Question

我遵循从现有数据库中为iOS填充值的所有说明：link

使用以下代码：

import SQLite from 'react-native-sqlite-storage';
var db; 
export default class App extends Component<Props> {
errorCB(err) {
  console.log("SQL Error: " + err);
};

successCB() {
  console.log("SQL executed fine");
};

openCB() {
  console.log("Database OPENED");
};

openDB() {
db = SQLite.openDatabase({name : "sqliteexample", createFromLocation : 1}, this.openCB, this.errorCB);

}

populateDB() {
  db.transaction((tx) => {
    tx.executeSql("SELECT * FROM Users", [], (tx, results) => {
        console.log("Query completed");

        // Get rows with Web SQL Database spec compliance.

        var len = results.rows.length;
        console.log('len' + len)
        for (let i = 0; i < len; i++) {
          let row = results.rows.item(i);
          console.log(`User: ${row}`);
        }
      });
  });
}

render() {
    return (
<View style={styles.container} >
<Button onPress={this. openDB}
         title="open Database"
         color="#841584"/>
<Button onPress={this. populateDB}
         title="Get Data"
         color="#841584"/>
      </View>
    );
  }
}

我收到此错误：

undefined不是对象（评估'db.transaction'）

但是在控制台中成功打开数据库获取以下消息：

2018-06-08 11:43:40.678 [info] [tid：com.facebook.react.SQLiteQueue] [SQLite.m：255] open cb 结束了2018-06-08 11：43：40.679 [info] [tid：com.facebook.react.JavaScript] DB打开：sqliteexample 2018-06-08 11：43：40.679165 + 0530 FlatListAppDemo [1018：61832] open cb 完成确定2018-06-08 11：43：40.679220 + 0530 FlatListAppDemo [1018：61820] DB已打开：sqliteexample

请帮我解决这个问题。提前谢谢。

Answer 1

您可以尝试这样

import SQLite from 'react-native-sqlite-storage';
var database_name = "sqliteexample"; // Add your Database name
var database_version = "1.0"; // Add your Database Version
var database_size = 200000; // Add your Database Size
var database_displayname = "SQL Database"; // Add your Database Displayname
var db; 

export default class App extends Component<Props> {
errorCB(err) {
  console.log("SQL Error: " + err);
};

successCB() {
  console.log("SQL executed fine");
};

openCB() {
  console.log("Database OPENED");
};

openDB() {

 db = SQLite.openDatabase(database_name, database_version, database_displayname, database_size, this.openCB, this.errorCB);

}

populateDB() {

  db = SQLite.openDatabase(database_name, database_version, database_displayname, database_size, this.openCB, this.errorCB);
  db.transaction((tx) => {
    tx.executeSql("SELECT * FROM Users", [], (tx, results) => {
        console.log("Query completed");

        // Get rows with Web SQL Database spec compliance.

        var len = results.rows.length;
        console.log('len' + len)
        for (let i = 0; i < len; i++) {
          let row = results.rows.item(i);
          console.log(`User: ${row}`);
        }
      });
  });
}

render() {
    return (
<View style={styles.container} >
<Button onPress={this. openDB}
         title="open Database"
         color="#841584"/>
<Button onPress={this. populateDB}
         title="Get Data"
         color="#841584"/>
      </View>
    );
  }
}

Answer 2

所以我认为这可能只是时间问题。获取数据库对象的最安全方法是在成功回调中，如果在openDatabase中一切顺利，它将接收有效的db对象。所以将你的代码更改为此并尝试...

openCB(myDB) {
  console.log("Database OPENED");
  db = myDB;
};

openDB() {
  SQLite.openDatabase({name : "sqliteexample", createFromLocation : 1}, this.openCB, this.errorCB);

}

错误：undefined不是ReactNative中的对象（评估'db.transaction'）

2 个答案: