RNImagePicker.h

//
//  RNImagePicker.h
//
//  Created by Dan Horrigan on 9/8/15.
//  Copyright (c) 2015 Tackk, Inc. All rights reserved.
//

#import "RCTBridgeModule.h"
#import <UIKit/UIKit.h>

@interface RNImagePicker : NSObject <RCTBridgeModule, UINavigationControllerDelegate, UIImagePickerControllerDelegate>

- (void)showImagePicker:(UIImagePickerControllerSourceType)sourceType;

@end

RNImagePicker.m

//
//  RNImagePicker.m
//
//  Created by Dan Horrigan on 9/8/15.
//  Copyright (c) 2015 Tackk, Inc. All rights reserved.
//

#import "RNImagePicker.h"

#define JPEG_QUALITY 0.7

@interface RNImagePicker ()

@property (nonatomic, strong) UIImagePickerController *imagePicker;
@property (nonatomic, strong) RCTResponseSenderBlock callback;

@end


@implementation RNImagePicker

RCT_EXPORT_MODULE();


RCT_EXPORT_METHOD(fromCamera:(RCTResponseSenderBlock)callback)
{
  #if TARGET_IPHONE_SIMULATOR
    NSLog(@"Camera not available on simulator");
    return;
  #endif

  self.callback = callback;

  [self showImagePicker:UIImagePickerControllerSourceTypeCamera];
}

RCT_EXPORT_METHOD(fromLibrary:(RCTResponseSenderBlock)callback)
{
  #if TARGET_IPHONE_SIMULATOR
    NSLog(@"Camera not available on simulator");
    return;
  #endif

  self.callback = callback;

  [self showImagePicker:UIImagePickerControllerSourceTypePhotoLibrary];
}


- (void)showImagePicker:(UIImagePickerControllerSourceType)sourceType
{
  self.imagePicker = [[UIImagePickerController alloc] init];
  self.imagePicker.modalPresentationStyle = UIModalPresentationFullScreen;
  self.imagePicker.delegate = self;

  self.imagePicker.sourceType = sourceType;

  dispatch_async(dispatch_get_main_queue(), ^{
    UIViewController *vc = [[[UIApplication sharedApplication] keyWindow] rootViewController];
    while (vc.presentedViewController) {
      vc = vc.presentedViewController;
    }

    [vc presentViewController:self.imagePicker animated:YES completion:nil];
  });
  
}

- (void)imagePickerController:(UIImagePickerController *)imagePicker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
  // Get rid of the view controller right away.
  dispatch_async(dispatch_get_main_queue(), ^{
    [imagePicker dismissViewControllerAnimated:YES completion:nil];
  });

  UIImage *image = info[UIImagePickerControllerOriginalImage];
  NSData *imageData = UIImageJPEGRepresentation(image, JPEG_QUALITY);
  NSString *dataString = [imageData base64EncodedStringWithOptions:0];
  
  self.callback(@[@"data", dataString]);
}

- (void)imagePickerControllerDidCancel:(UIImagePickerController *)imagePicker
{
    dispatch_async(dispatch_get_main_queue(), ^{
        [imagePicker dismissViewControllerAnimated:YES completion:nil];
    });
    
    self.callback(@[@"cancel"]);
}

@end

usage.js

import React from 'react-native';

var {
  NativeModules: {
    RNImagePicker,
  },
} = React;

// Take a new photo
RNImagePicker.fromCamera((type, response) => {
  // response is a base64 image.
  if (type === "data" && response) {
    console.log('Got Photo');
  } else {
    // No photo
    console.log('No Photo');
  }
});


// Import from the Library
RNImagePicker.fromLibrary((type, response) => {
  // response is a base64 image.
  if (type === "data" && response) {
    console.log('Got Photo');
  } else {
    // No photo
    console.log('No Photo');
  }
});