react-native-resource-saving-container

This is a very tiny React Native component that allows for saving memory by releasing resources attached to views that may are not visible on screen.

How it works?

When native views are rendered in your React Native app, the framework creates corresponding native views and mounts them in view hierarchy. Native views provides the platform with a way how they should be rendered on screen, but a part of that they can also consume memory. For example Image component keeps a reference to a bitmap that it needs to rende, Camera component keeps the camera session active which results in increased power consumption used by camera hardware and processor unit as well as memoty consumption used for buffering. When such a views are rendered but not visible on a screen (perhaps they are few levels down navigation hierarchy) they can still take up resources they need for rendering.

ResourceSavingContainer allows for such a components to release their resources using technique that has been in React Native forever -- removeClippedSubviews property. This property allows for components rendered in javascript to be instantiated in native but detached from the native view hierarchy when outside of their parent's visible bounds.

How to use it

Use <ResourceSavingContainer/> as a container in which you want to put resource intensive components (e.g. images, or even whole screens from navigation stack). When your components are not expected to be visible (e.g. they have been covered by other navigation card) set visible={false} to detach all children from native view hierarchy.

First import <ResourceSavingContainer/> component like this:

import ResourceSavingContainer from 'react-native-resource-saving-container';

Then use it in your render method:

    <ResourceSavingContainer
        style={{ backgroundColor: '#fcfcfc' }}
        visible={this.state.visible}>
        <Image source={require('./largeImageBackground.jpg')} />
    </ResourceSavingContainer>

Caveats

<ResourceSavingContainer/> uses relative positioning to move its childrent outside of the visible bounds therefore children rendered directly under ResourceSavingContainer should not use absolute positioning. If you need absolute positioning you can render relatively positioned <View/> inside <ResourceSavingContainer/> and then use absolute positioning inside of that <View/>.

Troubleshooting

Try searching over the issues on GitHub here. If you don't find anything that would help feel free to open a new issue!

You could also just read the source code - it only has a few lines.