Convert Base64 to png and save in the device React Native Expo - react-native

Question

I've been trying to save an image on a mobile device with React Native and Expo, i have tried with these packages:
import RNFetchBlob from 'react-native-fetch-blob';
import RNfs from 'react-native-fs ';
but both give me this error when implementing them
null is not an object (evaluating 'RNFetchBlob.DocumentDir')
then try expo-file-system but i don't see any clear example of how to convert base64 and download it to mobile
UPDATE
I was able to do it, my purpose was to save the base64 of a QR and convert it to png and at the same time be able to share it, I did it using expo-file-system and expo-sharing
this is mi code,
import * as FileSystem from 'expo-file-system';
import * as Sharing from 'expo-sharing';
//any image, I use it to initialize it
const image_source = 'https://images.unsplash.com/photo-1508138221679-760a23a2285b?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&w=1000&q=80';
share=()=>{
var self = this;
self.setState({loading:true})
FileSystem.downloadAsync(
image_source,
FileSystem.documentDirectory + '.png'
)
.then(({ uri }) => {
console.log(self.state.base64Code);
FileSystem.writeAsStringAsync(
uri,
self.state.base64Code,
{'encoding':FileSystem.EncodingType.Base64}
)
.then(( ) => {
this.setState({loading:false})
Sharing.shareAsync(uri);
})
})
.catch(error => {
console.error(error);
});
}
Actually, I don't know if it's the best way, first write a png image in the directory and then rewrite it with the base64 code, but it worked

Answer 1

This worked for me:
const data = "data:image/png;base64,ASDFASDFASDf........"
const base64Code = data.split("data:image/png;base64,")[1];
const filename = FileSystem.documentDirectory + "some_unique_file_name.png";
await FileSystem.writeAsStringAsync(filename, base64Code, {
encoding: FileSystem.EncodingType.Base64,
});
const mediaResult = await MediaLibrary.saveToLibraryAsync(filename);

Answer 2

Thanks for the update. I've been struggling for days with this on Android and base64 images!
In my case i was trying to upload a base64 image from a signature pad on expo and always got "Network request failed"
I managed to make it work like this hope it helps!
import * as FileSystem from 'expo-file-system';
const uploadBase64 = async (base64String) => {
this.setState({ uploading: true });
//Without this the FilySystem crashes with 'bad base-64'
const base64Data = base64String.replace("data:image/png;base64,","");
try {
//This creates a temp uri file so there's no neeed to download an image_source to get a URI Path
const uri = FileSystem.cacheDirectory + 'signature-image-temp.png'
await FileSystem.writeAsStringAsync(
uri,
base64Data,
{
'encoding': FileSystem.EncodingType.Base64
}
)
//At this point the URI 'file://...' has our base64 image data and now i can upload it with no "Network request failed" or share the URI as you wish
const uploadResult = await this.uploadImageAsync(uri).then(res => res.json())
if (uploadResult) {
this.setState({ image: uploadResult.location });
}
this.setState({ uploading: false });
} catch (e) {
this.setState({ uploading: false });
console.log('*Error*')
console.log(e)
}
}
//Just and ordinary upload fetch function
const uploadImageAsync = (uri) => {
let apiUrl = 'https://file-upload-example-backend-dkhqoilqqn.now.sh/upload';
let formData = new FormData();
formData.append('photo', {
uri,
name: `photo.png`,
type: `image/png`,
});
let options = {
method: 'POST',
body: formData,
headers: {
Accept: 'application/json',
'Content-Type': 'multipart/form-data',
},
};
return fetch(apiUrl, options);
}