items;

A 3

B 4

C 1

D Error occurs when modifying items

💡 Hint

Think about how the Items property is updated.

The code gets the current items, adds 'Four' to the list, then assigns it back. So the dropdown has 4 items after running.

Practice

1. Which MATLAB function is used to create a new interactive window for UI components?

easy

A. window

B. uifigure

C. uiwindow

D. figure

Solution

1. Step 1: Understand the purpose of UI windows

   MATLAB uses a special function to create windows that support interactive UI components like buttons and sliders.

2. Step 2: Identify the correct function for UI windows

   The function uifigure creates a window designed for UI components, unlike figure which is for plots.

3. Final Answer:

   uifigure -> Option B

4. Quick Check:

   UI window = uifigure [OK]

Hint: Use uifigure for UI windows, not figure [OK]

Common Mistakes:

• Confusing uifigure with figure
• Using non-existent functions like uiwindow
• Assuming window creates UI windows

2. Which of the following is the correct syntax to add a button to a UI figure named fig?

easy

A. btn = uibutton();

B. btn = button(fig);

C. btn = addbutton(fig);

D. btn = uibutton(fig);

Solution

1. Step 1: Recall the function to create buttons in UI figures

   MATLAB uses uibutton to create buttons inside a UI figure.

2. Step 2: Check the syntax for specifying the parent UI figure

   The parent figure must be passed as an argument to uibutton, so uibutton(fig); is correct.

3. Final Answer:

   btn = uibutton(fig); -> Option D

4. Quick Check:

   Button creation = uibutton(fig) [OK]

Hint: Always pass the figure handle to uibutton [OK]

Common Mistakes:

• Using button() instead of uibutton()
• Not passing the figure as argument
• Using non-existent addbutton() function

3. What will be the output when running this code?

fig = uifigure();
btn = uibutton(fig, 'Text', 'Click Me');
disp(btn.Text);

medium

A. Click Me

B. uibutton

C. btn

D. Error: Text property not found

Solution

1. Step 1: Understand button creation with text

   The button is created with the text property set to 'Click Me'.

2. Step 2: Display the button's Text property

   Using disp(btn.Text) prints the string assigned to the Text property.

3. Final Answer:

   Click Me -> Option A

4. Quick Check:

   Button text = 'Click Me' [OK]

Hint: disp(btn.Text) shows button label text [OK]

Common Mistakes:

• Expecting the variable name instead of text
• Thinking btn.Text is invalid property
• Confusing output with object type

4. Identify the error in this code snippet:

fig = uifigure();
btn = uibutton(fig);
btn.Callback = @(src,event) disp('Button clicked');

medium

A. Property name should be ButtonPushedFcn, not Callback

B. uifigure() cannot have buttons

C. Anonymous functions cannot be used as callbacks

D. disp cannot be used inside callbacks

Solution

1. Step 1: Check the correct callback property for uibutton

   In MATLAB UI buttons, the callback property is named ButtonPushedFcn, not Callback.

2. Step 2: Understand the effect of wrong property name

   Assigning to Callback does nothing; the button won't respond to clicks.

3. Final Answer:

   Property name should be ButtonPushedFcn, not Callback -> Option A

4. Quick Check:

   Button callback = ButtonPushedFcn [OK]

Hint: Use ButtonPushedFcn for button callbacks [OK]

Common Mistakes:

• Using Callback instead of ButtonPushedFcn
• Thinking anonymous functions are invalid
• Believing buttons can't be added to uifigure

5. You want to create a UI with a slider that updates a label text showing the slider value in real-time. Which approach correctly sets this up?

hard

A. Create slider and label, then use a loop to constantly check slider.Value and update label.Text

B. Create slider and label, then set label's ValueChangedFcn to update slider.Value inside the callback

C. Create slider and label, then set slider's ValueChangedFcn to update label.Text inside the callback

D. Create slider and label, then set slider's ButtonPushedFcn to update label.Text

Solution

1. Step 1: Understand slider and label interaction

   The slider's ValueChangedFcn triggers when the slider moves, perfect for updating the label.

2. Step 2: Set callback to update label text

   Inside the slider's callback function, update the label's Text property to show the current slider value.

3. Final Answer:

   Create slider and label, then set slider's ValueChangedFcn to update label.Text inside the callback -> Option C

4. Quick Check:

   Slider update uses ValueChangedFcn callback [OK]

Hint: Use slider's ValueChangedFcn to update label text [OK]

Common Mistakes:

• Using label's ValueChangedFcn instead of slider's
• Using ButtonPushedFcn on slider (not valid)
• Using loops instead of callbacks