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Ethereum in practice part 3: Ethereum in practice part 2: Ethereum is not meant to be a platform to build esoteric smart contract applications that require a STEM degree to understand, but it aims to be one pillar of a different architecture for applications on the world wide web.
Besides serving static web pages, they also keep private information, handle user authentication and deal with all the complicated ways in which data is analyzed and saved. All the user computer does — a device which would be considered a super computer when the web was invented — is to load and display that information to the user.
The user device keeps the user authentication and runs the application interface. Since all those protocols are decentralized, anyone can connect to the network and start providing a specialized service: A decentralized architecture also encourages innovation: If you want to experiment with the app before learning it, we recommend you download Mist and read our introductory tutorial to how to install the app and run it.
So how does this translates into a polling app? So we will use the URL of the app itself to keep the proposal text, and we will use that to display it to the user and generate a hash that can then be used to check the votes. The users can use social media to share which proposals they want to debate or simply use direct links. So grab your favorite html framework and get a basic website on your local machine and open it on Mist.
You can even run this command recursively, to try connecting to it again using another address in case you are actually on the testnet.
Privacy should not be a compromise we accept in exchange of practicality: Using Mist, apps have no information about the user, until the user decides to reveal itself to the app. When you want to query what you know about the accounts, you should call the getAccounts function:.
This will allow the user to have access to features currently available only to centralized authenticators, like two factor authentication or cloud backup, and to future improvements only available to smart contracts, like allowing a few trusted friends to give you access to an account for which you lost keys or having automatic inheritance of inactive accounts. Each future Ethereum browser will handle how users identify themselves to the App. In Mist we have two ways: If you require the user to prove their identity you need them to sign a message, while Mist will also support that in the future, keep it in mind that it would force the user to add an extra step and type their password, so you should only use that when absolutely necessary.
So first we will create two clickable objects that calls a vote function:. Notice that one calls the function with a true parameter and the other false. The function vote could be as simple as:. We pass the two parameters demanded by the function and then add a third object containing transaction informations, like who is it being sent from and optionally, how much gas to include or how much to pay for the gas.
You should only request an account once the user initiated an action: If we observe abuses from apps using this feature, we might add more strict requirements to when an alert will show up.
Finally, to count up all the votes we need to watch the contract events and see what votes were cast. So what would this function do? From the original solidity contract, you can see that the LogVote event comes with three argumenst, proposalHash, Pro and Addr:. So what this function does is that it will use the function web3. In this case we will be using the finney, which is a thousandth of an ether. One advantage of using a map instead of an array is that this will automatically overwrite any previous information about that same address, so if someone votes twice, only their last opinion will be kept.
Why do we want to tally up the votes on a separate function? Because since the vote weight is based on the current balance of each account, we should recalculate the balances at every new block, event if we received no new event.
To do this you can add this function that will execute automatically everytime a new block arrives:. Finally, up to calculating the final tally. We have previously used eth. Here, since we can be calling a lot of actions every block, we will use it in asynchronous mode: As you can follow on the code, what the app is doing is looping in each of the voting addresses and getting their balance, and as soon as it returns, it will either add it to the pro or against camp and sum the totals.
A few extra caveats: Now you can feel free to use all your current webdeveloper foo to work whatever magic you want. Use the numbers to build a nice visualization in 3D or connect to your favorite social media to share the best questions.
And if you want to use Mist itself to navigate on your app, you can use the Mist. One great thing about ethereum is that you can expand on this simple contract functionality without needing permission: It also means other people can use the contracts you created to their own apps and give new functionality. Meanwhile, all the apps use the same data and backend. The same app will also work as a local html file on your computer or on an IPFS network and in the future it will be downloaded directly via Mist using Swarm.
Alex, excellent post, thanks. You have a minor error in the contract. The code looks fine in github. Very well put together, you need to consider writing examples like this in the Eth docs. You may use these HTML tags and attributes: How to build server less applications for Mist Introduction. Stake Voice running on the Mist Browser. Author King Flurkel Posted at 5: Author Mukul Thakur Posted at 8: I closed my eth short after reading this Reply.
Author bordalix Posted at Author Samuel Hawksby-Robinson Posted at 9: Author Michael Horowitz Posted at 8: Now how do I hook up P2P trading in Mist connected to coinbase?