1

下面是我正在处理的代码。

应用程序.js

    /**
 * Sample React Native App
 * https://github.com/facebook/react-native
 *
 * Generated with the TypeScript template
 * https://github.com/react-native-community/react-native-template-typescript
 *
 * @format
 */

import * as React from 'react';
import {
  SafeAreaView,
  StyleSheet,
  ScrollView,
  View,
  Text,
  StatusBar,
} from 'react-native';

import {
  Header,
  LearnMoreLinks,
  Colors,
  DebugInstructions,
  ReloadInstructions,
} from 'react-native/Libraries/NewAppScreen';
import SQLite from "react-native-sqlite-storage";

const database_name = "Test.db";
const database_version = "1.0";
const database_displayname = "SQLite Test Database";
const database_size = 200000;
SQLite.enablePromise(true);

let db;
type InitState={
  firstTimeUsage:boolean,
  errorOccured:boolean,
  errorMessage:string
}

export default class App extends React.Component<{},InitState>{
  constructor(props:any){
    super(props);
    this.state={
      firstTimeUsage:null,
      errorOccured:false,
      errorMessage:null
    }
  }

  componentDidMount(){
    console.log("Component did mount called");
    SQLite.openDatabase(database_name, database_version, database_displayname, database_size).then((DB)=>{
      console.log("database opened");
      db = DB;
      if(this.checkFirstTimeUsage(db)){
        this.createTable(db);
      }else{
        this.setState({firstTimeUsage:false});
      }
    }).catch((error)=>{
      console.log("error occured opening database");
      this.setState({errorOccured:true,errorMessage:"Error validating app installation"});
    });
  }

  createTable = (database:any) => {
    console.log("Creating table");
    database.transaction((tx:SQLite.transaction)=>{
      tx.executeSql("CREATE TABLE IF NOT EXISTS PROFILE_MASTER (PLAYER_TAG VARCHAR(10) PRIMARY KEY NOT NULL,DEFAULT_IND VARCHAR(1) NOT NULL);")
      .then(([tx,results]) => {
        console.log("Table created");
        this.setState({firstTimeUsage:true});
      }).catch((_error: any)=>{
        console.log("error occured creating table");
        this.setState({errorOccured:true,errorMessage:"Error initializing app"})
      });
      tx.executeSql("INSERT into PROFILE_MASTER (PLAYER_TAG,DEFAULT_IND) values ('ASDC','Y')")
      .then(([results])=>{
        console.log("added data to table");
        console.log(results);
      }).catch((error: any) => {
        console.log("error adding data to table");
        console.log(error)
      })
    })
  }


  checkFirstTimeUsage = async (database:SQLite.SQLiteDatabase) => {
    return await database.transaction((tx)=>{
      tx.executeSql("SELECT name from sqlite_master where type='TABLE' and name = 'PROFILE_MASTER'",null).
      then(([tx,results])=>{
        if(results.rows.length===0){
          return true;
        }else{
          return false;
        }
      })
    }).catch((error)=>{
      console.log(error);
      return false;
    })
  }
  render(){
    console.log("first time usage is "+this.state.firstTimeUsage);
    return (
      <>
        <StatusBar barStyle="dark-content" />
        <SafeAreaView>
          <ScrollView
            contentInsetAdjustmentBehavior="automatic"
            style={styles.scrollView}>
            <Header />
            <View style={styles.body}>
              <View style={styles.sectionContainer}>
                <Text style={styles.sectionTitle}>Step One{this.state.firstTimeUsage}</Text>
                <Text style={styles.sectionDescription}>
                  Edit <Text style={styles.highlight}>App.tsx</Text> to change this
                  screen and then come back to see your edits.
                </Text>
              </View>
              <View style={styles.sectionContainer}>
                <Text style={styles.sectionTitle}>See Your Changes</Text>
                <Text style={styles.sectionDescription}>
                  <ReloadInstructions />
                </Text>
              </View>
              <View style={styles.sectionContainer}>
                <Text style={styles.sectionTitle}>Debug</Text>
                <Text style={styles.sectionDescription}>
                  <DebugInstructions />
                </Text>
              </View>
              <View style={styles.sectionContainer}>
                <Text style={styles.sectionTitle}>Learn More</Text>
                <Text style={styles.sectionDescription}>
                  Read the docs to discover what to do next:
                </Text>
              </View>
              <LearnMoreLinks />
            </View>
          </ScrollView>
        </SafeAreaView>
      </>
    );
  }
}

const styles = StyleSheet.create({
  scrollView: {
    backgroundColor: Colors.lighter,
  },
  engine: {
    position: 'absolute',
    right: 0,
  },
  body: {
    backgroundColor: Colors.white,
  },
  sectionContainer: {
    marginTop: 32,
    paddingHorizontal: 24,
  },
  sectionTitle: {
    fontSize: 24,
    fontWeight: '600',
    color: Colors.black,
  },
  sectionDescription: {
    marginTop: 8,
    fontSize: 18,
    fontWeight: '400',
    color: Colors.dark,
  },
  highlight: {
    fontWeight: '700',
  },
  footer: {
    color: Colors.dark,
    fontSize: 12,
    fontWeight: '600',
    padding: 4,
    paddingRight: 12,
    textAlign: 'right',
  },
});

包.json

{
  "name": "StatsRoyaleMulti",
  "version": "0.0.1",
  "private": true,
  "scripts": {
    "android": "react-native run-android",
    "ios": "react-native run-ios",
    "start": "react-native start",
    "test": "jest"
  },
  "dependencies": {
    "react": "16.9.0",
    "react-native": "0.61.1",
    "react-native-sqlite-storage": "^4.1.0"
  },
  "devDependencies": {
    "@babel/core": "^7.6.2",
    "@babel/runtime": "^7.6.2",
    "@react-native-community/eslint-config": "^0.0.5",
    "@types/jest": "^24.0.18",
    "@types/react": "^16.9.4",
    "@types/react-native": "^0.60.17",
    "@types/react-test-renderer": "16.9.0",
    "babel-jest": "^24.9.0",
    "jest": "^24.9.0",
    "metro-react-native-babel-preset": "^0.56.0",
    "react-test-renderer": "16.9.0",
    "typescript": "^3.6.3"
  },
  "jest": {
    "preset": "react-native",
    "moduleFileExtensions": [
      "ts",
      "tsx",
      "js",
      "jsx",
      "json",
      "node"
    ]
  }
}

控制台日志：

Running "StatsRoyaleMulti" with {"rootTag":1}
 LOG  first time usage is null
 LOG  Component did mount called
 LOG  database opened
 LOG  Creating table
 LOG  Table created
 LOG  first time usage is true
 LOG  added data to table
 LOG  {"db": {"dbname": "Test.db", "openError": [Function error], "openSuccess": [Function success], "openargs": {"dblocation": "nosync", "name": "Test.db"}}, "error": [Function error], "executes": [], "finalized": true, "fn": [Function anonymous], "readOnly": false, "success": [Function success], "txlock": true}


 LOG  Running "StatsRoyaleMulti" with {"rootTag":11}
 LOG  first time usage is null
 LOG  Component did mount called
 LOG  database opened
 LOG  Creating table
 LOG  Table created
 LOG  first time usage is true
 WARN  Possible Unhandled Promise Rejection (id: 0):
Object {
  "code": 0,
  "message": "UNIQUE constraint failed: PROFILE_MASTER.PLAYER_TAG (code 1555 SQLITE_CONSTRAINT_PRIMARYKEY)",
}

发生了什么：启动应用程序时，我正在检查表是否存在。如果它不存在，那么我正在创建表。我关闭应用程序并再次打开它，我看到该表正在再次创建。

我期望发生的事情：应用程序的第一次启动应该创建表，随后的启动应该发现表存在并且不应该再次创建它。

你们能告诉我我在这里做错了什么吗？

4

1 回答 1

1

行。在上述问题中，我做错了很多事情。

  1. 在选择查询中使用type = 'table'而不是检查数据库。type = 'TABLE'我正在浏览一些在线搜索结果并观察到这一点。

  2. 重写componentDidMount和checkFirstTimeUsage方法如下

组件DidMount

async componentDidMount(){
    console.log("Component did mount called");
    let db = await SQLite.openDatabase(database_name, database_version, database_displayname, database_size);
    let firstTimeUsage = await this.checkFirstTimeUsage(db);
    if(firstTimeUsage){
      this.createTable(db);
    }else{
      this.setState({firstTimeUsage:false});
    }
  }

checkFirstTimeUsage

checkFirstTimeUsage = async (database:SQLite.SQLiteDatabase) => {
    let firstTimeUsage = null;
    await database.transaction((tx)=>{
      tx.executeSql("SELECT name from sqlite_master where type='table' and name = 'PROFILE_MASTER'",null).
      then(([tx,results])=>{
        if(results.rows.length===0){
          firstTimeUsage = true;
        }else{
          console.log("rows length greater than 0");
          firstTimeUsage = false;
        }
      })
    }).catch((error: any)=>{
      console.log(error);
      firstTimeUsage = false;
    });
    return firstTimeUsage;
  }

我总是创建表的原因是由于我在componentDidMount方法中的条件错误。checkFirstTimeUsage是一个异步函数，它返回一个我直接在 if 条件中使用的 promise，它总是评估为 true，因为 promise 不是false, null, 中的一个undefined。

于 2019-10-04T22:25:54.090 回答