react native use variable for image file

For anyone getting to know the react-native beast, this should help :)

I visited a couple of sites in the past too, but found it increasingly frustrating. Until I read this site here.

It's a different approach but it eventually does pay off in the end. Basically, the best approach would be to load all your resources in one place. Consider the following structure

app  
   |--img
      |--image1.jpg
      |--image2.jpg
      |--profile
          |--profile.png
          |--comments.png
      |--index.js

In index.js, you can do this:

const images = {
    profile: {
        profile: require('./profile/profile.png'),
        comments: require('./profile/comments.png'),
    },
    image1: require('./image1.jpg'),
    image2: require('./image2.jpg'),
};

export default images;

In your views, you have to import the images component like this:

import Images from './img/index';

render() {
    <Image source={Images.profile.comments} />
}

Everybody has different means to an end, just pick the one that suits you best.

Da Man - Q: How is this answer using a variable?

Well, since require only accepts a literal string, you can't use variables, concatenated strings, etc. This is the next best thing. Yes, it still is a lot of work, but now you can do something resembling the OP's question:

render() {
  var images = { test100: "image100" };
  return (
    <View>
      <Text>
       test {images["test" + "100"]}
      </Text>
    </View>
  );
}

In JS require statements are resolved at bundle time (when the JS bundle is calculated). Therefore it's not supported to put variable expression as an argument for require.

In case of requiring resources it's even more trickier. When you have require('./someimage.png'), React Native packager will locale required image and it will be then bundled together with the app so that it can be used as a "static" resource when your app is running (in fact in dev mode it won't bundle the image with your app but instead the image will be served from the server, but this doesn't matter in your case).

If you want to use random image as a static resource you'd need to tell your app to bundle that image. You can do it in a few ways:

1) Add it as a static asset of your app, then reference to it with <Image src={{uri:'name_of_the_image_in_assets.png'}}/> (here is how you can add it to the native iOS app)

2) Require all the images upfront statically. Sth in a form of:

var randomImages = [
    require('./image1.png'),
    require('./image2.png'),
    require('./image3.png'),
    ...
];

Then in your code you can do:

<Image src={randomImages[Math.floor(Math.random()*randomImages.length)]}/>

3) Use network image with <Image src={{uri:'http://i.imgur.com/random.jpg'}}/>

class ImageContainer extends Component {
   this.state ={
     image:require('default-img')
   }
    <View>
           <Image source={this.state.image} />
    </View>
}

In the context of this discussion,I had this case where wanted to dynamically assign images for a particular background. Here I change state like this

this.setState({
  image:require('new-image')
})

I came to this thread looking for a way to add images in a dynamic way. I quickly found that passing in a variable to the Image -> require() was not working.

Thanks to DerpyNerd for getting me on the correct path.

After implementing the resources in one place I then found it easy to add the Images. But, I still needed a way to dynamically assign these images based on changing state in my application.

I created a function that would accept a string from a state value and would then return the Image that matched that string logically.

Setup

Image structure:

app  
  |--src
    |--assets
      |--images
        |--logos
          |--small_kl_logo.png
          |--small_a1_logo.png
          |--small_kc_logo.png
          |--small_nv_logo.png
          |--small_other_logo.png

        |--index.js
    |--SearchableList.js

In index.js, I have this:

const images = {
  logos: {
    kl: require('./logos/small_kl_logo.png'),
    a1: require('./logos/small_a1_logo.png'),
    kc: require('./logos/small_kc_logo.png'),
    nv: require('./logos/small_nv_logo.png'),
    other: require('./logos/small_other_logo.png'),
  }
};

export default images;

In my SearchableList.js component, I then imported the Images component like this:

import Images from './assets/images';

I then created a new function imageSelect in my component:

imageSelect = network => {
  if (network === null) {
    return Images.logos.other;
  }

  const networkArray = {
    'KL': Images.logos.kl,
    'A1': Images.logos.a1,
    'KC': Images.logos.kc,
    'NV': Images.logos.nv,
    'Other': Images.logos.other,
  };

  return networkArray[network];
};

Then in my components render function I call this new imageSelect function to dynamically assign the desired Image based on the value in the this.state.network:

render() {
  <Image source={this.imageSelect(this.state.network)} />
}

Once again, thanks to DerpyNerd for getting me on the correct path. I hope this answer helps others. :)

Here is a simple and truly dynamic solution(no renaming or import required) to the problem if you have a bigger no of files.

[Won't work for Expo Managed]

Although the question is old I think this is the simpler solution and might be helpful. But I beg a pardon for any terminological mistakes, correct me please if I do any.

INSTEAD OF USING REQUIRE WE CAN USE THE URI WITH NATIVE APP ASSETS FOR ANDROID (AND/OR iOS). HERE WE WILL DISCUSS ABOUT ANDROID ONLY

URI can easily be manipulated as per the requirement but normally it's used for network/remote assets only but works for local and native assets too. Whereas require can not be used for dynamic file names and dirs

STEPS

1. Open android/app/src/main/assets folder from your App.js or index.js containing directory, if the assets folder doesn't exist create one.
2. Make a folder named images or any NAME of your choice inside assets, and paste all the images there.
3. Create a file named react-native.config.js in the main app folder containing App.js or index.js.
4. Add these lines to the new js file:

module.exports = {
  project: {
    ios: {},
    android: {},
  },
  assets: ['./assets/YOUR_FOLDER_NAME/'],
};

at the place of YOUR_FOLDER_NAME use the newly created folder's name images or any given NAME

5. Now run npx react-native link in your terminal from main app folder, this will link/add the assets folder in the android bundle. Then rebuild the debug app.
6. From now on you can access all the files from inside android/app/src/main/assets in your react-native app. For example:

<Image
   style={styles.ImageStyle}
   source={{ uri: 'asset:/YOUR_FOLDER_NAME/img' + Math.floor(Math.random() * 100) + '.png' }}
/>