Navigator.push and pop in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens after Navigator.push is called?

In a Flutter app, when you call Navigator.push(context, MaterialPageRoute(builder: (context) => NewPage())), what is the immediate visible effect on the app UI?

Flutter

Navigator.push(context, MaterialPageRoute(builder: (context) => NewPage()));

A The app crashes because Navigator.push requires a pop before pushing.

B The app navigates to NewPage and displays its UI on top of the current page.

C The app reloads the current page without any navigation.

D The app closes the current page and returns to the previous page.

💡 Hint

Think about what 'push' means in navigation stacks.

Navigator.push adds a new page on top of the current stack, so the new page appears on screen.

❓ ui_behavior

intermediate

What is the effect of Navigator.pop(context)?

In Flutter, what happens when Navigator.pop(context) is called on a page that was pushed onto the stack?

Flutter

Navigator.pop(context);

A The current page is removed and the previous page becomes visible.

B The app closes completely.

C A new page is pushed on top of the current page.

D Nothing happens because pop requires a parameter.

💡 Hint

Pop means to remove the top page from the stack.

Navigator.pop removes the current route, revealing the one below it.

❓ lifecycle

advanced

What lifecycle method is called when a page is popped?

When you call Navigator.pop(context) to close a page in Flutter, which lifecycle method of the popped page is called just before it disappears?

A build()

B initState()

C dispose()

D didChangeDependencies()

💡 Hint

Think about cleaning up resources when a widget is removed.

dispose() is called when a StatefulWidget is removed from the widget tree, such as when popped.

❓ navigation

advanced

What is the result of this Navigator.push call with await?

Consider this Flutter code snippet: final result = await Navigator.push(context, MaterialPageRoute(builder: (context) => InputPage())); What does the variable 'result' contain after the pushed page is popped?

Flutter

final result = await Navigator.push(context, MaterialPageRoute(builder: (context) => InputPage()));

A The value passed to Navigator.pop(context, value) from InputPage.

B Always null because Navigator.push does not return a value.

C The current context object.

D An error because Navigator.push cannot be awaited.

💡 Hint

Navigator.push returns a Future that completes when the page is popped.

Navigator.push returns a Future that resolves to the value passed to pop on the pushed page.

🔧 Debug

expert

Why does this Navigator.pop call cause an error?

Given this Flutter code inside a widget: Navigator.pop(); Why might this cause a runtime error?

A Because Navigator.pop cannot be called inside a widget.

B Because Navigator.pop only works if there is more than one page in the stack.

C Because Navigator.pop requires a route name as a parameter.

D Because Navigator.pop requires a BuildContext parameter to know which navigator to pop.

💡 Hint

Navigator methods usually need context to find the right navigator.

Navigator.pop requires the BuildContext to find the Navigator in the widget tree to pop the current route.

Practice

1. What does Navigator.push do in a Flutter app?

easy

A. It clears all screens and shows a blank page.

B. It closes the current screen and returns to the previous one.

C. It restarts the app from the first screen.

D. It opens a new screen on top of the current one.

Solution

1. Step 1: Understand Navigator.push purpose

   Navigator.push adds a new screen on top of the current screen stack.

2. Step 2: Compare with other Navigator methods

   Navigator.pop removes the current screen, but push opens a new one.

3. Final Answer:

   It opens a new screen on top of the current one. -> Option D

4. Quick Check:

   Navigator.push = Open new screen [OK]

Hint: Push means add a new screen on top [OK]

Common Mistakes:

• Confusing push with pop
• Thinking push closes screens
• Assuming push restarts app

2. Which of the following is the correct syntax to open a new screen called SecondPage using Navigator.push?

easy

A. Navigator.push(SecondPage());

B. Navigator.push(context, MaterialPageRoute(builder: (context) => SecondPage()));

C. Navigator.push(context, SecondPage());

D. Navigator.push(MaterialPageRoute(SecondPage));

Solution

1. Step 1: Recall Navigator.push syntax

   Navigator.push requires context and a route, usually MaterialPageRoute with a builder function.

2. Step 2: Match syntax with options

   Navigator.push(context, MaterialPageRoute(builder: (context) => SecondPage())); correctly uses context and MaterialPageRoute with builder returning SecondPage.

3. Final Answer:

   Navigator.push(context, MaterialPageRoute(builder: (context) => SecondPage())); -> Option B

4. Quick Check:

   Correct Navigator.push syntax = Navigator.push(context, MaterialPageRoute(builder: (context) => SecondPage())); [OK]

Hint: Navigator.push needs context and MaterialPageRoute builder [OK]

Common Mistakes:

• Omitting context parameter
• Passing widget directly instead of route
• Wrong order or missing builder function

3. What will happen when the following code runs inside a button's onPressed callback?

Navigator.push(context, MaterialPageRoute(builder: (context) => SecondPage()));
Navigator.pop(context);

medium

A. The app opens SecondPage and then immediately closes it, returning to the first screen.

B. The app opens SecondPage and stays there.

C. The app crashes due to calling push and pop together.

D. Nothing happens because pop cancels push.

Solution

1. Step 1: Analyze Navigator.push call

   Navigator.push opens SecondPage on top of current screen.

2. Step 2: Analyze Navigator.pop call immediately after

   Navigator.pop closes the current screen, which is SecondPage just opened.

3. Final Answer:

   The app opens SecondPage and then immediately closes it, returning to the first screen. -> Option A

4. Quick Check:

   push then pop = open then close screen [OK]

Hint: Push adds screen, pop removes current screen [OK]

Common Mistakes:

• Assuming both happen simultaneously without effect
• Thinking pop cancels push before opening
• Believing app crashes on push-pop sequence

4. Identify the error in this code snippet that tries to open SecondPage and then close the current screen:

Navigator.push(MaterialPageRoute(builder: (context) => SecondPage()));
Navigator.pop(context);

medium

A. Missing context parameter in Navigator.push call.

B. Navigator.pop should be called before Navigator.push.

C. MaterialPageRoute cannot be used with Navigator.push.

D. SecondPage must be a StatefulWidget.

Solution

1. Step 1: Check Navigator.push parameters

   Navigator.push requires context as the first argument, missing here.

2. Step 2: Confirm other parts are correct

   MaterialPageRoute usage and pop call are correct; SecondPage widget type is unrelated.

3. Final Answer:

   Missing context parameter in Navigator.push call. -> Option A

4. Quick Check:

   Navigator.push needs context first [OK]

Hint: Navigator.push always needs context first [OK]

Common Mistakes:

• Forgetting to pass context to push
• Thinking pop order matters here
• Confusing widget type requirements

5. You want to open a new screen DetailsPage and pass back a result string when it closes. Which code correctly opens DetailsPage and waits for the result using Navigator.push and pop?

hard

A. final result = await Navigator.push(context, MaterialPageRoute(builder: (context) => DetailsPage()));
Navigator.pop(context, result);

B. Navigator.push(context, DetailsPage());
Navigator.pop(context, 'result');

C. final result = await Navigator.push(context, MaterialPageRoute(builder: (context) => DetailsPage()));
// Use result after this line

D. Navigator.pop(context);
final result = await Navigator.push(context, MaterialPageRoute(builder: (context) => DetailsPage()));

Solution

1. Step 1: Understand Navigator.push with await

   Navigator.push returns a Future that completes when the pushed screen pops with a result.

2. Step 2: Use the result after awaiting push

   final result = await Navigator.push(context, MaterialPageRoute(builder: (context) => DetailsPage())); // Use result after this line correctly awaits push and then uses the result; pop with result happens inside DetailsPage.

3. Final Answer:

   final result = await Navigator.push(context, MaterialPageRoute(builder: (context) => DetailsPage())); // Use result after this line -> Option C

4. Quick Check:

   Await push to get pop result [OK]

Hint: Await push to receive pop result from new screen [OK]

Common Mistakes:

• Calling pop immediately after push in same code
• Passing widget directly instead of route
• Not awaiting push to get result