CODEWITHSUNDEEP
asynchronousstreamdartflutter
Charles Jr
Charles Jr

Reputation: 9119

Getter "Snapshot" called on null with StreamBuilder in Flutter

I'm using a Flutter Streambuilder and my stream calls null for a second before it loads. I'm trying to load a "Loading..." Card but its not working. My simulator briefly shows a red error screen before displaying my desired card list. How can I get it to stop doing this? Here is my code...

new Expanded(
                  child: new StreamBuilder(
                      stream: streamQuery,
                      builder:
                          (BuildContext context, AsyncSnapshot<Event> event) {
                        if (event.data.snapshot.value == null) {
                          return new Card(
                            child: new Text('Loading...',
                                style: new TextStyle(
                                    fontSize: 12.0,
                                    fontWeight: FontWeight.bold,
                                    fontStyle: FontStyle.italic)),
                          );
                        }

                        Map myMap = event.data.snapshot.value; //store each map
                        var titles = myMap.values;

                        List onesTitles = new List();
                        List onesIds = new List();
                        List onesImages = new List();
                        List onesRank = new List();

                        for (var items in titles) {
                          onesTitles.add(items['vidTitle']);
                          onesIds.add(items['vidId']);
                          onesImages.add(items['vidImage']);
                          onesRank.add(items['Value']);
                        }

                        names = onesTitles;
                        ids = onesIds;
                        numbers = onesRank;
                        vidImages = onesImages;

                        switch (event.connectionState) {
                          case ConnectionState.none:
                            return new Card(
                              child: new Text('Loading...',
                                  style: new TextStyle(
                                      fontSize: 12.0,
                                      fontWeight: FontWeight.bold,
                                      fontStyle: FontStyle.italic)),
                            );
                          case ConnectionState.waiting:
                            return new Card(
                              child: new Text('Awaiting Results...',
                                  style: new TextStyle(
                                      fontSize: 12.0,
                                      fontWeight: FontWeight.bold,
                                      fontStyle: FontStyle.italic)),
                            );
                          default:
                            if (event.hasError)
                              return new Card(
                                child: new Text('Error: ${event.error}',
                                    style: new TextStyle(
                                        fontSize: 12.0,
                                        fontWeight: FontWeight.bold,
                                        fontStyle: FontStyle.italic)),
                              );
                            else
                              return new InkWell(

Upvotes: 3

Views: 5225

Answers (1)

Shady Aziza
Shady Aziza

Reputation: 53317

You need to explicitly state all your data manipulation inside the else that has the build layout for your if (snapshot!=null) {//do something}

Something like this:

else //event.data.snapshot.value != null
 { 
Map myMap = event.data.snapshot.value; //store each map
                        var titles = myMap.values;

                        List onesTitles = new List();
                        List onesIds = new List();
                        List onesImages = new List();
                        List onesRank = new List();

                        for (var items in titles) {
                          onesTitles.add(items['vidTitle']);
                          onesIds.add(items['vidId']);
                          onesImages.add(items['vidImage']);
                          onesRank.add(items['Value']);
                        }

                        names = onesTitles;
                        ids = onesIds;
                        numbers = onesRank;
                        vidImages = onesImages;

//return my layout 
}

So do no leave anything that is using your snapshot.value outside your if statement that works when snapshot!=null.

Upvotes: 5

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