Ufdjrw

Negative Resistance

Find a stone which is not the lightest one

How to keep bees out of canned beverages?

Scheduling based problem

A strange hotel

Can a stored procedure reference the database in which it is stored?

Does Mathematica have an implementation of the Poisson binomial distribution?

Can I criticise the more senior developers around me for not writing clean code?

A Paper Record is What I Hamper

Check if a string is entirely made of the same substring

Contradiction proof for inequality of P and NP?

Island of Knights, Knaves and Spies

Could moose/elk survive in the Amazon forest?

I preordered a game on my Xbox while on the home screen of my friend's account. Which of us owns the game?

What was Apollo 13's "Little Jolt" after MECO?

How does the mezzoloth's teleportation work?

My bank got bought out, am I now going to have to start filing tax returns in a different state?

Why must Chinese maps be obfuscated?

How long after the last departure shall the airport stay open for an emergency return?

How exactly does Hawking radiation decrease the mass of black holes?

Older movie/show about humans on derelict alien warship which refuels by passing through a star

Was Dennis Ritchie being too modest in this quote about C and Pascal?

How can I wire a 9-position switch so that each position turns on one more LED than the one before?

What is this word supposed to be?

Flutter Future:A build function returned null

Android - dataSnapshot.getValue() returns null on second call (but not first)(Firebase Unity SDK) Not entering ContinueWith() when called on GetValueAsync()AngularFire2 Query List Get Child ValuesAngular JS don't load value in the scope from function javascriptFirebase transaction returns null and completes without errorFlutter : Bad state: Stream has already been listened toInitialize object to show in my ScaffoldHow to download data from Firebase?Flutter: Question about async function to retrieve Firebase user IDHow to add child to a List in Firebase Realtime Database with a cloud function?

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty height:90px;width:728px;box-sizing:border-box;

1

I want to retrieve data from firebase to future builder.I use this function for that.

Future getAllData() async 
 ReseviorDataModel resModel;
 DatabaseReference ref = FirebaseDatabase.instance.reference();
 DataSnapshot childed =await 
 ref.child("Reservoir/$widget.placeName").once();
 Map<dynamic, dynamic> values;
 values = childed.value;
 resModel = ReseviorDataModel.customConstrcutor(values["sensor1"], 
 values["sensor2"], values["sensor3"]);
 return resModel;

I invoke this function inside my future builder.

 child: FutureBuilder(
 future: getAllData(),
 builder: (context, snapshot) 
 Center(child: Text(snapshot.data));
 

but it keeps throwing this "A build function returned null." error .i cant figure out what is the problem here

firebase firebase-realtime-database flutter

share|improve this question

asked Mar 9 at 7:19

NicoleZNicoleZ

529

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  replace Center with return Center
  
  – pskink
  Mar 9 at 7:22
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  it worked. highly appreciated
  
  – NicoleZ
  Mar 9 at 7:26
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  sure, your welcome
  
  – pskink
  Mar 9 at 7:26
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @pskink Please write it down as answer otherwise someone else may come up and write the same thing down.
  
  – CopsOnRoad
  Mar 9 at 7:50
  

  
  
  
  

add a comment | 

1

I want to retrieve data from firebase to future builder.I use this function for that.

Future getAllData() async 
 ReseviorDataModel resModel;
 DatabaseReference ref = FirebaseDatabase.instance.reference();
 DataSnapshot childed =await 
 ref.child("Reservoir/$widget.placeName").once();
 Map<dynamic, dynamic> values;
 values = childed.value;
 resModel = ReseviorDataModel.customConstrcutor(values["sensor1"], 
 values["sensor2"], values["sensor3"]);
 return resModel;

I invoke this function inside my future builder.

 child: FutureBuilder(
 future: getAllData(),
 builder: (context, snapshot) 
 Center(child: Text(snapshot.data));
 

but it keeps throwing this "A build function returned null." error .i cant figure out what is the problem here

firebase firebase-realtime-database flutter

share|improve this question

asked Mar 9 at 7:19

NicoleZNicoleZ

529

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  replace Center with return Center
  
  – pskink
  Mar 9 at 7:22
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  it worked. highly appreciated
  
  – NicoleZ
  Mar 9 at 7:26
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  sure, your welcome
  
  – pskink
  Mar 9 at 7:26
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @pskink Please write it down as answer otherwise someone else may come up and write the same thing down.
  
  – CopsOnRoad
  Mar 9 at 7:50
  

  
  
  
  

add a comment | 

I want to retrieve data from firebase to future builder.I use this function for that.

Future getAllData() async 
 ReseviorDataModel resModel;
 DatabaseReference ref = FirebaseDatabase.instance.reference();
 DataSnapshot childed =await 
 ref.child("Reservoir/$widget.placeName").once();
 Map<dynamic, dynamic> values;
 values = childed.value;
 resModel = ReseviorDataModel.customConstrcutor(values["sensor1"], 
 values["sensor2"], values["sensor3"]);
 return resModel;

I invoke this function inside my future builder.

 child: FutureBuilder(
 future: getAllData(),
 builder: (context, snapshot) 
 Center(child: Text(snapshot.data));
 

but it keeps throwing this "A build function returned null." error .i cant figure out what is the problem here

firebase firebase-realtime-database flutter

share|improve this question

asked Mar 9 at 7:19

NicoleZNicoleZ

529

Future getAllData() async 
 ReseviorDataModel resModel;
 DatabaseReference ref = FirebaseDatabase.instance.reference();
 DataSnapshot childed =await 
 ref.child("Reservoir/$widget.placeName").once();
 Map<dynamic, dynamic> values;
 values = childed.value;
 resModel = ReseviorDataModel.customConstrcutor(values["sensor1"], 
 values["sensor2"], values["sensor3"]);
 return resModel;

 child: FutureBuilder(
 future: getAllData(),
 builder: (context, snapshot) 
 Center(child: Text(snapshot.data));
 

firebase firebase-realtime-database flutter

firebase firebase-realtime-database flutter

share|improve this question

asked Mar 9 at 7:19

NicoleZNicoleZ

529

share|improve this question

asked Mar 9 at 7:19

NicoleZNicoleZ

529

asked Mar 9 at 7:19

NicoleZNicoleZ

529

asked Mar 9 at 7:19

NicoleZNicoleZ

529

1 Answer
1

active

oldest

votes

1

To clear things up here, your builder always has to return a widget to display. You can never return null, as the error message describes.

The problem in this case was that the OP didn't return anything from the builder, so just adding a return worked out fine.

Some things to keep in mind when using FutureBuilder. Always check the snapshot.hasData property and return a UI accordingly. This will prevent cases where the snapshot.data is null causing a new error to be thrown in your Widget taking in the null.

Example:

child: FutureBuilder(
 future: getAllData(),
 builder: (context, snapshot) 
 if(!snapshot.hasData) 
 // show loading while waiting for real data
 return CircularProgressIndicator();
 

 return Center(child: Text(snapshot.data));

share|improve this answer

answered Mar 9 at 9:35

Filled StacksFilled Stacks

1,1441917

add a comment | 

Your Answer

StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");

StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);

else
createEditor();

);

function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);



);

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55074996%2fflutter-futurea-build-function-returned-null%23new-answer', 'question_page');

);

Post as a guest

Name

Email

Required, but never shown

1

To clear things up here, your builder always has to return a widget to display. You can never return null, as the error message describes.

The problem in this case was that the OP didn't return anything from the builder, so just adding a return worked out fine.

Some things to keep in mind when using FutureBuilder. Always check the snapshot.hasData property and return a UI accordingly. This will prevent cases where the snapshot.data is null causing a new error to be thrown in your Widget taking in the null.

Example:

child: FutureBuilder(
 future: getAllData(),
 builder: (context, snapshot) 
 if(!snapshot.hasData) 
 // show loading while waiting for real data
 return CircularProgressIndicator();
 

 return Center(child: Text(snapshot.data));

share|improve this answer

answered Mar 9 at 9:35

Filled StacksFilled Stacks

1,1441917

add a comment | 

1

To clear things up here, your builder always has to return a widget to display. You can never return null, as the error message describes.

The problem in this case was that the OP didn't return anything from the builder, so just adding a return worked out fine.

Some things to keep in mind when using FutureBuilder. Always check the snapshot.hasData property and return a UI accordingly. This will prevent cases where the snapshot.data is null causing a new error to be thrown in your Widget taking in the null.

Example:

child: FutureBuilder(
 future: getAllData(),
 builder: (context, snapshot) 
 if(!snapshot.hasData) 
 // show loading while waiting for real data
 return CircularProgressIndicator();
 

 return Center(child: Text(snapshot.data));

share|improve this answer

answered Mar 9 at 9:35

Filled StacksFilled Stacks

1,1441917

add a comment | 

To clear things up here, your builder always has to return a widget to display. You can never return null, as the error message describes.

The problem in this case was that the OP didn't return anything from the builder, so just adding a return worked out fine.

Some things to keep in mind when using FutureBuilder. Always check the snapshot.hasData property and return a UI accordingly. This will prevent cases where the snapshot.data is null causing a new error to be thrown in your Widget taking in the null.

Example:

child: FutureBuilder(
 future: getAllData(),
 builder: (context, snapshot) 
 if(!snapshot.hasData) 
 // show loading while waiting for real data
 return CircularProgressIndicator();
 

 return Center(child: Text(snapshot.data));

share|improve this answer

answered Mar 9 at 9:35

Filled StacksFilled Stacks

1,1441917

child: FutureBuilder(
 future: getAllData(),
 builder: (context, snapshot) 
 if(!snapshot.hasData) 
 // show loading while waiting for real data
 return CircularProgressIndicator();
 

 return Center(child: Text(snapshot.data));

share|improve this answer

answered Mar 9 at 9:35

Filled StacksFilled Stacks

1,1441917

answered Mar 9 at 9:35

Filled StacksFilled Stacks

1,1441917

answered Mar 9 at 9:35

Filled StacksFilled Stacks

1,1441917