Questions tagged [dapps]

Questions about applications and projects on Ethereum: a decentralized application (dapp) does not require any servers or backends and runs independent on a distributed blockchain.

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11 views

What is a good wallet service for iOS applications

I am building an iOS app that rewards users with crypto tokens, just like Brave's BAT or Reddit's community points. I am trying to find a wallet service that I can integrate with my iOS app for users ...
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Unknown Accounts suddenly appearing in MetaMask wallet…?

My MetaMask wallet has multiple accounts which I did not create. I have no idea how they there. Is my MetaMask wallet compromised? Or is this normal that MetaMask creates new wallet addresses when ...
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What you mean by Off-Chain in Ethereum Blockchain? can i use geth as off-chain in DApp?

I have read several articles of off-chain definition and come to know that they are use for scale the ethereum blockchain. but my question is what is actually mean by off-chain word in ethereum ...
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vyper no mappings allowed when adding a function to initialize a struct that has a map inside

Version Information vyper Version (output of vyper --version): 0.1.0b17+commit.eaa6754 OS: Debian GNU/Linux 10 (buster) Python Version - 3.6.2 Environment (output of pip freeze): asttokens==2.0.3 ...
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Modifier accessing another smart contract function

I am trying to use a modifier that calls a function from another smart contract to check the type of user that is accessing the function. The user should only be allowed to access the function if ...
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Building a mobile DApp without a full node?

I'm new to blockchain and Ethereum and have a few questions: Does Apple's App Store allow mobile DApps other than wallets and browsers? Is it possible to build a mobile DApp that runs on your mobile ...
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Certificate Autority to Ethereum

Since there is no native support to Certificate Authorities in Ethereum, what are good ways to emulate it in a permission network (we are using Hyperledger Besu)?
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Best way to avoid transactions that create a new smart contract before submitting it

We are creating a permissioned network (using Besu) where anyone can create and submit transactions. In this context, the writer nodes need to verify that these transactions are not creating new ...
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21 views

How can I test someone else‘s ETH contract with only bytecode and ABI? [duplicate]

If I just have someone else's ETH contract bytecod an ABI, how can I test it's function?
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Possibilities of ERC721 image generation [closed]

What image generation techniques could you suggest for a DApp game that utilizes ERC721? I know that CrypoKitties has a unique DNA sequence and different pieces of the sequence correspond to the ...
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User Profile with access control to allow other users to edit information [duplicate]

Sorry if this has already been asked but ive been searching for days and cant find an answer to my question. I want to create a dapp that allows users to sign up and create a profile with private ...
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How to search for a dapp based on its address?

There are many websites that track dapps like http://dappradar.com or https://www.dapp.com. Unlike Etherscan one particular dapp doesn’t have to be registered on such specific website in order to be ...
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ERC20 Anyone can call approve if knows ABI on contract and my address?

I think I misunderstand something. I'm using a Ganache for developing dApp. I built a default ERC-20 smart-contract. I've built it with truffle. And just for test I write some code in NodeJS: ...
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I need help with ERC-777 usage possibilities of extra funcionality layer over ERC-20 for non-coder

Im interested in creating custom token (fungible), but with gas-less operations possibilities for V.I.P. customers. I need simple app (wallet is fine) which would: allow me to store custom ERC777-...
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1answer
32 views

Can an Ethereum account be used by several users at the same time?

I am developing a DApp for donations (the donations are not in cryptocurrencies). I want the donor to make donations without registering on the platform. In fact, I don't need to know who he is. So it ...
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18 views

How can conditional deployment of a contract be done? [closed]

This might be a very basic query, but, I would like to know how I can restrict the deployment of contracts based on some condition. More specifically, assume that I have an "Admin" who can assign "...
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Just not able to install Web3 through powershell

After reading a lot of articles about how to install Web3j in windows. I also tried following this article : https://kauri.io/generate-a-java-wrapper-from-your-smart-contract/...
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14 views

Web3 call should return different result based on time passed

I am experiencing a weird issue. I am building a DApp where I want the new season of the game to start every 5 minutes (for testing purposes). However, web3 call returns old data, seems that it cached ...
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how i can create a buy Ehter [closed]

i have a question : how i can create a app to buy ether ?, i know how to create a Token sale but i dont know what api or what i need to buy ether directly i see websites like coinbase to buy ether , ...
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Trying to connect Ethereum Wallet with ganache-cli on Windows

I am trying to connect Ethereum Wallet with Ganache-Cli but it starts looking for geth note instead of ganache-cli. Can someone please tell me the correct way of doing it. Or is there any specific ...
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78 views

Provable API for calling ETH-USD price in a contract

This contract is hosted at https://github.com/provable-things/ethereum-examples/blob/master/solidity/truffle-examples/kraken-price-ticker/contracts/KrakenPriceTicker.sol I have made the constructor ...
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setBill function isnt affecting the values

a beginner contract developer here pragma solidity ^0.5.0; contract waterBill{ address admin; uint public rateperliter; struct Individual{ string name; string addr; ...
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what is the best to signing a message , from javascript or solidity?

I am trying to make a small DApp using web3, ganache, Metamask, javascript and Remix. My DApp has to sign a message and verify it, and I see two ways to sign a message. One using web3.eth.sign(...), ...
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window.ethereum

When i made web3 instance and run index.html i lose ethereum and window.ethereum when i call it from console i got ethereum is not defined,i have installed metamask and use ropsten network.Why its ...
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Uncaught TypeError: Cannot read property 'fromWei' of undefined, working good in one tab and failing in another tab

I'm getting this error when I'm trying to convert Wei to Ether using the code window.web3.utils.fromWei("200000",'ether'). This error shows only on the single page and when I console.log in the same ...
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Metamask and Web3

I use this in html src="https://cdn.jsdelivr.net/npm/web3@1.2.6/dist/web3.min.js" and when i call some functions i get error.Why this happend?Example i cannot call ethereum.enable() for allow ...
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How to find the source code of my contract which is not yet verified

I had created a token using eth based blockchain via remix.ethereum.org But I need to verify the source code ,but I am not having the backup copy of source code How can I see the source code of the ...
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30 views

Creating complex queries from events emitted by a smart contract

I need to create complex queries from events emitted by a smart contract. For example, I need to make a kind of "sql join" between data from different events. I know a simple solution would be to ...
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How can I change the state of a contract if it's stored on the blockchain

Doesn't that contradicts the whole idea of blockchain that data stored there is immutable. If someone can alter the data stored in the state of the contract then how is it any different from any other ...
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Ethereum DApp example? [closed]

I am finding for the open source ethereum dapp example. Could anyone recommend me any dapp that is fully operable by my own? Thanks.
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49 views

Accessing database in solidity

I am developing a voting application using blockchain (ganache). So basically i am registering the candidates by a web form and storing the data in phpmyadmin database. Now i want to access this data ...
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webpack packing website and upload to ipfs but node_modules not found

After webpacking the website, I upload the dist folder to ipfs. The ethereum part is working fine, however no js files (except for app.js) and node modules can be found. But as you can see in the pics,...
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Can we trust a dApp as much as we would trust Ethereum?

I was reading about bridging Ethereum and IPFS and I stumbled upon an article that uploads the file to IPFS and records the hash of it as an Ethereum transaction. I then tried to understand the ...
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window.ethereum: 0 if use MetaMask

I try to connect to MetaMask from my DApp. It used two work well about two month ago, but now window.ethereum object is 0 (not undefined). For some reason ethereum object is 0. I am aware about ...
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1answer
28 views

Transaction working in remix but not errored from dapp

I have a master contract which deploys instances of other contracts. pragma solidity ^0.5.0; pragma experimental ABIEncoderV2; contract DataEntityContract { DataEntity DE; constructor(...
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1answer
99 views

What does MetaMask mean by stop injecting web3.js?

MetaMask announced that they will stop injecting web3.js here. I know previously MetaMask will add a global variable in browser window.web3 and this global lowercase web3 variable will be deprecated ...
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167 views

Web3.js eth.subscribe: on('changed', function(event){}) doesn't work with Metamask?

I write a demo DApp website with this javascript const web3 = new Web3(ethereum); const contractAddr = "0x0Aa27e4B13D5c08A8767B36a0ACb76ED4549B7EA"; const abi = ...; let inst = new ...
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What is the core difference between send and transfer method of address payable in solidity? [duplicate]

I'm learning solidity I got two methods for transferring ether <address payable>.send(1 ether) <address payable>.transfer(1 ether) Both are used to transferring ether to the recipient ...
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Retrieve block number from geth and display it on my webpage

I am running geth using this command: geth -testnet --syncmode light console and I am trying to retrieve the block number from geth and display it on my web app. In geth when I type: eth....
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Conditionally Return Content Based On Wallet Tokens

Hi all– new to building dapps. I'm working on a little web game that returns content based on what tokens you hold in your wallet. I'm used to building web apps and mobile apps, but I've never worked ...
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23 views

Using web3.js to interface with smart contract

I am a beginner in Dapp and don't know about web3.js. I complie myslef contracts with Truffle. I did write the following contract: pragma solidity ^0.5.12; contract TEST{ bytes public name="...
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Can I make a proper website by using ganache and truffle? Like maybe abc.com?

I have developed a voting system usinh dapp that runs on local host. It uses accounts from ganache and metamask for transactions of votes. Now if i want to buy a domain and make the thing work, is it ...
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134 views

how to build Dapp for Android using react-native

I have a ethereum Dapp for web application and have metamask extension installed in my chrome browser to make transactions. Now i want the same application to be developed in android using react-...
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1answer
115 views

Oraclize ( provable) updates the value only one time

I'm trying to write a smart contract that gives me the current timestamp. The very important part is that i want this to happen locally, not on test networks. After some research, i installed ethereum-...
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100 views

Invalid opcode exception when trying to resize a storage array

I wrote this function: function removeClaim(uint256 _claimId) public returns (bool success) { require(msg.sender == owner || msg.sender == claims[_claimId].issuer); // Emit event and store ...
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solidity smart contract thats uses off-chain ML model

I'm new. Hopefully this is an appropriate question for this forum. (This is a simplified example). I want to write a smart contract that receives a loan request, and based on certain features of ...
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38 views

Sharing an verifiable secret message in a contract

I would like to hear your opinion on my idea to share a proof of a secret message in a contract, that users can verify later in a second phase when the message will be revealed. If the message is a ...
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48 views

Use uint[] to map uint(address) to uint

Is there any reason not to use uint[2**160-1] addressIndex; instead of mapping(address => uint) addressIndex; ?
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1answer
27 views

Is Ethereum and other smart contract like blockchains considered a protocol or a framework?

I'm not sure how to explain Ethereum or other smart contract systems like eos/tron/ardor/waves. Are these protocols or are they frameworks? How should it be classified? I want to explain to clients ...
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1answer
58 views

Metamask not showing localhost “7545”

A happy new year to you all. I am trying to make a decentralised application. Everything was going well until I came across a snag. Metamask does not show localhost "7545" which I need to connect the ...

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