我使用来自react-native-sqlite-storage的SQLite数据库
我没有得到在警报中显示的结果
它显示未定义
我也尝试不使用等待和异步
MainFile
import DBHelper from './DBHelper.js';
export default class MainFile extends Component {
componentDidMount() {
this.dbTransaction();
}
dbTransaction = async () => {
var value = await DBHelper.getWatchList()
alert(value)
}
.....
}
DBHelper
import React, {Component} from 'react';
var SQLite = require('react-native-sqlite-storage');
var dbName = "test.db";
var tableName = "tableName";
const DBHelper = {
getWatchList: () => {
var db = SQLite.openDatabase({name : dbName, createFromLocation : 1}, openCB,errorCB);
db.transaction( (tx) => {
tx.executeSql("select * from " + tableName,
[], (tx, results) => {
console.log("\n\nQuery completed\n");
var resultItemIdArr = new Array();
for (let i = 0; i < results.rows.length; i++) {
resultItemIdArr.push(results.rows.item(i).itemId);
console.log(results.rows.item(i).itemId);
}
return resultItemIdArr;
});
});
},
}
const errorCB = (err) => {
console.log("SQL Error: " + err);
}
const successCB = () => {
console.log("SQL executed fine");
}
const openCB = () => {
console.log("Database OPENED");
}
export default DBHelper;
我想打印警报中的resultItemIdArr值
最佳答案
您在此处使用回调 db.transaction((tx) => {
,因此您将在回调内返回 resultItemIdArr
。如果库不支持 Promise你应该这样做:
getWatchList: (callback) => {
var db = SQLite.openDatabase({name : dbName, createFromLocation : 1}, openCB,errorCB);
db.transaction( (tx) => {
tx.executeSql("select * from " + tableName,
[], (tx, results) => {
console.log("\n\nQuery completed\n");
var resultItemIdArr = new Array();
for (let i = 0; i < results.rows.length; i++) {
resultItemIdArr.push(results.rows.item(i).itemId);
console.log(results.rows.item(i).itemId);
}
callback(resultItemIdArr);
});
});
},
并像这样调用getWatchList
:
dbTransaction = () => {
DBHelper.getWatchList(value=>{
alert(value)
})
}
关于javascript - react native react-native-sqlite-storage不返回结果,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51475821/