如何解决如果我已经保存了更改,我应该如何在返回时避免未保存更改的“警报”?
如果我已经通过为此目的创建的按钮保存了更改,我应该如何避免在返回上一屏幕时出现“未保存更改警报”?
我创建了两个页面来说明我遇到的问题:主页和第二页。通过主页我可以转到第二页,但是如果我将数据保存在第二页中,无论如何都会出现警告“放弃更改”。
首页(homeTest)
import React from 'react';
import { View,StyleSheet,Button } from 'react-native';
const homeTest = ({ navigation }) => {
return (
<View style={styles.containerStyle}>
<Button styles={styles.button}
title="GO TO SECOND PAGE"
onPress={() => navigation.navigate('Second page')}
/>
</View>
)
};
const styles = StyleSheet.create({
containerStyle: {
flex: 1,justifyContent: 'center',alignItems: 'center',},button: {
fontSize: 24,color: "black",textAlign: 'center',marginBottom: 20,width: '100%',borderRadius:20,txtInput: {
textTransform: 'capitalize',top:3,paddingHorizontal: 20,}
});
export default homeTest;
第二页(secondPageTest)
import React,{ useState } from 'react';
import { View,Button,Alert } from 'react-native';
import { TextInput,} from 'react-native-paper';
import AsyncStorage from '@react-native-async-storage/async-storage';
const secondPageTest = ({ navigation }) => {
const [name,setName] = useState('');
const [age,setAge] = useState('');
const [flagModify,setFlagModify] = useState(false);
const hasUnsavedChanges = Boolean(flagModify);
const checkAndSave = async (keyToSave,varName,varage) => {
if (varName == '' || varage == '') {
Alert.alert ("Attention","You must complete the fields!");
return;
}
let fields = {
name: varName,age: varage
};
try {
await AsyncStorage.setItem(keyToSave,JSON.stringify(fields));
} catch(e) {
console.warn("Error.");
return;
}
console.warn("The data has been saved !. However the unsaved changes alert appear.");
setFlagModify(false);
navigation.navigate('Home page');
};
const updateField = (fieldValue,fieldName) => {
setFlagModify(true);
switch (fieldName) {
case 'fName':
return setName(fieldValue);
case 'fAge':
return setAge(fieldValue);
default:
return;
}
};
React.useEffect(() => {
navigation.addListener('beforeRemove',(e) => {
const action = e.data.action;
if (!hasUnsavedChanges) {
return;
}
e.preventDefault();
Alert.alert(
'discard changes?','You have unsaved changes. Are you sure to discard them and leave the screen?',[
{ text: "Don't leave",style: 'cancel',onPress: () => {} },{
text: 'discard',style: 'destructive',onPress: () => navigation.dispatch(action),]
);
})
},[hasUnsavedChanges,navigation]);
return (
<>
<View>
<TextInput style={styles.txtInput}
label="name"
onChangeText={(value) => updateField(value,'fName')}
/>
<TextInput style={styles.txtInput}
label="age"
onChangeText={(value) => updateField(value,'fAge')}
/>
<Button styles={styles.button}
title="SAVE DATA"
onPress={() => checkAndSave('keySample',name,age)}
/>
<Button styles={styles.button}
title="CANCEL"
onPress={() => navigation.navigate('Home page')}
/>
</View>
</>
)
};
const styles = StyleSheet.create({
button: {
fontSize: 24,}
});
export default secondPageTest;
解决方法
您应该在按下丢弃按钮时将 hasUnsavedChanges 更改为 false。
const hasUnsavedChanges = useMemo(()=>{
return Boolean(text)
},[text])
Alert.alert(
'Discard changes?','You have unsaved changes. Are you sure to discard them and leave the screen?',[
{ text: "Don't leave",style: 'cancel',onPress: () => {} },{
text: 'Discard',style: 'destructive',onPress: () => {
setText("");
navigation.dispatch(action)
},},]
);
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