React Native does not currently offer full support for downloading and showing a file. The approach in this article shows you how to download and display a file using the react-native-fs and react-native-webview libraries respectively.

In this example, the file is of a PDF format, however, the same approach can be used for images or other text file formats.

Prerequisites:

A working React Native App. Not sure how to do this? Checkout the setup instructions on the React Native Website.

Downloading the file

Install react-native-fs:

yarn add react-native-fs

or

npm install react-native-fs

If you're using React Native version 0.60.0 or higher, it a does auto-linking for you. If not, check the extra setup instructions on react-native-fs page.
Install the CocoaPods dependencies (iOS specific):

cd ios && pod install

Using downloadFile function:

In this example, I will be retrieving a PDF file from an API endpoint using the downloadFile function from react-native-fs. This function has two required parameters - fromUrl and toFile , along with several other optional ones. I created an async function downloadPDF which requires a url and fileName. It also contains a basic header with an authorization token and content-type.

React-native-fs' DocumentDirectoryPath provides the Android or iOS where documents are stored. You can change this to your customised path if you wish.

downloadPDF = async (url: string, fileName: string): Promise<any> =>{
//Define path to store file along with the extension
const path = `${DocumentDirectoryPath}/${fileName}.pdf`;
const headers = {
  'Accept': 'application/pdf',
  'Content-Type': 'application/pdf',
  'Authorization': `Bearer [token]`
}
//Define options
const options: DownloadFileOptions = {
  fromUrl: [baseUrl] + url,
  toFile: path,
  headers: headers
}
//Call downloadFile
const response =  await downloadFile(options);
return response.promise.then(async res => 
  //Transform response
  if(res && res.statusCode === 200 && res.bytesWritten > 0 &&
  res.path){
    doSomething(res)
  }else{
    logError(res)
}};

The response from downloadFile contains statusCode , jobId and bytesWritten . To know if a request is successful, check whether the statusCode is 200 and the bytesWritten > 0. It is important to check both values because, I found it returning 200 even when no files were written.

I saved the path in the Redux's state to later retrieve the file.

Opening the saved file in a WebView

Install react-native-webview:

yarn add react-native-webview

or

npm install react-native-webview

Again, install the CocoaPods dependencies (iOS specific):

cd ios && pod install

Implementing the WebView:

Create a React Funcional Component containing a WebView .

const WebViewComponent: React.FunctionComponent = ({ navigation, route}: any): JSX.Element => (
<WebView
  source={{ uri: "file://"+ path}}
  style={{ flex: 1 }}
  originWhitelist={["*"]}
/>
)};
export default WebViewComponent;

The WebView source's URI should point to file:// + pathToFile . Don't forget to include the style property and set flex:1 as shown above.