More than 3 years have passed since last update.

【Flutter】遭遇したエラー&&解決策まとめ③

Last updated at 2021-01-13Posted at 2021-01-02

前回

【Bad state: Stream has already been listened to】

◆ エラー内容

Bad state: Stream has already been listened to.

◆ 解決策

pubspec.yaml

dependencies:
  rxdart: ^0.25.0

main.dart

// StreamController → BehaviorSubject
final _sample = StreamController<String>();  //before
final _sample = BehaviorSubject<String>();  //after

【setState() called after dispose();エラー】

◆ エラー内容

This error happens if you call setState() on a State object for a widget that no longer appears in the widget tree

◆ 解決策

main.dart

int _count = 0;

void _sampleCounter() {
  if(mounted) {  //追加
    setState(() {
      _count++;
  });
}

【cloud_firestore/permission-denied】

◆ エラー内容

cloud_firestore/permission-denied] The caller does not have permission to execute the specified operation.

◆ 解決策

Firebaseコンソール > プロジェクト選択 > Cloud Firestore > 　ルール

【Dart条件分岐】

◆ switch文

main.dart

const sample1 = "犬";
const sample2 = "猫";
var pets = "ペット";

switch (pets) {
  case sample1:   
    print('犬好き');
    break;
  
  case sample2:
    continue sample1;

  default:
    print('犬も猫も好き');
    break;
}

◆ if文

main.dart

var pets = "ペット";

if (pets == "犬") {
  print('犬好き');
} else if (pets == "猫") {
  print('猫好き');
} else
  print('犬も猫も好き');
}

【setStateメソッド】

◆ setState

main.dart

int _count = 0;

void _sampleCounter() {
  setState(() {
    _count++;
  });
}

参考文献

You get articles that match your needs
You can efficiently read back useful information
You can use dark theme

What you can do with signing up