318-oraclize入门







oraclize入门





我们可以通过oraclize在ethereum与外界通信

看下文档
https://docs.oraclize.it/#ethereum

看下示例代码





pragma solidity ^0.4.11;
import "github.com/oraclize/ethereum-api/oraclizeAPI.sol";

contract ExampleContract is usingOraclize {

   string public ETHUSD;
   event LogConstructorInitiated(string nextStep);
   event LogPriceUpdated(string price);
   event LogNewOraclizeQuery(string description);

   function ExampleContract() payable {
       LogConstructorInitiated("Constructor was initiated. Call 'updatePrice()' to send the Oraclize Query.");
   }

   function __callback(bytes32 myid, string result) {
       if (msg.sender != oraclize_cbAddress()) revert();
       ETHUSD = result;
       LogPriceUpdated(result);
   }

   function updatePrice() payable {
       if (oraclize_getPrice("URL") > this.balance) {
           LogNewOraclizeQuery("Oraclize query was NOT sent, please add some ETH to cover for the query fee");
       } else {
           LogNewOraclizeQuery("Oraclize query was sent, standing by for the answer..");
           oraclize_query("URL", "json(https://api.pro.coinbase.com/products/ETH-USD/ticker).price");
       }
   }
} 





这里的代码的意思是
通过updatePrice方法查询像现在ETH的价格
_callback就是请求的回调,
然后把价格存入到ETHUSD变量里面

然后我们只要访问ETHUSD就可以得到查询的结果



然后我们也可以请求各种不同的地址

// This code example will ask Oraclize to send as soon as possible
// a transaction with the primary result (as a string) of the given
// formula ("random number between 0 and 100") fetched from the
// data-source "WolframAlpha".
oraclize_query("WolframAlpha", "random number between 0 and 100");

oraclize_query("URL", "https://api.kraken.com/0/public/Ticker?pair=ETHXBT")

oraclize_query("URL",
  "json(https://www.therocktrading.com/api/ticker/BTCEUR).result.0.last")

oraclize_query("IPFS", "QmdEJwJG1T9rzHvBD8i69HHuJaRgXRKEQCP7Bh1BVttZbU")

// The URL datasource also supports a supplement argument, useful for creating HTTP POST requests.
// If that argument is a valid JSON string, it will be automatically sent as JSON.
oraclize_query("URL", "json(https://shapeshift.io/sendamount).success.deposit",
  '{"pair":"eth_btc","amount":"1","withdrawal":"1AAcCo21EUc1jbocjssSQDzLna9Vem2UN5"}')
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