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Account Linking With NBA Top Shot

Account Linking is a powerful Flow feature that allows users to connect their wallets, enabling linked wallets to view and manage assets in one wallet with another. This feature helps reduce or even eliminate the challenges posed by other account abstraction solutions, which often lead to multiple isolated wallets and fragmented assets.

In this tutorial, you'll build a simple onchain app that allows users to sign into your app with their Flow wallet and view NBA Top Shot Moments that reside in their Dapper Wallet - without those users needing to sign in with Dapper.

Objectives​

After completing this guide, you'll be able to:

  • Pull your users' NBA Top Shot Moments into your Flow app without needing to transfer them out of their Dapper wallet
  • Retrieve and list all NFT collections in any child wallet linked to a given Flow address
  • Write a Cadence script to iterate through the storage of a Flow wallet to find NFT collections
  • Run Cadence Scripts from the frontend

Prerequisites​

Next.js and Modern Frontend Development​

This tutorial uses Next.js. You don't need to be an expert, but it's helpful to be comfortable with development using a current React framework. You'll be on your own to select and use a package manager, manage Node versions, and other frontend environment tasks. If you don't have your own preference, you can just follow along with us and use Yarn.

Flow Wallet​

You'll need a Flow Wallet, but you don't need to deposit any funds.

Moments NFTs​

You'll need a Dapper Wallet containing some Moments NFTs, such as NBA Top Shot Moments.

Getting Started​

This tutorial will use a Next.js project as the foundation of the frontend. Create a new project with:


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npx create-next-app@latest

We will be using TypeScript and the App Router, in this tutorial.

Open your new project in the editor of your choice, install dependencies, and run the project.


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yarn install
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yarn run dev

If everything is working properly, you'll be able to navigate to localhost:3000 and see the default Next.js page.

Flow Cadence Setup​

You'll need a few more dependencies to efficiently work with Cadence inside of your app.

Flow CLI and Types​

The Flow CLI contains a number of command-line tools for interacting with the Flow ecosystem. If you don't already have it installed, you can add it with Brew (or using other installation methods):


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brew install flow-cli

Once it's installed, you'll need to initialize Flow in your Next.js project. From the root, run:


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flow init --config-only

The --config-only flag initializes a project with the just the config file. This allows the Flow CLI to interact with your project without adding any unnecessary files.

Next, you'll need to do a little bit of config work so that your project knows how to read Cadence files. Install the Flow Cadence Plugin:


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yarn add flow-cadence-plugin --dev

Finally, open next.config.ts and update it to use the plugin with Raw Loader:


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// next.config.ts
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import type { NextConfig } from "next";
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import FlowCadencePlugin from "flow-cadence-plugin";
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const nextConfig: NextConfig = {
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webpack: (config) => {
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config.plugins.push(new FlowCadencePlugin())
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return config;
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},
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};
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export default nextConfig;

Frontend Setup​

We'll use the Flow Client Library FCL to manage blockchain interaction from the frontend. It's similar to viem, ethers, or web3.js, but works with the Flow blockchain and transactions and scripts written in Cadence.


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yarn add @onflow/fcl

Go ahead and install dotenv as well:


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yarn add dotenv

Provider Setup​

A fair amount of boilerplate code is needed to set up your provider. We'll provide it, but since it's not the purpose of this tutorial, we'll be brief on explanations. For more details, check out the App Quickstart Guide.

Add app/providers/AuthProvider.tsx:


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'use client';
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/* eslint-disable @typescript-eslint/no-explicit-any */
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import { createContext, useContext, ReactNode } from 'react';
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import useCurrentUser from '../hooks/use-current-user.hook';
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interface State {
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user: any;
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loggedIn: any;
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logIn: any;
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logOut: any;
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}
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const AuthContext = createContext<State | undefined>(undefined);
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interface AuthProviderProps {
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children: ReactNode;
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}
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const AuthProvider: React.FC<AuthProviderProps> = ({ children }) => {
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const [user, loggedIn, logIn, logOut] = useCurrentUser();
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return (
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<AuthContext.Provider
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value={{
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user,
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loggedIn,
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logIn,
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logOut,
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}}
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>
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{children}
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</AuthContext.Provider>
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);
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};
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export default AuthProvider;
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export const useAuth = (): State => {
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const context = useContext(AuthContext);
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if (context === undefined) {
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throw new Error('useAuth must be used within a AuthProvider');
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}
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return context;
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};

Then, add app/hooks/use-current-user-hook.tsx:


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import { useEffect, useState } from 'react';
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import * as fcl from '@onflow/fcl';
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export default function useCurrentUser() {
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const [user, setUser] = useState({ addr: null });
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const logIn = () => {
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fcl.authenticate();
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};
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const logOut = () => {
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fcl.unauthenticate();
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};
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useEffect(() => {
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fcl.currentUser().subscribe(setUser);
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}, []);
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return {user, loggedIn: user?.addr != null, logIn, logOut};
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}

.env​

Add a .env to the root and fill it with:


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NEXT_PUBLIC_ACCESS_NODE_API="https://rest-mainnet.onflow.org"
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NEXT_PUBLIC_FLOW_NETWORK="mainnet"
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NEXT_PUBLIC_WALLETCONNECT_ID=<YOUR ID HERE>

warning

Don't forget to replace <YOUR ID HERE> with your own Wallet Connect app id!

Implement the Provider and Flow Config​

Finally, open layout.tsx. Start by importing Flow dependencies and the AuthProvider:


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import flowJSON from '../flow.json'
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import * as fcl from "@onflow/fcl";
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import AuthProvider from "./providers/AuthProvider";

Then add your Flow config:


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fcl.config({
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"discovery.wallet": "https://fcl-discovery.onflow.org/authn",
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'accessNode.api': process.env.NEXT_PUBLIC_ACCESS_NODE_API,
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'flow.network': process.env.NEXT_PUBLIC_FLOW_NETWORK,
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'walletconnect.projectId': process.env.NEXT_PUBLIC_WALLETCONNECT_ID
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}).load({ flowJSON });

warning

We're going to force some things client side to get this proof-of-concept working quickly. Use Next.js best practices for a production app.

Add a 'use client'; directive to the top of the file and delete the import for Metadata and fonts, as well as the code related to them.

Finally, update the <body> to remove the font references and suppress hydration warnings:


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<body suppressHydrationWarning={true}>

Your code should be:


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// layout.tsx
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'use client';
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import "./globals.css";
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import flowJSON from '../flow.json'
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import * as fcl from "@onflow/fcl";
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import AuthProvider from "./providers/AuthProvider";
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fcl.config({
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"discovery.wallet": "https://fcl-discovery.onflow.org/authn",
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'accessNode.api': process.env.NEXT_PUBLIC_ACCESS_NODE_API,
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'flow.network': process.env.NEXT_PUBLIC_FLOW_NETWORK,
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'walletconnect.projectId': process.env.NEXT_PUBLIC_WALLETCONNECT_ID
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}).load({ flowJSON });
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export default function RootLayout({
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children,
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}: {
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children: React.ReactNode;
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}) {
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return (
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<html lang="en">
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<body suppressHydrationWarning={true}>
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<AuthProvider>
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{children}
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</AuthProvider>
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</body>
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</html>
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);
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}

Add the Connect Button​

Open page.tsx and clean up the demo code leaving only the <main> block:


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import Image from "next/image";
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export default function Home() {
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return (
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<div className="grid grid-rows-[20px_1fr_20px] items-center justify-items-center min-h-screen p-8 pb-20 gap-16 sm:p-20 font-[family-name:var(--font-geist-sans)]">
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<main className="flex flex-col gap-8 row-start-2 items-center sm:items-start">
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<div>TODO</div>
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</main>
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</div>
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);
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}

Add a 'use client'; directive, import the useAuth hook and instantiate it in the Home function:


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'use client';
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import { useAuth } from "./providers/AuthProvider";


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const { user, loggedIn, logIn, logOut } = useAuth();

Then add a button in the <main> to handle logging in or out:


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<main className="flex flex-col gap-8 row-start-2 items-center sm:items-start">
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<div>Welcome</div>
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<button
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onClick={loggedIn ? logOut : logIn}
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className="px-6 py-2 text-white bg-green-600 hover:bg-green-700 rounded-lg shadow-md transition duration-200 ease-in-out focus:outline-none focus:ring-2 focus:ring-green-500 sm:ml-auto"
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>
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{loggedIn ? "Log Out" : "Log In"}
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</button>
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</main>

Testing Pass​

Run the app:


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yarn dev

You'll see your Log In button in the middle of the window.

Welcome

Click the button and log in with your Flow wallet.

Flow Wallet

Account Linking​

Now that your app is set up, you can make use of Account Linking to to pull your NFTs from your Dapper Wallet, through your Flow Wallet, and into the app.

Setting Up Account Linking​

If you haven't yet, you'll need to link your Dapper Wallet to your Flow Wallet.

warning

The Dapper Wallet requires that you complete KYC before you can use Account Linking. While this may frustrate some members of the community, it makes it much easier for app developers to design onboarding rewards and bonuses that are less farmable.

Discovering the NFTs with a Script​

With your accounts linked, your Flow Wallet now has a set of capabilities related to your Dapper Wallet and it's permitted to use those to view and even manipulate those NFTs and assets.

Before you can add a script that can handle this, you'll need to import the HybridCustody contract using the Flow Dependency Manager:


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flow dependencies add mainnet://d8a7e05a7ac670c0.HybridCustody

Choose none to skip deploying on the emulator and skip adding testnet aliases. There's no point, these NFTs are on mainnet!

You'll get a complete summary from the Dependency Manager:


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📝 Dependency Manager Actions Summary
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🗃️ File System Actions:
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✅️ Contract HybridCustody from d8a7e05a7ac670c0 on mainnet installed
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✅️ Contract MetadataViews from 1d7e57aa55817448 on mainnet installed
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✅️ Contract FungibleToken from f233dcee88fe0abe on mainnet installed
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✅️ Contract ViewResolver from 1d7e57aa55817448 on mainnet installed
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✅️ Contract Burner from f233dcee88fe0abe on mainnet installed
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✅️ Contract NonFungibleToken from 1d7e57aa55817448 on mainnet installed
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✅️ Contract CapabilityFactory from d8a7e05a7ac670c0 on mainnet installed
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✅️ Contract CapabilityDelegator from d8a7e05a7ac670c0 on mainnet installed
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✅️ Contract CapabilityFilter from d8a7e05a7ac670c0 on mainnet installed
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💾 State Updates:
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✅ HybridCustody added to emulator deployments
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✅ Alias added for HybridCustody on mainnet
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✅ HybridCustody added to flow.json
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✅ MetadataViews added to flow.json
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✅ FungibleToken added to flow.json
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✅ ViewResolver added to flow.json
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✅ Burner added to flow.json
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✅ NonFungibleToken added to flow.json
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✅ CapabilityFactory added to emulator deployments
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✅ Alias added for CapabilityFactory on mainnet
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✅ CapabilityFactory added to flow.json
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✅ CapabilityDelegator added to emulator deployments
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✅ Alias added for CapabilityDelegator on mainnet
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✅ CapabilityDelegator added to flow.json
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✅ CapabilityFilter added to emulator deployments
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✅ Alias added for CapabilityFilter on mainnet
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✅ CapabilityFilter added to flow.json

Add app/cadence/scripts/FetchNFTsFromLinkedAccts.cdc. In it, add this script. Review the inline comments to see what each step is doing:


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import "HybridCustody"
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import "NonFungibleToken"
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import "MetadataViews"
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// This script iterates through a parent's child accounts,
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// identifies private paths with an accessible NonFungibleToken.Provider, and returns the corresponding typeIds
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access(all) fun main(addr: Address): AnyStruct {
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let manager = getAuthAccount<auth(Storage) &Account>(addr).storage.borrow<auth(HybridCustody.Manage) &HybridCustody.Manager>(from: HybridCustody.ManagerStoragePath)
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?? panic ("manager does not exist")
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var typeIdsWithProvider: {Address: [String]} = {}
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var nftViews: {Address: {UInt64: MetadataViews.Display}} = {}
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let providerType = Type<auth(NonFungibleToken.Withdraw) &{NonFungibleToken.Provider}>()
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let collectionType: Type = Type<@{NonFungibleToken.CollectionPublic}>()
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for address in manager.getChildAddresses() {
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let acct = getAuthAccount<auth(Storage, Capabilities) &Account>(address)
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let foundTypes: [String] = []
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let views: {UInt64: MetadataViews.Display} = {}
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let childAcct = manager.borrowAccount(addr: address) ?? panic("child account not found")
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// Iterate through storage paths to find NFTs that are controlled by the parent account
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// To just find NFTs, check if thing stored is nft collection and borrow it as NFT collection and get IDs
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for s in acct.storage.storagePaths {
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// Iterate through capabilities
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for c in acct.capabilities.storage.getControllers(forPath: s) {
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if !c.borrowType.isSubtype(of: providerType){
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// If this doen't have providerType, it's not an NFT collection
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continue
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}
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// We're dealing with a Collection but we need to check if accessible from the parent account
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if let cap: Capability = childAcct.getCapability(controllerID: c.capabilityID, type: providerType) { // Part 1
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let providerCap = cap as! Capability<&{NonFungibleToken.Provider}>
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if !providerCap.check(){
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// If I don't have access to control the account, skip it.
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// Disable this check to do something else.
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//
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continue
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}
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foundTypes.append(cap.borrow<&AnyResource>()!.getType().identifier)
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typeIdsWithProvider[address] = foundTypes
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// Don't need to keep looking at capabilities, we can control NFT from parent account
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break
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}
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}
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}
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// Iterate storage, check if typeIdsWithProvider contains the typeId, if so, add to views
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acct.storage.forEachStored(fun (path: StoragePath, type: Type): Bool {
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if typeIdsWithProvider[address] == nil {
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return true
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}
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for key in typeIdsWithProvider.keys {
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for idx, value in typeIdsWithProvider[key]! {
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let value = typeIdsWithProvider[key]!
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if value[idx] != type.identifier {
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continue
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} else {
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if type.isInstance(collectionType) {
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continue
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}
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if let collection = acct.storage.borrow<&{NonFungibleToken.CollectionPublic}>(from: path) {
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// Iterate over IDs & resolve the Display view
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for id in collection.getIDs() {
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let nft = collection.borrowNFT(id)!
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if let display = nft.resolveView(Type<MetadataViews.Display>())! as? MetadataViews.Display {
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views.insert(key: id, display)
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}
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}
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}
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continue
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}
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}
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}
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return true
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})
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nftViews[address] = views
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}
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return nftViews
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}

warning

The above script is a relatively naive implementation. For production, you'll want to filter for only the collections you care about, and you will eventually need to add handling for very large collections in a wallet.

Running the Script and Displaying the NFTs​

Add a component in app/components called DisplayLinkedNFTs.cdc.

In it, import dependencies from React and FCL, as well as the script you just added:


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import React, { useState, useEffect } from 'react';
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import * as fcl from "@onflow/fcl";
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import * as t from '@onflow/types';
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import FetchNFTs from '../cadence/scripts/FetchNFTsFromLinkedAccts.cdc';

As we're using TypeScript, you should add some types as well to manage the data from the NFTs nicely. For now, just add them to this file:


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type Thumbnail = {
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url: string;
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};
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type Moment = {
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name: string;
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description: string;
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thumbnail: Thumbnail;
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};
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type MomentsData = {
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[momentId: string]: Moment;
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};
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type ApiResponse = {
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[address: string]: MomentsData;
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};
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interface AddressDisplayProps {
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address: string;
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}

Then, add the function for the component:


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const DisplayLinkedNFTs: React.FC<AddressDisplayProps> = ({ address }) => {
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// TODO...
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return (
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<div>Nothing here yet</div>
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)
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}
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export default DisplayLinkedNFTs;

In the function, add a state variable to store the data retrieved by the script:


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const [responseData, setResponseData] = useState<ApiResponse | null>(null);

Then, use useEffect to fetch the NFTs with the script and fcl.query:


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useEffect(() => {
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const fetchLinkedAddresses = async () => {
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if (!address) return;
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try {
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const cadenceScript = FetchNFTs;
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// Fetch the linked addresses
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const response: ApiResponse = await fcl.query({
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cadence: cadenceScript,
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args: () => [fcl.arg(address, t.Address)],
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});
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console.log(JSON.stringify(response, null, 2));
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setResponseData(response);
_23
} catch (error) {
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console.error("Error fetching linked addresses:", error);
_23
}
_23
};
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_23
fetchLinkedAddresses();
_23
}, [address]);

Return to page.tsx, import your new component, and add an instance of <DisplayLinkedNFTs> that passes in the user's address and is only displayed while loggedIn.


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{loggedIn && <DisplayLinkedNFTs address={user.addr} />}

Testing​

Run the app again. If you have linked your account and have NFTs in that account, you'll see them in the console!

Displaying the Moments​

Now that they're here, all to do is display them nicely! Return to DisplayLinkedNFTs.tsx. Add a helper function to confirm each returned NFT matches the Moments format. You can update this to handle other NFTs you'd like to show as well.

warning

Remember, you'll also need to update the script in a production app to filter for only the collections you want, and handle large collections.


_15
// Type-checking function to validate moment structure
_15
// eslint-disable-next-line @typescript-eslint/no-explicit-any
_15
const isValidMoment = (moment: any): moment is Moment => {
_15
const isValid =
_15
typeof moment.name === 'string' &&
_15
typeof moment.description === 'string' &&
_15
moment.thumbnail &&
_15
typeof moment.thumbnail.url === 'string';
_15
_15
if (!isValid) {
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console.warn('Invalid moment data:', moment);
_15
}
_15
_15
return isValid;
_15
};

Next, add a rendering function with some basic styling:


_19
// Function to render moments with validation
_19
const renderMoments = (data: ApiResponse) => {
_19
return Object.entries(data).map(([addr, moments]) => (
_19
<div key={addr} className="border border-gray-300 rounded-lg shadow-sm p-4 mb-6 bg-white">
_19
<h4 className="text-lg font-semibold mb-4 text-gray-800">Linked Wallet: {addr}</h4>
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<div className="grid grid-cols-1 gap-4 md:grid-cols-2 lg:grid-cols-3">
_19
{Object.entries(moments).map(([momentId, moment]) => (
_19
isValidMoment(moment) ? (
_19
<div key={momentId} className="border border-gray-200 rounded-lg p-4 shadow hover:shadow-lg transition-shadow duration-200 bg-gray-50">
_19
<h5 className="text-md font-bold text-blue-600 mb-2">{moment.name}</h5>
_19
<p className="text-sm text-gray-600 mb-4">{moment.description}</p>
_19
<img src={moment.thumbnail.url} alt={moment.name} className="w-full h-32 object-cover rounded" />
_19
</div>
_19
) : null
_19
))}
_19
</div>
_19
</div>
_19
));
_19
};

Finally, update the return with some more styling and the rendered NFT data:


_16
return (
_16
<div className="p-6 bg-gray-100 min-h-screen">
_16
{address ? (
_16
<div className="max-w-4xl mx-auto">
_16
<h3 className="text-2xl font-bold text-gray-800 mb-4">Moments Data:</h3>
_16
<div>
_16
{responseData ? renderMoments(responseData) : (
_16
<p className="text-gray-500">No Moments Data Available</p>
_16
)}
_16
</div>
_16
</div>
_16
) : (
_16
<div className="text-center text-gray-500 mt-8">No Address Provided</div>
_16
)}
_16
</div>
_16
);

Further Polish​

Finally, you can polish up your page.tsx to look a little nicer, and guide your users to the Account Linking process in the Dapper Wallet:


_50
'use client';
_50
import DisplayLinkedNFTs from "./components/DisplayLinkedNFTs";
_50
import { useAuth } from "./providers/AuthProvider";
_50
_50
export default function Home() {
_50
const { user, loggedIn, logIn, logOut } = useAuth();
_50
_50
return (
_50
<div className="grid grid-rows-[auto_1fr_auto] items-center justify-items-center min-h-screen p-8 sm:p-20 bg-gray-100 font-sans">
_50
<main className="flex flex-col gap-8 row-start-2 items-center w-full max-w-5xl px-12 py-12 bg-white rounded-lg shadow-lg border border-gray-200">
_50
{/* Message visible for all users */}
_50
<p className="text-center text-gray-700 mb-4">
_50
Please link your Dapper wallet to view your NFTs. For more information, check the{" "}
_50
<a
_50
href="https://support.meetdapper.com/hc/en-us/articles/20744347884819-Account-Linking-and-FAQ"
_50
target="_blank"
_50
rel="noopener noreferrer"
_50
className="text-blue-600 hover:text-blue-800 underline"
_50
>
_50
Account Linking and FAQ
_50
</a>.
_50
</p>
_50
_50
<div className="flex flex-col sm:flex-row sm:items-center sm:justify-between w-full gap-6">
_50
{/* Display user address or linked NFTs if logged in */}
_50
{loggedIn ? (
_50
<div className="text-lg font-semibold text-gray-800">
_50
Address: {user.addr}
_50
</div>
_50
) : (
_50
<div className="text-lg font-semibold text-gray-800">
_50
Please log in to view your linked NFTs.
_50
</div>
_50
)}
_50
_50
{/* Login/Logout Button */}
_50
<button
_50
onClick={loggedIn ? logOut : logIn}
_50
className="px-6 py-2 text-white bg-blue-600 hover:bg-blue-700 rounded-lg shadow-md transition duration-200 ease-in-out focus:outline-none focus:ring-2 focus:ring-blue-500 sm:ml-auto"
_50
>
_50
{loggedIn ? "Log Out" : "Log In"}
_50
</button>
_50
</div>
_50
_50
{/* Display NFTs if logged in */}
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{loggedIn && <DisplayLinkedNFTs address={user.addr} />}
_50
</main>
_50
</div>
_50
);
_50
}

Your app will now look like the simple onchain app demo!

Conclusion​

In this tutorial, you took your first steps towards building powerful new experiences that meet you customers where they are. They can keep their assets in the wallet associate with one app, but also give your app the ability to use them - seamlessly, safely, and beautifully!