Use an image picker

Install expo-image-picker

To install the library, run the following command:

Tip: Any time we install a new library in our project, we must stop the development server by pressing Ctrl + c in the terminal and then running the installation command. After the installation, we can start the development server again by running npx expo start from the same terminal window.

Pick an image from the device's media library

expo-image-picker provides the launchImageLibraryAsync() method that displays the system UI for choosing an image or a video from the device's media library.

We can use the button with the primary theme we created in the previous chapter to pick an image from the device's media library. We'll create a function to launch the device's image library to implement this functionality.

In App.js, import the expo-image-picker library and create a pickImageAsync() function inside the App component:

// ...rest of the import statements remain unchanged
import * as ImagePicker from 'expo-image-picker';

export default function App() {
  const pickImageAsync = async () => {
    let result = await ImagePicker.launchImageLibraryAsync({
      allowsEditing: true,
      quality: 1,
    });

    if (!result.canceled) {
      console.log(result);
    } else {
      alert('You did not select any image.');
    }
  };

  // ...rest of the code remains same
}

Let's learn what the above code does.

• The launchImageLibraryAsync() receives an object in which different options are specified. This object is an ImagePickerOptions object. We can pass the object to specify different options when invoking the method.
• When allowsEditing is set to true, the user can crop the image during the selection process on Android and iOS but not on the web.

Update the button component

When the primary button gets pressed, we need to call the pickImageAsync() function. To call it, update the onPress property of the <Button> component in components/Button.js:

export default function Button({ label, theme, onPress}) {
  // ...rest of the code remains same
  if (theme === "primary") {
    return (
      <View>
        {/* ...rest of the code remains same */}
        <Pressable
          style={[styles.button, { backgroundColor: '#fff' }]}
          onPress={onPress}
        >
      </View>
    );
  }
}

In App.js, add the pickImageAsync() function to the onPress prop on the first <Button>.

export default function App() {
  // ...rest of the code remains same

  return (
    <View style={styles.container}>
      {/* ...rest of the code remains same */}
      <Button theme="primary" label="Choose a photo" onPress={pickImageAsync} />
    </View>
  );
}

The pickImageAsync() function is responsible for invoking ImagePicker.launchImageLibraryAsync() and then handling the result. The launchImageLibraryAsync() method returns an object containing information about the selected image.

To demonstrate what properties the result object contains, here is an example result object:

{
  "assets": [
    {
      "assetId": null,
      "base64": null,
      "duration": null,
      "exif": null,
      "height": 4800,
      "rotation": null,
      "type": "image",
      "uri": "file:///data/user/0/host.exp.exponent/cache/ExperienceData/%username%252Fsticker-smash-47-beta/ImagePicker/77c4e56f-4ccc-4c83-8634-fc376597b6fb.jpeg",
      "width": 3200
    }
  ],
  "canceled": false,
  "cancelled": false
}

Use the selected image

The result object provides the assets array, which contains the uri of the selected image. Let's take this value from the image picker and use it to show the selected image in the app.

Modify the App.js file in the following steps:

• Declare a state variable called selectedImage using the useState hook from React. We'll use this state variable to hold the URI of the selected image.
• Update the pickImageAsync() function to save the image URI in the selectedImage state variable.
• Then, pass the selectedImage as a prop to the ImageViewer component.

import { useState } from 'react';
// ...rest of the import statements remain unchanged

export default function App() {
  const [selectedImage, setSelectedImage] = useState(null);

  const pickImageAsync = async () => {
    let result = await ImagePicker.launchImageLibraryAsync({
      allowsEditing: true,
      quality: 1,
    });

    if (!result.canceled) {
      setSelectedImage(result.assets[0].uri);
    } else {
      alert('You did not select any image.');
    }
  };

  return (
    <View style={styles.container}>
      <View style={styles.imageContainer}>
        <ImageViewer
          placeholderImageSource={PlaceholderImage}
          selectedImage={selectedImage}
        />
      </View>
      {/* ...rest of the code remains same */}
    </View>
  );
}

Now, modify the components/ImageViewer.js file to conditionally display the selected image in place of the placeholder image. We'll need to pass the selectedImage prop to the component.

The source of the image is getting long, so let's also move it to a separate variable called imageSource. Then, pass it as the value of the source prop on the <Image> component.

export default function ImageViewer({ placeholderImageSource, selectedImage }) {
  const imageSource = selectedImage  ? { uri: selectedImage } : placeholderImageSource;

  return <Image source={imageSource} style={styles.image} />;
}

In the above snippet, the <Image> component uses a conditional operator to load the source of the image. This is because the image picked from the image picker is a uri string, not a local asset like the placeholder image.

Let's take a look at our app now:

The images used for the demo in this tutorial were picked from Unsplash.