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https://github.com/gre/react-native-view-shot

Snapshot a React Native view and save it to an image
https://github.com/gre/react-native-view-shot

capture react-native snapshot

Last synced: 29 days ago
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Snapshot a React Native view and save it to an image

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# react-native-view-shot ![](https://img.shields.io/npm/v/react-native-view-shot.svg) ![](https://img.shields.io/badge/react--native-%2040+-05F561.svg)



Capture a React Native view to an image.






## Install



```bash

yarn add react-native-view-shot



# In Expo



expo install react-native-view-shot

```



Make sure `react-native-view-shot` is correctly linked in Xcode (might require a manual installation, refer to [React Native doc](https://reactnative.dev/docs/linking-libraries-ios.html)).



**Before React Native 0.60.x you would have to:**



```bash

react-native link react-native-view-shot

```



**Since 0.60.x, [autolink](https://github.com/react-native-community/cli/blob/master/docs/autolinking.md) should just work**, on iOS, you'll need to ensure the CocoaPods are installed with:



```bash

npx pod-install

```



## High Level API



```js

import ViewShot from "react-native-view-shot";



function ExampleCaptureOnMountManually {

  const ref = useRef();



  useEffect(() => {

    // on mount

    ref.current.capture().then(uri => {

      console.log("do something with ", uri);

    });

  }, []);



  return (

    

      ...Something to rasterize...

    

  );

}



// alternative

function ExampleCaptureOnMountSimpler {

  const ref = useRef();



  const onCapture = useCallback(uri => {

    console.log("do something with ", uri);

  }, []);



  return (

    

      ...Something to rasterize...

    

  );

}



// waiting an image



function ExampleWaitingCapture {

  const ref = useRef();



  const onImageLoad = useCallback(() => {

    ref.current.capture().then(uri => {

      console.log("do something with ", uri);

    })

  }, []);



  return (

    

      ...Something to rasterize...

      

    

  );

}



// capture ScrollView content

// NB: you may need to go the "imperative way" to use snapshotContentContainer with the scrollview ref instead

function ExampleCaptureOnMountSimpler {

  const ref = useRef();



  const onCapture = useCallback(uri => {

    console.log("do something with ", uri);

  }, []);



  return (

    

      

        ...The Scroll View Content Goes Here...

      

    

  );

}

```



**Props:**



- **`children`**: the actual content to rasterize.

- **`options`**: the same options as in `captureRef` method.

- **`captureMode`** (string):

  - if not defined (default). the capture is not automatic and you need to use the ref and call `capture()` yourself.

  - `"mount"`. Capture the view once at mount. (It is important to understand image loading won't be waited, in such case you want to use `"none"` with `viewShotRef.capture()` after `Image#onLoad`.)

  - `"continuous"` EXPERIMENTAL, this will capture A LOT of images continuously. For very specific use-cases.

  - `"update"` EXPERIMENTAL, this will capture images each time React redraw (on did update). For very specific use-cases.

- **`onCapture`**: when a `captureMode` is defined, this callback will be called with the capture result.

- **`onCaptureFailure`**: when a `captureMode` is defined, this callback will be called when a capture fails.



## `captureRef(view, options)` lower level imperative API



```js

import { captureRef } from "react-native-view-shot";



captureRef(viewRef, {

  format: "jpg",

  quality: 0.8,

}).then(

  (uri) => console.log("Image saved to", uri),

  (error) => console.error("Oops, snapshot failed", error)

);

```



Returns a Promise of the image URI.



- **`view`** is a reference to a React Native component.

- **`options`** may include:

  - **`fileName`** _(string)_: (Android only) the file name of the file. Must be at least 3 characters long.

  - **`width`** / **`height`** _(number)_: the width and height of the final image (resized from the View bound. don't provide it if you want the original pixel size).

  - **`format`** _(string)_: either `png` or `jpg` or `webm` (Android). Defaults to `png`.

  - **`quality`** _(number)_: the quality. 0.0 - 1.0 (default). (only available on lossy formats like jpg)

  - **`result`** _(string)_, the method you want to use to save the snapshot, one of:

    - `"tmpfile"` (default): save to a temporary file _(that will only exist for as long as the app is running)_.

    - `"base64"`: encode as base64 and returns the raw string. Use only with small images as this may result of lags (the string is sent over the bridge). _N.B. This is not a data uri, use `data-uri` instead_.

    - `"data-uri"`: same as `base64` but also includes the [Data URI scheme](https://en.wikipedia.org/wiki/Data_URI_scheme) header.

  - **`snapshotContentContainer`** _(bool)_: if true and when view is a ScrollView, the "content container" height will be evaluated instead of the container height.

  - [iOS] **`useRenderInContext`** _(bool)_: change the iOS snapshot strategy to use method `renderInContext` instead of `drawViewHierarchyInRect` which may help for some use cases.



## `releaseCapture(uri)`



This method release a previously captured `uri`. For tmpfile it will clean them out, for other result types it just won't do anything.



NB: the tmpfile captures are automatically cleaned out after the app closes, so you might not have to worry about this unless advanced usecases. The `ViewShot` component will use it each time you capture more than once (useful for continuous capture to not leak files).



## `captureScreen()` Android and iOS Only



```js

import { captureScreen } from "react-native-view-shot";



captureScreen({

  format: "jpg",

  quality: 0.8,

}).then(

  (uri) => console.log("Image saved to", uri),

  (error) => console.error("Oops, snapshot failed", error)

);

```



This method will capture the contents of the currently displayed screen as a native hardware screenshot. It does not require a ref input, as it does not work at the view level. This means that ScrollViews will not be captured in their entirety - only the portions currently visible to the user.



Returns a Promise of the image URI.



- **`options`**: the same options as in `captureRef` method.



### Advanced Examples



[Checkout react-native-view-shot-example](example)



## Interoperability Table



> Snapshots are not guaranteed to be pixel perfect. It also depends on the platform. Here is some difference we have noticed and how to workaround.



Model tested: iPhone 6 (iOS), Nexus 5 (Android).



| System                | iOS              | Android           | Windows                |

| --------------------- | ---------------- | ----------------- | ---------------------- |

| View,Text,Image,..    | YES              | YES               | YES                    |

| WebView               | YES              | YES1   | YES                    |

| gl-react v2           | YES              | NO2    | NO3         |

| react-native-video    | NO               | NO                | NO                     |

| react-native-maps     | YES              | NO4    | NO3         |

| react-native-svg      | YES              | YES               | maybe?                 |

| react-native-camera   | NO               | YES               | NO 3        |



>



1. Only supported by wrapping a `` parent and snapshotting it.

2. It returns an empty image (not a failure Promise).

3. Component itself lacks platform support.

4. But you can just use the react-native-maps snapshot function: https://github.com/airbnb/react-native-maps#take-snapshot-of-map



## Performance Optimization



During profiling captured several things that influence on performance:



1. (de-)allocation of memory for bitmap

2. (de-)allocation of memory for Base64 output buffer

3. compression of bitmap to different image formats: PNG, JPG



To solve that in code introduced several new approaches:



- reusable images, that reduce load on GC;

- reusable arrays/buffers that also reduce load on GC;

- RAW image format for avoiding expensive compression;

- ZIP deflate compression for RAW data, that works faster in compare to `Bitmap.compress`



more details and code snippet are below.



### RAW Images



Introduced a new image format RAW. it correspond a ARGB array of pixels.



Advantages:



- no compression, so its supper quick. Screenshot taking is less than 16ms;



RAW format supported for `zip-base64`, `base64` and `tmpfile` result types.



RAW file on disk saved in format: `${width}:${height}|${base64}` string.



### zip-base64



In compare to BASE64 result string this format fast try to apply zip/deflate compression on screenshot results

and only after that convert results to base64 string. In combination zip-base64 + raw we got a super fast

approach for capturing screen views and deliver them to the react side.



### How to work with zip-base64 and RAW format?



```js

const fs = require("fs");

const zlib = require("zlib");

const PNG = require("pngjs").PNG;

const Buffer = require("buffer").Buffer;



const format = Platform.OS === "android" ? "raw" : "png";

const result = Platform.OS === "android" ? "zip-base64" : "base64";



captureRef(this.ref, { result, format }).then((data) => {

  // expected pattern 'width:height|', example: '1080:1731|'

  const resolution = /^(\d+):(\d+)\|/g.exec(data);

  const width = (resolution || ["", 0, 0])[1];

  const height = (resolution || ["", 0, 0])[2];

  const base64 = data.substr((resolution || [""])[0].length || 0);



  // convert from base64 to Buffer

  const buffer = Buffer.from(base64, "base64");

  // un-compress data

  const inflated = zlib.inflateSync(buffer);

  // compose PNG

  const png = new PNG({ width, height });

  png.data = inflated;

  const pngData = PNG.sync.write(png);

  // save composed PNG

  fs.writeFileSync(output, pngData);

});

```



Keep in mind that packaging PNG data is a CPU consuming operation as a `zlib.inflate`.



Hint: use `process.fork()` approach for converting raw data into PNGs.



> Note: code is tested in large commercial project.



> Note #2: Don't forget to add packages into your project:

>

> ```js

> yarn add pngjs

> yarn add zlib

> ```



## Troubleshooting / FAQ



### Saving to a file?



- If you want to save the snapshotted image result to the CameraRoll, just use https://github.com/react-native-cameraroll/react-native-cameraroll

- If you want to save it to an arbitrary file path, use something like https://github.com/itinance/react-native-fs

- For any more advanced needs, you can write your own (or find another) native module that would solve your use-case.



### The snapshot is rejected with an error?



- Support of special components like Video / GL views is not guaranteed to work. In case of failure, the `captureRef` promise gets rejected (the library won't crash).



### get a black or blank result or still have an error with simple views?



Check the **Interoperability Table** above. Some special components are unfortunately not supported. If you have a View that contains one of an unsupported component, the whole snapshot might be compromised as well.



### black background instead of transparency / weird border appear around texts?



- It's preferable to **use a background color on the view you rasterize** to avoid transparent pixels and potential weirdness that some border appear around texts.



### on Android, getting "Trying to resolve view with tag '{tagID}' which doesn't exist"



> you need to make sure `collapsable` is set to `false` if you want to snapshot a **View**. Some content might even need to be wrapped into such `` to actually make them snapshotable! Otherwise that view won't reflect any UI View. ([found by @gaguirre](https://github.com/gre/react-native-view-shot/issues/7#issuecomment-245302844))



Alternatively, you can use the `ViewShot` component that will have `collapsable={false}` set to solve this problem.



### Getting "The content size must not be zero or negative."



> Make sure you don't snapshot instantly, you need to wait at least there is a first `onLayout` event, or after a timeout, otherwise the View might not be ready yet. (It should also be safe to just wait Image `onLoad` if you have one). If you still have the problem, make sure your view actually have a width and height > 0.



Alternatively, you can use the `ViewShot` component that will wait the first `onLayout`.



### Snapshotted image does not match my width and height but is twice/3-times bigger



This is because the snapshot image result is in real pixel size where the width/height defined in a React Native style are defined in "point" unit. You might want to set width and height option to force a resize. (might affect image quality)



### on Android, capture GL Views



A prop may be necessary to properly capture GL Surface View in the view tree:



```js

/**

  * if true and when view is a SurfaceView or have it in the view tree, view will be captured.

  * False by default, because it can have signoficant performance impact

  */

handleGLSurfaceViewOnAndroid?: boolean;

```



### Trying to share the capture result with `expo-sharing`?



`tmpfile` or the default capture result works best for this. Just be sure to prepend `file://` to result before you call `shareAsync`.



```js

captureRef(viewRef)

  .then((uri) => Sharing.shareAsync(`file://${uri}`, options)

```



---



## Thanks



- To initial iOS work done by @jsierles in https://github.com/jsierles/react-native-view-snapshot

- To React Native implementation of takeSnapshot in iOS by @nicklockwood

- To Windows implementation by @ryanlntn