React native 为什么react native中未定义领域对象
我第一次使用Realm,我只是尝试初始化一个数据库并向其写入一条记录。这是我的密码React native 为什么react native中未定义领域对象,react-native,realm,React Native,Realm,我第一次使用Realm,我只是尝试初始化一个数据库并向其写入一条记录。这是我的密码 import React, { Component } from 'react'; import {StackNavigator} from 'react-navigation'; import Realm from 'realm'; import { AppRegistry, StyleSheet, Text, View, Linking } from 'react-native';
import React, { Component } from 'react';
import {StackNavigator} from 'react-navigation';
import Realm from 'realm';
import {
AppRegistry,
StyleSheet,
Text,
View,
Linking
} from 'react-native';
class Home extends Component {
static navigationOptions = {
title: 'Login',
headerStyle: {
backgroundColor:'#000000'
},
headerTitleStyle: {
color:'#fff'
}
};
initDB()
{
const realm = new Realm({schema: [CompatibilityProduct]});
this.realm = realm;
console.log(realm);
};
loadResults()
{
const realm = this.realm;
console.log(realm);
// Write
realm.write(() => {
realm.create('CompatibilityProduct', {
compatibilityId: 18,
productId: 17,
});
});
};
constructor(props)
{
super(props);
}
render() {
const {navigate} = this.props.navigation;
return (
<View>
<Text onPress={this.initDB}>
Init DB
</Text>
<Text onPress={this.loadResults}>
Load Results
</Text>
</View>
);
}
}
const myscreens = StackNavigator({
Home: {screen: Home}
});
class CompatibilityProduct {}
CompatibilityProduct.schema = {
name: 'CompatibilityProduct',
properties: {
compatibilityId: {type: 'int'},
productId: {type: 'int'},
},
};
export default myscreens;
import React,{Component}来自'React';
从“react navigation”导入{StackNavigator};
从“领域”导入领域;
进口{
评估学,
样式表,
文本,
看法
连接
}从“反应本机”;
类Home扩展组件{
静态导航选项={
标题:“登录”,
头型:{
背景颜色:'#000000'
},
头饰样式:{
颜色:'#fff'
}
};
initDB()
{
const realm=新领域({schema:[CompatibilityProduct]});
this.realm=领域;
log(领域);
};
加载结果()
{
const realm=this.realm;
log(领域);
//写
realm.write(()=>{
realm.create('CompatibilityProduct'{
相容性ID:18,
产品编号:17,
});
});
};
建造师(道具)
{
超级(道具);
}
render(){
const{navigate}=this.props.navigation;
返回(
初始化数据库
加载结果
);
}
}
const myscreens=StackNavigator({
主页:{屏幕:主页}
});
类兼容性产品{}
CompatibilityProduct.schema={
名称:'CompatibilityProduct',
特性:{
兼容性ID:{type:'int'},
productId:{type:'int'},
},
};
导出默认屏幕;
我在AVD中启动应用程序,单击Init DB(console.log(realm)在initDB()函数中为空)
,然后当我单击Load Results时,应用程序崩溃,因为此.realm
未定义
我做错了什么?要访问域,需要调用
realm.Open()。然后()…
将代码更改为如下所示
class Home extends React.Component {
constructor(props) {
super(props);
this.state = { realm: null }; // initial the state with null
}
initDB()
{
Realm.open({ // open connection
schema: [CompatibilityProduct]
}).then(realm => { // here is realm
console.log('realm1', realm);
this.setState({ realm }); // set it to state
});
};
loadResults()
{
const {realm } = this.state; // access it from state
console.log('realm2', realm);
// Write
realm.write(() => { // write to it
realm.create('CompatibilityProduct', {
compatibilityId: 18,
productId: 17,
});
});
this.setState({ realm }); // set it to state to see updates
};
render() {
// read data from it
const info = this.state.realm ? 'Number of CompatibilityProduct in this Realm: ' + this.state.realm.objects('CompatibilityProduct').length : 'Loading...';
return (
<View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}>
<Text onPress={this.initDB.bind(this)}> // bind to access this
Init DB
</Text>
<Text onPress={this.loadResults.bind(this)}> // bind to access this
Load Results {info}
</Text>
</View>
);
}
}
const CompatibilityProduct = { // schema is object not class
name: 'CompatibilityProduct',
properties: {
compatibilityId: {type: 'int'},
productId: {type: 'int'},
},
};
class Home扩展了React.Component{
建造师(道具){
超级(道具);
this.state={realm:null};//用null初始化状态
}
initDB()
{
Realm.open({//open connection
架构:[兼容性产品]
}).然后(realm=>{//这里是realm
log('realm1',realm);
this.setState({realm});//将其设置为state
});
};
加载结果()
{
const{realm}=this.state;//从state访问它
log('realm2',realm);
//写
realm.write(()=>{//写入它
realm.create('CompatibilityProduct'{
相容性ID:18,
产品编号:17,
});
});
this.setState({realm});//将其设置为state以查看更新
};
render(){
//从中读取数据
const info=this.state.realm?'此领域中CompatibilityProduct的数量:'+this.state.realm.objects('CompatibilityProduct')。长度:'Loading…';
返回(
//绑定以访问此文件
初始化数据库
//绑定以访问此文件
加载结果{info}
);
}
}
常量CompatibilityProduct={//架构不是对象类
名称:'CompatibilityProduct',
特性:{
兼容性ID:{type:'int'},
productId:{type:'int'},
},
};