react native react-native-sqlite-storage 不返回结果 [英] react native react-native-sqlite-storage not return result
问题描述
我使用的是 react-native-sqlite-storage 中的 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 await 和 async
<块引用>主文件
从'./DBHelper.js'导入DBHelper;导出默认类 MainFile 扩展组件 {componentDidMount() {this.dbTransaction();}dbTransaction = async() =>{var value = await DBHelper.getWatchList()警报(值)}.....}
<块引用>
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, 结果) =>{console.log("\n\n查询完成\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);}返回 resultItemIdArr;});});},}const errorCB = (err) =>{console.log("SQL 错误:" + err);}const successCB = () =>{console.log("SQL 执行正常");}const openCB = () =>{console.log("数据库已打开");}导出默认的 DBHelper;
我想在警报中打印 resultItemIdArr 值
您在此处使用回调 db.transaction((tx) => {
所以您正在返回 resultItemIdArr
在回调中.如果 lib 不支持 promises,你应该这样做:
getWatchList: (回调) =>{var db = SQLite.openDatabase({name : dbName, createFromLocation : 1}, openCB,errorCB);db.transaction( (tx) => {tx.executeSql("select * from " + tableName,[], (tx, 结果) =>{console.log("\n\n查询完成\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);}回调(resultItemIdArr);});});},
并像这样调用getWatchList
:
dbTransaction = () =>{DBHelper.getWatchList(value=>{警报(值)})}
I'm use SQLite database from react-native-sqlite-storage
I'm not getting result for display in alert
it display undefined
I'm also try without await and async
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;
I want to Print resultItemIdArr value in alert
You are using a callback here db.transaction((tx) => {
so you are returning resultItemIdArr
inside the callback. If the lib doesn't support promises you should do it like this:
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);
});
});
},
and call the getWatchList
like this:
dbTransaction = () => {
DBHelper.getWatchList(value=>{
alert(value)
})
}
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