InheritedWidget concept in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a custom InheritedWidget class named MyData.

Flutter

class MyData extends InheritedWidget {
  final int data;
  const MyData({required this.data, required Widget child, Key? key}) : super(key: key, child: child);

  @override
  bool [1](covariant MyData oldWidget) {
    return oldWidget.data != data;
  }
}

Drag options to blanks, or click blank then click option'

Abuild

BupdateShouldNotify

CcreateState

Ddispose

Attempts:

3 left

💡 Hint

Common Mistakes

Using lifecycle methods like build or dispose instead of updateShouldNotify.

Not overriding updateShouldNotify causes dependents to not update.

The updateShouldNotify method tells Flutter when to notify widgets that depend on this InheritedWidget about changes.

2fill in blank

medium

Complete the code to access the MyData instance from the widget tree.

Flutter

final myData = context.dependOnInheritedWidgetOfExactType<[1]>();

Drag options to blanks, or click blank then click option'

AInheritedWidget

BStatefulWidget

CStatelessWidget

DMyData

Attempts:

3 left

💡 Hint

Common Mistakes

Using the base InheritedWidget class instead of the custom one.

Trying to access StatefulWidget or StatelessWidget which are unrelated.

To get the data, you must specify your custom InheritedWidget class MyData in the generic type.

3fill in blank

hard

Fix the error in the method to get the shared data value from MyData.

Flutter

int getData(BuildContext context) {
  final inherited = context.dependOnInheritedWidgetOfExactType<MyData>();
  return inherited?.[1] ?? 0;
}

Drag options to blanks, or click blank then click option'

Adata

Bchild

CupdateShouldNotify

Dcontext

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access the child widget instead of the data.

Using lifecycle methods or context instead of the data field.

The shared value is stored in the data field of MyData, so we access inherited.data.

4fill in blank

hard

Fill both blanks to create a widget that uses MyData to show the shared integer.

Flutter

class DisplayData extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final value = context.dependOnInheritedWidgetOfExactType<[1]>()?.[2] ?? 0;
    return Text('Value: $value');
  }
}

Drag options to blanks, or click blank then click option'

AMyData

Bdata

Cchild

DupdateShouldNotify

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong class names or fields that do not exist.

Trying to access the child widget instead of data.

You must specify MyData to get the inherited widget and access its data field to read the shared value.

5fill in blank

hard

Fill all three blanks to create an InheritedWidget that updates dependents when data changes.

Flutter

class CounterData extends InheritedWidget {
  final int count;
  const CounterData({required this.count, required Widget child, Key? key}) : super(key: key, child: child);

  @override
  bool [1](covariant CounterData oldWidget) {
    return oldWidget.[2] != [3];
  }
}

Drag options to blanks, or click blank then click option'

AupdateShouldNotify

Bcount

Dchild

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names or comparing wrong fields.

Not overriding updateShouldNotify causes dependents to not update.

The method updateShouldNotify compares the old count with the current count to decide if dependents should rebuild.

Practice

1. What is the main purpose of an InheritedWidget in Flutter?

easy

A. To handle user input events.

B. To create animations between widgets.

C. To manage network requests.

D. To share data efficiently down the widget tree without passing it manually.

Solution

1. Step 1: Understand the role of InheritedWidget

   InheritedWidget is designed to share data with its child widgets efficiently.

2. Step 2: Compare with other options

   Animations, user input, and network requests are handled by other Flutter classes, not InheritedWidget.

3. Final Answer:

   To share data efficiently down the widget tree without passing it manually. -> Option D

4. Quick Check:

   InheritedWidget shares data down the tree = C [OK]

Hint: InheritedWidget shares data down widget tree [OK]

Common Mistakes:

• Confusing InheritedWidget with animation or input handling
• Thinking it manages network calls
• Assuming it rebuilds widgets manually

2. Which of the following is the correct way to access data from an InheritedWidget named MyData inside a child widget?

easy

A. MyData.get(context)

B. MyData.of(context)

C. MyData.fetch(context)

D. MyData.access(context)

Solution

1. Step 1: Recall the standard access method

   The convention to access InheritedWidget data is using a static of method.

2. Step 2: Verify method names

   Only MyData.of(context) follows Flutter's standard pattern; others are incorrect.

3. Final Answer:

   MyData.of(context) -> Option B

4. Quick Check:

   Use of() method to access InheritedWidget data = A [OK]

Hint: Use .of(context) to get InheritedWidget data [OK]

Common Mistakes:

• Using non-existent methods like get or fetch
• Trying to access data without context
• Confusing with Provider package syntax

3. Given this code snippet, what will be printed when MyInheritedWidget updates its data and updateShouldNotify returns true?

class MyInheritedWidget extends InheritedWidget {
  final int data;
  MyInheritedWidget({required this.data, required Widget child}) : super(child: child);

  static MyInheritedWidget? of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<MyInheritedWidget>();
  }

  @override
  bool updateShouldNotify(MyInheritedWidget oldWidget) {
    return data != oldWidget.data;
  }
}

// In a child widget's build:
final inherited = MyInheritedWidget.of(context);
print('Data is: ${inherited?.data}');

medium

A. No output printed

B. Data is: old data value

C. Data is: new data value

D. Runtime error occurs

Solution

1. Step 1: Understand updateShouldNotify behavior

   When updateShouldNotify returns true, dependent widgets rebuild and get new data.

2. Step 2: Analyze the print statement

   The child widget accesses the updated data value, so it prints the new data.

3. Final Answer:

   Data is: new data value -> Option C

4. Quick Check:

   updateShouldNotify true triggers rebuild with new data = A [OK]

Hint: True updateShouldNotify means child rebuilds with new data [OK]

Common Mistakes:

• Assuming old data is printed after update
• Thinking no rebuild happens
• Expecting runtime errors from updateShouldNotify

4. Identify the error in this InheritedWidget implementation:

class MyData extends InheritedWidget {
  final int value;
  MyData({required this.value, required Widget child}) : super(child: child);

  static MyData of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<MyData>()!;
  }

  @override
  bool updateShouldNotify(MyData oldWidget) {
    return false;
  }
}

medium

A. updateShouldNotify always returns false, so dependents never rebuild.

B. Missing call to super constructor.

C. Static method of() should return nullable type.

D. value field should be mutable.

Solution

1. Step 1: Check updateShouldNotify logic

   Returning false always means widgets depending on this InheritedWidget won't rebuild on data change.

2. Step 2: Verify other parts

   Constructor calls super correctly; of() returns non-null with !; value can be final.

3. Final Answer:

   updateShouldNotify always returns false, so dependents never rebuild. -> Option A

4. Quick Check:

   False updateShouldNotify blocks rebuilds = D [OK]

Hint: updateShouldNotify false means no rebuilds triggered [OK]

Common Mistakes:

• Ignoring updateShouldNotify effect on rebuild
• Thinking constructor call is missing
• Confusing nullable return types
• Assuming value must be mutable

5. You want to create a theme color shared across your app using InheritedWidget. Which approach correctly ensures that widgets rebuild only when the color changes?

class ThemeColor extends InheritedWidget {
  final Color color;
  ThemeColor({required this.color, required Widget child}) : super(child: child);

  static ThemeColor? of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<ThemeColor>();
  }

  @override
  bool updateShouldNotify(ThemeColor oldWidget) {
    // What should go here?
  }
}

hard

A. return color != oldWidget.color;

B. return true;

C. return false;

D. return oldWidget.color == null;

Solution

1. Step 1: Understand updateShouldNotify purpose

   This method decides if dependents rebuild when data changes.

2. Step 2: Compare current and old color values

   Return true only if the color changed to trigger rebuilds correctly.

3. Step 3: Evaluate options

   return color != oldWidget.color; returns true if colors differ, which is correct. return true; always rebuilds unnecessarily, return false; never rebuilds, return oldWidget.color == null; is irrelevant.

4. Final Answer:

   return color != oldWidget.color; -> Option A

5. Quick Check:

   Rebuild only if color changes = B [OK]

Hint: Compare old and new data in updateShouldNotify [OK]

Common Mistakes:

• Always returning true causing unnecessary rebuilds
• Always returning false blocking updates
• Checking for null instead of value change